Replacing rear beam bushes: 3 questions for you

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Y_Cymro
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Replacing rear beam bushes: 3 questions for you

Post by Y_Cymro » Tue 07 Feb, 2017 22:17

My Indie is concerned about replacing the rear beam bushes on my year 2000 2.8 in case the bolts holding the beam are corroded, snap when being dismantled. and have to be re-drilled and tapped, thus taking a lot of time and costing me more money.

Does anyone have experience of changing the bushes and encountered problems caused by corrosion?

Also, I plan to use polybushes inseam of OEM voided rubber ones. Anyone with experience of these and can comment on harshness or vibration?

My Indie's also concerned about changing the trailing arm bushes in case they're corroded in place and cannot be easily removed, and because he says some cars have eccentric bushes which cannot be identified before work starts - and because swapping bushes can adversely affect alignment.

Would appreciate the thoughts of anyone with experience of the above.

Juvvajuvva
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Re: Replacing rear beam bushes: 3 questions for you

Post by Juvvajuvva » Tue 07 Feb, 2017 23:02

I have just done all those jobs this week. :D

Y_Cymro
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Re: Replacing rear beam bushes: 3 questions for you

Post by Y_Cymro » Wed 08 Feb, 2017 00:53

Great. How did you get on, any problems removing the beam or old bushes?
Did you replace the trailing arm bushes too? Were there any problems, and did you use ordinary or eccentric bushes?

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BladeRunner919
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Re: Replacing rear beam bushes: 3 questions for you

Post by BladeRunner919 » Wed 08 Feb, 2017 08:01

I've also done it. Getting the old bushes out is a bit of a pain, but other than that it's very straightforward. I'm not really sure what the chap is concerned about, unless you have significant corrosion underneath? Seems like a strange concern for a mechanic, unless he normally only works on brand-new cars.

Y_Cymro
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Re: Replacing rear beam bushes: 3 questions for you

Post by Y_Cymro » Wed 08 Feb, 2017 08:48

BladeRunner919 wrote:I've also done it. Getting the old bushes out is a bit of a pain, but other than that it's very straightforward. I'm not really sure what the chap is concerned about, unless you have significant corrosion underneath? Seems like a strange concern for a mechanic, unless he normally only works on brand-new cars.
He's not seen my car yet but seemed genuinely concerned about extra work needed around corroded, snapped bolts becoming an additional cost to me. He's an ex-dealer mechanic but has been running his own garage for many years.
The car's in good condition and regularly used so there shouldn't be problems, but it's good to know the experience of others.
Did you fit polybushes to the beam?

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BladeRunner919
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Re: Replacing rear beam bushes: 3 questions for you

Post by BladeRunner919 » Wed 08 Feb, 2017 08:57

Yes, I did, as well as polybushing the front control arms. I didn't replace the trailing arm bushes but I believe that the recommendation is to replace those with original bushes as polybushes tend to start squeaking after a while.

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Re: Replacing rear beam bushes: 3 questions for you

Post by Y_Cymro » Wed 08 Feb, 2017 09:01

BladeRunner919 wrote:Yes, I did, as well as polybushing the front control arms. I didn't replace the trailing arm bushes but I believe that the recommendation is to replace those with original bushes as polybushes tend to start squeaking after a while.
Thanks for confirming. I've also fitted polybushes to the front and they're fine. More feedback than standard bushes but I don't find them harsh. What difference did the rears make?

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Re: Replacing rear beam bushes: 3 questions for you

Post by Joycey » Wed 08 Feb, 2017 10:39

I'm around the 20 mark now for Z3 rebuilds and the only real bit that makes me nervous every time is removing the 4 m6 cap heads (2 each side) that hold the beam plate in place. If you round these heads they are a pain to get to, the fuel tank is inches away.

You might need to look at the exhaust bolts to because they're usually well past it.

Old beam bushes I pressed out with some heat. Arm bushes I used some threaded bar. I have never encountered worn bushes on those arms on every build I've done. I've also use mostly OEM bushes but have fitted a few poly. If you were to drive the car back to back (on public roads!) you wouldn't be able to notice the difference.
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Deano1712
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Re: Replacing rear beam bushes: 3 questions for you

Post by Deano1712 » Wed 08 Feb, 2017 11:58

I wouldn't bother with poly for rhe the trailing arms but defo worth it for the beam and diff mount. My z3m caught me out a few times when on the limit. With solid bushes it's lots more predictable when you lose traction and a safer car.
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Del
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Re: Replacing rear beam bushes: 3 questions for you

Post by Del » Wed 08 Feb, 2017 12:18

I used a local BMW specialist who had a special support jig and commercial puller - cost around £100 to insert the main beam bushes, which I bought myself. After at first being reluctant, I am now a convert to the Powerflex purple polyurethane buses. They are extremely high quality, a perfect fit and the various bolts and washes which come with certain kits are extremely well engineered. I have not found them harsh and when manipulated by hand they do not seem much different to the OE rubber ones. There are harsher polyurethane bushes around which are designed for track use etc - Powerflex do a black range - I would avoid these.

