47RH problems

[EasternAggie]

Hey guys I'm helping a guy work on his truck, I'm not new to diesels or manual trannies but I am new to auto tranny's. The truck is a 1995 160hp 47RH truck with 351k miles. He's not hard on the truck, his granddad had it before him, but it does have some miles and wear on it. I've fixed several fuel related issues on the truck but the auto tranny is having a fit and I don't have any experience with them. The pump is still 100% stock.

When using the shifter, the transmission will go through all gears (park, reverse, neutral, drive, 2nd and 1st) without problem. Under medium acceleration the transmission will shift all the way to overdrive with only minor hesitation between gears.

The biggest problem is the transmission will get stuck in overdrive with the torque converter locked up once it shifts to it, and the only way to get it out is to manually shift down to 2nd or 1st. If you have the OD off button pressed, it will not ever shift into overdrive, but if not it will shift into OD. Once in goes into OD I don't care if you floor it in OD at 1200rpm, it won't downshift, and if you try to slow down to a stop it will kill the engine because the converter stays locked when it stays in gear, and you have to manually shift down.

Under WOT, the 1-2 shift is fine, a bit rough, but fine. On the 2-3 shift it will hang at 3000rpm until you let off the throttle and it will shift. the 3-OD shift is similar to the 1-2 shift. Another thing thats weird is that if you are driving along in 3rd gear at about 2000rpm and go WOT, it will downshift to 2nd and instantly over-rev the engine up to about 3500rpm, which it should not do.

I know its a lot of info for one post, but I want to help this guy out and figure out if its the valve body, the torque converter, the linkage, or something else. Thanks in advance guys :welcome:

 

[Big Blue24]

Sounds like a tranny with multiple problems, mostly related to debris floating around in the fluid. Debris doesn't just come out of nowhere, it's probably time for a rebuild.

How many miles are on it?
Have you dropped the pan yet?
Is the fluid on the dipstick dark or burnt?

The funny 1-3 shifting sounds like a partially blocked filter in the governor or a worn governor that's getting hung up.

The hanging overdrive sounds like either an electrical problem where the OD solenoid is staying grounded when it shouldn't, or debris causing the shift valve to hang up even if the solenoid is firing and releasing correctly.

 

[EasternAggie]

Sounds like a tranny with multiple problems, mostly related to debris floating around in the fluid. Debris doesn't just come out of nowhere, it's probably time for a rebuild.

How many miles are on it? It has 351k miles, and as far as I know has never been rebuilt, most likely due time.
Have you dropped the pan yet? No, I've only drove the truck once, haven't got to all that yet.
Is the fluid on the dipstick dark or burnt? Will check next time I'm around the truck.

The funny 1-3 shifting sounds like a partially blocked filter in the governor or a worn governor that's getting hung up.

The hanging overdrive sounds like either an electrical problem where the OD solenoid is staying grounded when it shouldn't, or debris causing the shift valve to hang up even if the solenoid is firing and releasing correctly.

Answers in red in the quote. Thanks for the help I'll get back to you on some of the stuff. I figure its just time for a rebuild.

 

[Cantankerous1]

OD and lockup are under computer control operated by the 2 solenoids. Wire switches into the control circuits and break the circuit to see if it is mechanical or electrical. The computer on that year truck is pretty limited so its no unusual to see if freak and forget what it is supposed to do.

 

[EasternAggie]

If you hit the overdrive off button before you get up to speed it will never shift into overdrive and will stay in third. Could it still be electrical? Still haven't got to see the truck again, it'll probably be Monday. I'll keep you guys posted.