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George H.
George H., ASE Certified Technician
Category: GM
Satisfied Customers: 18769
Experience:  15+years ASE Master W/L1 Drivability
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My turbo 400 transmission is leaking at the shifter linkage

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My turbo 400 transmission is leaking at the shifter linkage seal area. I recently had the seal replaced. The person I bought the vehicle from also replaced the seal not long ago and it still leaked. Is there a trick or technique to get this common leak to stop? Can I drop the pan and make some kind of adjustment from the inside? It's a small leak but very annoying. Thanks!

Hello I will help you with your question,


If the bushing for the shift shaft is worn the shaft will move too much for the seal to be effective. The solution is to replace the bushing and the seal at the same time



I cannot access your previous questions at this time, can you please tell me the year of your truck?


Customer: replied 8 years ago.
It's a '82 C10. The TH400 and 396 engine are not original. I don't know the year of the trans. Is the bushing an easy replacement at the same time as the seal? Can this be done without droping the pan? When you say the shaft will move too much... do you mean in and out or up and down (so to speak)? It currently moves approx. 1/16th in and out.

There may be a groove worn in the shaft where the seal rides allowing the leakage, I mean the shaft moves up and down, if you cannot feel any movement we will have to look elsewhere for the source of the leak.


The pan will have to come off is the bushing needs replacement as the shaft will have to be removed.


I have been looking for diagrams to help with the bushing replacement but so far I have come up empty, if you can give me a couple of hours I will keep trying



Customer: replied 8 years ago.
no problem... I'm in no hurry. The diagrams would be very helpful. I checked again... it's hard to tell if there is any up and down movement... maybe a very very small amount?


The oilpan and the valve body will have to come off to replace the bushing. The valve body has check balls that WILL fall out when you remove it from the transmission,




  1. Remove vacuum modulator retainer attach in bolt and the retainer, then the modulator assembly and O-ring.
  2. Using magnet, remove modulator valve from case.
  3. Remove oil pan attaching bolts, then the oil pan, gasket and magnet.
  4. Remove oil filter attaching bolt and the valve body to filter spacer, if equipped, then the filter, intake pipe and O-ring.
  5. Remove manual detent spring and roller retaining bolt, then the manual detent spring and roller.
  6. Remove valve body retaining bolts.
  7. Remove overnor oil pipes by moving them up from case and rotating them

away from their holes.

  1. Remove governor oil screen, if equipped, from inboard hole.
  2. Remove valve body.

If you have never done this before I would NOT advise learning on this one to cure a small oil leak. Have it done by a Pro.


The bushing can be accessed in the case once the valve body is out


Let me know if you are determined to do this yourself and I will provide what help I can





Customer: replied 8 years ago.
I have never done this and will have someone else do it. Do you suggest that I go ahead hand have the shaft replaced also, or first inspect for wear? Also, I use a local shop (not a transmission shop). Is this within the scope of a general repair shop, or should I go to a transmission shop? I don't knos of any good transmission shops.


Inspect the shaft for wear it can be cleaned up to give the seal a good surface to ride on


Find a general repair shop with an older tech that has experience with these transmissions, this is not a hard repair if you have done a few but those that have are mostly retired now, a trans shop should be alright also the owner usually is a tech that retired from turning wrenches to running the shop and has done a few in his time. A leak at the shaft is not unusual,


You are right having a shop repair this, they may try to sell you a complete rebuild, let them know upfront you are not in the market for that, some shops that is the only way they will do this job







George H. and 3 other GM Specialists are ready to help you
Customer: replied 8 years ago.
thanks again!!

Glad to help and thank you for using JA!!