Rear Diff Support Moving Too Much?

[Mike]

There have been several of us looking at controlling the rear diff movement, so I thought it would be a good idea to give this topic its own thread.

The standard Sierra D-mount is designed to allow a significant degree of movement within the rubber bracket. I observed my diff while the car was up on stands, and was horrified to see just how much movement there is with NO wheel load: what must it be like under hard acceleration with 200bhp on tap? Some owners have recognised this and packed the lower hole to prevent this movement, but there is debate as to how effective this is.Some owners saying oit does not last long, others saying they can keep theirs in for years?
I would like something that will last the life of my car and allow me the odd severe start if I want to.

IMG_0876.jpg



Mark Scott has loaned me his Polybush bracket, and it greatly reduces the diff movement, in the drive shaft plane, but I am concerned with the NVH (Noise-Vibration-Harshness) from the stiff polybush material.

IMG_0881.jpg


The solid steel mount in Lee's photo will make for a noisey back end with a lot of vibration - I really would not recommend it for a road going car - track days maybe?

The Ford Scorpio Ultima 7.5" diff had a "Koala" type double rubber bush at the rear, and a single one at the front, which Ford had invested a lot of time and money in , in an attempt to compete with the smoothness of their German competitors.

IMG_2281.jpg

From the photo of the Koala arrangement, you can see that this will significantly reduce the degree of movement in the drive shaft plane compared to the old Sierra D bracket. And with two widely spaced connecting points it will reduce the rotation in the propshaft plane. Two sets of rubber will help dissipate the vibration too. For me, this seems to offer a good solution.



I'm currently considering making a similar twin rubber mount arrangement which bolts to the back of the standard Sierra 7" diff - as per the diagram below (courtesy of Jason). Hopefully it will have the added advantage of limiting the rotation around the drive shaft plane, and around the propshaft plane, as well as being retro fitable to any Sierra diff.

Diff Mounting.jpg



I am considering two options. One is to cut two steel brackets from two front diff mounts from two Scorpios brackets (see photo below of standard bracket), and weld them up as above: alternatively I could cut the two mounts off the Ultima diff case, and make it from aluminium.

IMG_2282.jpg


I have now bought a second steel bracket for £10 from ebay, so I'll definitely make one in steel first. Then, if it is successful, I may make a second one in aluminium.
When its complete and I've had a chance to test it I'll let you know how I get on - but don't hold your breath - its taken me 6 years to build my car!

[CosworthCabrioLee]

Re: Rear Diff Support Moving Too Much?

Hello mike I think you will be fine with that poly diff and that is what I am going to upgrade too, it's a bit more trouble for me to swap my mount as the diff has to come out, the sierra cosworth boys rave about them, and some of them are 400+ bhp, perhaps if there is enough interest in a poly mount then we could negotiate discount off the manufacturer ??????
I will drop some emails away today see what discounts versus quantity I can get.

[Mark]

Re: Rear Diff Support Moving Too Much?

I don't see the diagram that Jason made for you, Mike. Do others see it?

Having shelled out for the polybush mount I think I'll be sticking with that - unless your post-IVA road tests or reports from others in the meantime are particularly negative. I'll be following your Scorpio-inspired alternative with interest though.

[greyV8pete]

Re: Rear Diff Support Moving Too Much?

My diff mount is Polybush and was made & fitted by Marlin when I bought the car through them (as 3rd user - previous customer's car). I have only driven the car with this bush set up so cannot compare with a standard Sierra set up. I can only hear the diff a bit if the hood is up and that is only if it is pouring with rain! Maybe some blue polybushes would be softer / quieter? However the V8 exhaust tends to overwhelm all other noises so not a problem

Link below shows my post about this from some time ago. Scroll down to post #6. Peter.

http://www.marlinownersclub.com/forum/showthread.php?2106-Diff-Mounting&highlight=diff+mount

[Mike]

Re: Rear Diff Support Moving Too Much?

I don't see the diagram that Jason made for you, Mike. Do others see it?

