94' Caterpillar 623F Will Lose Reverse After Warmed Up

[CEvans]

Hi,

SN: 6BK00136
1994 Caterpillar 623F

I have a 94' 623F Scraper that has a reverse problem. I can't see anything behind me! Jk, jk. My real issue is that my machine has reverse when the machine and all its fluids are cold but after warmed up, it won't go into reverse. I do feel it engage because when I take it out of reverse and shift back into neutral, you can feel a little nudge, if that makes any sense? After the machine is warmed up and you go to throw into reverse, you can hammer down on the pedal and it revs the motor as if it's in neutral. Although, if I mess with it long enough while everything is warm, going from neutral to reverse, it will sometimes all of a sudden find reverse and work normal. As soon as I take it out of reverse, back into neutral, and back again into reverse, reverse is gone again. Is this situation familiar with anyone? I've got a quote from CAT for $36,000.00 USD worst case scenario of a reman transmission swap, labor included.

Thanks,
Chad

 

[Nige]

Have you changed the transmission oil & filter recently.? if so, was the magnetic screen also removed and inspected.?
If not then I think cutting open the filter to look for particles and taking a look at the screen ought to be your first step.
If the transmission goes into reverse when cold but balks when it's warm the first suspect is a failing reverse (#7) clutch. That ought to have left some indication in the filter or the screen, or both.

 

[CEvans]

Have you changed the transmission oil & filter recently.? if so, was the magnetic screen also removed and inspected.? No, I have not done either. I have not changed the filter, oil, and I have not looked at the magnets recently.
If not then I think cutting open the filter to look for particles and taking a look at the screen ought to be your first step. I will do this first thing and report back when it's done.
If the transmission goes into reverse when cold but balks when it's warm the first suspect is a failing reverse (#7) clutch. That ought to have left some indication in the filter or the screen, or both. I believe you're right. I'll go ahead and have it pulled and get back with you. Thank's Nige, for your response and also the picture detail.

 

[Bluox]

After you check filters if no swarf.
Might be wise to go thru the shift linkage adjustment before removing transmission.
You know the KISS principle.
Bob

 

[Nige]

If it had cable shifting I would agree but the F Series have an electronically-controlled transmission.

If the filters and screen come up clear for debris then the next thing would be to start looking for the presence of Diagnostic Codes.

 

[Nige]

Here's the Service Manual for the EPTC-II transmission control. It is similar to what was used years ago on the large mining trucks.
See pages 22 onwards for the section on Troubleshooting. It would be interesting to see what Codes the Control is seeing, if any.

The "Service" and "Clear" switches referred to in the text that are used to change modes in the Control are located right beside it, Ref #49. See illustration below.