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Old 03-01-2011, 12:59 PM   #1
cmpcpro
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$$$ Spent, Diff, Mounts, Subframe all Replaced, still gear engage thump.

Hi guys, I have asked about this before and gotten advice on the common problems but they have all been taken care of and checked and the problem still persists. This time I have pictures and videos! The subframe was replaced about a year ago under lawsuit, so it's brand new. The rear suspension has all been replaced too, along with brakes. I went ahead and replaced the rear diff as someone thought that was worn and it seemed like the problem was gone for a few days but it slowly came back to exactly how it was.. driveshaft looks brand new, guibo does too, I can turn the driveshaft a good inch or so maybe 3/4 but it doesn't have much play up and down if I lift the car and push on it, however it does have a small amount..

Diff bushings are all good, what happens is, if I push the clutch in and shift the car I get a thump when I engage the gear, even with the clutch still in.. so obviously the clutch is dragging or it's part of the design for the syncros no idea.. anyway, when I do this I get a pretty good thump inside the cabin.. when driving if I let in the clutch it takes a second but I get it moving too, almost with a delay... I am going crazy here as it gets pretty lound and it drives me nuts.. I've got into the thousands invested in this thump and I still have it exactly the same..!

Here are some pictures I took of random underbody areas.. I also took a few movies of the rear half shafts when doing this at a stop.. they don't move too much but the thump coinsides with that movement 100%.. If anyone has any ideas I'd really appreciate it..

As a side note, if anyone remembers me asking about that noise I get from the engine compartment during shutdown in the last video I recorded it if anyone has any ideas on that too.





I will work on the photos right now and get them up in a few moments, thanks guys!

PS. In the second video I tried to record the thump from inside but the camera didn't pick it up, but it is quite noticable.
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Old 03-01-2011, 01:11 PM   #2
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Here are some random pictures:
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Old 03-01-2011, 01:16 PM   #3
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Thump occurs when... gonig from Park to Reverse/Drive?
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Old 03-01-2011, 01:24 PM   #4
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Originally Posted by Penguin Koolaid View Post
Thump occurs when... gonig from Park to Reverse/Drive?
It's a manual so it occurs when I push the clutch in and just shift to reverse, or 1st, but not all the time, I have to take foot off clutch and push back in a couple times.. which obviously means the clutch is either dragging or it's a design for the syncros but the play is still in the rear, so even if the clutch didn't drag it would happen when letting out the clutch to go, which it does when I do that too.. driveshaft looks tight.. diff has been replaced, which made the sound go away, and then it started coming back after the car was warmed up, now it does it all the time again like before.. going crazy here.. can't blow anymore money on something like this.. this is really a joke that nobody has had this problem before..

I'll try to go take a better movie of the sound inside the car..
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Old 03-01-2011, 02:03 PM   #5
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I have a couple questions..
Did they weld the new subframe on to the frame "properly" when they replaced it?
Are the subframe bushings new?
Does it do thump on any gear under load?

My car does it if the RPM is high / torque is at its peak and if i press the clutch in and let the pressure go. It also does it when I re-engage the previous gear.
It doesn't do it all the time but 90% of the time it makes the thumping noise. It also does it when shifting gears. (any gear doesn't really matter)

So I'm thinking, the problem persists when theres load on the differential. And the differential is held on by the subframe which is welded on to the main frame.
So if theres even a slight crack on the weld it would make this noise because the subframe will be moving around slightly.. I say its probably the welding point because if you have a new subframe and new bushings in it there shouldn't be any noise coming from that area.. with the exception of the cracked weld..
If you think about it, theres a lot of pressure on the differential when the torque is at the peak..
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Old 03-01-2011, 02:28 PM   #6
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Quote:
Originally Posted by G-Hots View Post
I have a couple questions..
Did they weld the new subframe on to the frame "properly" when they replaced it?
Are the subframe bushings new?
Does it do thump on any gear under load?

My car does it if the RPM is high / torque is at its peak and if i press the clutch in and let the pressure go. It also does it when I re-engage the previous gear.
It doesn't do it all the time but 90% of the time it makes the thumping noise. It also does it when shifting gears. (any gear doesn't really matter)

So I'm thinking, the problem persists when theres load on the differential. And the differential is held on by the subframe which is welded on to the main frame.
So if theres even a slight crack on the weld it would make this noise because the subframe will be moving around slightly.. I say its probably the welding point because if you have a new subframe and new bushings in it there shouldn't be any noise coming from that area.. with the exception of the cracked weld..
If you think about it, theres a lot of pressure on the differential when the torque is at the peak..
Thanks but we even took a prybar to the diff and it is solid as solid could be.. if you watch my video and see the half shafts engaging when I put it in gear with the clutch in that is the noise I am talking about.. it looks minor but it's very noticable in a quiet cabin.. the noise isn't when there is a load it's only when engaging/disengaging the clutch and the mass gets moving or slows down.. seems to happen more when the car warms up, but that may just be the clutch dragging more making it more noticable when I put it in gear.. basically I can put the clutch in and just start to put it in reverse, not even get it in reverse but when I put the shifter to the begining of the reverse it will thunk.. someone said the half shafts could be bad.. but if I grab them and try and move them they are solid.. but if you guys look at my other late post entitled Flange Play, I would almost say that's the sound but this is the second diff doing it.. however again, after installing this diff it went away for a couple days..
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Old 03-01-2011, 02:29 PM   #7
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Originally Posted by cmpcpro View Post
It's a manual...
Oh. I apologize if that was evident in the video you posted (I assume it was a video). My work filters out that kind of content.