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Re: Replacing rear beam bushes: 3 questions for you

Post by Y_Cymro » Wed 08 Feb, 2017 13:48

Joycey wrote:I'm around the 20 mark now for Z3 rebuilds and the only real bit that makes me nervous every time is removing the 4 m6 cap heads (2 each side) that hold the beam plate in place. If you round these heads they are a pain to get to, the fuel tank is inches away.

You might need to look at the exhaust bolts to because they're usually well past it.

Old beam bushes I pressed out with some heat. Arm bushes I used some threaded bar. I have never encountered worn bushes on those arms on every build I've done. I've also use mostly OEM bushes but have fitted a few poly. If you were to drive the car back to back (on public roads!) you wouldn't be able to notice the difference.
Great advice, thanks.
OK, I'll give the m6 screws a few squirts of release oil before the day. The exhaust is stainless and recent so that shouldn't be a problem. As you've not encountered huge issues with trailing arm bushes I wont replace them unless there's obvious degradation.

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Re: Replacing rear beam bushes: 3 questions for you

Post by Y_Cymro » Wed 08 Feb, 2017 13:49

Deano1712 wrote:I wouldn't bother with poly for rhe the trailing arms but defo worth it for the beam and diff mount. My z3m caught me out a few times when on the limit. With solid bushes it's lots more predictable when you lose traction and a safer car.
Thanks, hadn't thought too much about the diff mount. Will check it out.

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Re: Replacing rear beam bushes: 3 questions for you

Post by Y_Cymro » Wed 08 Feb, 2017 13:52

Del wrote:I used a local BMW specialist who had a special support jig and commercial puller - cost around £100 to insert the main beam bushes, which I bought myself.
Wow, is that price for just inserting the bushes or for the whole job? I've been quoted more than twice that for just labour for it all.

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BladeRunner919
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Re: Replacing rear beam bushes: 3 questions for you

Post by BladeRunner919 » Wed 08 Feb, 2017 15:03

Y_Cymro wrote:
Deano1712 wrote:I wouldn't bother with poly for rhe the trailing arms but defo worth it for the beam and diff mount. My z3m caught me out a few times when on the limit. With solid bushes it's lots more predictable when you lose traction and a safer car.
Thanks, hadn't thought too much about the diff mount. Will check it out.
I'd stick with an original diff mount - there is a school of thought (including the rear-subframe expert Randy Forbes) that a poly diff mount can exacerbate the potential for the rear subframe failure. The recommended solution at the rear is poly for the two beam mounts and original for the diff and the trailing arms.

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Re: Replacing rear beam bushes: 3 questions for you

Post by gookah » Wed 08 Feb, 2017 17:07

I just polybushed my rear beam, roll bar and trailing arms. a lot better.

Oh... and if you go with a poly diff bush... you can have a load of fun....
This is what happened to mine on Saturday after 1 week, 40 miles from home..... a big bang from underneath.

Image

Image


the chain was to get me home, as the diff rubbed on the tarmac grinding the drain plug away.
No I didnt cut into the circle removing the old one and didnt have to press or hammer the new bush in place.

Oh and how long to get a new diff cover from BMW?
try April 18th?
Last edited by gookah on Sun 05 Mar, 2017 19:21, edited 1 time in total.
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Deano1712
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Re: Replacing rear beam bushes: 3 questions for you

Post by Deano1712 » Wed 08 Feb, 2017 17:14

The diff moves around loads on the soft rear mount. There is a youtube video somewhere. Three problems from this:
1. Driveshaft angular alignment compromised, leads to wear and failure in driveshaft joints.
2. Dynamic loads higher into boot floor.
3. If you have solid front beam bushes you dont want the diff moving in pitch since there is no compliance in the bushes and you will impart bending loads into the big M14 studs.
Other benefit is you get some diff noise coming into the car, and it sounds ace :-)
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Re: Replacing rear beam bushes: 3 questions for you

