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Adjusting 7308 Pressure Relief Valve Setting

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cdcole
Join Date: Jul 2003
Posts: 66 Saukville, WI
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2003-05-08          54540


Very surprised this morning when I went to lift a 1952 Dodge Power Wagon axle (about 800lbs). The relief valve stopped the lifting but I was able to curl the bucket back with the chain over the front of the bucket - such that I could get the unit off the ground to move it. Very disappointing to say the least. Called New Holland and they want me to bring it there to be adjusted - 35 miles away - with a fee.

Any advice? You can email me at: my 3 boys at execpc dot com

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drcjv.
Join Date: Jul 2003
Posts: 334 southeastern pa
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2003-05-09          54556


I had similar problem and found out my loader pressure was set 300lbs psi too low from factory. I also know of two other loaders set too low and have heard of others. When I ask the dealer he told me it was fairly common and sent a mechanic out to test and set the pressure. He increased the pressure about 600lbs psi. I tested the loader after the adjustment and it lifted 2016lbs with ease it would of lifted more but I could not fit anything else in the bucket. The tractor (TC33D, 7308FEL) has worked flawlessly for about a year. There are some saftey and sructural concerns with doing this and I have discussed these in detail in some other threads but, good commonsence should keep you and your tractor safe. If the tractor is still under warranty I would tell the dealer to come to you and there should not be a charge for the service call. I would not recommend you do this yourself unless you have the proper gauges and tools as well as understanding to do so. ....

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Mrwurm
Join Date: Feb 2002
Posts: 184 South East Michigan
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2003-05-09          54558


I have posted this very same question myself. I suspect that someone out there knows how to adjust the pressure but they are not talking. For you situation, I would suggest doing a simple adjustment. The 7308 loader is spec'ed to lift about 900lbs on a TC33. So, place the 800lb object (axle) in your bucket along with another 100lbs of stuff. Make small adjustments to the pressure relief until the loader will just barely lift the load. Now, of course, we need someone to tell us where the adjustment point is.
Jerry ....

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DRankin
Join Date: Jan 2000
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2003-05-09          54565


Reading this thread and the other one about the fan blades hitting the radiator makes me wonder if the two are connected.

Maybe they turn the pressure down at the factory to reduce the frame flexing that causes the fan blade/radiator interference.

What do you guys think? ....

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Adjusting 7308 Pressure Relief Valve Setting

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AC5ZO
Join Date: Jul 2003
Posts: 928 Rio Rancho, NM 87144
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2003-05-09          54567


The FEL advertised specifications are a little bit optimistic. I believe that the lifting force for one thing is specified from the bucket pivot point which is closer to the tractor than the end of the bucket. I also believe that the lifting weight specifications in some cases do not include the bucket weight. Still, most people find that the 7308 is a very capable loader that can easily lift a full bucket of the heaviest material. And, if the loader pressure is at the high end of the allowed pressure range, it will lift beyond the advertised load. We only seem to approach the limits of its capability when lifting machinery.

The reason that you can rotate the bucket and lift a heavy load when the main cylinders will not lift the same load is that the bucket cylinders have a higher mechanical advantage. The bucket lifting force is specified as the breakout force and it is significantly above the lifting capability of the loader. This force is required when you are using the loader bucket to pry out a rock or something but you need to be careful. Using the bucket to lift a heavy load causes higher than normal pressures to be in the hoses of the main lift cylinders when the spool valve is closed. This is dangerous and I don't think that the relief valve can perform its safety relief function in this situation.

Adjusting the relief valve pressure is not complicated. If as in drcjv's case, your pressure is low, it would help to have it adjusted to specification. But, it is not advisable to go beyond the specified maximum pressure. It can be adjusted with some very inexpensive NH parts and a more expensive guage system for the hydraulic pressure. This is not an area for untrained mechanics to be working in. The final pressure that you set will determine how much stress and strain are placed on your FEL and tractor.

I would not advise that you do this yourself unless you have all the proper parts, tools and experience to know the whole story and potential consequences. It is possible to "hot rod" the hydraulic system to exceed the NH specifications, but you have to ask yourself if it is worth doing so since you will be exposing yourself, anyone else around, and your equipment to potentially dangerous overload conditions. A skilled operator may never experience any problems, but the dangers and potential liability will still be there.

