onthedge928s4

folks,
I have a 88 s4 auto when i shift from park to rev or nuetral to drive i get a delayed bang or clunk in the rear that jars the whole car.I put it on a alignment rack and had someone select gears to isolate the noise .It appears to be in the area or the auto trans and diff?i can`t tell.i replace the ds axel shaft and re greased the ps one but did not rr and inspect .also there is a hissing sound near the center of the trans ,i don`t want to get too out in left field for you guys just wanna give you all the symtoms.
maybe the filter is somewhat clogged for the trans?would the ps shaft do this?I had the same noise on my 85 auto ,but the trans went because
of a bad input bearing not serviced.........i`m sure someone has had this but who has a good answer.also i checked the trans mounts and they are not cracked and i also looked to see if the trans was hopping and hitting something ,it appears to have clearance.i also looked at the torgue convertor bolts to see if they had movement or the bolts were loose or elongated no for both.also there is no history on the trans service and the fluid is pink but has a rather slightly burnt smell which i am gonna address now with a service.also the diff fuid was ck and is of good color and level .I f you folks can come up with something on this i really would appreciate it thanks.... <img src="graemlins/cussing.gif" border="0" alt="[grrrrrrr]" />

2V4V

rtl,

There's a veritable corucopia of stuff this could be but sounds like you've started out well.

I would first check the bolts that hold the rear brake calipers to the hub carrier. If one of these is missing/really loose, you will get this symptomology if the brakes are applied while you shift into reverse (which they generally are).

Also, check the tightness of all the rear crossmember bolts, the axle (cv) nuts.

Do take a really hard look at those transmission mounts, they can appear ok at first glance, but if you start poking on them you'll find the vulcanization has broken between the rubber and the metal.

Could also be an internal trans problem, in which case, at least Steve Cattaneo's in your state (MasterTech Transmission). He's a master trans tech and a fellow 928'er (if you haven't see his posts).

HTH,

Greg

Steve Cattaneo

If you have done what Greg has outlined and found nothing wrong:

I have improved the condition you have describe in a couple of Mercedes Benz transmission by changing the fluid and refilling with MB fluid p/n 00198907 I use a flushing machine, but the flint stone method will work just as well. <img src="graemlins/roflmao.gif" border="0" alt="[hiha]" />
Check the vacuum for the modulator, it must equal engine vacuum at an idle. Any reading lower then engine vacuum will increase the transmission working pressure (line pressure). High working pressure at an idle equals harsh engagements.

Good Luck
Steve C
The Great White

<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

Rob from NH 87 S4

Hi - I just had my transmission fluid changed at my local Porsche Performance shop and while they were at it, they replaced a CV boot that needed replacing. Well, now I've noticed the same clunk from the rear end when I put the car in reverse.

I will check these things that were suggested. I'd love to hear what the result is if you find a solution or cause for the problem.

Bill Ball

Try this. Jack up one rear wheel. Rotate it back and forth. I'll bet you hear the same clunk. Also, note how much play you have. It is normal to have 3/4" at the rim, but most 928s will not make a loud clunk. Mine makes a clunk, although I don't get it shifting from P to R like you. That sounds possobly even worse than mine. I checked the axles, etc, then I removed the differential cover and checked the play in the ring/pinion gear pair. It was OK. However, the small central gears (I ave a NON-limited slip diff) had excessive play - they rocked back and forth, although they did not look at all worn on the surfaces of the teeth. I puzzled over it and closed it back up. Most of the time I either can't hear or don't notice the clunk. Someday I will order a used limited slip diff from 1928 International and pop it in.

onthedge928s4

I have researched this problem and found myself at mercedes benz technical guys.as soon as i mentioned the clunk in the trans they did not hesitate to tell me why .It is rather technical
but if you have this problem i`m sure they can help .Now ,understand there are a few things that can produce this sound but if you have gone every possble route and have isolated the problem to inside the trans not the diff. then for a more exact answer you can contac dominic fettatini at 732-599-1830 .If your in a hurry he will tell you to go Elsewhere , so have some patients .he will not rr the trans because this is an internal problem and will be the demise of your trans if not corrected.tell him bob lucarello sent you the bmw tech in morristown . good luck I happen to have a spare auto trans ,no worries here .
good luck I thank all that responded and helped in my dianoisis process,and steve c. at trans masters for the axtra efforts and follow ups.have any questions just let me know... thanks bob <img src="graemlins/wave.gif" border="0" alt="[byebye]" />

Steve Cattaneo

If all else fails:


The INTERNAL harsh reverse engagement problem is the result of the flat steel plate not providing enough of a cushion for the application of the B3 clutches (reverse clutches) and weak B3 piston return springs.

The internal fix is the remove the transmission from the car, remove the front pump, install; the updated B3 dished plate in place of the flat one, part number 140-993-1526. Changing the weak reverse pistons spring to updated part number 126-993-2702. This modification does not require rebuilding the transmission or a total disassemble there of


Good luck
Steve C
The Great White.
<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />