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      03-22-2017, 02:11 PM   #1
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F chassis diff lockdown kit

I got my lockdown kit from here: http://www.n54tech.com/forums/showpo...33&postcount=1 and thought it would be nice to share the info with the community.

Last edited by feuer; 03-22-2017 at 04:27 PM.. Reason: to fix the broken link
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      03-22-2017, 03:36 PM   #2
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Quote:
Originally Posted by feuer View Post
I got my lockdown kit from here: http://www.n54tech.com/forums/showpo...33&postcount=1 and thought it would be nice to share the info with the community.
This should be in the powertrain subforums. Your link is also dead.

Either way, what's wrong with the current F chassis diffs (stock and M Performance)? What problem is this "lockdown kit" trying to remedy?

I just replaced my stock open differential with a M Performance LSD and wrote a DIY here.

Last edited by Polo08816; 03-22-2017 at 03:41 PM..
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      03-22-2017, 04:11 PM   #3
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Quote:
Originally Posted by Polo08816 View Post
This should be in the powertrain subforums. Your link is also dead.

Either way, what's wrong with the current F chassis diffs (stock and M Performance)? What problem is this "lockdown kit" trying to remedy?

I just replaced my stock open differential with a M Performance LSD and wrote a DIY here.
I was experiencing a wheel hop. This kit remedied the issue.
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      03-22-2017, 05:25 PM   #4
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Quote:
Originally Posted by feuer View Post
I was experiencing a wheel hop. This kit remedied the issue.
I've looked through a few DIY of the "lockdown kit" for other BMW chassis and it seems like it's supposed to make the differential harder to move under power. However, usually differential bushings/mounts are overbuilt.

I checked the condition of my bushings/mounts at 75k miles and they're fine. No significant wear.

I'm not having the wheel hop issues at all.

Would you be able to provide a bit more information about your car?
- Powertrain mods
- Drive train configuration
- Describe your current LSD
- What type of tires do you use
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      03-22-2017, 05:42 PM   #5
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Quote:
Originally Posted by Polo08816 View Post
Would you be able to provide a bit more information about your car?
- Powertrain mods
- Drive train configuration
- Describe your current LSD
- What type of tires do you use
-JB4 with pump gas BEF
-Afe intake
-Wagner 5" IC
-catless DP
-RWD
-open diff
-Federal RSR-R tread wear 140
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      03-22-2017, 05:47 PM   #6
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Quote:
Originally Posted by feuer View Post
-JB4 with pump gas BEF
-Afe intake
-Wagner 5" IC
-catless DP
-RWD
-open diff
-Federal RSR-R tread wear 140
I think that's the real deficiency.

I wonder if you would be experiencing wheel hop issues with a limited slip rear differential. I'm not convinced that you are experiencing true wheel hop which is a first modal coupling problem between the drivetrain and suspension.

I suspect that you're experiencing inner wheel hop which can lead to wheel hop especially considering your powertrain mods. I had this issue at stock power levels with an open rear differential.

Out of curiosity, with your powertrain mods, why haven't you considered a limited slip rear differential before going to this differential lockdown kit?

Last edited by Polo08816; 03-22-2017 at 06:01 PM..
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      03-23-2017, 07:56 AM   #7
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Quote:
Originally Posted by Polo08816 View Post
I think that's the real deficiency.

I wonder if you would be experiencing wheel hop issues with a limited slip rear differential. I'm not convinced that you are experiencing true wheel hop which is a first modal coupling problem between the drivetrain and suspension.

I suspect that you're experiencing inner wheel hop which can lead to wheel hop especially considering your powertrain mods. I had this issue at stock power levels with an open rear differential.

Out of curiosity, with your powertrain mods, why haven't you considered a limited slip rear differential before going to this differential lockdown kit?
LSD helps but even cars equipped with it are experiencing wheel hop. LSD is next on my mod list. Haven't done it yet due to lack of resources. LSD cost about the same if not more than all my other mods combined.
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      03-23-2017, 08:18 AM   #8
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Quote:
Originally Posted by feuer View Post
LSD helps but even cars equipped with it are experiencing wheel hop. LSD is next on my mod list. Haven't done it yet due to lack of resources. LSD cost about the same if not more than all my other mods combined.
I haven't experienced it, but I'm primarily using my car for DD and HPDE/track use. What are you trying to accomplish? Are you tracking the car or are you just drag racing?