If you need to lift the full specified load on any loader, you should lift in line with the loader pivot pin. If you have a quick attach bucket, then take the bucket off and lift from the frame. It is best to use lifting straps that are made for hoisting. Use rear ballast to maintain the balance of the tractor/FEL/load. ....

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AC5ZO
Join Date: Jul 2003
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2003-05-09          54568


Mark, I think that the reported fan blade interference problem has been on the next frame size tractors. (35-45 HP)

I have a TC45 w 16LA and I have not seen the fan issue. I lift very heavy loads with it. I try to balance loads as best I can, but I do move over uneven terrain.

Relief valve pressure can certainly be set to limit the maximum load on a loader. It is adjustable, at a risk. Alternately you could also install larger lift cylinders, modify the attachment points for the cylinders and other things to increase the load capability. Proceed at your own risk. ....

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drcjv.
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Posts: 334 southeastern pa
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2003-05-09          54572


AC is this de'ja vue or what. Mrwurm the adjustment is under the joystick cover on the right fender.I would not recommend doing this on your own unless you have the proper training and tools as in the past I do not always agree with AC but, his safety and stuctural concerns are very valid. I had the dealer do this for me and the mechanic was not even sure what to do the first time out. I love the increased lifting capacity but, the risk of accident has also increased. Mark I have not heard of any fan problems on the TC33D. ....

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Adjusting 7308 Pressure Relief Valve Setting

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cdcole
Join Date: Jul 2003
Posts: 66 Saukville, WI
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2003-05-09          54577


Lot's of very good advice - Not sure what I will do yet.

Also - very surprising to me that my JD318 would raise the front tires off the ground with a snowblade. My old Ford 600 with it's Bush Hog loader could easily raise the tires off the ground too. With the Boomer - only the bucket curling down will raise the tires. Definitely need to fix this. Often to get good down pressure - I intentionally lift the front end up with the loader - right now I am missing that capability. Tractor is out of warranty. ....

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drcjv.
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2003-05-09          54583


Lifting the front on the 7308 is limited by the length of the main cylinders not only by lifting ability. Put a 6 inch block under your bucket and it should lift the front end although in your case if the pressure is low it could effect this. I think it would be well worth the money and time to have a dealer check and adjust the loader pressure. ....

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Mrwurm
Join Date: Feb 2002
Posts: 184 South East Michigan
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2003-05-09          54590


"place a block under the bucket and see if it will lift the front end"

Nope, no way. My TC30 with 7308 won't do it and my neighbor's 1920 with 7308 won't do it.

When I was shopping for my TC30 last year I mentioned the limited loader capacity to the dealer. He sent it into the repair bay with a tech. Five minutes later it returned and could lift the front with the loader. I did'nt end up buying from that dealer. So, what did he do and where did he do it. I know he did not have time to tap into a line and install a gauge. Maybe he put a quick-connect gauge on after the selective control valve between the valve and the quick connect for the hose??

I would like to have mine spec'ed out by the dealer but he is 30 miles away and would probably charge me for transport and labor if there turns out to be nothing wrong.

Jerry

Jerry ....

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AC5ZO
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2003-05-10          54600


This adjustment can be done in the field by a mechanic. Your loader should be able to lift the front end with the main cylinders (requires blocking bucket or tilting it down). You can connect a gauge in the quick connections. The problem is that without the gauge, you cannot tell how high the pressure relief is set.

Perhaps it would be less expensive to have the mechanic come to your place rather than hauling the tractor 30 miles. If it is warranty work, it would be best to use the NH mechanic, but any mechanic qualified for hydraulic work should have the gauges and experience necessary to do this. ....

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TomG
Join Date: Feb 2002
Posts: 5406 Upper Ottawa Valley
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2003-05-10          54608


Well, this is theory and there is no substitute for training and experience. If I were trying to adjust the relief pressure on a loader valve, I'd take a pressure gauge with a quick-connect on it and connect is to one of the bucket cylinder line ports. I'd raise the tractor with the lift and take a pressure reading while holding both the lift and bucket valves open. However, I guess that holding both valves open might be a bit tricky with a joystick linkage.

