A few months back I installed a Pettit blueprinted transmission. When it arrived via UPS one of the outside corners of the shifter tower was smashed in a bit. The bolt hole on that side was oblong. There was also a hairline crack on the bottom half (not the cap) that extended a few inches under it, and was also visible on the inside of the bowl. It was very small. I used a tap to fix the bolt hole, and a thin layer of RTV on the crack, both inside and out, and filed down the top mating surface where the cover goes on with a file so that it was flat. I then installed the cover onto the tower, filled it with oil, and installed the tranny into the car.

I discovered almost immediately that oil was leaking out of the bottom of that hairline crack. A month or two later I pulled the transmission out again, and removed the cover from the shifter tower. All the oil was gone.

This time I removed the thin layer of RTV, more thoroughly cleaned the area around the crack inside and out, roughed it up with some 400 grit, and applied a thin layer of JB Weld inside and out where the RTV had been previously. I think re-filed the top lip/mating surface down to again make sure it was flat. I then applied a thin layer of Hylomar to both the top mating surface on the tower, and the bottom mating surface on the cover, installed the cover, filled it with oil, and installed back into the car. Over the next few weeks, when driving the car after it had been sitting for a few days, I could smell oil burning on the exhaust, and there was some small oil drop marks on the driveway. It was still leaking.

TODAY I pulled the shifter tower cover off from within the car, transmission still installed, and found that, thankfully, the crack on the bottom side that I had JB Welded was not leaking! However what WAS leaking was the mating surface between the bottom portion, and the cover on top, as the oil level was exactly level with that mating surface. I guess the Hylomar wasn't doing a good job sealing the oil.


I looked at the mating surface on the bottom of the cover and it didn't look like it had been filed, and taking a file to it seemed to indicate that it was perhaps not perfectly flat. So maybe I forgot to file that surface the first two times.

ANYWAY, what would make a good gasket for these two surfaces?

 

My mechanic friend is telling me to use Right Stuff. Makes sense.

 

There are a variety of products that will likely work, but I’ve always been partial to Hondabond. I’ve had good success with it for my transmission, differential, and even oil pan. I think most recently I’ve used the HT version. Put it on thin.

 

I could never get hylomar to seal over large surfaces like that. It seems to only be good for o rings and other smaller stuff. Toyota fipg has proven to be best rtv ever. Its more rubberized than goopy, oil safe in only 3 hours and extremely easy to remove. You don't need much of it either. Its very good and at 15$ a tube its worth every $

 

For a quarter century, I've only ever entrusted the Mazda Sealant on EVERYTHING...
'ner a drop has ever escaped its rubbery vail.

 

fwiw, The various colors of RTV have slight variations in properties. If using RTV, I'd either use the gray RTV (which Mazda specifies for oil pans on the Miata and is supposed to do well in "torqued" oil sealing situations or something like that) or some black.
Right Stuff and Honda Bond are also good options.

Does that area need to be so full? If it doesn't, maybe remove some oil to try and address the problem.

Good luck. Shitty situation

 

Thanks for the words of encouragement I used Right Stuff. However I filled it with oil when the bolts were still only finger tight, and then I realized and cranked them down.

Does it need to be full? I don't know. But the large ball and bushings on the shift lever are situated near the top of the cover, so I would think submerging them in oil would contribute to a nice smooth shifter feel. Cam actually told me to mix about 50/50 gear oil & something like Motor Honey (I used Lucas stabilizer) to make it shift real nice. Seems to have worked well!

Will report back in a week or so.

 

…or just grease the ball and lower bushing per FSM along with the 3 or 4 oz of gear oil. That makes for a smooth feel too. I use a red tacky grease.




Re: your cracked shifter reservoir…made me think of what a lot of owners do with the recirculating-ball manual steering boxes on antique cars. The bronze bushing that seals the output tends to start leaking gear oil with even minimal use. So instead of gear oil we just fill the whole box with grease. The bushings actually last longer, the steering is just as smooth and no leaking.

 

Hey, hey... don't come in here with your "RTFM", that is way too straight forward. Nobody will have anything to talk about.

Thanks for the suggestions.