Cat 938g 6y SER# No Reverse !!

[Ashton Cooke]

please help I have a cat 938g with a 6y serial number , it’s has no reverse . I swapped solenoids number 2 solenoid on valve body , still no reverse . I also bought an entire new cartridge and solenoid for number 2 and still no reverse. The fluid is clean with no clutch material and doesn’t smell burnt . Please help !!!! Forward but no reverse .when put in reverse I can feel something engage , but machine won’t move

 

[Chisumtrail]

Is it a series I or II, don't see a 6y serial number, the one you changed was in the middle of the 3 valves?

 

[Ashton Cooke]

Yes I replaced the entire solenoid and cartridges in the middle of the two on the top of control valve solenoid number #2

 

[Nige]

As above - no such thing as a 6Y-prefix. (Well there is but it's a D8L)
Below are your options.



EDITA: Sorry didn't look at your photo before. S/No 6WS00902. That makes more sense.
All comments in the post below still apply.

 

[Nige]

Another thing. Have you been into the transmission suction screen to look for clutch material.?
I know it's not likely but a clutch could have de-laminated a friction disc.



The other possibility that springs to mind is that a piston seal failure on the reverse clutch. That would not generate large amounts of material in the screen.

If you eliminate material in the screen then IMHO it's break out the pressure gauges time.

 

[Nige]

A further observation. You say you swapped solenoids and even bought a new valve cartridge c/w solenoid for the reverse position but it made no difference.

Have you checked voltage at all the solenoids (with them still connected to the harness. Youll have to back probe them) so determine if power is actually reaching the solenoids that it should do for each gear in the transmission from the control selector in the cab.? If not then I would suggest that you check the voltage being applied to the solenoids all speeds in both the forward and reverse direction.

If you want to check the resistance of the solenoid coils the specification is 31 +/- 3 ohms

 

[Ashton Cooke]

Yes I have 24 V going to reverse solenoid the middle one on top When the machine is in reverse . The back up alarm sounds and I feel something engage but the machine will not move. I did in fact inspect the screen and it was very very clean not any type of clutch material whatsoever . Should I suspect the modulating valve inside the control for the transmission

 

[Nige]

I would suggest checking the P1 (speed) & P2 (direction) clutch pressures as you cycle the transmission through all the forward and reverse gears.
Get the power train up to normal operating temperature. Record P1 & P2 pressure at Low Idle & High Idle in neutral and compare them to specification (see attached).
Then engage each gear in turn at Low Idle and watch what happens to P1 & P2. Both pressures should dip momentarily then recover. Increase engine speed to High Idle and watch what the pressures do. NOTE: In 1st speed the service brake may not hold the machine from moving. You may have to put the bucket or the counterweight up against something soldi to prevent any undesired machine movement.

Record all your results and post back here.

EDITA: If, as I suspect, there is internal leakage in the reverse clutch then P2 will drop to zero when you engage any reverse gear and will not move from that pressure whether you are at Low or High Idle RPM. It should only return to spec pressure when you return the transmission control to the neutral position.

 

[Ashton Cooke]

I cannot view your attachment . Which port do I test for p2 drop and recover ?

 

[Nige]

I cannot view your attachment . Which port do I test for p2 drop and recover ?

it's a pdf document. You will be able to open or download it if you get on a PC.