[kern417]

I have a 6MT and I feel a hard jolt when shifting fast. I think it's probably from slop in the diff or control arm bushings, but not really sure. It's rough when shifting 1-2 or 2-3, but not as noticeable at higher speeds.

Has anyone experienced similar? And what did you do to correct it? It might not be limited to 6MT. I'm guessing if your 8AT downshifted to 2nd when you floor it, you'd feel something similar.

Options I'm considering now:
1. Diff bushings/supports
2. Control Arm (Trailing Arm) bushings
3. Motor mount bushings, but that's a big maybe since I don't want the car to rattle to pieces

[BMWILUVU]

http://ultraracing.my/ecatalog/index...-lower-bar-4p/

[andino]

I would start with the diff bushings. That's where I've helped reduce the amount of slop in previous cars. I haven't felt the need to it with my f31 yet but I'll probably want to do it after an LSD.

[kern417]

Originally Posted by BMWILUVU

http://ultraracing.my/ecatalog/index...-lower-bar-4p/

I doubt that will help. I'm not really bought into chassis bracing to be honest. I'm looking for something more like this, that helps lock down the diff or control arms.

https://www.lowgo-shop.de/shop/diffe...r-modelle-f3x/

Originally Posted by andino

I would start with the diff bushings. That's where I've helped reduce the amount of slop in previous cars. I haven't felt the need to it with my f31 yet but I'll probably want to do it after an LSD.

Yeah and I'm still on the stock diff. I'm not sure an LSD would help, or if it would potentially make it worse. I really hope it's not the diff itself.

On my VW a lot of people did motor mount bushings to reduce engine slop, because the issue was the engine torquing hard with the axles. Kind of like how you see fast drag cars pull a wheel off the ground. I think that *might* be a part of the issue as well, I just don't like how motor mounts ruin the NVH.

Also should note that I don't feel any wheel hop. Just a sharp thud when i bang into the next gear. So I assume it's something in the drivetrain shifting hard.

[andino]

Originally Posted by kern417

Yeah and I'm still on the stock diff. I'm not sure an LSD would help, or if it would potentially make it worse. I really hope it's not the diff itself.

On my VW a lot of people did motor mount bushings to reduce engine slop, because the issue was the engine torquing hard with the axles. Kind of like how you see fast drag cars pull a wheel off the ground. I think that *might* be a part of the issue as well, I just don't like how motor mounts ruin the NVH.

Also should note that I don't feel any wheel hop. Just a sharp thud when i bang into the next gear. So I assume it's something in the drivetrain shifting hard.

Yeah I would be hesitant to go with motor mounts on a car that's daily driven. I suspect stiffening up the diff mount would help reduce the shock from the engine moving down the driveshaft. Alternatively, you could also look into rear subframe inserts to help tighten up the rear of the car. I notice a lot of flex/vagueness when pushing hard from the rear of the car because my front end is pretty tight now after replacing a lot of bushings.

[brigade24]

vagueness and thudness sounds like a broken sway bar end link...did you check them?

[kern417]

Originally Posted by andino

Yeah I would be hesitant to go with motor mounts on a car that's daily driven. I suspect stiffening up the diff mount would help reduce the shock from the engine moving down the driveshaft. Alternatively, you could also look into rear subframe inserts to help tighten up the rear of the car. I notice a lot of flex/vagueness when pushing hard from the rear of the car because my front end is pretty tight now after replacing a lot of bushings.

That's probably a lot of it. I have coilovers/camber plates already and control arms going in soon. Just can't make up my mind on what to do first for the rear.

Originally Posted by brigade24

vagueness and thudness sounds like a broken sway bar end link...did you check them?

No but i doubt that would cause the issue I'm having. It's when accelerating in a straight line. After the shift, i feel the drivetrain lurch.

[nate158]

Has anyone tried this bracket from Burger?

https://burgertuning.com/collections...-f-chassis-bmw

I haven't done much research but the description on the product page sounds like it does a great job of stabilizing the diff.

[kern417]

Originally Posted by nate158

Has anyone tried this bracket from Burger?

https://burgertuning.com/collections...-f-chassis-bmw

I haven't done much research but the description on the product page sounds like it does a great job of stabilizing the diff.

Nope, but I agree. That's why I made this thread to see some options. It's interesting that I never see anyone upgrading these. I guess maybe it's not as obvious with the auto.