Post by gookah » Wed 08 Feb, 2017 17:17

Deano1712 wrote: Other benefit is you get some diff noise coming into the car, and it sounds ace :-)
I had some diff noise coming into mine. the sound of it grinding on tarmac.... wasn't keen tbh :D
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Deano1712
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Re: Replacing rear beam bushes: 3 questions for you

Post by Deano1712 » Wed 08 Feb, 2017 17:34

Haha thats a different noise!
Here is that video
https://youtu.be/trYjnmeFqZU
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Re: Replacing rear beam bushes: 3 questions for you

Post by gookah » Wed 08 Feb, 2017 18:07

I am loath to change it back to normal,
after all, you run polybush diff with far more power than mine exerts on it,
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I have an element of 'M-styling' on my car, If that's a good enough reason for the manufacturers to adorn a 320 with the M badge, then its certainly a good enough reason for me..

Joycey
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Re: Replacing rear beam bushes: 3 questions for you

Post by Joycey » Wed 08 Feb, 2017 21:44

That's rare to see in the U.K. Gook I don't suppose it failed where you hacksawed the old bushe out did it...

Just going by marks on the side of the exhaust look alot like hacksaw scuffs
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Re: Replacing rear beam bushes: 3 questions for you

Post by gookah » Wed 08 Feb, 2017 23:40

Joycey wrote:That's rare to see in the U.K. Gook I don't suppose it failed where you hacksawed the old bushe out did it...

Just going by marks on the side of the exhaust look alot like hacksaw scuffs
As I said no cuts in the circle, I took the bush out with the diff off the car
Image

beam, trailing arms and diff all removed for new bushes
Image

Image
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Z3 2.8 Progress Journal (Mine)
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I have an element of 'M-styling' on my car, If that's a good enough reason for the manufacturers to adorn a 320 with the M badge, then its certainly a good enough reason for me..

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Re: Replacing rear beam bushes: 3 questions for you

Post by Joycey » Wed 08 Feb, 2017 23:55

Hoping it was an easy one to spot. Have you messaged spurs? He has 3 cars in at the moment. Might be worth grabbing a cover from him? Unless your in no rush.
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Re: Replacing rear beam bushes: 3 questions for you

Post by gookah » Thu 09 Feb, 2017 16:10

Joycey wrote: Have you messaged spurs? He has 3 cars in at the moment. Might be worth grabbing a cover from him? Unless your in no rush.

Been in touch with Andy, and although reluctant to sell one on its own unsurprisingly, and be left with an unsaleable diff, he kindly offered to loan me one until the new one arrives in April. What a Star!
However I got one of my engineers on the case yesterday and this is what he came up with......:

Image

Image


So when my new oil comes, this will get me away until April.
How much for a new diff cover including standard bush from BMW? £81.... that took me by surprise. I was thinking in the £100s
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I have an element of 'M-styling' on my car, If that's a good enough reason for the manufacturers to adorn a 320 with the M badge, then its certainly a good enough reason for me..

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pingu
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Re: Replacing rear beam bushes: 3 questions for you

Post by pingu » Thu 09 Feb, 2017 19:04

I'd be tempted to swap that one with Andy. I doubt that many people wanting a diff won't already have a cover, and if they do, they will get one in April.

I disagree with your thinking about the poly bush on the diff - I think that was the cause of your failure.

The video in Deano's post clearly shows how much energy the diff bush has to absorb. If it's not absorbed by the bush it will be absorbed by the diff cover or the floor.
Pingu

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Re: Replacing rear beam bushes: 3 questions for you

Post by bertiejaffa » Fri 10 Feb, 2017 17:58

Is your camera broke Gookah.... the bottom of your car is all silver and black... cant see the mud and the brown... :wink:
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Re: Replacing rear beam bushes: 3 questions for you

Post by gookah » Sat 11 Feb, 2017 11:45

bertiejaffa wrote:Is your camera broke Gookah.... the bottom of your car is all silver and black... cant see the mud and the brown... :wink:
the car won't stay like that for long as a daily driver, but as I had everything off, and some black and silver paint, it was rude not to.... :D
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Re: Replacing rear beam bushes: 3 questions for you

Post by c_w » Sat 11 Feb, 2017 18:27

pingu wrote:I'd be tempted to swap that one with Andy. I doubt that many people wanting a diff won't already have a cover, and if they do, they will get one in April.

I disagree with your thinking about the poly bush on the diff - I think that was the cause of your failure.

