Zf Transmission

[piper109]

Has anyone on this forum ever rebuilt a ZF transmission?

It looks like I am going to have to but I would love to be able to compare notes with someone who has already been there.

Thanks,

Steve

[ngoma]

Does this help?
http://www.disgruntledgoat.com/content/vehicles/dakar/ZF4HP22.php

[piper109]

Thanks, I had seen that link. I have done some serious Googling on this !!

I have now pulled down a tranny, not the one in the car but one that I had in another car that was working OK (with some issues) when I pulled it out.

I have discovered why ZFs sometimes dont want to change out of 1st gear on cold mornings. The seals on the inside of the governor wear grooves in the aluminum governor housing and leak so the governor does not transfer pressure to the right place to make the gear change. Its actually quite easy to fix and involves removing only the rear cover and could easily be done with the transmission in the car.
I have taken some pics if anyone is interested.

This transmission is 25 years old but I can still see the printing on the clutch linings so very little wear takes place. I also now know all about the fix for the residual clutch A pressure and thats easy to do also but removal is necessary for that.

I have the Volvo Green book and actually its quite easy to work on and special tools are only really needed to compress the springs so you can replace piston O rings in the clutches and the brakes.. I plan to make mine out of large diameter PVC fittings.

I will keep you posted.

Steve

[v8volvo]

Interesting. I am glad to hear that clutch pack wear does not seem to be much of an issue. I'll be paying attention to this to see what more you end up finding out about these transmissions.

Any theories yet on what might be going wrong with your ZF in your wagon? Sounds like an unusual failure mode for these units. From what I understand they usually just quit working suddenly, rather than letting go slowly like yours is doing.

[piper109]

Well I have now removed the transmission from the car. I had figured out what the problem had to be beforehand. It slipped in every gear so reading the documentation, Clutch A is used in all forward gears.
Knowing the traditional Clutch A problem I figured that's what it was so I pulled it down part way and confirmed that this indeed the cause of the failure.

The input shaft seals which provide clutch A pressure are quite worn and I suspect the stator may have wear where these seals run. Clutch A is quite worn but not destroyed though it is clearly on the way. I only drove about 2 careful miles after the "shudder" and I think it prevented the clutch from destroying itself completely.

So, it is indeed the "classic" ZF failure. Fortunately I have enough stuff that I can fix it and its not difficult.

I would recommed to anyone with an ageing ZF that's still working to yank it and do 2 fixes.
1 Replace the input shaft seals and drill the relief hole in Clutch A piston etc. See http://www.disgruntledgoat.com/conte...ar/ZF4HP22.php I have another article on the drilling etc.
2 Replace the governor body and the 3 seals on the back end as the shaft seals wear into the aluminum body and pressure is lost. The centrifugal governor spool itself becomes sticky so dismantle it and polish the spool with crocus cloth (1200 grit emory cloth).
This is what stops it from coming out of 1st on a cold morning.
The rest of the transmission appears to stay in good condition and by doing these 2 improvements it could continue to give you wonderful service for a long time....assuming you catch it before Clutch A tears up.

If anyone wants further details, I can probably provide.

Steve

[piper109]

Well the ZF is now reassembled with all new seals, replacement clutch A and B plates and mods to clutch A and governor seals. All is installed and the car is back on the road.

I am happy to say that it appears to be working well. I may have to make fine adjustments to the kick down cable but otherwise I am happy with it. I am going to do a fluid change soon and install a filter into the coolant line.

It was an interesting project and I learnt a lot. I would not hesitate to work on another one. Total repair cost about $200 (lots of free labor).

I still prefer stick shifts though....better mileage, better control.

Steve

[v8volvo]

Is the delayed/harsh morning shift out of 1st gear gone?

Congrats on tackling the job and getting it fixed. I have been afraid of tearing into one of these units after hearing all the stories about them, but after reading your comments I will now feel more brave when the time comes. Thanks again for posting this valuable info.

George

[piper109]

Yes it is. That was caused by a worn governor housing or sticking governor centrifugal valve. Transmission changes well. Its still a bit harsh going into 2 at very light throttle.
I will investigate that. Its a valving issue I believe or related to the kickdown cable adjustment.

Steve