Just had my 97 xk8 gearbox totally rebuilt new torque converter, new valve body had the tcm reprogrammed and it still flares between 2nd and 3rd. the flaring is mild at low rpms and sometimes it shifts like brand new but most of the time it flares and then hits hard or sometimes double hits 3 times on hard acceleration it hits hard followed by a gearbox fault. it is not popping any codes. the shop is as confused as i they have totally con through my tranny a second time looking for problems and found none the fluid looks good as well.
they suggested the tcm could be the culprit, I found a used one with warranty that came from a good running car. now I have found conflicting information on installing the tcm some say I have to have it reprogrammed and if I dont it will tear up the new transmission, others state its plug and play and that it will adapt.
can anyone help me with this?
Thanks in advance

 

If the replacement has matching numbers it may be plug and play, but it won't hurt anything to try. I bought a spare and it works fine, but I have been told that you may get the 'wrong part fitted ' message and have to visit a shop with Jag software to get the ECU to accept it.

 

the numbers all match, i also read that a weak battery can cause problems with the tcm, after sitting overnight my battery is at 11.5 when I turn on the key car starts right up tho. I hope this new /used tcm solves this issue, its sucks when you spend 3650.00 and the trans still isnt shifting right

 

The battery should be at least 12.5V after standing overnight.

 

Well I put in the new TCM and now it not only flares it double bangs and then does not go into 3rd until i let off the throttle

 

has your rebuilder in wash. talked to tech at ATRA . I'm assuming they are ATRA members. I would throw the old V.B back on and see what happens . may give them a direction. whos doing the work on the car ,the trans shop or yourself . I ask because you've spent the money , you should step back and tell them to call you when it's ready. That's the way it is at our shop . a flare is usually a clutch clearance issue . when you say "new" VB , you mean brand new from ZF??

 

when they rebuilt the tranny the installed a re-manufactured VB. when the flaring and hitting from 2-3 they ordered and installed a brand new VB. when that didn't cure the problem they removed the tranny and went through it making sure nothing was missed. There has been no fault codes. So I installed the other TCM it still flares between 2-3. now at low RPM it seems ok but a little throttle and it gets worse and hits harder just on the 2-3 shift, some times it will shift like its supposed to at any rpm but that is intermittent at best

 

if the tcm sees a slip on the shift it will ramp up mainline pressure to try to reduce the slip . that will often create a slide -bump shift . I would at this point, if it was me building the trans , be turning to ATRA for help . That's what we ,trans shops , pay them for .

 

I was told that if there was slipping it would pop a check engine lite but as I said it hasnt thrown any codes. My battery is always showing 11.2-11.5 volts after sitting a bit while driving its at 13 volts could this be causing this?

 

I would also be interested in the part # of the new V.B. . Not all 5hp 24 VB's are created the same . there are many color coded plastic orifice discs inside . there job is to control how long a shift is ,hard or soft, . one zf for one car and motor ,tcm software, is going to be setup different than another.

 

I will find out tomorrow I am stopping by to talk to the shop, thanks

 

it will only code if the slip is too long and out of the peramiters of the software and the computer can't reduce it by ramping up pressures . theres an epc sol that controls mainline . also some of the shift sols and accumulating sols that are all pulse width sols, meaning that they all are capable of changing pressure and timing .

 

I will find out tomorrow I am stopping by to talk to the shop, thanks

 

I have had many ,many problems that I would love to blame on battery and computers and software .... battery voltage and ground are important and should be right ,,, however rarely fixes a tranny problem after a build

 

being intermittent could it be a sticky valve in the VB? Someone mentioned a sticking solonoid

 

Earlier you mentioned clutch clearances The other day it shifted awesomely all afternoon then the next day 2-3 shift flares

 

I've not seen low battery voltage cause a transmission shift issue, but you do have a failing battery none the less. 11.2 - 11.5 volts for a 12 volt rated battery is a failing one. Even though it starts the car, just get the battery replaced. All the computers need proper voltage and amperage while cranking the engine over. You'll have piece of mind that it starts the next time and it just might help with your situation.

 

I totally agree with addicted to boosts statement.
the reasoning or the inconsistantcy is that the computer is trying to manage the problem.

 

Talked to my tranny guy, he said they matched up the valve body from the original I mentioned your suggestions and he is looking into it. I put the original tcm back in and still the same at low speeds it shifts fine give her a little rpm and the flare is longer as the rpms increase then hits hard

 

This is worth reading. Audi A8 Quattro ZF5HP24 TCC Cycling Bang - Sonnax


Whether or not it relates to your problem, it does show what is involved with a proper approach to troubleshooting, and that approach would be similar I would think.