ford 7710 pto/dual-power problems

Hey Bern or Rod help !! I recently purchased a 1985 model 7710 with cab got it home and found the dual power was sliping put it in the shop and disconected the line that feeds the dual power and instaled gage found only 35-psi coming from the pump. I drained the oil and removed the pump found the line that feeds the pto control valve had a broken clip and had come unseated from the control valve. I ordered new updated 2 piece line and instaled it and reinstalled the pump, filled with oil and retested it. I found the following tractor ideling at 850-rpm pto disengaged d/p in turtle pressure 215-psi with needle fluctuating. pto engaged d/p in turtle 160-psi, pto engaged d/p in rabit 130-psi,pto disengaged d/p in rabit 150-psi.All presures came up alot with in rpm. It didn't seem right, but thought I would give it a try. Test drove it on the road in hi gear, shifted d/p up and down on some grades it seemed ok.A few weeks later had some mowing to do, hooked up my 15-ft batwing and headed out all was well for about 2hr I throtteled back to slip between two trees when I throtteled back up the pto didn't. Took it back to the shop and put the gage back on it, found a significant drop between pto on and off. I did the rear split removed the cluch and valve, found lots of damage, thrust washer broken, bushings gone from cluch housing valve support groved, one of the three sealing rings missing and that the valve had been messed with and the releaf valve shimed with a ball bearing! decided to put all new parts back in. I bought a factory assembled clutch, thrust washer, sealing rings, valve support housing,and valve. I installed all, removed the pump so I could watch and make sure I didn't mess anything up, reasembled the tractor filled it back up and put the gage back on. 850-rpms 135-lbs pto in or out d/p in turtle 120 d/p in rabbit, test drove, d/p will break loose in high gear on a hill, haven't tryed the pto. I disconnected the line to the d/p and pluged it. Rechecked the pressure, still 135-psi pto in or out. Checked the screen on the pump and it was clean. I think I need to add shims to the releaf valve. you think N-H would set that valve at the factory! Is there a way to get valve out without respliting the tractor? Also how many shims would you add? P.S. this is a cab tractor so geting the hyd. unit off is no small task either. How about through the pump hole or the round cover on the other side? Thanks, Skyp Harmon [email protected]

Yes, it seems like you need to add a shim or two. I don't know why it's slack like that, but it seems to be regulated that way unless your gauge is off... but if it's slipping, the gauge is probably right.

I would probably go in through the lift cover for the purpose of re-shimming the valve. I think I did that in place last time... but you are right. It's not a small job.
Cab floor comes up, priority pack off, unbolt all the linkages, remove the remotes, unbolt the lift cover, bolt a piece of chanel to the cover and clamp that to a fork lift or pallet fork of some kind... then lift the cover an inch or two. Remove the load monitor link at the right rear corner, then gently keep lifting and wiggeling until you get the cover up and out. Why not go through the lift cover while it's off....

While you're reshimming the valve, make sure you don't get into the cooler relief valve instead of the system relief you want.

Othe than that I think you covered all the bases on testing, or at least all I'd have checked. Re-shimming is where I'd be heading at this point...

Rod

This is going to be one of those rare times that I will disagree with Rod. Based on everything you have told me, I suspect rear pump damage, either blown seals and/or worse. I’ve seen this happen in a similar situation. Whoever shimmed the valve with a ball bearing was a moron, and the resultant EXTREME high pressure I’m sure likely damaged the pump and broke the clip at the same time. I also suspect some DP damage based on your differences in readings between high and low.

If you put in a new factory valve assembly, I would be reasonably certain that it is shimmed properly. I would remove the hydraulic pump and take a close look at the REAR pump, which supplies oil for the PTO/4WD/DP circuits. There is also a special fitting available whereby you can pressure and flow test this pump directly. However, it would be quicker to simply remove the pump and disassemble it. That is your quickest option at this time.

Any access to the PTO valve at this point, is, like Rod says, likely best done thru the top cover. If the tractor does not have Load Monitor (a 10-series option), this is also the easiest and safest way to R&R the PTO clutch assembly.

Yeah, you may well be right Bern. It's just funny to me that it would make pressure before unless the pump was marginal before and now it's shot...
I've just never had a rear pump section fail. Front's have always failed first on me, so the rear is not something I look to immediately...
I agree with you that there is likely some degree of leaking at the DP as well, and who knows what other damage at this point.

It will be much easier to see what's going on when there's pressure holding on the balk end first, then attack the Dual Power.

Rod

The tractor is load monitor equiped also the pump appers to be a fairly new replacement pump it is lacking the blue paint,and it was making excess prsssure just befor I tore it down with the jimmed up control valve.and the pressure did not improve when I pluged the port where D/P line connects. I do think that the D/P may be leeking in direct drive,but not a lot was hoping that if I can get the pressure up to spec I could put off doing the front splt and going threw it untill after hay making time It pulls good in under drive.could just use under drive untill then.Gess I will pull the pump and take a close look will let you know what I find. Thanks Skyp