Many valve assemblies have a passage between the control valve sections called a 'power-passage.' A power passage feeds pressure to downstream valves in the assembly when an upstream valve is operated. When two valves are operated simultaneously each gets pressure, but the cylinder with the lightest load moves first. That should provide a decent test for relief valves that are contained in the inlet section of the valve assembly and the system relief valve as well. Not all valves have a power passage, but it's my guess that's how a dealer mechanic did a fast adjustment. Of course, I haven't tried any of this stuff. I looked but ended up not getting a gauge. Everything's working well enough.

Many but not all valves have circuit relief valves to protect against high pressures in closed cylinder lines due to load shocks mentioned by AZ. Such valves usually are set well above system working system pressures.
....

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drcjv.
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Posts: 334 southeastern pa
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2003-05-10          54612


Tom I can't agree or disagree with you because I'm not sure I understand your entire post. I must say that someone who is not well trained and does'nt have the proper tools should not make these adjustments. So far it seems I am the only person on this board who has actually had his 7308 adjusted. I can only speak from my experiance. The first mechanic sent out did not have a clue and actually adjusted the wrong valve. The second mechanic seemed to know much more, this did not take only a few minutes and he did use gauges (they wrere not quick conects). As I have said before my loader now can easily lift over a ton. I rarely if ever need to do this but, it is nice to know I can. The loader also lifts much lighter loads easier than it did before. I recently spread 95 tons of stone it worked great. Having enough ballast also makes a big differance. With filled tires, wheel weights and weight box I have about 1,700lbs.
....

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cdcole
Join Date: Jul 2003
Posts: 66 Saukville, WI
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2003-05-10          54625


Wurm,

You are right on. It don't matter - if you add a foot of blocking under the bucket then pull the cylinders in - it won't lift the front. I am aware of the differences in the cylinder forces (between the bucket cylinders and the lift arms) but still feel a tractor must be able to lift it's front end off the ground with the power of the lift arm cylinders. I admit - the stroke length is just about exhausted when the bucket is flat - but hey - I curled the bucket down first - then lowered it to the ground - then tried to lift the front tires - NO WAY!

I am calling my dealer on Monday.

Actually - I am amazed that only one of us on this board has had it adjusted. Also - when really digging - hard to believe that others have not noticed this. I have run loaders for close to 20 years - without this feature - I would estimate that 15% of what I have done would not be accomplished. Example: Packing down soil in reverse with the front tires off the ground (you should not have to curl bucket down to lift - you should be able to curl bucket down - touch it to the ground - then pull in lift arms - thereby raising the front end and applying down pressure to the blade edge to pack down dirt into ruts from say a tractor pull). Just like a New Holland skid steer.

Well in any case - I will get the adjustment.

Cliff in Wisconsin
....

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drcjv.
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Posts: 334 southeastern pa
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2003-05-11          54641


I would recommend anybody with a 7308 get the loader pressure checked. It just seems too many are low. I also can't believe I'm the only one who has had this done, as soon as I got my tractor I knew something was wrong. I chose to raise my prsseure past factory settings. This is not for everyone but, at least make sure it is up to spec. Mine was over 300lbs psi low. ....

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Adjusting 7308 Pressure Relief Valve Setting

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TomG
Join Date: Feb 2002
Posts: 5406 Upper Ottawa Valley
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2003-05-11          54642


I agree with Cliff that a loader should be able to lift the front of a tractor, and my Ford with an Allied can if the bucket is angled down slightly. Most people who have tried probably had a 3ph implement on and that weight would make lifting the front even easier.

However, I'm thinking that a low relief valve adjustment may not be the only explanation for a loader that can't lift the front. I did a real rough think-through, and maybe some loaders with long reaches on front heavy tractors just may not be able to do it. I think that most 2.5" lift cylinders would produce between 5 and 6 thousand lbs. on the down-stroke. That's figuring a relief pressure something over 2,000 lbs. and a hydraulic advantage of the ratio of a 5/8" hose to a 1.5" piston. Down-pressure is on the weak side of a double-acting cylinder so the shaft diameter is subtracted from piston diameter to figure the hydraulic advantage.

A loader frame seems basically like a third-class lever with the longer arms on the load side. The effect is to gain travel at the expense of power. Power produced by the cylinder would be reduced by loader frame geometry. I believe that the weight distribution of many 4wd compacts is further forward than on older tractors to take better advantage of traction from the front axle and to reduce back-flips so there'd be more weight on the front.

This think-through is pretty impressionistic (including the 5-6 thousand lbs.) but I think I can see how some designs could be pretty marginal for lifting the front unless there's heavy weight on the 3ph.
....

