1986 Automatic Transmission Leak

[birdyhues]

Hi! I’m new to the forum and to transmission maintenance, but a long time GM owner with good analytical skills. I need some help identifying the source of a transmission leak in my 86 C10.

A few months back, the power steering went out. Around that time I also noticed a good sized pool of transmission fluid under the truck. I don’t drive it much, but I keep it on a trickle charger and have taken it on short distance drives since then.

Recently, it’s started having trouble shifting into reverse, and only reverse. I did some googling and it seems likely that this is due to low fluid, which isn’t surprising given the puddle from earlier.

I took it to a store a few miles from home recently and it struggled to shift from a low gear to a higher gear in drive once in the way home.

So, now I’m looking to fix it and want to try some things on my own to build my skills first. I’m planning to change the fluid and filter since that seal is probably needing to be replaced, but I got under it today and got some pics of the pan and noticed fluid in some other places that may need attention. I’d love to know what I’m looking at and if I should plan to do anything more than the fluid and filter while I’m at it. Looks like a new pan might be a good idea, too, for example.

 

[NickTransmissions]

Replace your pan gasket (DO NOT USE a cork gasket), speedometer cable/housing seals snd rear transmission mount. Check the governor cover seal, replace that also if leaking. Double check the selector shaft seal - replace if leaking.

 

[Blue Ox]

I'd also suggest giving it a cleaning. You can use a spray-on engine cleaner and a garden hose. Leaking fluid migrates all over and makes it impossible to tell where it's coming from.

It's also preferable to clean it before you do the service work Nick recommend so you don't get grit and crud in it while you have things opened up.