ZF 4HP22 Gearbox - Pops Tech Tip - Gearbox mount

[poprivet]

An updated and revised article by the original author, previously posted on the ‘Nine Lives’ CDROM and on the Jag Lovers web site

This article covers the ZF HP-22 automatic gearbox as used in the 3.6 litre XJ-S and the XJ40 saloons (AKA Basil’s) It may apply generally to others as well.


'Should I change my gearbox fluid?' you ask.

Well probably yes, but its quite likely you need to do a little more as well. Most owners only think of changing the fluid once some problem or other has come to mind. A fluid change can help and certainly will not make a problem worse, although it may bring other problems to the surface.

The manuals say change the fluid if its not pink in colour anymore, so you've looked at the dipstick and it looks pink. The trouble is your looking at a thin film of fluid on a white plastic stick, of course it looks pink! How about draining some into a clean glass jam-jar using the rear drain plug. Doesn’t look pink any more does it? More like black tar with shiny glittery bits floating in it!

A quick drain and refill is better then nothing, but I bet that old fluid you've just drained looks really black now doesn't it? Better to drop the pan and inspect the magnets and strainer. I always wondered what these magnets were that everyone spoke about, its easy really, there are two small bar magnets attached to the bottom (inside) of the sump pan. Not stuck as such, just held there by their own magnetism. These magnets actually do the bulk of the filtering by catching the minuscule particles floating around the system. They will likely look twice their actual size, covered in a sort of metallic grey mud, and are easy to pull off and wipe clean. The strainer is attached by 3, size 27 torx screws. Some people will tell you to just rinse it and re-use it, it evens comes apart if you carefully prise the folded edges apart, personally I would just buy a new one and be done with it.
Using a new gasket, refit the pan and top up with new fluid to the correct level. Job is done.

Well, not completely. It is impossible to drain all the fluid in the gearbox, some remains in the torque converter, coolant pipe work and innards, so all this will need doing again soon. Eventually most of the nasty gunk will be taken out by your efforts. There is one proviso I would mention. Gearbox fluid is a detergent type hydraulic oil, that is, it is designed to clean and hold impurities. A good thing? well yes, but adding a new supply of fresh fluid to an old and dirty gearbox can flush long resting dirt from crevices long forgotten, to cause new problems either now or in the near future. Gearbox failures are not unknown following a flush and re-fill, this is indicative of the previous neglect not of the flush itself. A really old gearbox that is working well might be better left alone!

While you have access under the car, its worth overhauling the rear mount.
On the 3.6, the engine and gearbox assembly is supported by two mounts either side of the engine and one at the rear of the gearbox. Failure of the rear mount will likely make its presence with an annoying grinding sound from the engine cooling fan rubbing its housing during acceleration or thumping noises from underneath the car when going over bumps.
The Haynes XJ6 (XJ40) manual describes how to tackle the problem, but take note that they show the final assembly incorrectly. The correct way of assembling the parts is shown in the Jaguar parts catalogue. The 'foam' mounting that usually fails, confuses many, it has two main purposes, to act as a top insulator to the large spring and to provide lateral cushioning to the spring housing that is attached to the gearbox itself. The genuine Jag part really is foam rubber, but after market replacements are sensibly of a solid rubber construction which is much durable and longer lasting. When fitted, and the weight of the gearbox is in its normal position, the upper housing ‘floats’ within the foam mount (see diagram below). While apart, there are three rubber items to change, the foam mount itself and two spring seats, the seats hold up quite well and may be ok, but the foam buffer will be in pieces so it is better to get all the new components at the same time.
Early models relied on a retaining strap to stop the gearbox bouncing too far upwards, later ones have a foam rubber cushion fitted between the box and the bodywork to buffer movement.

Foam mount - Guess which is the new one?

http://i11.photobucket.com/albums/a183/ ... foam-1.jpg

Gearbox mount as removed. Note how the foam mount had collapsed, allowing the lower spring to push up the whole assembly - this results in the gearbox knocking on the transmission tunnel and against the mount assembly itself.
http://i11.photobucket.com/albums/a183/ ... mount1.jpg

As overhauled, new rubbery bits, all cleaned and treated with Waxoyl ready to be fitted back into the car.
http://i11.photobucket.com/albums/a183/ ... mount4.jpg

THE WRONG WAY! If you follow Haynes, it will look like this. Very similar, but the spring and locating weight is much too high. See text above.
http://i11.photobucket.com/albums/a183/ ... mount5.jpg

OK - This is how it should look when back in place. Note how the upper spring housing floats within the foam mount. Also the three rubber bump stops should be in place at the very bottom and the top to stop any knocking. If you had assembled it using the method described in Haynes, the upper spring housing will be stuck in mid-air suspended on the spring bouncing your gearbox all over the place.

http://i11.photobucket.com/albums/a183/ ... mount3.jpg

Pop

[MARKPEARSON]

I have been there with the buffer ring failiure it drives you mad.I fitted after market unit and the knock came back very quickly.So I bought a jaguar one and it was a slightly different shape to aftermarket one.The jaguar one has now been fine for three years.I changed the original at 40k so it should last me a few more years.I would personaly recommend a genuine jaguar one but the choice is yours. The jaguar one cost £22.18 the other one cost £12.93.

Mark Pearson 1993 4.0

[nigel1]

Thanks Pop

Nigel