# Manual Shifting Causing Transmission "Thunk"



## bsm325xi (Mar 24, 2002)

I have a 2002 325xi that is only a few weeks old and has about 800 miles on it. When I shift gears, especially from 1st to 2nd and from 2nd to 3rd, I sometimes hear a "thunk" or "clunk" when I engage the clutch. The sound is like the transmission has a bit of "freeplay" in the gears and when engaging the clutch, this process quickly takes up the slack, causing this sound. There is a slight jar when this happens.

I notice that generally if I rev match (within 250 rpms) that this minimizes the number of incidents of this thunking. Also, on hills, the thunking does not seem to happen as often -- maybe the freeplay is taken up.

My BMW service center looked at the car this morning and told me that it was "normal for some cars" and that the M3 have a really loud clunking sound (I suppose I could live with that if I had an M3 . . . ).

1. Is this normal, or is it just my shifting technique (I have not had any trouble shifting). Could it be that for DBW I need to press the accelerator a fraction of a second before I start to engage the clutch?

2. What causes this?

3. Is it harmful to the transmission? (Service says no, wait to see if it gets worse.)

Note that I have driven a 330xi, a friend's new 325xi, and a 5 series car and none of them do this when I drive it.

Your comments and suggestions would be greatly appreciated.

TIA.

BTW, I have done a search on a number of boards, including this one, and have only found 1 thread that seem directly related to this problem.


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## Nick325xiT 5spd (Dec 24, 2001)

In my experience, I've only experienced a clunk when I screw up a shift. :dunno: Maybe you need to take a look at some of my CDV threads?


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## CH_325xiT (Dec 21, 2001)

It only happens for me too when I miss time a shift. It happens if I shift from 2nd to 3rd at low revs (2000rpm).

Sure does not sound or feel pleasant, but seems to be related to the Xis mostly.


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## bsm325xi (Mar 24, 2002)

Nick325xiT 5spd said:


> *In my experience, I've only experienced a clunk when I screw up a shift. :dunno: Maybe you need to take a look at some of my CDV threads? *


Actually, I have been following the CDV threads very closely. The thing is that I drive my friend 325xi with only 750 miles on it (and so is just as new as mine) and his does not do this.


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## chukiechz (May 15, 2002)

I get this on my car sometimes.

I get a clunk when the clutch is engaged, and then I shift it into gear. I was told it happens cause of excess backlash in the gears. If I were to hold the clutch down for a while, then put it into gear, it wouldnt happen. Im not 100% positive how the drivetrain works and stuff, so Im sure someone can better explain it


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## bsm325xi (Mar 24, 2002)

CH_325xiT said:


> *It only happens for me too when I miss time a shift. It happens if I shift from 2nd to 3rd at low revs (2000rpm).
> 
> Sure does not sound or feel pleasant, but seems to be related to the Xis mostly. *


What happens if you shift to 1st gear from a stop? If I shift to 1st from idle or around 1000 rpms, it will happen. Rev to 1500 to 2000 rpms to 1st and SLOWLY let out the clutch and there is a much reduced chance of this happening (but, it seems, a greater chance of wearing out the clutch).

My rpms also seem to drop fairly quickly thus, the way I shift now is to almost always keep some pressure on the accelerator (as opposed to completely taking my foot off when disengaging the clutch) and thus slowing the drop on rpms. I then engage with the gas still on.

How do you deal with it and is this technique a problem?


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## bsm325xi (Mar 24, 2002)

chukiechz said:


> *I get this on my car sometimes.
> 
> I get a clunk when the clutch is engaged, and then I shift it into gear. I was told it happens cause of excess backlash in the gears. If I were to hold the clutch down for a while, then put it into gear, it wouldnt happen. Im not 100% positive how the drivetrain works and stuff, so Im sure someone can better explain it *


Do you mean when you disengage the clutch and shift into a gear?


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## chukiechz (May 15, 2002)

bsm325xi said:


> *
> 
> Do you mean when you disengage the clutch and shift into a gear? *


no,

step on the clutch, and hold it

put into first *clunk*

if I put it into 3rd first, and then first, no clunk


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## genaplex (May 9, 2002)

Chukiechz,

Sounds like a bad first gear Synchro ... I had a 2000 323i with
a similar problem of getting into first. After pestering my local 
service center to replace it they finally did. Definitely fixed the 
problem. 