A search for threads dealing with 'wheel hop' show that the first relevant result is buried almost 4 pages in:

http://f30.bimmerpost.com/forums/sho...27wheel+hop%27

Maybe Chicken_Joe can comment.

However, a cursory look at his signature says that he has a bunch of powertrain modifications, but stock suspension and stock open differential.
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      03-23-2017, 09:13 AM   #9
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Quote:
Originally Posted by Polo08816 View Post
I haven't experienced it, but I'm primarily using my car for DD and HPDE/track use. What are you trying to accomplish? Are you tracking the car or are you just drag racing?

A search for threads dealing with 'wheel hop' show that the first relevant result is buried almost 4 pages in:

http://f30.bimmerpost.com/forums/sho...27wheel+hop%27

Maybe Chicken_Joe can comment.

However, a cursory look at his signature says that he has a bunch of powertrain modifications, but stock suspension and stock open differential.
I have accomplished what I wanted in regards to wheel hop. Is gone. What tires do you run? Not sticky tires tend not to hop.
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      03-23-2017, 09:29 AM   #10
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Quote:
Originally Posted by feuer View Post
I have accomplished what I wanted in regards to wheel hop. Is gone. What tires do you run? Not sticky tires tend not to hop.
Michelin Pilot Super Sport 255/40/18 square setup.
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      03-23-2017, 09:52 AM   #11
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Quote:
Originally Posted by Polo08816 View Post
Michelin Pilot Super Sport 255/40/18 square setup.
I didn't have much of a problem with them either. They are 300tw and just span. Then I went to 200tw and not 140tw.
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      03-23-2017, 08:01 PM   #12
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IMHO you need an LSD. Staying with open diff and going 'fun' with power is really not ideal. JMHO
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      03-24-2017, 03:52 AM   #13
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Quote:
Originally Posted by feuer View Post
I didn't have much of a problem with them either. They are 300tw and just span. Then I went to 200tw and not 140tw.
Quote:
Originally Posted by enjoythemusic View Post
IMHO you need an LSD. Staying with open diff and going 'fun' with power is really not ideal. JMHO
+1.

A differential lockdown kit is still not going to stop your inner tire fire/inner tire burnout with those powertrain mods.

MPSS has been fine for me so far. I may consider Bridgestone RE-71R next time around but those are only 200 tread wear - which is about the lowest I would probably go for a street driven car.

OP, you should make an LSD your next mod. With your powertrain mods, you really need it.
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      03-26-2017, 03:24 AM   #14
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Quote:
Originally Posted by Polo08816 View Post
+1.

A differential lockdown kit is still not going to stop your inner tire fire/inner tire burnout with those powertrain mods.

MPSS has been fine for me so far. I may consider Bridgestone RE-71R next time around but those are only 200 tread wear - which is about the lowest I would probably go for a street driven car.

OP, you should make an LSD your next mod. With your powertrain mods, you really need it.
So on this note, I've been looking at LSDs. I have the ActiveHybrid 3 which is a 2.81 final ratio. I assume since the M LSD is a 3.15, I can't just swap that in without pissing off the transmission correct? Please excuse my ignorance, this is the first RWD car I've ever owned so I've never needed to upgrade a diff before. I see that Quaife makes a kit specifically for the AH3, but it seems pretty expensive overall.
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      03-26-2017, 04:20 AM   #15
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Quote:
Originally Posted by afranke View Post
So on this note, I've been looking at LSDs. I have the ActiveHybrid 3 which is a 2.81 final ratio. I assume since the M LSD is a 3.15, I can't just swap that in without pissing off the transmission correct? Please excuse my ignorance, this is the first RWD car I've ever owned so I've never needed to upgrade a diff before. I see that Quaife makes a kit specifically for the AH3, but it seems pretty expensive overall.
I'm unfamiliar with the AH3 trims. As long as the AH3 is not AWD, the transmission itself won't care, however the DSC/VSC may.

The BMW M Performance LSD is, surprisingly, a good value since you're getting the entire final drive unit without needing to pay a core charge.