The video in Deano's post clearly shows how much energy the diff bush has to absorb. If it's not absorbed by the bush it will be absorbed by the diff cover or the floor.
I'm not sure, the opposite in fact IMO; a poly bush will just transfer more force to the body of the car, much like solid engine mounts are a recipe for chassis cracks. The standard bush has voids to dampen and reduce NVH, but after that void movement hits a "bump stop"; the poly bush doesn't have that initial give, so yes the movement of the diff is more controlled at the expense of more force transferred to the car.

IMO, we just see the diff bush doing it's job here; the diff might look like it's wobbling, but drive the car hard with the bonnet off and you'll think the engine mounts are broken. I was actually expecting more twisting from a single eared diff.

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Re: Replacing rear beam bushes: 3 questions for you

Post by pingu » Sat 11 Feb, 2017 18:40

c_w wrote:
pingu wrote:I'd be tempted to swap that one with Andy. I doubt that many people wanting a diff won't already have a cover, and if they do, they will get one in April.

I disagree with your thinking about the poly bush on the diff - I think that was the cause of your failure.

The video in Deano's post clearly shows how much energy the diff bush has to absorb. If it's not absorbed by the bush it will be absorbed by the diff cover or the floor.
I'm not sure, the opposite in fact IMO; a poly bush will just transfer more force to the body of the car, much like solid engine mounts are a recipe for chassis cracks. The standard bush has voids to dampen and reduce NVH, but after that void movement hits a "bump stop"; the poly bush doesn't have that initial give, so yes the movement of the diff is more controlled at the expense of more force transferred to the car.

IMO, we just see the diff bush doing it's job here; the diff might look like it's wobbling, but drive the car hard with the bonnet off and you'll think the engine mounts are broken. I was actually expecting more twisting from a single eared diff.
I think we are agreeing :)
Pingu

Del
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Re: Replacing rear beam bushes: 3 questions for you

Post by Del » Sat 11 Feb, 2017 19:33

I can't believe that fitting a marginally harder polyurethane bush would cause the diff bracket to rip away after a relatively short time - I've never seen this reported anywhere else. In my view it's more likely to be pre-existing damage/flaw either in manufacture or due to an old, wobbly OE bush. Even by a blow (possibly by some object or bump in the road), the diff has received earlier in its life. :shock:

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Re: Replacing rear beam bushes: 3 questions for you

Post by c_w » Sat 11 Feb, 2017 19:47

pingu wrote:
c_w wrote:
pingu wrote:I'd be tempted to swap that one with Andy. I doubt that many people wanting a diff won't already have a cover, and if they do, they will get one in April.

I disagree with your thinking about the poly bush on the diff - I think that was the cause of your failure.

The video in Deano's post clearly shows how much energy the diff bush has to absorb. If it's not absorbed by the bush it will be absorbed by the diff cover or the floor.
I'm not sure, the opposite in fact IMO; a poly bush will just transfer more force to the body of the car, much like solid engine mounts are a recipe for chassis cracks. The standard bush has voids to dampen and reduce NVH, but after that void movement hits a "bump stop"; the poly bush doesn't have that initial give, so yes the movement of the diff is more controlled at the expense of more force transferred to the car.

IMO, we just see the diff bush doing it's job here; the diff might look like it's wobbling, but drive the car hard with the bonnet off and you'll think the engine mounts are broken. I was actually expecting more twisting from a single eared diff.
I think we are agreeing :)
Oh I see, sorry! :)

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pingu
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Re: Replacing rear beam bushes: 3 questions for you

Post by pingu » Sat 11 Feb, 2017 20:45

Del wrote:I can't believe that fitting a marginally harder polyurethane bush would cause the diff bracket to rip away after a relatively short time - I've never seen this reported anywhere else. In my view it's more likely to be pre-existing damage/flaw either in manufacture or due to an old, wobbly OE bush. Even by a blow (possibly by some object or bump in the road), the diff has received earlier in its life. :shock:
The poly bush is not marginally harder; it is significantly harder.
Pingu

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Re: Replacing rear beam bushes: 3 questions for you

Post by Deano1712 » Sat 11 Feb, 2017 21:00

I think whats going on with the rear suspension is quite complicated. Whether a solid bush is good or bad for load transfer is a matter of opinion unless someone measures it.
You can certainly see why driveshaft failure is common fron the video. The motion will take driveshaft alignment outside normal limits. This is exacerbated by deformation in the boot floor - every z3 i have cheched has a slight downwards bow in the boot floor due to overload of the weak metalwork.
So the alignment of the driveshaft is out a bit due to the diff hanging lower than as designed.
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Del
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Re: Replacing rear beam bushes: 3 questions for you

Post by Del » Sat 11 Feb, 2017 22:53

pingu wrote:The poly bush is not marginally harder; it is significantly harder.
Depends on the type of polyurethane. The hardness of the purple Powerflex ones only sits at the upper end of the scale for typical OE rubber ones.

