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Rimmer's Polybush diff mounts


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I was about to get the diff re-mounted on new (blue) polybush mounts from Rimmer's. The cones seem very loose on the diff pins, concerned the diff would be able to move excessively; I was expecting them to be a neat fit, is this correct?

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They were the same on mine.

The play you describe was very useful when it came to fitting the diff and it bolted up fine.

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Personally I would have fitted rubber bushes on the diff rather than the harder polybush mounts. I would be concerned that the harder mounts would lead to problems with cracked chassis mounting points. The harder mounts would in my view transmit every vibration up through the mounting pins. Just my thoughts. I would be interested in other views on this.

Keith

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I agree with Keith,

but the new aftermarket rubber bushes I ordered are terribly rock-hard, so maybe a  soft PU is the better option. If they appear to hard (noise), I will replace with soft PU items.

Wish I had known this when I bought them 3 years ago.

The original Metalastic bushes that came off the car were made of a soft rubber compound, and despite their age, very flexible. But I could not get these any longer.

Waldi

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Yes I had considered rubber for the diff mount for the reasons stated, but the blue polybushes are fairly soft and pliable, just didn't think they would be so loose on the pins. I'm waiting to see what Rimmers say when they are open tomorrow

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19 hours ago, qkingston said:

I was about to get the diff re-mounted on new (blue) polybush mounts from Rimmer's. The cones seem very loose on the diff pins, concerned the diff would be able to move excessively; I was expecting them to be a neat fit, is this correct?

qkingston (or whatever your name is?) You mention cones so I assume you are referring to the front mounts. The top "convex" bush seats into a dish in the steel diff cross mounting bridge while the lower "concave" bush seats up against the same steel dish. When bolted up tight with the correct large dia steel washer underneath they all centralise naturally around their relevant parts and form a rigid fixing. I wouldn't be too concerned that they are a little loose on the pins. As Pod One (or whatever his name is?) says, that helps with manoeuvering the diff into position.

If it's the rear mounts with the steel sandwich plate they should have a steel sleeve down the centre to make them a reasonably tight fit on the diff mount pins.

Dave McD

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Hi,

I have been told they should be better strong than soft.

Rear soft ones will be compressed more while accelerating and while brake the car in both directions.

So the diff seesaws and bends on the front diff mounts  and the tin plate - until the tin plate around them brakes.

Just another story from the bonfire? But this sounds reasonable, doen't it?

Ciao, Marco

Edited by Z320
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I fitted the poly bushes when I had the diff rebuilt and they transmitted a lot of road vibration through to the drivers floor pan. 

I replaced them with new rubber ones and it’s been fine since. This was over 5 years ago so components may be different now.

Chris

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3 hours ago, Dave McDonald said:

qkingston (or whatever your name is?) You mention cones so I assume you are referring to the front mounts. The top "convex" bush seats into a dish in the steel diff cross mounting bridge while the lower "concave" bush seats up against the same steel dish. When bolted up tight with the correct large dia steel washer underneath they all centralise naturally around their relevant parts and form a rigid fixing. I wouldn't be too concerned that they are a little loose on the pins. As Pod One (or whatever his name is?) says, that helps with manoeuvering the diff into position.

If it's the rear mounts with the steel sandwich plate they should have a steel sleeve down the centre to make them a reasonably tight fit on the diff mount pins.

Dave McD

Thanks Dave, it's the front and rear mounts, my diff is the other type that uses the cones front and back, no steel sleeve. I was kinda hoping that the tightening up would sort the issue, but didn't want to do that until I've checked with you chaps who've done this before. The older rubber mounts I removed (original I guess), were a tighter fit on the pins

Thanks

David

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1 minute ago, ChrisR-4A said:

I fitted the poly bushes when I had the diff rebuilt and they transmitted a lot of road vibration through to the drivers floor pan. 

I replaced them with new rubber ones and it’s been fine since. This was over 5 years ago so components may be different now.

Chris

Thanks Chris, where did you source your rubber ones from? I'm aware there's a lot of rubbish "rubber" components out there

Rgds

David

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17 hours ago, qkingston said:

 

 it's the front and rear mounts, my diff is the other type that uses the cones front and back, no steel sleeve. 

David

????????????????????????

New to me

Roy

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2 hours ago, roy53 said:

????????????????????????

New to me

Roy

TR4A back plate..?

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The problem with the rubber available today is that it simply doesn't last long when compared to poly (and often "harder") which I've gone over to in quite a few cars over the years mainly Super Pro. True it can transmit vibration but generally if over tightened/compressed too much as stiction prevents it doing its job. As for the pins/bridges they are weak anyway so the usual strengthening is worth while if you can while the diff is out although welding upside down is no fun. I completely boxed in the rear bridge and it made a massive improvement to the rigidity which I can't see failing anytime soon.

From the pic you can see some of the additional metal added to the rear bridge. It's a complete box section and the point where it meets the rails was also reinforced given the shocks mounts as have various other points around the chassis. 

Andy

DSC05075.JPG

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On 4/22/2019 at 11:22 AM, keith1948 said:

Personally I would have fitted rubber bushes on the diff rather than the harder polybush mounts. I would be concerned that the harder mounts would lead to problems with cracked chassis mounting points. The harder mounts would in my view transmit every vibration up through the mounting pins. Just my thoughts. I would be interested in other views on this.

Keith

Hi Keith,

 the SuperPro diff bushes are no harder than the original rubber (they have holes moulded into them to allow them to give a little) 

These will last a life time.

 

Roger

Edited by RogerH
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Thanks all, that's useful. I just measured the pin and bush, the pin o/d is 14mm, the polybush i/d is 16.5mm, quite a difference no? Photos below (I know the cone is upside down, just for illustration)

David

IMG-20190423-WA0004.jpg

IMG-20190423-WA0003.jpg

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I think this clearance allows for some misalignment.

if all was a tight fit, the cones would only contact at one side. With this clearance, they can perfectly centre themselves. 

If all were perfectly aligned and the pitch of pins and brackets were the same, yes, this would give lateral movement.

Waldi

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13 hours ago, PodOne said:

The problem with the rubber available today is that it simply doesn't last long when compared to poly (and often "harder") which I've gone over to in quite a few cars over the years mainly Super Pro. True it can transmit vibration but generally if over tightened/compressed too much as stiction prevents it doing its job. As for the pins/bridges they are weak anyway so the usual strengthening is worth while if you can while the diff is out although welding upside down is no fun. I completely boxed in the rear bridge and it made a massive improvement to the rigidity which I can't see failing anytime soon.

From the pic you can see some of the additional metal added to the rear bridge. It's a complete box section and the point where it meets the rails was also reinforced given the shocks mounts as have various other points around the chassis. 

Andy

DSC05075.JPG

You do also need to plate the top of the front bridge round the pins BTW.

Stuart.

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Hi Stuart 

The pins are boxed in below with 2mm plate will this be enough from your experience or would you add one to the top as well

Thanks

Andy

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I add one on top as the front right hand pin has a habit of punching up through the bridge.

Stuart

post-3753-0-92123200-1525080237_thumb.jpg

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2 hours ago, stuart said:

You do also need to plate the top of the front bridge round the pins BTW.

Stuart.

Thanks Stuart, full CTM strenghtening kit fitted

Rgds

David

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