With the Quaife unit, you'll probably need to send your final drive in because I'm not confident a diff shop will have spare AH3 cores with the 2.81 final drive.
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      03-26-2017, 04:21 AM   #16
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Yes, i've got a quaife for my AH3, very happy, and price is similar to the M performance LSD at least in Europe.

You're correct about the different gear ratio, so fitting the m performance LSD would result in higher rpm for same speed/same gear, which can be desirable in some situations, but results in lower fuel economy at least.

I'm not sure what the car ECUs would do with that, perhaps works like a charm (likely - changing final drive ratio is common in racing), perhaps not, but it's expensive to find out...
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      03-26-2017, 04:25 AM   #17
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Quote:
Originally Posted by Polo08816 View Post
I'm unfamiliar with the AH3 trims. As long as the AH3 is not AWD, the transmission itself won't care, however the DSC/VSC may.

The BMW M Performance LSD is, surprisingly, a good value since you're getting the entire final drive unit without needing to pay a core charge.

With the Quaife unit, you'll probably need to send your final drive in because I'm not confident a diff shop will have spare AH3 cores with the 2.81 final drive.
We did a differential exchange for my car.

The AH3 has the same diff as diesel engines and potentially 330i/328i as well, so it's rather commonplace (in Europe, but no problem sourcing one for Birds in UK to ship you one)
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      03-26-2017, 04:32 AM   #18
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Quote:
Originally Posted by feuer View Post
I got my lockdown kit from here: http://www.n54tech.com/forums/showpo...33&postcount=1 and thought it would be nice to share the info with the community.
Thanks, i didn't know this existed.
Would replacing diff bushings with stronger polyurethane bushings (e.g. Superpro) not be a cheaper way of achieving the same result?
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      03-26-2017, 04:45 AM   #19
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Quote:
Originally Posted by Lancelot View Post
Thanks, i didn't know this existed.
Would replacing diff bushings with stronger polyurethane bushings (e.g. Superpro) not be a cheaper way of achieving the same result?
My opinion would be that bushings is the proper way to address this if this is an issue for you.

Replacing the bushings is not necessarily "cheaper" because the rear differential bushing (not the 2 front bushings) will require you to drop the rear sub-frame.

I'm not 100% on the installation procedures for this "lockdown kit".
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      03-26-2017, 08:11 AM   #20
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Quote:
Originally Posted by Lancelot View Post
Thanks, i didn't know this existed.
Would replacing diff bushings with stronger polyurethane bushings (e.g. Superpro) not be a cheaper way of achieving the same result?
Quote:
Originally Posted by Polo08816 View Post
My opinion would be that bushings is the proper way to address this if this is an issue for you.
Replacing the bushings is not necessarily "cheaper" because the rear differential bushing (not the 2 front bushings) will require you to drop the rear sub-frame.
I'm not 100% on the installation procedures for this "lockdown kit".
Yes, replacing bushings definitely isn't cheaper nor will remedy the issue of wheel hop as the diff is mounted on 3 bushings only and will continue twisting under load. A lot of examples with solid diff bushings that are experiencing hop. All of this and including installation is cover in the thread I linked from n54tech.
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      03-26-2017, 03:28 PM   #21
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Quote:
Originally Posted by feuer View Post
Yes, replacing bushings definitely isn't cheaper nor will remedy the issue of wheel hop as the diff is mounted on 3 bushings only and will continue twisting under load. A lot of examples with solid diff bushings that are experiencing hop. All of this and including installation is cover in the thread I linked from n54tech.
Perhaps. I know of no wheel hop with my existing setup.

I suppose if I needed 400+ HP, then I'd just save myself the headache and buy an M3.
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      03-26-2017, 03:53 PM   #22
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Quote:
Originally Posted by Polo08816 View Post
Perhaps. I know of no wheel hop with my existing setup.
I suppose if I needed 400+ HP, then I'd just save myself the headache and buy an M3.
Why do you think that M3 isn't experiencing wheel hop? They have big diff brace for M3 to remedy the issue. The diffs are interchangeable. Subframe is different. You aren't experiencing hop with your existing setup. Great, but there are people that do! Your comments make you sound less informed.
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