Rear end pop/clunk -- at a loss

[Boost112]

Hello everyone!

I hope someone has had this issue before...because im grasping at straws.

I have a clunk/pop in the rear of the car that i cannot seem to pinpoint. Recently we had a BMWCCA event in homestead and had a little track day. After the event on the way home i noticed the rear making a rotating clikcking sound and some clunking/popping. It was the reason why i had the rear axles rebuilt becuase they were in fact going out...so the thought process was the noise was attributed to the axles. Once i installed the new axles and new rear bearings/hubs, im left with this clunk.

The pop/clunk happens once when going from a stop either forward or in reverse...and when turning sometimes. I have been rebuilding the rear end over the last 18 months...doing bits at a time. I have checked...rechecked...and torqued everything down. What could it possible be? The only thing that hasnt been replaced is the Diff itself. Im about to swap out the poly RTAB for Monoball units. I have checked the front Diff bolt...the subframe...trailing arms and pockets...everything is tight...i just need a little help here or another approach. Any help is greatly appreciated

Items that have been installed/replaced with in the last 18 months:
PSS9 Coilovers
Driveshaft -- Guibo -- CSB was replaced (Driveshaft specialist of texas)
All locations at RTAB and rear subframe have no tears or any damage.
Revshift subframe bushings 95A
Revshift Diff Bushings 95A
Revshift RSM 95A
AA Diff Brace
New Diff Bolt
Eibach Adjustable rear control Arms
Whiteline outter Control Arm Bushings
Whiteline inner upper Control Arm Bushings (at subframe)
Whiteline RTAB with washers/limiters
New/Refurbished Axles from CVSource
New FAG rear wheel bearings
New Rear hubs

[E36 Em Tree]

Are you sure its the rear end?

I know when I had PSS9s the spring perches had the "gear" looking adjustable collars but there are open spots in that gear/teeth (if that makes sense)
My springs were rotating when I turned my front wheel (could happen in the rear if theyre not seated right) but the spring would rotate around the collar and catch on that toothed gear (to adjust ride height) and it would make a popping/clunk noise. I only found out after a few rides because it was messing up that plastic blue washer/spacer that sat on top of the collar and between the coil. Check those out. Also maybe jack the front of the car up and take the tires off and then see if that spring is catching on anything

[Boost112]

I honestly dont know...it sounds like its happening in the rear half of the car 90% sure...it doesnt sound like its on one side only...i will look into this real quick over the weekend...please keep the suggestions coming.

[E36 Em Tree]

Could be sway bar links possibly?

Id say rear strut mount but you replaced with PSS9s so Im assuming you replaced the RSMs?

Would maybe the diff bushings be causing the rougher start/stop? especially if youre running OEM rubber trans/motor mounts.

[Boost112]

YES!...sorry i missed that...i put in new revshift RSM when i installed the coilovers and topped it off with a rear strutbar...i have literally rebuilt the entire rear end.

[E36 Em Tree]

Since you changed out everything and re-torqued it all, that's why I'm thinking its a binding issue with something... the coilovers (like i had which were also PSS9s) or the strut bars/bushings or something. Obviously its something that moves so I'd probably check those.


Are you sure there are no rips at the subframe area or mounts?

Id also suggest ball joints

[Braymond141]

Ugh. I’d start by getting rid of all of the mods you did and go back to stock.

Ditch the PSS9 as well.

[Boost112]

Ugh. I’d start by getting rid of all of the mods you did and go back to stock.

Ditch the PSS9 as well.

...thanks for the help...much appreciated...

[SIIDEWAYS]

Did you replace the rear shock mounts? I didn't see that on your list, and that's usually the first thing you need to replace/upgrade.

[Boost112]

Are you sure there are no rips at the subframe area or mounts?

Id also suggest ball joints

...yes...without dropping the subframe completley...i see no tears...the ball joints i took a chance because i really like the white line offerings...that and the early e36 have bushings and they were changed to ball joints so i thought what could be the big deal...they have been quiet for over a year...maybe they are just done...but man everything feels tight....i did the subframe and rear suspension first.

- - - Updated - - -

Did you replace the rear shock mounts? I didn't see that on your list, and that's usually the first thing you need to replace/upgrade.