Justin


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## chukiechz (May 15, 2002)

genaplex:
thanks for the idea, but I dont think its the synchros. It did it in my old getrag tranny and it still does it in the new zf tranny. the only things not replaced are the driveshaft and diff, so it's gotta be the diff.


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## genaplex (May 9, 2002)

Engine mounts?

Justin


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## bsm325xi (Mar 24, 2002)

genaplex said:


> *Engine mounts?
> 
> Justin *


I do not think so since the noise is coming from the rear diff.

This car definately shifts differently than my previous Rabbit, Subaru and Honda (and is alot more fun to drive also). I am not sure if this is an artifact of DBW, hydraulic clutch, CDV, variations in the transmission manufacturing process, or some combination of those factors.


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## ·clyde· (Dec 26, 2001)

bsm325xi said:


> *I do not think so since the noise is coming from the rear diff.
> *


I've had since day one. When I get it, it always comes from the rear. It only seems to happen at very low revs, ie at a stop, putting it into first from neutral. I don't recall hearing it for the 1-2 or 2-3 shift. I've been thinking that it has something to do with clutch take up. If I'm extra smooth and slow with the clutch, it doesn't happen. If I'm quicker with it, but not launch with any real revs is when it happens.


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## bsm325xi (Mar 24, 2002)

Thanks to those who responded so far, you have been very helpful. Aside from the noise, it seems to make driving when shifting very abrupt because the car jerks forward alittle each time it thunks, although not what I would call "jerky". 

Is this your driving experience also?

After reading your reponses, I also noticed that the thunk sometimes happens when I shift into gear -- syncros problem?

Thank you for your insights.


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## FrancisK (Apr 8, 2002)

synchro problem is very common. Shift it gentaly... with around 0.5 sec pause from 1st to N then N to 2nd (instead of 1st to 2nd immediately). If that noise didn't comming again then that should be the synchro. I have heard some new mini have the same problem... see the curren mini review in edmunds.


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## DougDogs (Dec 26, 2001)

On my 325xi if "feel" a thunk when shifting from 2nd to 3rd.

It is not an audible noise, just a feeling in the shift lever.

Have not tried reving when shifting, but will try that tonight.


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## joes325xi (Jan 9, 2002)

i actually just noticed something similar the other day. I have a 2001 325xi with about 6000 miles on it. I noticed that when i am in stop and go traffic or at a stop light that there is a thunk when the clutch is depressed and i just row the stick through the gears: 1st, 2nd or even 3rd. Is this just a synchro problem, or some other underlying process?

I feel like i may have f'ed somethig up since this is my first stick-shift and i still get some jerky shifts once in a while. I'm going to try to take out that CDV one weekend because i notice that when i shift and don't depress the clutch fully (ie: depress the clutch just after it disengages from the gear i'm in) and then shift gears and let up the clutch, that i have much smoother, quicker and funner (word? ) shifts. Anyone else notice this?

[EDIT: after reading genaplex's comment more carefully, does anyone think my "learning" how to drive stick on this car may have destroyed the first gear synchro. I'll admit i have no idea what i'm talking about (mechanically) so i have very little reference.]


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## AF (Dec 21, 2001)

It might go away with time . . . sometimes parts need to break in.

If it were still happening at 3000 miles, I would have it checked again but there is a good chance this might go away by then.


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## bsm325xi (Mar 24, 2002)

Brought my car to Gearhart BMW in NJ for them to check out the car and give me a second opinion. They were very good about looking at the car and put the car on the lift, checked the drivetrain (by hand) for freeplay and checked the fluid levels. All were okay according to them. In addition, they said that it may be simply that it is AWD model and they tend to be noisier or that the car may be rocking a little back and forth when shifting. 

Does this may any sense?

Of course, when I brought it in this morning, it was more difficult to replicate the problem and when it did thunk, it was faint. Wish it was just jerky, then I would know it was just me. Anyway, this appears to be most noticable if I am more than 250 rpm off the finally rpms for the shifted gear.

I will wait a few more thousand miles, but in the mean time, any other thoughts in addition the great advice already given would be appreciated. Thanks!


