BMW diff removal

[ScottR400D]

Good idea. I will do that this time. But I do know what pad rattle sounds like and this doesn't sound like that but you never know. 

[Tazio]

Just a thought as the discs/pads expand and contract, and at least it eliminates a possible source.

[ScottR400D]

I shall check. The other thing it sounds like 2 knocks per wheel rev, I can't imagine anything on the disc assembly that would do that.

[Geoff Brown]

Loose brake pad catching as the run out of the disc passes through?

[ScottR400D]

Well, after completely dismantling the rear end for a second time and taking the diff back to Phil, it appears there was a small mark, or something on the pinion, causing the tapping sound. Phil was very apologetic, they've never seen it before, but he stripped and rebuilt the diff whilst I went down the road for an hour to get a sandwich.

So, all back together again. On my own refitting the diff this time but I knocked up a simple wooden jig to support the diff level and square on the 3 flat surfaces on its base. Cable tied that to the jack, put diff on, raised on jack and slid straight into position, no problem.

The tapping has gone. Only issue is that it's still got the chatter that it's always had from new, the only difference is what where before it did it when you eased gently off the throttle, now it does it when you lift off altogether, which is harder to work around. Hopefully, I'll get used to it. No noise under power or when braking, just on overrun, when the engine braking slows the car.

 

[Doctor]

Buy proper diffs. Titan is - not the best. There is a reason the pre-load spring is breaking down...

[ScottR400D]

#32 How do you know the pre load spring is breaking down? What is the reason they do that if so?

What ‘proper diff’ can it be replaced with? 

[Doctor]

When the preload spring breaks, the diff will stop locking. The car struggles to exit the corners properly on the race track and you can't steer it with your right foot. When you jack the rear up and spin the wheel, the other rotates the other way. 
 

the reason the preload spring breaks is metal fatigue as it is pressed flat every time the diff locks.

 

there are products on the market that don't do this. 

[ScottR400D]

I don’t see the relevance in my case. The diff has just been fully rebuilt. The spring isn’t broken. Both wheels act as they should the car drives out of corners fine, 

It’s the chattering noise on overrun that is my issue.

But I’d like to know of these other products. I’d certainly consider changing if it solves my issue. I’m just not sure it would and don’t know what these alternatives, for my diff, are. 

 

[Doctor]

Sorry about that, I was reacting to some other posts describing an impending diff catastrophe. 
 

you might be right about the alternatives for the BMW diff, my car still uses 7" Sierra. 

[ScottR400D]

That’s OK, you got my hopes up that there’s some alternative to an £800 rebuild every 8k!

My current problem is the excessive CW&P chatter. It was always there but it’s now louder and on full overrun instead of just with a light lift which was easier to avoid. 

 

 

 

[7 wonders of the world]

Scott,

Your alternative is to look out for a prop and driveshafts and convert to a Sierra final drive assembly, this way you can put a Tracsport LSD in.

 

The reason the Bellevilles break is down to one of poor design I'm afraid, when they break you will still have an LSD that operates, however it will do so like a barn door in the wind - with a bang ! as theres nothing to cushion the ramp blocks as they move, you will however loose what ever preload setting you had.

Likewise the reason the clutch plates suffer extensive wear or burn out is simply they cant handle the amount of torque, with increased levels of torque and / or sticky tyres this situation only worsens.

 

 

 

[ScottR400D]

7 Wonders. 

That’s a route I’m considering. I see Westermann offer a full conversion kit for about £4K. That doesn’t sound cheap for a diff, prop and driveshafts but I don’t know how much the diff would cost or which LSD it would be  

My concern then would be will the Ford diff  be any quieter? There’s be an advantage in not having the chocolate LSD, of course but I’d like a bit more for my money than just that. 

I assume I could buy shafts and prop from CC at about £850, and a Ford LSD diff is £2250 from them. Again which LSD is that? 

They don’t list a propshaft that specifies SV, 6 speed, Ford diff. Presumably they have one but I couldn’t see it.  

Disgraceful, IMO, that anyone should even have to be considering such a thing on such a relatively young low mileage car, really but I’ve long despaired of CC engineering. 

 

[Doctor]

propshaft and driveshafts are diff specific - they would have to be changed with the diff..  