Unfortunately, I don't know. I'm sure someone else will chime in though.
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Old 03-01-2011, 02:35 PM   #8
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Every manual I have driven would have a thud sound from the rear when enaging 1st or reverse. Nothing catastrophic has ever come of it. It is a characteristic of a manual car.
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Old 03-01-2011, 02:38 PM   #9
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It is the problem with the clutch. Just change #1 http://www.realoem.com/bmw/showparts...93&hg=21&fg=05 this is from 330i so find which one is for your car.
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Old 03-01-2011, 03:48 PM   #10
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It is the problem with the clutch. Just change #1 http://www.realoem.com/bmw/showparts...93&hg=21&fg=05 this is from 330i so find which one is for your car.
I am inclined to agree with the clutch possibility.
After watching the video, a good working clutch would not allow the half-shafts to move when you engage a gear. The fact that the half-shafts move when you put into gear leads me to believe that your clutch is not working properly.
How many miles on the clutch?
Do you keep your foot on the clutch when the car is moving(rest the foot on the clutch pedal while rolling down the road)?
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Old 03-01-2011, 03:53 PM   #11
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I think it's from the transmission internal gearlash. Which runs all the way down to the diff when it engages and the well known "rear clunk" when all slack is taken up and first initial torque driven to mounting points.

Anyway, hope you find it, but hate to tell you so but I was pretty adamant that it was not going to be your diff. Hope you saved your old diff as it's still good.
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Old 03-01-2011, 03:55 PM   #12
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remove your backseat bottom and see how loud the thump is then and have someone in back to see if it's transmitted through the rear by the mounting points or perhaps somewhere else.
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Old 03-01-2011, 04:16 PM   #13
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Quote:
Originally Posted by Alex323Ci View Post
remove your backseat bottom and see how loud the thump is then and have someone in back to see if it's transmitted through the rear by the mounting points or perhaps somewhere else.
thats a good idea actually
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Old 03-01-2011, 04:41 PM   #14
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Thanks guys, I placed my camera which shoots Dolby Digital audio and a digital recorder on the floor in the back and neither picked up the sound but I can hear it.. I agree that it is in the transmission, I have pretty much come to that conclusion on my own.. which throws me off is that when I let the clutch out sometimes when it's warm I get the thump too as soon as power is transfered to driveshaft, but I think that could just be the slop in the tranny too.. basically I think the original owners had this problem and gave up.. the clutch is new, has 18k on it but it does chatter if you let it out slowly after the car is warm (Also around the same time the thump appears), atleast I am guessing it's chatter.. it doesn't slip at all, I can put the brake one and let the clutch out and the rear of the car will drop down and kill the motor.. anyway I don't leave my foot on the clutch at a stop if it's going to be more than 20-30 seconds but I have only driven this car for 1k, as I've only owned it a few months.. I haven't checked the link above on what I was told to change but I hope that helps... otherwise what am I looking at, a new tranny? Which means I should obviously look at redoing the clutch again, which means 7-800 on a new OEM flywheel I am looking at thousands more!..

Thanks again Alex, I was originally going to put another 3.07 diff in but I figured there was a good chance it wasn't the diff so atleast I got the 3.46 upgrade which I have to say made a huge difference, the car is way more enjoyable to drive and I just cruise it.. Can you take a look at my Flange play thread and you're subframe thread I replied to? Thanks!
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Old 03-01-2011, 05:57 PM   #15
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Still thinking to myself.. I realize the clutch drags, and it gets worse when the car is warm but why did this problem go away with the new diff for a few days? Could it really be the half shafts are worn? One mechanic told me that's what's making the thunk, which is obviously correct, but my question is, even if the tranny shouldn't have power with clutch in like that, shouldn't the rear be tight enough not to clunk? Otherwise everyone would have it when they start letting their clutch out.. Here is a video of my output flange, see it moving when I move the shaft.. is that normal? Pass side is fine.

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Old 03-01-2011, 09:16 PM   #16
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This is a long shot, but check if your motor mounts and transmission mounts are in good shape. I had a mystery clunk when letting out the clutch in 1st gear, and while I thought it was coming from the back, it turned out to be busted motor mounts were letting the motor rock around in the engine compartment under load. I did watch your video, and if the noises you hear are coming exactly when the half shafts are moving and clicking in the video, then I guess the problem must be in your half-shafts/diff., which is why my suggestion is a long shot.

