Transmission slipping when hot?

[transman]

I do not have a tach. Under normal driving there is nothing out of the ordinary. The only slipping I'd experienced was under wide open throttle, shifting from 2-3, after 5 runs with no problem. The first time it happened I heard the engine suddenly rev a little higher, as if I had not timed a shift perfectly in a manual. The really bad slip I experienced at the racetrack felt like someone had left his foot partially on the clutch as the transmission shifted from 2-3. I could feel the engine revving much higher than before and could also feel that the engine was not pulling the car anywhere near what it should. Then when I feathered the gas, it settled into 3rd - no clunk or anything, just sort of settled.

Fluid level is normal. On the advice of the transmission guy I cannot afford, I've been adding TransX in place of ATF to keep the level up, hoping it might slow the leak. It hasn't.

The car has only its stock transmission cooling lines running to the radiator, which has a new core. I did not clean out the transmission cooling lines, nor have I ever replaced the fluid that was in there. It had been sitting a long time and the level was low but it didn't look or smell weird.

Regarding the kickdown - I installed the Lokar system about 8 months ago. I followed the instructions pretty carefully and the transmission kicks down from 3-2 on the highway as it should - seems fine for the most part and works according to the factory specs (about 65 mph or lower). I have occasionally wondered if maybe it shouldn't be adjusted slightly as I am used to automatics downshifting at any speed, even over 70 mph.

TransX and all other seal swellers are usually a waste of time and money. Yes, they may for a very short period of time swell the seal enough to kind of stop the leak, but not for very long. I was told once that you might as well put in brake fluid, as it will swell the seal as well as any commercial product.
As others have said, it's time for a rebuild unless there is a linkage issue.

Do it RIGHT - ONCE.

 

[TrailBeast]

I was told once that you might as well put in brake fluid, as it will swell the seal as well as any commercial product.

That is true too, but it's the same as any of the commercial temporary fixes. (temporary)

 

[Trevor B]

who...or what is shifting this transmission ?
are you allowing it to shift itself, or are you shifting it?
and if you are shifting it, are you using the stock shifter linkage or a ratchet type shifter?
and if your using a ratchet type shifter, when was the last time you cleaned and lubed it...and maybe inspected and adjusted the cable?

Car has stock column shifter.
I was starting in "2" (this was before we fixed the linkage), letting it shift automatically between first and second gears, and then popping it up to "D" to shift to third.

"When it does it, pull over, put in reverse and power brake it and see if still feels like it is slipping. What I'm trying to determine is if you have a 2-3 overlap issue or direct clutch issue, and the kickdown could not be set right. Did you confirm if throttle is to full position, the kickdown lever is 100% stroked?"

As the car seems perfectly driveable right now, I am going to do the following:
1) Drain the transmission fluid and drop the pan to look at the fluid and what's in there.
2) Clear out the cooling lines.
3) Disconnect the kickdown linkage and re-install it.
4) If I can get to it (exhaust pipes don't give much room to work down there) I'll adjust the kickdown band according to the manual.
5) See if there is any way I can pinpoint the leak and hope it is coming from the dipstick filler tube or something more easily repaired.
6) Refill with normal transmission fluid and stop messing around with TransX - it clearly hasn't helped anyway.

Afterwards I'll try it out and see what happens, doing the above test as well.

As I won't be doing any racing until next summer and plan on cleaning up the engine some more over the winter and spring, I think I'll wait on doing anything with the actual transmission. It would seem that if I ended up working on the heads and putting in a cam, it might like to have a different torque converter anyway - something with a higher stall perhaps.

Also, as I picked up an old 727 a while back, I may see about taking it apart and rebuilding it myself so if I decide to try my 904, I'll have some familiarity with the innards and potential trouble spots.

 

[diymirage]

so we KNOW the shifter linkage was questionable, and we know the kickdown may not have been adjusted properly?

what I don't know (I'm sure someone will chime in) is if it is possible to short shift the transmission from 2nd into 3rd and get caught in between?

I could see that causing slippage
(and since it would be operator error, it would be free to fix...gotta love that)