Yes I did replace the RSM...when I put the coilovers on. You are correct i missed it in the original post. I will edit it now...

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Would this potenitaly be a symptom of the diff going out?...i have 190k on the car and the diff is still original...and i havent been the easist on it for the last 50k miles.

[Boost112]

UPDATE:

I did get a chance to look at the car agian...E36 Em Tree...you were right in that the spring was in between the "teeth" of the adjuster...however that did not do the trick...but thank you for pointing this out.

So im thinking that the rear diff is the issue...only other thing would be to lower the subframe and take a look at the mounintg points and see if they are torn or damaged.

What are the characteristics of a defective diff or one goin out?...i honeslty have only experianced it in my s4 and that started to whine at highway speeds.

[golgo13]

Is your rear subframe loose? I speak from experience here. A few trackdays after I installed my rear subframe bushings I developed a new clunk on accel/decel and couldn't figure out what the hell it was. Everything looked good and with the car on the lift I couldn't reproduce the sound. Shaking the suspension and drivetrain couldn't reproduce it. I thought it might be an endlink or a swaybar bracket or my RSM. All of it checked out.

I took a prybar and started gently wiggling things around and saw the whole subframe shift slightly a few millimeters. I couldn't believe it. When the rear subframe went back in, everything was torqued to spec but track vibration from having full solid mounts and sphericals caused it to come loose.

Everything is now tight again and of course paint marked.

[E36 Em Tree]

Another thing that comes to mind since you did your giubo/flexdisc. Can you make sure they installed it the correct way? The symptoms that you're saying are also a sign that the guibo is "springing" back into place because it is installed on the wrong orientation: transmission output/driveline.

[AJLM34A]

Hello everyone!

I hope someone has had this issue before...because im grasping at straws.

I have a clunk/pop in the rear of the car that i cannot seem to pinpoint. Recently we had a BMWCCA event in homestead and had a little track day. After the event on the way home i noticed the rear making a rotating clikcking sound and some clunking/popping. It was the reason why i had the rear axles rebuilt becuase they were in fact going out...so the thought process was the noise was attributed to the axles. Once i installed the new axles and new rear bearings/hubs, im left with this clunk.

The pop/clunk happens once when going from a stop either forward or in reverse...and when turning sometimes. I have been rebuilding the rear end over the last 18 months...doing bits at a time. I have checked...rechecked...and torqued everything down. What could it possible be? The only thing that hasnt been replaced is the Diff itself. Im about to swap out the poly RTAB for Monoball units. I have checked the front Diff bolt...the subframe...trailing arms and pockets...everything is tight...i just need a little help here or another approach. Any help is greatly appreciated

Items that have been installed/replaced with in the last 18 months:
PSS9 Coilovers
Driveshaft -- Guibo -- CSB was replaced (Driveshaft specialist of texas)
All locations at RTAB and rear subframe have no tears or any damage.
Revshift subframe bushings 95A
Revshift Diff Bushings 95A
Revshift RSM 95A
AA Diff Brace
New Diff Bolt
Eibach Adjustable rear control Arms
Whiteline outter Control Arm Bushings
Whiteline inner upper Control Arm Bushings (at subframe)
Whiteline RTAB with washers/limiters
New/Refurbished Axles from CVSource
New FAG rear wheel bearings
New Rear hubs

Loosen up the AA diff brackets front drivers side bolt, put a pry between the diff and the subframe from the rear, pull/push the pry bar up/down.
I had one of those "updated" factory front diff bolts snap in no time. I got a better bolt from a hardware store and it has lasted 2.5 years.

[TostitoBandito]

Are you running OEM rubber trans mounts or poly/solid? I ask because running stiff trans mounts (even 80A) gives you all sorts of fun feedback from the trans and diff. In my case I get some vibration when passing a certain RPM range. I'm sure it's a relic of my original un-rebuilt transmission, but is the sort of thing that's mild enough to be hidden by stock rubber mounts. You stiffen that stuff up you feel everything, it's just how it is.

Other than that, the comment above about loose rear subframe bolts is good. Make sure those four bolts/nuts are torqued to spec with a jack under your subframe. I've also had a diff throw nuts internally and chew them up but it doesn't really sound like what you're describing. It was more of ticking with a frequency based on speed as the stuff bounced around in the diff. Single clunks when starting/stopping sound more like something loose under the car or driveline noise/vibration being transmitted through hard bushings and mounts. Also, dumbest thing to mention but I will just in case, make sure your wheel lugs are torqued.

