let me say, i thought all the cautions about fluid level were over zealous. I'd been an import mechanic for 10 years, mostly pre 1975 rolls royce, bentley, mgb, and jaguar. So, i bought a beat down 1997 XK8, the previous owner had bought it to do a LS1 swap but thought the car was just a little too complete to give up on so he stalled on the project. while getting it running he blew the trans cooler hose from a scrub against something, and replaced it with some spliced in hose, checked the fluid, called it good, and realized the trans was on it's last legs and decided to pass it along. So i drove it home with every warning light imaginable and some id never even seen before. I had a definate and whine, and pressure loss in right turn while cold. So being a pragmatic guy i said , that the hell, and added a half litre down the cooler line. little better, so rince and repeat, repeat, and repeat. Then i had a lack of positive shift under WOT in 2nd, it just couldn't get all the way in, so i just kept adding. Now i never got rid of the WOT issue, but the trans was doing pretty well during 'normal' driving up to half throttle so I thought, 'hey, maybe this is all i can expect from a 125,000 mile 5hp24 that had lost pressure and had some kind of red fluid added after the line repair. So, i grabbed all me empty pentosin atf1 bottle and added them up, 5 litres...... Now, i thought that was excessive, figuring the most the PO could have been off was 2.75 litres, so well, i probably screwed up, and there was no need to actually kill a 70% useful transmission by leaving it overfilled, so i finally bit the bullet today and got it up on ramps. (i know already, but my driveway is is REALLY slanted so trust me, i got close to level) i started here up and removed that demonic fill plug out, burned my hand, dropped the fill plug into the drain pan, watched it fall of the plastic harbor freight POS, swapped pans, poured out ATF into empty liter bottles till i could fish out the drain plug, REALLY burned my hand trying to reinstall, etc. spilled atf everywhere, etc. total circus, had to bite the bullet and lay in puddle etc. you know. Anyway.....
When for a test drive and the car shifted BETTER, i mean much better. I was actually only overfilled by 1.6 litres, but strangely it made a big difference in the shift points between 3-4. Go figure. WHY? no idea. The trans pump pick up through a filter that has a bottom oppening. I'd overfilled in case the filter edges or oring were leaking. What a sensitive transmission. So, lesson learned.

 

I suppose there's a way to edit the original post into something a little more literate but i cannot find it.

 

That's okay, I was able to follow your story, and have seen much worse. You may not be able to edit until you have posted more messages, maybe ten. Did you get the plug in when the transmission fluid was between 30-50 deg C?

 

honestly? Probably not, I had a MODIS set up to monitor temp etc, but when the fill plug spiraled down the plastic drain pan into the inside of it, well it took so long to get it out I was probably over temp. I did go drive it for 30 minutes in traffic and the shifts were a little more solid than when overfilled, haven’t tried WOT yet, but the kick down to 4th @60 felt appropriately firm but not harsh.

 

Stephjac,

Yeah, the ZF5HP24 gearbox is really sensitive to the ATF fill level and also to the right ATF Spec.

I used the lift at my mechanic’s garage, and he had a special tool for easier access to the fill plug. Seen some other forum members’ innovative ways to wrench around the hot exhaust too.



You’re probably aware this ATF drain and fill has to be done twice in order to get the ATF out of the Torque Converter.

I went for the Transgo PR valve upgrade too.



Cheap mod of the “while you’re in there” type that reduced the risk of ATF pressure spikes in the Valve body of the ZF5HP24. Hopefully it’ll extend the life of my gearbox.

As for overfilling ATF, it’s a major problem in the ZF5HP24 gearbox, that is well documented here. It causes foaming in the sump pick up, overheating and you’ll have symptoms of bad gear changes. Also the overheating will vastly reduce the life expectancy of the ATF.

There is an after market mod available able to add a dip stick/fill pipe to the ZF5HP24 gearbox but at USD200 IMHO it seems a bit much for some pipes and bends for a job done every 80k miles. IMHO Might be useful for those who really are having gearbox troubles and want to keep an eye on their ATF.

 

I guess i'd wrongly assumed that any aerated fluid would ride on top of any non aerated fluid, that the aeration would subside faster and that you'd always have an inch of solid fluid riding in the bottom of the sump. I guess my expectations of the rate of 'de- foam' were optimistic. I'm not convinced that this transmission filter to valve body oring is a good seal anyway, just waiting for the parts i ordered to arrive. nobody in portland oregon seems to have a ZF or Filtrans filter in stock, all i could find were taiwanese or some brand named 'Mark,' so i just ordered a Hastings and a ZF online