Clunk / Thud When Downshifting

[wasabinuki]

I have an 89 325i with an automatic transmission and 175K on the clock. I very much like this car, but there is one major annoyance - something "clunks" when I am coming to a stop.

There is never a clunk when accelerating / up shifting, but when I am slowing to come to a stop something (from the transmission to the differential) clunks. It is almost like a hard downshift, but the funny thing is that if I put the car in neutral while coming to a stop it still clunks, just not as bad. Something else strange is that the severity of the clunk is inconsistent, but it seems to clunk more consistently when the car is warmed up.

This is very annoying, and I have searched a ton of threads and replaced a ton of parts trying to fix this issue. Without success :sad:

Over the past 5 months I have replaced the following parts:

Shock (front and rear)
Springs (front and rear)
Front Shock Tower Bushings
Rear Shock Tower Bushings
Sway Bar Links
Tie Ends/Ball Joints
Used 4.10 LSD (quiet and smooth)
Diff. Mount
Front Control Arms
Front Control Arm Bushings
Rear Wheel Bearings
Rear Half Shafts (rebuilt)
Drive Shaft (new U-Joints and CSB) (rebuilt)
Guibo


I have not replaced the sub-frame bushings or TAB's, but visually they look ok. A few forum threads mention this exact issue, but none of them shows a solution. So, can anybody shed some light on this for me?

Added more to the discussion a few posts down.

[lateracer]

Subscribed....same car. EXACT same problem. EXACT.

The only thing that I've seen - but doubt - that's not on your list is the diff bushing. How's that?

I've only replaced one set of subframe busings, but one of the things I saw that car do that was b/c of the bad bushings was that when you jacked up the rear end (not using the rear subframe) you could watch the subframe drop a little once the tires lifted.

[E30Gus]

This may sound far fetched but after my diff swap, the 4 bolts holding it to the subframe started to come loose and my car started doing the same thing. I'm glad I found out sooner than later that they weren't tight.

[wasabinuki]

Subscribed....same car. EXACT same problem. EXACT.

The only thing that I've seen - but doubt - that's not on your list is the diff bushing. How's that?

I've only replaced one set of subframe busings, but one of the things I saw that car do that was b/c of the bad bushings was that when you jacked up the rear end (not using the rear subframe) you could watch the subframe drop a little once the tires lifted.

Sorry - I did replace the diff mount and forgot to put it on the list.

This may sound far fetched but after my diff swap, the 4 bolts holding it to the subframe started to come loose and my car started doing the same thing. I'm glad I found out sooner than later that they weren't tight.

When the newer diff went in all the bolts were tightened to spec. The car did the same thing before the newer diff went in too, so it has to be something else.

[lateracer]

This may sound far fetched but after my diff swap, the 4 bolts holding it to the subframe started to come loose and my car started doing the same thing. I'm glad I found out sooner than later that they weren't tight.

Good point. My diff bolts came loose on my track car after a day of auto-x following a swap. I'll take a look...can't hurt.

[lateracer]

Diff was tight. While I haven't checked and/or replaced several potential culprits (CSB, U joints, CV joints, etc) like wasabi did, I'm inclined to think that the problem is the transmission making rough downshifts.

I know the clunk still happens when in neutral, which would normally point to some other part of the drive train; but these transmissions don't really "let go" completely in neutral either, which might explain the reduced - but still there - clunk when making the 2-1 shift.

[wasabinuki]

Diff was tight. While I haven't checked and/or replaced several potential culprits (CSB, U joints, CV joints, etc) like wasabi did, I'm inclined to think that the problem is the transmission making rough downshifts.

I know the clunk still happens when in neutral, which would normally point to some other part of the drive train; but these transmissions don't really "let go" completely in neutral either, which might explain the reduced - but still there - clunk when making the 2-1 shift.

Yeah - I am thinking it's the actual transmission that is causing the problem. I'm going to be doing a 5 speed swap in the near future, I just hope that the clunk goes away then.

[sohc12vm20]

I would say the valve body in the trany.. It controls the down shifts and up shifts.. Mine does the same thing, I was thinking about a 5speed swap, or replacing the valve body with a high peformance one!:)

Yeah - I am thinking it's the actual transmission that is causing the problem. I'm going to be doing a 5 speed swap in the near future, I just hope that the clunk goes away then.

[wasabinuki]

I would say the valve body in the trany.. It controls the down shifts and up shifts.. Mine does the same thing, I was thinking about a 5speed swap, or replacing the valve body with a high peformance one!:)

How difficult / expensive is it to replace the valve body? Do you happen to know what part(s) I would need?

[sohc12vm20]

http://www.youtube.com/watch?v=fsR1WWaKNh4 I came across this video here on youtube. He has a modded valve body.There about $750, and from what i'm told its as easy as doing a trany service. $750 is quite expensive, thats why i'm leaning more to doing a trany swap.

How difficult / expensive is it to replace the valve body? Do you happen to know what part(s) I would need?

[wasabinuki]

http://www.youtube.com/watch?v=fsR1WWaKNh4 I came across this video here on youtube. He has a modded valve body.There about $750, and from what i'm told its as easy as doing a trany service. $750 is quite expensive, thats why i'm leaning more to doing a trany swap.

Thanks for the link/info, but $750 is way too expensive. A 5 speed swap will be about the same amount of $$$, so I'm going that route. The only drawback will be driving in traffic now.

[lateracer]

Thanks for the link/info, but $750 is way too expensive. A 5 speed swap will be about the same amount of $$$, so I'm going that route. The only drawback will be driving in traffic now.

^x2...the only reason I got the stupid automatic (instead of a 5 speed) was for mindlessly sitting in traffic. I'll be damned if I'm gonna pay that kind of money to fix the slushbox.

Think I'm gonna just clunk through life with the 4hp22 until it shits the bed (or the 805), tow it home and do the 5 speed swap.

[wasabinuki]

OK - I am still working on locating the source of the problem, and I have a little more information to share. I can get the clunk to happen every time I pump the gas, though not as pronounced as when I am coming to a stop / downshifting - it is the same noise coming from the rear end ( sound like under rear seat). If I place my hand on the driveshaft tunnel in front of the rear seat I can feel the clunk coming from further back in the driveline.

If my rear SFB and/or RTAB are bad, would this cause the problem? Any way to test those without removing the rear end?

Another odd thing also happens. If I have my car in park and put it into reverse, the whole rear end of my car raises about 1". If I put the car in neutral it goes back to park height. If I put the car in any forward gear the rear end drops about 1". I have driven other auto E30's and they don't do this. Is this normal for autos? Could this be a cause/symptom of the clunk? Tranny mounts?

Any further help with this issue would be very much appreciated.

[twistednut]

Just replaced the sub frame mounts on the kids car (325is auto) and the problem went away.

[wasabinuki]

Just replaced the sub frame mounts on the kids car (325is auto) and the problem went away.

The clunking issue, or the car ride height difference between gears? Or both?