[nate158]

My car is a 6-speed as well and I seem to have the same feel. I think it could also have something to do with the Clutch Delay Valve in these cars. CDVs make shifting a lot more rough. The CDV in the F30 is built into the slave cylinder on the clutch, but there is a write up somewhere on these forums where someone removed it.

I might install the brace I mentioned above. Seems like an easy and effective. Worth a shot. CDV delete would be a good idea too.

[exE36M3]

Now this is interesting. I recently got the motorsport LSD in my 8spd-auto. Been doing some rolling start 20-80 runs in manual and sport mode testing a JB+ I just put in. On hard acceleration and shifts, I can feel the rear-end twist mildly. This what you are experiencing?

[Eschmacher]

Originally Posted by nate158

Has anyone tried this bracket from Burger?

https://burgertuning.com/collections...-f-chassis-bmw

I haven't done much research but the description on the product page sounds like it does a great job of stabilizing the diff.

This probably will increase NVH considerably, wouldn't you think? Also, $130 for some bolts and a bracket :/
If someone gives this a shot, let us know how it is!

Edit: I just noticed the "drilling required" note...

[kern417]

Originally Posted by nate158

My car is a 6-speed as well and I seem to have the same feel. I think it could also have something to do with the Clutch Delay Valve in these cars. CDVs make shifting a lot more rough. The CDV in the F30 is built into the slave cylinder on the clutch, but there is a write up somewhere on these forums where someone removed it.

I might install the brace I mentioned above. Seems like an easy and effective. Worth a shot. CDV delete would be a good idea too.

mine is already removed.

Originally Posted by percychow

Now this is interesting. I recently got the motorsport LSD in my 8spd-auto. Been doing some rolling start 20-80 runs in manual and sport mode testing a JB+ I just put in. On hard acceleration and shifts, I can feel the rear-end twist mildly. This what you are experiencing?

it's basically like a slow, swaying motion. The car drives straight enough that I don't need to do any correction in steering angle, but it just doesn't feel direct. It's mostly on a low gear rolling start, right when you peg the throttle.

The initial feedback I got was it's due to the open diff, so that's disappointing if you still get a similar feel with an LSD. I've also heard that it's indicating the rear shocks are worn or too soft, but it's not really a bouncy feeling that I would expect from it being a suspension issue.

On my vw, I got a great improvement from doing motor mounts and it prevented a lot of vagueness in the steering and wheel hop. So i figured similar bushings in the rear would alleviate this effect.

[Jvac]

Originally Posted by kern417

mine is already removed.

it's basically like a slow, swaying motion. The car drives straight enough that I don't need to do any correction in steering angle, but it just doesn't feel direct. It's mostly on a low gear rolling start, right when you peg the throttle.

The initial feedback I got was it's due to the open diff, so that's disappointing if you still get a similar feel with an LSD. I've also heard that it's indicating the rear shocks are worn or too soft, but it's not really a bouncy feeling that I would expect from it being a suspension issue.

On my vw, I got a great improvement from doing motor mounts and it prevented a lot of vagueness in the steering and wheel hop. So i figured similar bushings in the rear would alleviate this effect.

I don't agree that there is any squirm on acceleration with the LSD in back. The difference after going from the stock diff to the m performance is substantial in improving power delivery and rear end stability during acceleration and braking. And I don't even have any engine mods. If you have increased power from stock and or upgraded front suspension gear for added stiffness, then the rear should feel sloppy in comparison. From what others on the forum have said, the next steps to address the problem would be diff mounts, solid rear subframe mounts and/or rear control arms to dial out the stock system's compliance and bring it up to par with the front end. I have yet to take those steps on my own car because they require more time and money than I have right now, but the LSD was well worth the price and is highly recommended.
Sorry if any of this has been said already.

[kern417]

Yeah I'm still thinking bushings will be the best fix. I don't have any slip so I know an LSD would be better, but in my experience it doesn't make a hug difference in straight line acceleration.

People in the WhatsApp group have been raving about solid subrame mounts. I think I'd start with the diff mount first, and then do the whole subframe if it still doesn't fix it.

And yes, my front end is very tight now. But it's not so much sloppy in "comparison," just sloppy period. I'm also wondering if increasing my tire pressure would help, so I'll probably try that first.

[Jvac]

Originally Posted by kern417

Yeah I'm still thinking bushings will be the best fix. I don't have any slip so I know an LSD would be better, but in my experience it doesn't make a hug difference in straight line acceleration.

