This is the original trans to this 1970 Cutlass S that had a 350/TH350. Now that it is all back together, trans fluid slowly leaks out of the where the dipstick tube is inserted. When I had it out, the tube slid in a little too easily, so I replaced the O-ring with one that made it much more snug. I am not sure this dipstick tube is even right now. It seemed like a tight seal when I installed it, but it leaks now that it is in and full of fluid (to the right level running in park on level ground).

I would like to get something in there that WON'T LEAK no matter what it is.

Suggestions? I have a pan under it right now catching all of the fluid until it gets down to the level that it will stop. I'll buy something new. I'll buy a flexible aftermarket one (if there is such a thing). I just want something that will insert correctly and NOT LEAK.

I wanna take this damned thing for a drive!

 

I went through this problem with a TH400 that I built. The replacement o-rings for the dipstick tube were too small in cross section and thus didn't seal properly. I ended up getting a couple of different sizes from McMaster Carr until I found one that worked and sealed correctly.

 

Thanks for the reply, Joe, I did exactly that when I had the trans out. I had bought a kit that had different thickness O-rings in multiple sizes and I selected one that was a little thicker than the one that I replaced.

I am about ready to drain the pan (I put in a drain plug), pull the tube, clean everything dry with Brakleen and silicone the damned thing in place...

 

It’s also common to find corrosion and cracks in the groove where the Oring fits.

The best, no nonsense no leak solution is a aftermarket dipstick and tube that uses the boot style seal. You can get them from summit for about 45-50 bucks. Just make sure you specify BOP bellhousing. Most of the sales people are unaware that there are engines and transmissions other than brand “X” Chevy stuff.

 

Thanks Matt, when I had the trans out, the tube and trans casting all looked great so not sure what is going on even with the new o-ring. But, yeah, I remember in a former life, I had an Impala with a TH350 and it had a boot like you’re describing and it never leaked no matter how many times I had it apart.

If you happen to have a link or part # on Summit that would be great. Of course, I will call and ask for guidance from them if necessary. I just never feel like I can trust some random salesperson on the other end of the phone to get me a good part for the application that I won’t have to send back…

 

The best guarantee is the Lokar locking dipstick. The bottom end uses a nut to squeeze the boot and expand in the hole. That does mean it requires dropping the pan to install it. Their non-locking dipstick doesn't have the nut.

Otherwise, half a tube of silicone usually helps, too.

 

I have to say that I've never had to do any of this crap, nor buy an expensive aftermarket part.

 

Well, I may just do the silicone thing and be done with it.

 

I went through this recently. I ended up using 2 O-rings. 1 where your supposed to, but also another, thin o-ring up top where the plastic housing starts to taper near the flange for the hold down bolt. this gave it a second layer of protection and it hasn't leaked a drop since. that was 4 months ago at this point. It took some testing to find the right ring which was frustrating, but it worked out great. Hope this helps, good luck!

 

What plastic housing and what hold down bolt? This tube is one o-ring, a formed flange in the tube metal and a tube hold tab up at the trans to block bolt. I cannot picture what you are talking about.

 

Because I was tired, and mixed up the kickdown cable end and dip stick tube end in my head... sorry. My goof. I also went with silicone on the dip stick tube and it worked well. Small amount and no leaks.

 

Ah, cool, I think I am gonna just do the silicone thing for now. I want to drive the damned thing.

 

That was my motive as well, just getting on the road safely. And its surprisingly dry after a few months.

 

Big difference between kickdown cable and dipstick tube!!

The early cables used a o-ring, the later ones use a boot similar to the dipstick. Once again, make sure the cable is on good condition. Old plastic tends to get brittle and crack easily.

I would think any transmission shop would be able to get the proper o-ring or seal.

 

Ok, back to the dipstick tube which is what this is about, not the kickdown cable.

I'm just gonna silicone it. A trans shop would have done what I did and then had a leak. Then THEY would have likely silicone’d it.

 

Done and curing overnight tonight. Thanks for the replies everyone!