Having shelled out for the polybush mount I think I'll be sticking with that - unless your post-IVA road tests or reports from others in the meantime are particularly negative. I'll be following your Scorpio-inspired alternative with interest though.

Mark

That is strange as it shows on what I am looking at?

Mike

[CosworthCabrioLee]

Re: Rear Diff Support Moving Too Much?

Spoken to Motor sport developments today and they are looking at a price for a bulk buy of diff mounts, i should have the prices Monday Tuesday.If your interested Please register a interest here.

[CosworthCabrioLee]

Re: Rear Diff Support Moving Too Much?

Motor sport development can do the solid billet diff mounts for £105 If we order 6 and £100 if we order 10 normal price is £124
If anyone is interested in this please pm me and I will add you to the list.

[cameronfurnival]

Re: Rear Diff Support Moving Too Much?

Hi Mike, Mark, the place holder is showing instead of the diagram. I beleive this is due to it being linked to another website url? Maybe the url is incorrect or has moved. Mike, you may still be seeing it as its in your browser cache.
Hth

[Mike]

Re: Rear Diff Support Moving Too Much?

Mark
Can you see Jason's sketch in my thread now?
Mike

[Mike]

Re: Rear Diff Support Moving Too Much?

Hi Lee

That's a good saving. I hope you can find enough to make your order up. You may have to go through Pitstop though to get other owners involved!!!! Paul from Leicester was on here a while back, so he may be interested, and there may be a few Rover V8 owners who have problems with the standard Sierra D - bracket. You could ask Derek Jones to send an email out to all Cabrio owners- that's what I did with the servo, and have now received another 24 orders.

For myself, I would still like to explore my adaptation of the Scorpio design with it widely spaced two rubber mounts bolted to the rear of the Sierra diff, as I think it should be quieter, and pass less vibration in to the chassis. But that's just my theory..............? If it does not work out I will go down the aluminium polyflex route, but it will be a while before I make that decision, so count me out this time.

But thanks for your efforts on securing a good offer from the supplier: it just shows again what we can achieve collectively through the Forum.
Regards
Mike

[Mark]

Re: Rear Diff Support Moving Too Much?

Hi Mike,

Mark
Can you see Jason's sketch in my thread now?
Mike

Yes thanks, that's sorted it!

[dcunn]

Re: Rear Diff Support Moving Too Much?

Picture visible now, many thanks Mike

[Mike]

Re: Rear Diff Support Moving Too Much?

Some progress has been made with my Scorpio style rear diff support.

I bought just the back plate from a Scorpio diff, and cut the two aluminium eyelets off.




I then welded these to a 25mm thick aluminium bar, and drilled two holes to attach to the standard Sierra diff mounting point, ala GOO's drawing.





This is the final article - with a hole to spare!:




This is then bolted directly to the Sierra diff:


I made an aluminium cradle, but it is too soft, so I'll make version 2 from steel.
I'm confident this will greatly reduce the amount of diff movement as the two rubber mounts are spaced apart by 150mm, so will be much more rigid than the old Sierra D mount, and hopefully will be vibration free too.

[djj_engineer]

Re: Rear Diff Support Moving Too Much?

You could try liquid rubber poured into the mounting, Using the sides as the mould. The rubber would eliminate the voids but not result in a 'stiff' mounting.

[Mike]

Re: Rear Diff Support Moving Too Much?

You could try liquid rubber poured into the mounting, Using the sides as the mould. The rubber would eliminate the voids but not result in a 'stiff' mounting.

Hi Derek

This has been tried with mixed success. I believe Peter Morris added rubber to his void, and it worked for 2+ years: others have stated it failed in a very short period.
I need to control my diff movement much more than most as I narrowed and lowered my transmission tunnel in order to fit wider reclining seats (from an A4). I have imitated Ford's Scorpio diff arrangement, by adding a T-bar to the standard diff mounting position. This has two rubber filled bushes spaced 100mm apart. This should significantly reduce rotation in both the prop plane and the drive shaft plane. Only time will tell if is successful?!

This is the final article fitted to my Cabrio:

- it will not let me add more photos - grrrrrrrrrrrrrrrr!!!!!!!!!!!!!