Bavooz Flo

Hello,

what are the symptoms of a torque converter? And what can cause it to fail?

Thank for your feedback

sofakingdom

iTrader: (1)

Well, being able to put the trans in gear, and not stall the engine.

But I'm guessing you're REALLY asking, what are the symptoms of a torque converter FAILURE. In which case, usually it's strange noises, or metal in the fluid. Or in the case of a lockup one, failure to lock up.

The usual cause is ... failure. There's a sprag in there that can fail (it can sort of "strip"), which in a non-lockup one, is about the only thing that typically ever goes bad. It makes noise and sheds metal into the fluid. Lockup ones such as the 700-4R can fail by the lockup clutch material wearing out, or the hydraulic circuits that work it, having problems such as leeeeeks.

Bavooz Flo

ok, then I am not on this problem, in fact, I have a problem on downshifting on 2-1, with a little clunking or bump or litle jump(sorry for the term I am french), only in D, in OD no problem !

For example when I arrive at a stop, when I brake gently => problem detected and if I brake hard, it is not detected....

I have changed the mount trans, yokes are good...check the tv cable, flush fluid trans........ where could this come from? Gouvernor ?

naf

iTrader: (7)

when in D the over run clutch is engaged and a little clunking or bump when downshifting is normal

Bavooz Flo

Ah ok "the over run clutch" is engaged only on D and not in OD ? if it is normal, I could try a same vehicule for compare..

Perhaps a problem resolved after 1987 on the TH700R4 ? I don't know the evolution of TH700R4 ...

sofakingdom

iTrader: (1)

Correct. That clutch is not actuated in OD. These 2 clutches are stacked up in the same drum. The overrun clutch both operates the forward clutch AND at the same time "locks up" a sprag, which otherwise would be free to free-wheel in OD when you take your foot off the gas. Having it "locked up" allows the engine to act as a brake in non-OD. The clutch itself isn't likely to be the culprit of any clunk or bump; rather, it makes it more likely that you'll feel whatever imperfect shift timing might happen to be going on in your transmission. By "timing" I mean the relative application and release of clutches during a shift: in the 700, one clutch (the band actually, which is just a differently shaped clutch) has to let go to get out of 2nd and another (3-4 clutch) has to apply, and vice-versa to downshift. If the band lets go too early or the clutch applies too late during a shift, the engine RPM flares up during the shift, and if the band releases too slowly and the 3-4 clutch applies before it's fully released, the car is effectively in 2 gears at the same time, which tries to instantly stop the car. This creates that familiar "stutter" kind of feel as it shifts and also causes a HUGE "clunk" from the transmission, drive shaft, and rear end all quitting propelling the car (applying torque in the "drive" direction) to braking the car (torque in the opposite direction) for a fraction of a second. This is one of the hardest things to get "perfect" in this transmission; ideally they should "overlap" just enough to keep the engine RPM under control, but not so much that it "clunks" on an upshift. It's EVEN HARDER to make the trans get upshifts right, AND downshifts too. So, while maybe not "perfect", in a properly-working 700, some degree of mis-timing of that shift is natural during a downshift. It shouldn't be harsh or aggressive or anything like that; just, not as smoothly and perfectly timed as the upshift. The overrun clutch transmits more of that to the driver when it's engaged.

Yes newer transmissions had more refined valve and fluid passage control of things, improving all of that. The 4L60E and 4L65E use the same clutch arrangement, and similar refinements continued during its production run as well.

Bavooz Flo

ok thank for your detailed feedback ! .. and a new adjustment of the cable TV will not correct this sensation ?
I have already done but that never change anything ... with minimal adjustment only because I know, it can be dangerous... for transmission

sofakingdom

iTrader: (1)

Probably not. It's internal to the transmission. A new servo (the thing that applies the band) might help. Get a "Corvette" one.

Bavooz Flo

https://transgo.com/product-details/...eDOeQFPbVFVjN-

This one for example.

There is this kit also, perhaps it can be benefit ? => https://transgo.com/product-details/700-jr-shift-kit/