[Boost112]

Loosen up the AA diff brackets front drivers side bolt, put a pry between the diff and the subframe from the rear, pull/push the pry bar up/down.
I had one of those "updated" factory front diff bolts snap in no time. I got a better bolt from a hardware store and it has lasted 2.5 years.

So just to provide an update on this...as im still trying to track down the clunk...lol...i travel alot for work so im only able to work on the car in small bursts...however i did try to taking a look the diff bolt...ordered a new bolt just in case...everything was tight and the bolt and all associated items have been taken apart and re assembled and retourqed.

the search continues...le sigh...thanks for all the feed back everyone.

- - - Updated - - -

Are you running OEM rubber trans mounts or poly/solid? I ask because running stiff trans mounts (even 80A) gives you all sorts of fun feedback from the trans and diff. In my case I get some vibration when passing a certain RPM range. I'm sure it's a relic of my original un-rebuilt transmission, but is the sort of thing that's mild enough to be hidden by stock rubber mounts. You stiffen that stuff up you feel everything, it's just how it is.

Other than that, the comment above about loose rear subframe bolts is good. Make sure those four bolts/nuts are torqued to spec with a jack under your subframe. I've also had a diff throw nuts internally and chew them up but it doesn't really sound like what you're describing. It was more of ticking with a frequency based on speed as the stuff bounced around in the diff. Single clunks when starting/stopping sound more like something loose under the car or driveline noise/vibration being transmitted through hard bushings and mounts. Also, dumbest thing to mention but I will just in case, make sure your wheel lugs are torqued.

Thank you for the feedback...i feel kind of silly...but the trans mount is the only thing i havent checked and or included in the list...i have the UUC black mounts with enforcer cups...it is literally the first thing i did on the car when i got...its been over 5 years at this point and they ahve seen alot of autox, track days, and about 6 weeks of thrashing in Fontana. I will take a look this weekend.

[RRSperry]

I wouldn't be surprised if you have had a bolt in the LSD come loose. Most clunks and be found with a big prybar.

[scooper]

Assuming the clunk is really emanating from the rear did you pre-load the wheels when tightening down the rear sway bar/end links? My next suggestion is to swap out your poly rtabs for stock ones plus UHMW limiters. Great for the street, great for the track (assuming dual duty but then that's a compromise as you know). Since you are working the rear you might as well put in a m14 diff bolt with matching UHMW diff bushing. RRT of Sterling sells these.

[bluptgm3]

When was the last time the differential fluid was changed? Could be LSD clutches complaining.


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[Boost112]

UPDATE:

I ended up replacing the transmission mounts thinking it was the culprit...nope still clunks...i have a set of bimmerworld monoball rtabs waiting to go in...lets see what happens...i dont know but im going to find out.

Could something be clunking in the front and transmitting to the rear/middle?...or maybe it is the diff, i just have no idea what symptoms of a bad diff would feel/sound like...i guess ill find out once i put the rtab's...if that doestn work...then ill just drop the rear sub frame and pull the cover on the diff and see whats up...

I appreciate all the feedback everyone!

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When was the last tome the differential fluid was changed? Could be LSD clutches complaining.


Sent from my iPhone using Tapatalk

...it was one of the first things i did to see if it helped...

[Boost112]

UPDATE:

Issue has been solved...ill be honest i feel kinda dumb when i realized what the problem was.

SSSSSoooooooo...this weekend my friend and i were going to tear apart the rear end to take another look...as we are about to get ready to drop the subframe we had remove the drivehaft from the diff flange...guess what four bolts were loose, to the point they werent even finger tight...yup...it was the four bolts attached to driveshaft and to the diff that had loosened themselves free...i good round of cursing and celebrations later...i ended up putting blue loctite ont the threads and retorqued everything...and she is tight as a drum and silent!!!....thank you to everyone who were helpful and tried to provide some form of advise. i Greatly appreciate it....to any one with the same issue i just wanted to provide an end to the issue so hoepfully someone else wont spend this much time chasing the sound.

[E85STI]

Glad you got this figured out. I am now going to check my bolts!