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Mrwurm
Join Date: Feb 2002
Posts: 184 South East Michigan
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2003-05-11          54648


TomG, I now you were looking for some fittings to plumb a gauge into your power steering system a while back. If i remember correctly the fittings were non-standard size and outrageously expensive. I saw that Northern Equipment catalog sells quick connects for about $13 a set. If I get the quick connects, a glycerin-filled gauge 'A grade' gauge ($20), and a high pressure tee from the local hydraulic shop I should be able to build a testing tool to place in-line after the selective control valve. Just thinking out loud...

Jerry ....

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Mrwurm
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2003-05-11          54654


Ok, I could'nt wait. I went out a tweaked the adjustment screw with an allen wrench untill I could lift the front end with the lift cylinders. I've tested it several times and nothing has burst. I think that adjusting the selective control valve relied is relatively safe as the hoses and connections are rated for 3000psi and the main system relief is supposed to be set for 2150psi. Does this make sense? Even if the control valve had not relief, it still would not max out the hydraulic system components. I think the risk is in overlaoding the mechanical components such as the lift arms and attachment points. What do you think?

jerry
....

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DRankin
Join Date: Jan 2000
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2003-05-11          54660


I think they limit it for some reason, just hard to know exactly why. Tires, front axle strength? Maybe the loader bracket attachments?

It would be interesting to test some tractors to see if the limitations are published and not real. For instance my BX will lift one hell of a lot more weight with the 3 point than the brochures say, but you should see what it does to the rear tires. ....

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Mrwurm
Join Date: Feb 2002
Posts: 184 South East Michigan
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2003-05-11          54678


Regarding my earlier post about adjusting my control valve relief pressure, another potential problem that I must be aware of relates to the following.
Before I had my tires filled, the loader had enough power to lift the rear end off the ground. After I loaded my tires the loader would go into 'relief' before it had enough power to lift the rear. This made for an 'almost' fool-proof operation. Now, I must 'relearn' the behavior of the loader in relation to the rear ballast.
Should be a pretty easy test. (1) Attach loader via chain to an immovable (relative concept) object. (2) Apply power slowly and see if the rear-end comes off the ground.

Jerry ....

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TomG
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2003-05-12          54698


I think a test for relief pressure can be taken without hooking a t-fitting into the high-pressure line ahead of the valve. I think that just connecting a gauge with a quick connect fitting into one of the cylinder line ports and then operating the valve just long enough to take a reading should work and would be easier. In such a hookup, the gauge should simulate an infinite load on the loader and the gauge should read relief pressure since both the loader and system relief valves would be upstream. What I mentioned in an earlier post about simultaneously operating valves would be useful for measuring working. SAE standards for hydraulic hose requires bursting pressures at least 4 times greater than rated pressures.

Similar to MarkH's comment, this tweaking buz doesn't answer the question of whether the loader is designed to operate at the relief pressure speced for the loader valve or at the system relief pressure of the tractor, which might be greater. For that matter, whether a particular tractor is designed for the full speced pressure of any after-market loader that might fit on it also is a guess. Loaders do break after long use and loaders do sometimes break tractors.

Aside from safety issues, there's probably enough 'padding' in most designs to tolerate considerable tweaking. However, it's good to keep in mind that engineering design generally works to specified life-expectancies. However, these are probability concepts and it's hard to say what's going to happen to a particular unit. Even within designed operation, some abused units go on forever and some babied ones produce warranty work.

In terms of safety stuff, I tend to depend on feel rather than measurement. If I lower a heavy bucket and stop it, I know I need more 3ph weight if the tractor feels like it wants to pitch forward. I know I can't lift the rear with the loader when a backhoe is mounted but the 3ph weight is going to change. Making something bomb-proof for the worst case may be overly conservative and doesn't allow that the operator should be the best ultimate safety feature.
....

