Thread: zf AUto converter lock up

I run a GMC 6.5tdv8 in my RRC and fitted the t700 GM tranny as well.

I converted the T700 to have a locking TC very simply as it has an solenoid connection which just requires a switch to do that. It also required an internal rewire as well. It automatically disconnects at low speeds so if the switch if left on the engine does not stall although the tranny rebuilder wasn't aware of that and warned me to ensure that I switch the TC lock off when polling up.

I'd imagine that the ZF tranny would function very similarly.

The ZF lockup is 100% hydraulic and needs expensive mods just to get it to lock in 3rd. I can't see any likelihood of getting lockup on demand. The 700R tranny is a far better bet if you want lockup on demand, there are various ways of controlling lockup, most common being a vacuum switch on 4th only.

Originally Posted by bee utey

The ZF lockup is 100% hydraulic and needs expensive mods just to get it to lock in 3rd. I can't see any likelihood of getting lockup on demand. The 700R tranny is a far better bet if you want lockup on demand, there are various ways of controlling lockup, most common being a vacuum switch on 4th only.

I use a adjustable vacuum switch kit as well in the t700 which i got from summit racing $75 and also have a bypass switch which I can lock the converter in any gear. If you can afford it install the t700.

There is a mob that can mod the zf valve body to lock in 3rd gear but it was well over $1000. They were from Melbourne. I looked at all this myself years ago with chev to zf (blew up 2 zf's) and finally went to a modified t700 to chev in the end.

The only problem with the T700 is the massive cost in hooking it up to the LT230T. In the end I wished I hadn't done it! There is simply not enough side clearance to allow the mainshaft to clear the output shafts = 230mm.
We had to modify the width of the T700 main case and sump and even then extend the T700 with a custom made stub shaft and then the front and rear prop shafts and the list just went on and on.

When I had the ZF in my car reconditioned, I enquired about some way of getting the convertor to lock up on demand and was told it was near impossible- can't recall the details. The reconditioner suggested I try a low-stall convertor instead. I've been very pleased with the result; it makes a surprising amount of difference to engine braking on steep descents.