People in the WhatsApp group have been raving about solid subrame mounts. I think I'd start with the diff mount first, and then do the whole subframe if it still doesn't fix it.

And yes, my front end is very tight now. But it's not so much sloppy in "comparison," just sloppy period. I'm also wondering if increasing my tire pressure would help, so I'll probably try that first.

A guy in the f80 forum uploaded a video that he took with a gopro mounted under the rear end doing some acceleration runs where you can see the rear subframe dancing around with the stock setup. There's definitely a good bit of slop there that can be dialed out between the diff mounts and subframe mounts. If I can find it again I will post a link.

[kern417]

Originally Posted by Jvac

A guy in the f80 forum uploaded a video that he took with a gopro mounted under the rear end doing some acceleration runs where you can see the rear subframe dancing around with the stock setup. There's definitely a good bit of slop there that can be dialed out between the diff mounts and subframe mounts. If I can find it again I will post a link.

Thanks man. That's actually what I was wishing I could do, but I don't have the balls to do lol. I just know something is shifting under there.

[Jvac]

Originally Posted by kern417

Thanks man. That's actually what I was wishing I could do, but I don't have the balls to do lol. I just know something is shifting under there.

I've searched for a while, and can't find that thread anywhere now. Must have been deleted or something. I came across it last time I researched the rear end mods about a year ago. This was something I always wanted to do but it is a big job. I haven't seriously considered moving forward yet because this is my daily driver and the economy is on shaky footing at the moment so I am saving, not spending. The entire subframe usually needs to be removed because the stock bushings are so hard to extract. One guy said he needed to blowtorch them out because they were stuck so bad...
Anyway the gist of all the research is this: the solid subframe mounts didn't add vibration or harshness. Only some reported a little additional noise, but if the car was already modded with things that increased nvh (ie monoball up front), then the mounts weren't noticeable. The majority of drivers who went down this road said that the differential and tranny mounts were the ones that really increased nvh. Here is a snapshot from a thread where the shop who is doing the installs gives feedback based on the work they've done and how their customers felt. It's not my personal experience but everyone appears to be very happy with the results.

[Jvac]

Originally Posted by Jvac

I've searched for a while, and can't find that thread anywhere now. Must have been deleted or something. I came across it last time I researched the rear end mods about a year ago. This was something I always wanted to do but it is a big job. I haven't seriously considered moving forward yet because this is my daily driver and the economy is on shaky footing at the moment so I am saving, not spending. The entire subframe usually needs to be removed because the stock bushings are so hard to extract. One guy said he needed to blowtorch them out because they were stuck so bad...
Anyway the gist of all the research is this: the solid subframe mounts didn't add vibration or harshness. Only some reported a little additional noise, but if the car was already modded with things that increased nvh (ie monoball up front), then the mounts weren't noticeable. The majority of drivers who went down this road said that the differential and tranny mounts were the ones that really increased nvh. Here is a snapshot from a thread where the shop who is doing the installs gives feedback based on the work they've done and how their customers felt. It's not my personal experience but everyone appears to be very happy with the results.

Pic

[kern417]

Originally Posted by Jvac

I've searched for a while, and can't find that thread anywhere now. Must have been deleted or something. I came across it last time I researched the rear end mods about a year ago. This was something I always wanted to do but it is a big job. I haven't seriously considered moving forward yet because this is my daily driver and the economy is on shaky footing at the moment so I am saving, not spending. The entire subframe usually needs to be removed because the stock bushings are so hard to extract. One guy said he needed to blowtorch them out because they were stuck so bad...

Found one on E90Post. I'd bet ours is similar if not worse from the E92 ///M3.

https://www.m3post.com/forums/showth...2#post21135012

[Eschmacher]

I just wanted to add my two cents... I have the bimmerworld solid subframe mounts, it was worth it. There was no increase in NVH at all. But it did accentuate the diff mounts weaknesses. Wish I had done the diff mount in the subframe at the same time, but I understand that one does add NVH.

[kern417]

Originally Posted by Eschmacher

I just wanted to add my two cents... I have the bimmerworld solid subframe mounts, it was worth it. There was no increase in NVH at all. But it did accentuate the diff mounts weaknesses. Wish I had done the diff mount in the subframe at the same time, but I understand that one does add NVH.

What do you feel that indicates the diff mounts are an issue?