Transmission problem?

KAHALL2010

MEMBER
1991 CHEVROLET TRUCK
5.7L
V8
4WD
AUTOMATIC
368,000 MILES

I have the truck listed above k2500 4x4 with the 350 and standard cab. I think I know the issue but hopefully someone can confirm before I spend money. Recently replaced the input and output shaft seals and transmission adapter gasket on my transfer case to fix some leaks. Also, I replaced the transmission filter and pan gasket. Since then, I can't seem to get fluid to stay in my transmission. 3rd and 4th gear slip horribly now but no issues in 1st or 2nd. I'm pretty sure I need to have it rebuilt. I added the 5 quarts back the book said but after driving and checking it the fluid didn't show on the dip stick. I added another half quart and it was still low. So, I topped it off, but 3rd and 4th gear still slip. There is no sign of an external leak so I believe it may be leaking through the input shaft seal but I'm not sure. Is there anywhere else it could be going? Is there anything else I should be checking before having the transmission rebuilt? I will say prior to changing those seals it shifted fine until it got low from the leaks. The first week after changing those seals it had no issues either. The problems shifting started in the last 2 days along with the low fluid issue. The transmission is an MD8 with 16 bolt pan. Thanks in advance for any advice!

5 Replies

KEN L

MASTER CERTIFIED MECHANIC
48,363 POSTS

Is the leak coming from the front? If so, you have a front pump seal that is leaking, and the transmission will need to be removed but with the 3rd and 4th gear slipping I would have the unit rebuilt. here is a video that shows the steps on how to remove the transmission on a similar vehicle with instruction for your truck in the images below.

https://youtu.be/3vJAojsrfuU

1. Disconnect battery ground cable.
2. Remove air cleaner assembly.
3. Disconnect TV cable at its upper end.
4. Raise and support vehicle.
5. Remove propeller shaft from vehicle.
6. Disconnect speedometer cable, shift linkage assembly and electrical connectors from transmission.
7. Remove transmission support brace attaching bolts from converter cover, if equipped.
8. Remove converter cover, then mark flywheel and torque converter for installation.
9. Remove exhaust crossover pipe and catalytic converter attaching bolts from vehicle.
10. Remove torque converter to flywheel bolts and/or nuts.
11. Disconnect catalytic converter support bracket.
12. Position a suitable jack under transmission and raise slightly.
13. Remove transmission crossmember to transmission mount bolt.
14. Remove transmission crossmember to frame bolts and/or insulators, if equipped.
15. Slide crossmember rearward and remove from vehicle.
16. Lower transmission.
17. Disconnect and cap transmission fluid cooler lines.
18. Disconnect TV cable from transmission.
19. Position a suitable jack under engine, then remove transmission to engine attaching bolts.
20. Carefully separate transmission from engine. Install torque converter holding tool No. J-21366.
21. Remove transmission from vehicle.
22. To install transmission, reverse removal procedure.

Check out the images (below). Please let us know if you need anything else to get the problem fixed.

Images (Click to make bigger)

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Monday, January 2nd, 2023 AT 12:11 PM

KAHALL2010

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4 POSTS

There is no external leak around the transmission. It's been cleaned top to bottom and there is no sign of a leak. Also, before having it rebuilt, I'm going to try one more part. I was reading another forum and it talked about the shift solenoid being bad, so this evening I dropped the pan again and pulled the shift solenoid. When I tested it there was no click or anything so I think that may be the problem. The new one will be in on Thursday, so I'll know for sure then. Here's to hoping that fixes the problem before spending 2 grand to have it rebuilt.

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Tuesday, January 3rd, 2023 AT 3:48 PM

KEN L

MASTER CERTIFIED MECHANIC
48,363 POSTS

Yep, good call a shift solenoid maybe weak not supplying the pressure needed to hold the transmission gear. Let me know how it goes here is how you change the solenoid out.

1. Raise and support vehicle.

2. Remove two oil pan bolts from below servo cover.

3. Install servo cover compressor tool No. J-29714 or equivalent on oil pan flange and depress servo cover.

4. Remove servo cover retaining ring.

5. Remove servo cover and seal ring.

6. Remove servo piston and bore apply pin assembly.

7. Reverse procedure to install. Whenever any servo parts are replaced, apply pin length must be checked.

Pressure Control Solenoid to Valve Body. 8 ft. Lbs.
Solenoid Assembly to Case. 18 ft. Lbs.
Solenoid Assembly to Pump. 8 ft. Lbs.

Let me know please.

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Wednesday, January 4th, 2023 AT 7:58 PM

KAHALL2010

MEMBER
4 POSTS

Got the shift solenoid changed out on Saturday and test drove it. It will now shift and stay in all gears, but the problem isn't 100% fixed. Now when it shifts it only does so when the rpms are extremely high and then I let off the gas a little bit. From my research I have found that it could possibly be a bad torque converter since I have a lock up torque but over all I'm not sure. Looks like I may be having this thing rebuilt now. Any other ideas would be appreciated.

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Monday, January 9th, 2023 AT 9:35 AM

KEN L

MASTER CERTIFIED MECHANIC
48,363 POSTS

It could be a partially clogged catalytic converter which will make the engine have low vacuum under load. This guide can help test the converter. Does the speedometer work okay?

https://www.2carpros.com/articles/how-to-test-a-catalytic-converter

Please go over this guide and report back.