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boatman
Join Date: Jul 2003
Posts: 49 Idaho
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2003-05-12          54741


Mrwurm, What you have actually adjusted by turning that screw is the "Front (Double-Spool) Remote Control Valve" or ,in other words, the loader pressure relief valve. Correct procedure according to NH Service Manual: 1.Install a 0-3000 PSI pressure guage to the high-pressure tube.2.Start engine and operate the hydraulic system to warm the fluid. 3. Set throttle RPM at full throttle. 4. Move the control lever to lift control-raising position and observe pressure indication on the gauge. Pressure should be 1750 PSI. 5.If required, adjust the relief valve setting by loosening the locknut and turning the adjusting screw.
Adjust the Main System Relief Valve as follows: Note, if equiped with the rear (single-spool) valve kit, perform this procedure with the gauge connected to the remote piping. Otherwise, connect the gauge to the diverter valve manifold. 1.Remove the manifold plug from the diverter valve and install fitting#FNH07560 into the(power out,P) port. Connect a 0-3000 PSI pressure gauge to the fitting. 2. Start engine and warm fluid . 3. Set throttle rpm at full throttle. 4.Move the diverter valve to the 10 o'clock position and observe pressure indication on the gauge. Pressure should be 2130+/- 70 PSI. 5.If required, adjust the pressure setting by adding or removing shims from the relief valve. One shim, 0.008" thickness, will change the pressure setting approximately 100PSI. Note: Shim kit # SBA340293230 contains three 0.008" and three 0.015" shims.
I hope that helps. ....

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Mrwurm
Join Date: Feb 2002
Posts: 184 South East Michigan
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2003-05-12          54745


Boatman, thanks for the detailed information. Information is good and more information is better. Iíll bet there are drawings of the locations of the ports you mentioned. If you are able, scanning those pages and sending them to mrnetwurm(at sign)netscape.net would be great!!! I know this is a lot to ask, but if you have time and a scanner that would help me to do this correctly.
My tractor does not have rear remotes or any other valves installed. Your post said to check the remote control valve in the raising position. Hmmm, Iím confused. Do I disconnect the FEL lift hose and replace with a gauge and then apply pressure to the gauge only. Or, is the gauge to be applied Ďin-lineí and observed while the loader is connected to the circuit and the lift arms are rising?
Thanks again for providing the details.
Jerry
....

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TomG
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Posts: 5406 Upper Ottawa Valley
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2003-05-13          54777


Shop manuals sometimes have peculiar ways of calling things. In this case the single rear remote may well be the 3ph. With only a 3ph, nothing would be connected to the auxiliary system ports on the manifold block (a box on side of the engine that the pipe from the pump goes to). The aux out port is just a convenient place to tap into the system. Rotating the diverter valve (a slot screw head) feed pressure to the port. The system relief valve sees both the remote and auxiliary system ports.

Dead ending a gauge into a circuit that still contains a relief valve simulates a high load and a pressure reading should be accurate. Tapping in with a t-fitting would read working pressure, but sufficient weight to open the relief valve would have to be on the bucket or 3ph. In addition, any orifices between the gauge and the relief port may create different pressures at the gauge and valve when there is flow.

It sounds like Boatman knows the specific loader valve. If the relief is in the inlet section, then it's pressure relief setting also would affect the 3ph capacity. The loader relief may well be in the lift circuit. I don't know.

I was thinking that if the loader cylinder lines used quick-connects, just plugging a gauge into a lift circuit port should read the relief pressure. That might be easier than taking apart the high-pressure line. There may be a problem of bleeding off the pressure to reconnect the lines though, so who knows? If I used threaded fittings for the gauge, I'd check look for some at a hydraulic shop or someplace like Northern Tool. The special tools from NH are very expensive. The aux ports are a NPT and hose fittings are likely standard so inexpensive generic hydraulic fittings likely would work.
....

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boatman
Join Date: Jul 2003
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2003-05-13          54782


Mrwurm, I'll get those diagrams scanned and have them to you within a couple of days. ....

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Mrwurm
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2003-05-13          54790


You are most kind, boatman.

jerry ....

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cdcole
Join Date: Jul 2003
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2003-05-13          54792


Wurm,

When you are done with them - Can you forward a set to me?

My dealer wants $150 to visit my house to perform the adjustment.

Thanks,

Cliff ....

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Mrwurm
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2003-05-13          54798


OK, will do. I see that your email is on your profile page.

Jerry ....

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Brushypoint
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2017-02-12          196257


Mrwurm I noticed that you might have diagram for adjusting 7308 pressure relief valve on a NH c35d tractor and was wandering if you would be so kind to send them to me,just bought one and I also believe it has low pressure cuz it won't lift a full bucket of material. It on has 440 hrs. Thank you. ....

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