My automatic transmission has had a slow leak ever since I had it overhauled at 100,000 miles some 30 years ago. The cause is a bad seal. I think the reason I never tried any stop leak fluids is because my mechanic told me back then that they did more harm than good.

Is this true? The leak has been getting worse lately, and now I'm obliged to top-off every two months. I'd like to try Blue Devil Sealer (liquid rubber) but thought it would be wiser to put the issue before this forum first to see what is recommended by those with experience with these stop-leak transmission products.

 

Is the leak where the drive shaft exits? If so, the problem is more than likely due to a worn tailshaft bushing. If you replace the rear seal without changing the bushing then the new seal will most likely leak as well.

 

First determine where the leak is from - and address it. Don't use any seal swelling stop leak products - you may regret it.

 

Thank you friends. My mechanics all have located the leak at various times over the past 30 years. It's on the underside of the transmission casing. It can't be fixed, according to them, without another transmission overhaul. Am I risking more than that expense by trying stop-leak products? Would it be more cost effective to go straight to a full overhaul? Finding new seals would probably be a challenge.

 

The bell housing orings can leak - there's really no cure other than replacement - the parts are available - and it does not require "overhaul". It does require removal of the transmission to be able to get the bellhousing on and off. Below is a link to one of the orings - there are 2 different part numbers for the 2 orings. I would not count on a seal swelling stop leak product to make an old hardened oring swell up enough to solve anything. (the rubber orings would usually break apart during removal the rubber was so hard)

 

Many Thanks, Hoonk. I guess that's why I've just let it leak all these years. I'm just trying to keep this old boat afloat until somebody offers a fully self-driving all-electric vehicle.
But most of the leaking fluid ends up in a pan under the Volvo in my garage. I've been collecting it and recycling it back through the transmission and then occasionally hauling it off to a recycling point. I suppose dust and debris that doesn't collect at the bottom of my recycling container while the fluid is awaiting reuse could cause problems in my transmission, but so far, so good. False economy?

 

Definitely false economy. You want the fluid in your transmission to be clean. Any grit or dirt that from your collection pan can be bad news for your transmission. On the flip side, these AW70 transmissions are extremely robust and can take a lot of neglect. Makes me wonder why your transmission needed to be "rebuilt" at 100,000 miles. Bad mechanic?

 

Cowden Automotive was my mechanic for close to thirty years. The recommended procedure at 100,000 miles may not have been a rebuild, but it cost over $1,000 and was done by a local transmission specialist recommended by Cowden. The specialist said the servicing would insure the transmission ran smoothly for another 100,000 miles. That was 200,000 miles ago, and it has leaked ever since. Did Cowden get a kickback? I was a casual friend of the owner and he was a very honest guy. Just don't know. Thanks again. I'll use only new Dexron III.

 

You might try what worked for me on my '93 940.
A similar product is endorsed by Scotty Kilmer,
which is why I tried it and it worked almost instantly. It's not a stop leak per se. Instead it rejuvenates the rubber so it can seal. Obviously, if the seal is torn this won't work. But like you, I had a slow but steady leak from the front seal and it stopped within 15 minutes of using this. I also had a valve cover gasket leaking on my '03 Lexus and it stopped that one, also in a few minutes. Worth a try.

 

I'll be happy to try anything that won't cause damage, but my seal was leaking very soon after it was installed. "Bad kit" was the explanation my mechanic gave. So restoring the seal to where it was when installed would mean it would still leak, but maybe less than it does now. Would using this product involve risk to the transmission?

 

I haven't noticed any change. And I've used it in the transmission fluid and the motor oil. Kilmer wouldn't recommend it if there we're risks. He's used it for years.

 

Then I'll give it a try. Thank you!

 

People have different opinions about that guy -

ANY leak fixer is going to work by using solvents to make rubber swell. But - hey it's xx years old and still running, not worth much, what do you have to lose? (other than your daily transportation)

 

I can afford to have the transmission repaired if it stops functioning, depending on the availability of repair services and parts. I just don't know my Volvo automatic transmission well enough to know what could go wrong and whether the damage could be fixed. The fact that it started leaking right after it was serviced the first time 30 years ago reduces the chance of a completely successful stoppage of the leak, but it might slow it down. I don't even know how much it would cost to have it disassembled and the seal replaced. A tempest in a teapot dilemma! Thanks for your input, Hoonk. I'll sleep on it.

 

There are many seals that can leak and the fluid ends up dripping from the oil pan. Cooler fittings, selector shaft, bellhousing orings and the pan gasket itself. Not included in the list below is the oring on the kickdown cable. Only the bell housing orings (and the front seal) require removal of the trans to replace.

 

Three different mechanics have advised me over the years that my leaking seal, which is near the solenoid, can't be fixed without removal of the transmission.

 

That would be the bell housing oring - 7a

 

Good to know!

 

Does that information affect a decision about whether to try AT-205 re-sealer?

 

Interesting side note - Before I added the seal fix I pulled out my dipstick to check the oil level. It was snug (I put a new o ring on the dipstick a month before) but it came out ok. After the seal fix stopped the leak I shut off the engine and went to check the oil level again and I couldn't pull the dipstick out. The o ring had swollen enough to require a good yank to pull it out. So, if the cause of your leak is due to a cheap, aftermarket seal that isn't the exact diameter needed the seal fix my swell it up enough to seal. As far as the bell housing seal leaking, you may just want to put some in a spray bottle and spray some on from the outside just to see if it has an effect? Either way, it's a cheap $10 experiment that may work.