[ScottR400D]

That’s what I’m talking about. 

[Doctor]

[7 wonders of the world]

Prop - there are others circa £250 so a quick email to confirm

https://caterhamparts.co.uk/propshaft/630-propshaft-sv-a-csr.html?search_query=propshaft&results=21

Driveshafts

L/H

https://caterhamparts.co.uk/driveshafts/7047-driveshaft-sv-lh-short-ford-diff.html?search_query=driveshaft&results=25

R/H

https://caterhamparts.co.uk/driveshafts/7041-driveshaft-sv-rh-long-ford-diff.html?search_query=driveshaft&results=25

 

Then call Steve @ SPC and he will give you the price for a complete Ford final drive complete with a Tracsport LSD.

https://www.tracsport.com/lsds

Then ebay all your bits.

[ScottR400D]

Thanks for that. I think it’s a winter project

Is the Ford diff likely to be quieter than the BMW though?

[ScottR400D]

Another question, I see CC sell ‘diff struts’ of various types. What are these? When are they used? 

[DJ.]

Is the Ford diff likely to be quieter than the BMW though?

In my experience, no

But the Ford fits the chassis without a heavy steel cage and also has an alloy housing so is lighter (I assume) than the BMW diff. The Ford diff also has proper taper roller bearings whereas the BMW has twin ball races and has a reputation for not lasting well in BMWs, the Sierra diff seemed to cope well with extremely powerful turbo Sierras back in the day and the noise problems seem to have appeared around the time the metric chassis appeared, and the requirement to drive the top diff bolt in with a club hammer because the bushes aren't in the right place................

Duncan

[ScottR400D]

I’ve heard about the bolt needing to be hammered home. 

Interestingly, you have to do that with the bracket on the BMW. They must have made the bracket not to match the chassis as well.......

[John Vine]

I’ve heard about the bolt needing to be hammered home.

Indeed.  When I queried this with CC during my build, they said "Don't worry, that's what we do in the factory!"

And, IIRC, the 620 comes with the Ford diff because it can handle the power/torque.

JV

 

[Doctor]

With regards to the drive shaft - having been dealing with this recently on another car (CSR 175 EU4 spec) after quite lengthy conversation with CC we ended up using 620 SV prop as the one above is in reality an S3 prop wrongly labelled as SV&CSR.

https://caterhamparts.co.uk/propshaft/6176-sadev-sv-ford-propshaft.html?search_query=propshaft+CSR&results=382

[ScottR400D]

7 Wonders.......

The link that you offered earlier was to the Salisbury type diff offered by SPC at £527. He also offers the 7" LSD, which has no price on the SPC site but Simon at Meteor offers for £1100 odd. Presumably either can be fitted into the Sierra diff?
 

Which is best and why would you choose one or the other?

 

 

[Shortshift]

Replying to # 47

Yup - the Sierra diff is fitted to all 620s and is also, I understand, the preferred diff for any car fitted with a sequential box (eg: option fit on 420).

Although strong, the issue (as I understand it) with the Sierra diff is that all units supplied by CC in recent years are, in effect, reconditioned.  Even in a new car... The diffs are no longer available new from Ford or their original supply sources and whilst they may contain new components they are no longer assembled on the original OEM manufacturing equipment and fixtures.  This means that they are prone to noise due to minute internal misalignment issues (I'm sure someone will come along to add detail to this - I can't remember if it is mainly a bearing or a CWP issue). 

You could say that the BMW diff (available new, and modified externally for fitment to a Caterham, with the 'cage' or frame) is the default unit and that the (reconditioned) Sierra unit is used where necessary because of greater power or shock-loading capability.

The diff struts that were mentioned above are vertical bars that are fixed to the rear of the diff and go through the boot floor and fix, at the top, to the underside of the cross bar that the shoulder straps are secured to.  They can be fitted to both Sierra and BMW diff types.  They help react driveline torque on higher-powered cars (and they are pretty effective noise transmission paths, too).  I think they were added as standard fit on all R500s and CSRs around 2010, and are also fitted on 620s.  They are a simple retrofit item (the biggest challenge is calculating the exact shape and position of the holes needed in the boot floor).

James