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## chet325xi (May 31, 2002)

*cluth impossible to navigate*

I have (2) 2002 325xi's, one sedan, one wagon, both 5 speed, they both have less than 5000 miles on them. I have noticed that it is virtually impossible to get into 1st or second gear without the car either thunking and lurching forward or stalling or near stalling. I have has the dealer and factory rep look at the cars and they are recommending clutch replacements. I have noticed that many people have been complaining about the uneven and sloppy clutch function and that coupled with a long shift throw and AWD, the cars are virtually impossible to drive without either lunging forward, stalling or generally looking like an amateur when you drive. I am looking to BMW to resolve these issues, I would appreciate all affected BMW owners to contact me at [email protected] so that we can approach BMW once about this and get some resolution. I have been driving stick for 25 years and have owned at least 10 BMW's and other 5 speed and have never experienced anything of this nature with any vehicle. I consider this to be a factory flaw and/or a mis-engineered defect. Again, I would appreciate anyone with similar clutch, shifting and or 5 speed problems to contact me at: [email protected]


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## Hadley (May 22, 2002)

*Thunk is from transmission...*

A thunk WHEN a gear is selected is coming from the transmission, problems with the differential has other ways of manifesting. This can be due to; 
*clutch not disengaging properly 
* faulty synchromesh ring 
* manner the transmission is used 
Depending on the severity of the case, (thunks occuring) this can be considered to be a problem or not. 
When the transmission is forced, e.g. when shifts (especially downshifts) are made in a hurry at rpms that do not match, or when clutch pedal is not properly depressed (sometimes a simple thing like a floor mat can prevent proper operation of the clutch), or with faulty synchromesh rings/clutch the synchromesh rings can not properly equalize gear speeds, hence the gears engage with a thunk. During easy driving, and when shifts are not forced (e.g. undue force is not used on the gear selector lever, and enough time is given to the synchromesh to operate), there should be no thunk (except downshifting into 1st. where this may be permissable). If thunks occur frequently due to any of the above reasons, in time serious problem with transmission gears is likely to develop. In difficult shifts not to force the transmission so much (and risk breaking gear teeth), the shift lever can be advanced to the point where resistance will be felt and held there a couple of split seconds when the syncromesh rings will be buzy equalizing gear speeds (a whine can be heard, syncromesh rings rubbing against each other) and when proper synchronizing has been achieved the lever will easily move to its proper position (this is especially the case when downshifting into 1st. where there is considerable difference in speed of gears to be equalized). If the thunk is heard when the shift lever easily moves to its position without any resistance and when the clutch is properly depressed and functioning fine then this is almost for certain a case of faulty synchromesh rings. When the car is forced the transmission fluid heats up decreasing viscosity which increases tendency to generate a thunk (which also indicates the problem will soon be apparent). Sometimes a new transmission (or that has been newly overhauled) has this tendency and chances are there that the problem will go away after some mileage. After more than 10 years intensively dealing with cars, I have learned that even a fine car like a BMW should not be expected to be flawless, if the synchromesh or the clutch is faulty this should be fixed before gears are damaged, but if the situation is not severe then the car should be driven in such a way that the transmission does not keep thunking.


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## bsm325xi (Mar 24, 2002)

*Re: Thunk is from transmission...*



Hadley said:


> *..... During easy driving, and when shifts are not forced (e.g. undue force is not used on the gear selector lever, and enough time is given to the synchromesh to operate), there should be no thunk (except downshifting into 1st. where this may be permissable).... *


Hadley, excellent post. I would say that generally there is little to no thunk during shifting. I do not force shifts and allow the car to shift into gear. Sometimes I can hear a very faint thunk when shifting if, for example, I run through the gears at a stop sign.

The real problem is AFTER shifting and I begin to release the clutch. Then, a thunk often occurs as if the clutch had just immediately engaged. (I note that if you simply engage the clutch too quickly, I would expect a quick, jerky start, but not a thunk. In this case the car shudders due to the force of the thunk.)

If I keep the revs up, VERY slowly release the clutch a little (and modulate the engagement) that helps, but not always.

What do you think is happening? I only have about 2,000 miles on it. Continue to wait? TIA for your advice.

If I keep this up, I am concerned of premature clutch wear and/or damage to the differential gears. (And tiring my left leg because I am always tense in trying to modulate the engagement.)


