Th700r4 transmission

chevrolet
1500
transmissions

#1

overhal trans, new old pump,but doesn’t ingage in drive. reverse and all three low work fine.drive will only work when rpm’s are applyed.but without any power.


#2

Maybe you mean that Over drive won’t engage. There were several set ups to trigger OD when a high cruise was reached. If you will post the year model hopefully transman will spot your question and give you some details.


#3

Please clarify your question. I am having difficulty understanding what your situation is, and so is everybody else, I presume. From what I gather from your post, you have a rebuilt TH700R4 transmission with a used pump from a different transmission, and I’m guessing the gear selector position between Neutral and “3” does not do anything? Or does the vehicle drive normally, but does not shift into overdrive? And can I infer that by “drive will only work when rpm’s are applied but without any power” that the transmission is slipping? Engine revs freely with little acceleration? Until you clarify your question, nobody will be able to advise you.


#4

I would first make sure that the manual shift linkage is adjusted spot on, i.e. there is no chance that the manual valve is slightly out of the Drive position tending toward Neutral.

Once that is done, I would do a line pressure check and see if there is the correct line pressure when in Drive and what it tends to when you rev the engine. If the line pressure is low, the cause is not likely to be the pump, the filter, or the inlet seal because you have good Reverse and lower gear operation.

If you do have low line presssure in Drive, to trouble shoot further, the pan has to be dropped; the manual valve put into Drive position; and air pressure introduced into the line pressure port. You should be able to hear and/or feel the air pressure escaping. This should direct you to the source of the leakage.

Hope this helps. Please feedback if you find the problem.
TNX


#5

Thats a sprag problem. Either the sprag was assembled backwards and is holding in the wrong direction, which is very easy to do, or it is bad and is not holding. Who did the overhaul?? Did they replace the input sprag and the low-roller assembly?? Thats what it sounds like to me.

transman