BMW diff removal

[ScottR400D]

I think you may have a point. I can’t get on to it till next week but will think that through. 

 

[aerobod - near CYYC]

So Peter, I have an old diff carrier (from before the modified one to take the current style cover was sent to me due to the upgrade to prevent the cover bolts hitting the deDion tube). The holes that the M12 bolts use to attach the diff are 13.25mm in diameter and the hole that the long 1/2" bolt passes through is 13mm in diameter. The M12 bolt shanks will be nominally 11.9mm and the 1/2" bolt nominally 12.6mm, giving a variation from one extreme to the other of the diff and carrier relative to the frame mount point of up to 1.75mm and a distance between the holes of 125mm.

Consequently there will be the possibility of up to 0.8 of a degree of movement from one extreme to the other in the hole positions, assuming the metalastic bushes have no appreciable slack in the bores to the bolts. That might be enough to at least change the diff position to see if the noise changes, even if perfect parallelism can't be achieved for the propshaft flanges.

[ScottR400D]

Thanks for taking the time to do that by the way, I really appreciate it!  

The thing is the diff isn’t held by the long through bolt, so it will pivot on the through bolt at the top of the back plate increasing the distance and reducing the angular change, won’t it? 

If there was any play in the two M12 that hold the bracket to the chassis then that would have the effect of pivoting on the long bolt bringing the front up and rear down. But as the bolts go through met bushes and into a thread I guess the fit will be reasonably close. 

 

[ScottR400D]

I still wonder if there’s some reason the whole assembly should be dropped and not just the diff dropped from the carrier. 

When you replaced your old style carrier presumably it was bolted to the diff before the assembly was put in the chassis? 

[ScottR400D]

Just re read the first pages of this thread and see that Ivan posted:

I recently took my BMW diff out leaving the carrier in the car.  This was  fairly easy.  I took the A frame off to give more room, which was also easy.  The problem was to get the diff back in.  Plan A was to leave the carrier in the car.  However, this turned out to be very difficult.  Plan B was to take the carrier out, fit the diff to the carrier and then fit carrier plus diff back in the car.  This wasn't easy, but it was possible. 

I think the reason that Plan B worked better than Plan A is that there is no give between the diff and the carrier, but there is some give between the carrier and the chassis.

Luckily a fellow member with much more skill and experience than me helped.  Many thanks Graham.

Hope that helps.  Good luck.

Ivan

Maybe it is important to do it that way?

 

[aerobod - near CYYC]

I don't see a reason why it matters, but depending on how the diff is supported when being put in, the M12 diff to carrier bolts could be at the top or bottom of the holes in the carrier, whereas if the carrier is in place before insertion they should be at the bottom of the hole due to the carrier weight pressing it down and thus the diff will be tilted down less by the hole tolerance (1.35mm, or about 0.6 of a degree).

[ScottR400D]

I understand that, yes, it’s a possibility. 

Current plan is to get car off ground properly and measure everything I can about diff position. 

Then remove it complete with carrier and measure what I can re position related to carrier. Then release carrier, check what clearances are there in holes and refit making sure square and tilted up as much as poss. Record any differences.  Then refit as per manual, already on bracket and see.

While it’s off I’ll drain oil from box and remove prop so joints can be checked.

Thanks, as always! 

[Billy.Whizz]

So as a replacement LSD for a 420R if or when required would the Tracsport version be the better option, and does anyone know the cost of one. Thanks.

[ScottR400D]

It might be, but I don’t think it fits in the BMW housing, you have to replace with the Ford diff. 

Then you need new driveshafts. 

And a new propshaft. 

I’m not aware that any other LSD will fit in the BMW housing but stand to be corrected.

 

 

 

 

[aerobod - near CYYC]

There maybe the possibility of using a BMW small diff LSD from companies such as Wavetrac or Quaife (Torsen helical gears) or OS Giken (clutch packs) and possibly other manufacturers. Most of the non-///M BMWs had one of 3 sizes of differential which is common for most cars from the mid 90s even into current models. The Caterham diff is the smallest of the 3 standard diffs.

[Tazio]

Tracsport is around £1100.....

[ScottR400D]

A small price to pay if it doesn’t need rebuilding every 5 minutes, it’s only £100 more than the Titan from CC. But it doesn’t fit the BMW housing, does it?

If it does I’d be up for changing. 

[Nigel B]

I was looking at Drexler differentials the other day. Would this be suitable? Is it the 168 diff that Caterham use? I might be wrong...

[Drakman]

I think the idea of angling the diff was back when cars ran leaf springs, under hard acceleration the springs would try to "S" bend.  These days the springs are coil and the trailing arms hold everything in place.  I believe the correct set up is to make absolutely sure that the diff pinion gear shaft is dead parallel with the gearbox output shaft to avoid the tail shaft vibration issues.

I just went through the replace the Titan LSD game as well, I was told that the Wavetrac, (torsen ATB but with lock up because of the wave design) and the O.S.Giken, (plated diff) were not currently available for the BMW 168 diff housing.  I don't think a Quaife ATB would be any good for me so i opted for a Drexler. The drexler has adjustable ramps and can be set to suit the individual car.  RRT had it built by drexler to their specifications for my car, I ordered it last September and it just arrived yesterday.  Happy days, I have the car on the hoist now with the old diff waiting to come out.

 

Cheers

Dave