High revving automatic - what's wrong?

[kpytoi1]

Can anyone weigh in on the following issue:
A '68 2+2 has to rev to 4000 rpm just to keep up with 65 mph traffic. The transmission seemingly works ok in other respects, as in, it shifts and drives in reverse, the same for D2 and the two gears there, and all the three gears in D1 without noise or any audible issues. The rear diff is a 43/13 (3.31) but 4000 rpm still seems too high for 65 mph, even for an automatic. It has the right amount of Type F fluid, check while it was running. Is something not locking together/meshing in the transmission? and it's running on just hydrolic pressure? (if that makes sense)
Any suggestions or comments are much appreciated.
Thank you,

Peter

[kpytoi1]

Could it be that the converter is not locking? or that the car is shifting from 1st to 2nd, and what seems like a shift to 3rd is actually the converter locking, but the car is not really going into 3rd gear? The shift from "2nd" to "3rd" only seems to drop 500 rpm. How does one check for that?

[christopher storey]

There is no lock up on the converter on your car. Only the earlier DG box had this . On a 3.31 axle you should be reaching 65 mph at about 2800 rpm, so it sounds very much as though you are staying stuck in intermediate gear . As a first test, get the car apparently in 3rd gear at say 45 mph, and move the selector to L ; you should feel the car change from 3rd to 2nd gear. If it not doing so, then either your selector is mis-rigged or you have pump or clutch troubles. You can check the rear pump by selecting N at about 35 mph and switching off the engine . At about 30 mph switch on and select L when the car should re-start . Obviously, don't do this with anyone behind you . With the car stationary, held hard on the brakes with L selected, full throttle - for no more than 10 seconds - should give about 1700 rpm . If it is significantly more than this - say 2000 or more, then something is slipping. If the car fails any of these tests, then you need specialist help to diagnose the exact problem

[mystery type]

some good info here...

http://dl.dropboxusercontent.com/u/8496 ... ission.pdf

[kpytoi1]

Thank you very much for all the suggestions, here's what I've tested thus far - the car shift from 3rd to 2nd, at speed when the lever is moved to L (engine revs higher, rpm goes up). Doing the stall test, in D1 showed about 2100 rpm, as opposed to the earlier suggested 1700. Also, when the car shifts from 1st to 2nd, rpm drop by about 500-600, from 2nd to 3rd by about 700. I will most likely be taking this to a shop this weekend, but if this is of any help for additional advice, it's certainly welcome.

Thank you all,

Peter