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c_w
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Re: Replacing rear beam bushes: 3 questions for you

Post by c_w » Sun 12 Feb, 2017 18:40

Del wrote:
pingu wrote:The poly bush is not marginally harder; it is significantly harder.
Depends on the type of polyurethane. The hardness of the purple Powerflex ones only sits at the upper end of the scale for typical OE rubber ones.
But that's on like for like comparison with a solid piece of rubber vs solid poly. The OE bushes isn't solid rubber and has a void by design to cushion movement. It's a bit like a stock wishbone bush vs a z3m bush - they could both be the same rubber shore hardness but one has hardly any voids, the other has big holes in so lots of flex.

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c_w
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Re: Replacing rear beam bushes: 3 questions for you

Post by c_w » Sun 12 Feb, 2017 18:46

Deano1712 wrote:I think whats going on with the rear suspension is quite complicated. Whether a solid bush is good or bad for load transfer is a matter of opinion unless someone measures it.
You can certainly see why driveshaft failure is common fron the video. The motion will take driveshaft alignment outside normal limits. This is exacerbated by deformation in the boot floor - every z3 i have cheched has a slight downwards bow in the boot floor due to overload of the weak metalwork.
So the alignment of the driveshaft is out a bit due to the diff hanging lower than as designed.
I think poly subframe bushes with stock diff bush should work well, with the poly bushes preventing the overall subframe float and an "axial"(?) rotation of the subframe. Since they are at the far extensions of the subframe and the diff bush is fairly central I think you can argue they can be different in type. It's what I reckon anyway :lol:

From your video it looks like the diff just pulls down on the bush rather than twists (visibly anyway), that's why I reckon a twin eared diff would spread that load more evenly (and it's why it's no surprised it's always the left side of the bootfloor that pulls away).

I suppose what we're seeing here is the downside to this type of setup vs a modern multi link which would cope with a lot more power with stock type bushes without so much movement of diff and suspension.

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pingu
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Re: Replacing rear beam bushes: 3 questions for you

Post by pingu » Sun 12 Feb, 2017 20:45

c_w wrote:I think poly subframe bushes with stock diff bush should work well, with the poly bushes preventing the overall subframe float and an "axial"(?) rotation of the subframe. Since they are at the far extensions of the subframe and the diff bush is fairly central I think you can argue they can be different in type. It's what I reckon anyway :lol:
Exactly my thoughts. If I were to change to poly bushes, I'd do the subframe at the rear and anti-roll bar and the lollipops at the front, but I'd leave the others as OEM.
Pingu

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c_w
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Re: Replacing rear beam bushes: 3 questions for you

Post by c_w » Mon 13 Feb, 2017 19:02

I think the Z3M bushes on the front are fine, no need to upgrade. Not sure about anti roll bars but I do have them on mine as they come with the H&R anti roll bars.

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Re: Replacing rear beam bushes: 3 questions for you

Post by Y_Cymro » Sun 05 Mar, 2017 14:31

The subframe bushes have been replaced with Powerflex purple poly bushes and whilst there's a minor difference to the ride quality, it's certainly not harsh. The tail still wiggles when the rear crosses transverse ridges on curves (such as bridge expansion joints) but the rear is more precisely controlled than before. It's probably highlighted that new, firmer dampers are needed as the ones fitted (replacement KY's fitted about 20k ago) are soft and floaty, especially on rebound.
One brake fitting was sheared during the fitting which necessitated a new brake line, and the 4 horizontal M8 cap screws were difficult to remove but other than that, all went well. The trailing arm bushes are in good condition so were left alone.

Thanks everyone for the good advice.

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Re: Replacing rear beam bushes: 3 questions for you

Post by c_w » Wed 08 Mar, 2017 16:29

Do you notice any difference in differential noise? In the Coupe I imagine it's more likely to change more than the roadster. Is it via OBD?

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Re: Replacing rear beam bushes: 3 questions for you

Post by Y_Cymro » Sat 11 Mar, 2017 13:01

c_w wrote:Do you notice any difference in differential noise? In the Coupe I imagine it's more likely to change more than the roadster. Is it via OBD?
If you concentrate you can hear a slight diff noise, though it's not noticeable most of the time. Similarly, there's a slight increase in vibration though it's not noticeable unless you look/feel for it.

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