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## Hadley (May 22, 2002)

*Oh I did not read your initial post carefully...*

If you get the "thunk" as you are engaging the clutch chances are less that this is something to do with the transmission. There is still possibility that this is due to the transmission, but freeplay between the gears can not be that great to generate an annoying "thunk", one (again less) possibility is that the synchromesh and gears are not completely engaged even if you have the gear lever in its proper place, then as you engage the clutch the gears are suddenly engaged, as if the gears catch each other under power with a mechanical sound (this can be caused by improper linkage (lever to trans) adjustment or a faulty synchromesh again. But in all these cases the thunk should be occuring only one one or two gears, not all of them. My guess is that this is related to the drivetrain and typically the back differential (could even be one of the universal joints) that has more than normal endplay. You can try this, on level ground, get into the car, keep the door open, have an ear on the sound that will be coming from the underside of the car (you can have a friend carefully kneel next to the car for more easier identification), put into first gear, engage the clutch while the engine is idling or is a little fast, just normally as if you would move the car just a little bit. Then stop and do the same using reverse. If you do this 5-10 times using also higher gears (while the car is stationary not moving), (2nd., 3rd. etc.), then you will be able to tell from where and why the sound is coming. If the thump is there for all the gears and the sound is coming from the back then this is the differential, if the sound is there for only one or two gears, then transmission (unlikely), if the sound is there for all the gears but not coming from the back, then there is something wrong with the clutch (although this is unlikely and the clutch normally even if problematic does not generate a thunk like sound). Then to my view you should demonstrate this to your mechanic, and he should identify for certain whether this is coming from the differential or any of the universal joints. If the sound is coming from a universal joint it should definitely be fixed (changed), otherwise it will breakdown unexpectedly (could even be dangerous). If the differential is generating the thunk, this will not get better with mileage, on the contrary will slowly degenerate, though it is hard to predict what it will do in time, if you can hear the thunk while the car is moving and shifted into different gears, my guess is that the differential has something that could be serious and should be fixed under warranty (in any case something as such with the differential will not most likely breakdown unexpectedly but slowly degenerate to the point that it is obvious that it should be fixed). If the thunk is audible only when rocking the car fore and aft as is described in the above, this can be considered to be something within normal limits (although even this should not be there with a proper differential). Good luck, let me know if I can be of any help. The 325x drivetrain is obviously complicated, so the slack/fault generating the thunk can be anywhere on the drivetrain from the transmission to the wheels.


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## chet325xi (May 31, 2002)

Hadley,
I guess I have not made myself as clear as I thought.
The Thunk I am referring to occurs only from a complete stop when you are trying to successfully get into 1st gear without lurching forward or stalling the vehicle. I am aware of differential noises and this is definately not one of them. The main issue is that while trying to successfully engage 1st and sometimes 2nd gear, the car lurches, lunches forward or stalls flat.


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## Hadley (May 22, 2002)

*O.K...*

For bsm325xi the thunk comes after engaging the gear and when/while the clutch is released; this is most probably due to the fact that the gears do not engage fully, the gears are designed to hold together under force, if the gears are not fully engaged when the clutch is released the remaining engagement is completed by the force of the engine transferred to the gears generating a thunking noise. Probably there was something wrong in the way the trans was put together at the plant, especially if the problem was there from the very first day. It does not behave like when you release the clutch rapidly since the gears are not actually engaged and complete engagement is achieved abruptly when power is applied by the clutch. If the syncros were faulty the thunk would be prominent as the gear was selected before the clutch was released. My opinion is that the transmission should be looked at.

For chet325xi the thunk comes as the shift lever is put into gear while clutch is disengaged, and the car stalls. This is due to clutch not properly disengaging even if the clutch pedal is pushed down. As the gear is selected power is being transferred to the trans with the result that the gears engage abruptly and car stalls. Clutch and clutch activating mechanism/system should be definitely checked, otherwise damage to the transmission is likely. Probably nothing wrong with the transmission, e.g. synchros, since car is jerked or stalls, this can only be possible if the clutch is transferring power when clutch pedal is depressed which it should not.

A low mechanical noise (like coming from a big mass of metal) typically in the case of BMW comes from the transmission (if not from the differential) and it can be felt at the gear selector lever. In both cases apparently the sound is the same and coming from the abrupt engagement of the gears. But in the first case the fault is at the transmission, in the second due to the clutch not properly disengaging.


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## 10chi (Jan 11, 2002)

read on bimmer.org that its normal


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