Looking at your first video, our half shaft is moving (rotating) a bit under load even when the wheels are not moving. I don't think the slop is where the half-shaft connect to the diff. It's either inside the diff or where the half shafts connect to the hubs (like the CV joints). If you think the noise is from inside the diff, you could try putting your original diff back into see if the problem goes away. If you think the noise is coming from the half-shafts themselves or closer to the wheel end of things, check your half-shaft CV joint boots to make sure they didn't fail and let the grease out.

Another way to feel for subframe damage, besides removing rear seat cushion, is to remove trunk carpet and put your hand on the trunk floor right above where you think the rear subframe mounts connect. I think the area right above the left rear subframe mount bolts in was the most likely part to tear, so you could try to feel there to see if it's creaking when you get that noise.

Or do same to your motor mounts... open the hood and have someone watch the motor while you recreate the clunking. If your left motor mount is completely broken, you should see the left side of your motor rotate upward then fall back down as you engage the clutch (let pedal up) then release it (push pedal down). Just be sure you've got your other food on the brake and the wheels chocked, so you don't accidentally run over your helpful friend that is observing the motor or feeling the trunk floor for you. (Danger is lower if your friend is sitting on the bare rear seat or inside the trunk.)
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Old 03-01-2011, 09:23 PM   #17
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Check for play in differential internal gears....
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Old 03-01-2011, 10:07 PM   #18
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Originally Posted by LivesNearCostco View Post
This is a long shot, but check if your motor mounts and transmission mounts are in good shape. I had a mystery clunk when letting out the clutch in 1st gear, and while I thought it was coming from the back, it turned out to be busted motor mounts were letting the motor rock around in the engine compartment under load. I did watch your video, and if the noises you hear are coming exactly when the half shafts are moving and clicking in the video, then I guess the problem must be in your half-shafts/diff., which is why my suggestion is a long shot.

Looking at your first video, our half shaft is moving (rotating) a bit under load even when the wheels are not moving. I don't think the slop is where the half-shaft connect to the diff. It's either inside the diff or where the half shafts connect to the hubs (like the CV joints). If you think the noise is from inside the diff, you could try putting your original diff back into see if the problem goes away. If you think the noise is coming from the half-shafts themselves or closer to the wheel end of things, check your half-shaft CV joint boots to make sure they didn't fail and let the grease out.

Another way to feel for subframe damage, besides removing rear seat cushion, is to remove trunk carpet and put your hand on the trunk floor right above where you think the rear subframe mounts connect. I think the area right above the left rear subframe mount bolts in was the most likely part to tear, so you could try to feel there to see if it's creaking when you get that noise.

Or do same to your motor mounts... open the hood and have someone watch the motor while you recreate the clunking. If your left motor mount is completely broken, you should see the left side of your motor rotate upward then fall back down as you engage the clutch (let pedal up) then release it (push pedal down). Just be sure you've got your other food on the brake and the wheels chocked, so you don't accidentally run over your helpful friend that is observing the motor or feeling the trunk floor for you. (Danger is lower if your friend is sitting on the bare rear seat or inside the trunk.)
Thanks guys, but this is the second diff with the same exact noise.. it went away for a couple days with this diff but came back..

Either something is wrong with clutch, gearbox, master cylinder causing clutch to drag, or something with driveshaft or half shafts.. the noise IS the halfshafts moving, well maybe not them, but it's the backlash somewhere that is causing that.. now my theory is, the driveshaft feels good, there is almost an inch of rotational play but it was in nuetral so who knows.. but what could cause this to happen and go away when the new diff was put in but only temp. could there be something in the halfshafts causing this?

What would really help me is if someone could do me a huge favor and make a video like mine.. place camera under back looking at diff/halfshafts, start car, keep clutch pushed in and put it in gear, take out of gear, let clutch out, push back in and put in reverse, take out of reverse, let out clutch, push back in and reverse again.. and see if halfshafts have the same play.. if both diff's are doing it I would say it has to be half shafts.. right? Either that or I got two bad diffs...
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Old 03-02-2011, 12:40 AM   #19
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Okay guys just drove the car again for the first time since this morning.. When the car is cold it's all perfect, no noises, thumps nothing.. once warm I can push clutch in and as soon as shifter hits 1st gear gate I get the thump, also get it sometimes letting out clutch, so it makes me think maybe it is something in the tranny, but, when moving when I push clutch in to shift it does it too, while it's in nuetral too! So there has to be something in the driveline causing this.. unless I got two bad diff's it has to be the halfshafts.. I mean, if you watch the video's you see them move, well I understand the halfshafts have play, someone said so in the other guys halfshaft play post tonight but my shafts are bolted to my wheels and on the ground.. so why are they moving? Shouldn't those shafts be solid when on the ground?
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Old 03-02-2011, 12:57 PM   #20
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Did you check the CV boots on the half shafts?
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