JCB Sitemaster Backhoe suddenly stopped going in reverse

cgarai · Oct 24, 2014

Hi,

I have an 1990 JCB Sitemaster 4wd with a Syncro Shuttle transmission. The other day I was backing up a small hill when it seemed to drop out of gear. I put it in forward and it works fine. No reverse.

Here is what I have tried so far:

Removed the F/R solenoid valve. When switched from foreward to reverse I can see the valve shaft moving back and forth. I dissasembled the coils from the valve body and reversed them and they still actuate the valve shaft. The coils ohm out the same (~5homs) and both draw the same amperage. I reassembled and still no joy.

Recently (a week before this happened) the hose to the cooler popped off and drained a couple of gallons of fluid. I topped it up and replaced the filter. I have not checked the screen at the bottom of the sump yet.

Any ideas?

A simple question:
What fluid is equivalent to JCB brake fluid?

Thanks,

Chris

Backhoe Info:
mach-s/n: SMBT4010/354682/7
eng: AC532616T
fnt ax: 03633
rr ax: 03400
gearBx 445/164/6/00585

AJ. · Oct 24, 2014

If your forward drive is normal you know that the charge pump,torque and forward clutch pack is ok,first thing I would do is swap the plugs on the solenoids,when you select forward on the shift you now should have reverse,and when reverse is selected you should have forward,those F/R shift switches do fail,they are quit expensive and you need to know it is ok, if you have still have no reverse put the plugs back in place,a pressure test is needed as you need to establish if the pressure is enough to engage the reverse clutch pack,it can be something as simple as a o'ring on the clutch piston but that is inside,if you have a manual look up the modulator valve and have a look at it,I can't remember if there is one for each clutch pack or only one for the two,it acts like a cushion to select the clutch,at my place the fluid used in brakes is Shell Tellus 32 hydraulic oil.
AJ

cgarai · Oct 27, 2014

I reversed the solenoid plugs and I got forward when the selector was in reverse and nothing when the selector was in forward. When I had the solenoid off the tranny I reversed the coils and I could still see the same amount of motion in the valve shaft in either direction.

I'm trying to figure out how to test the pressure. I've never done it.

Thanks,

Chris

AJ. · Oct 28, 2014

Enable your email or private messages and I will give you a link to a JCB manual that you can download,its got troubleshooting and test procedure,now that you know the electrics are out of the equation and seeing its one direction only the reverse clutch is suspect #1.
AJ

cgarai · Oct 28, 2014

Hi AJ,

Can't figure out how to enable messaging. My mail is chris-jcb at araidesign .com

It does seem as though it is the reverse clutch pack, but it went out like someone flicked a switch: no ominous noises, slipping or jerkyness. Since this happened a few days after the tranny cooler hose slipped off and I lost 2+ gal of tranny fluid, I'm curious whether or not a piece of debris got into the line and has lodged itself in an inconvenient location.

Thank you,

Chris

AJ. · Oct 28, 2014

I just sent you an email, its 4am where I am so goodnight.
AJ

cgarai · Oct 29, 2014

Hi AJ,

Thanks for the manual. I checked the pressure at G and H (pp 306,307) and I get 120psi +/- 10 psi in both ports when direction selector is the appropriate direction for the port under test. This says to me that for sure the solenoid is working. I don't have a flow meter or the various adapters so I can't do the rest of the tests on those pages.

I followed the trouble shooting guide and it gets me to the solenoid. I can't figure out why the reverse clutch would just stop working!?

Thanks,

Chris

(quoted from post at 20:58:51 10/28/14) I just sent you an email, its 4am where I am so goodnight.
AJ

AJ. · Oct 30, 2014

A flow meter is not needed as you already know that the pump is working as the torque and forward is ok,the pressure too is ok,each of the clutch packs has a Belleville washer,this is a saucer shaped washer that acts like a pressure plate it keeps the squeeze on the clutch pack discs,should that washer crack the tension is lost and that clutch loses drive,the other thing that could have happened is the drilling through the shaft that takes the oil to the clutch piston is blocked,that is a long shot but if you think dirt got in?,it looks like it can't be fixed in situ,before pulling it out have you removed the suction strainer to see what's there,if you have to remove the unit keep it level till it is clear of the torque converter,often at this point it is best to have a service man a look at it.
AJ

JCB Sitemaster Backhoe suddenly stopped going in reverse

cgarai

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AJ.

Well-known Member

cgarai

New User

AJ.

Well-known Member

cgarai

New User

AJ.

Well-known Member

cgarai

New User

AJ.

Well-known Member

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