Tranny troubles!!!

I would not say that 700R4 were ever weak but the did have some design flaws with the overdrive unit and lock of converter and cooling oil routing that were mostly worked out by 84 and any year 700R4 can easily be brought up to lastest standards on a overhaul. The 700R4 is based on the THM350 which itself was a pretty trouble free unit  

I thought shift kits were supposed to make your transmission last longer because of the hard shifting, which dosen't really makse sense because the harder it shifts the harder it is on parts. The 700R4 is a TH350 with an overdrive unit on it.  

You have the picture now. It is a balancing act in a automatic tranny but stiffer shifts do put more strain on internal parts and even more so in a heavy SUV. It also depends on what they are doing to get the firmer shift too as to how bad it might be.  

Increasing line pressure is usually how shift kits obtain firmer shifts. This does reduce slip on friction surfaces, extending the life of said friction surfaces, but also increases shock load or impact forces on all other parts in the transmission. Your friction surfaces will probably last longer, but you are more likley to damage or break all other tranny components.   

Then there is the increased pressure on seals in clutch packs and such and added strain and front pump to maintain higher pressures and extra heat because of higher oil pressure. It is a balancing act and I myself am a big believer in just leaving trannies stock and anding a aux cooler for long tranny life.  

I dont need any research I know a guy who has a 700r4 with a two stage shift kit and he hasnt had one single problem whatsoever with it it was his back brakes and rearend that started *** up from it.  

And I can find tons of 700R4 and 4L60's that have failed from use of shift kits. Usually it is the sprags that go first in stock units with shift kits. When you build up one of these trannies you must upgrade the sp  

your need to echange for a later unit, manufactures correct weak links all thje time, make sure your relacing the torque convertor and flushin the lines and radiators if its not pluged already  

It is not the unitas any version can be easily upgraded to lastest standards. Any 700R4 from a 87 or later is a good as they get from factory and anything after 85 pretty safe too. Stay away from 84 and back model that have not been upgraded to latest standards but upgraded or not they all have weak sprags that can fail with some shift kits over time but will last forever with stock trannies.