BMW diff removal

[aerobod - near CYYC]

Hi Scott, on the question of oil, I did change from 75w90 to 75w140 early on in the cars life, I believe that is now the recommended grade for the latest cars.

From your recordings the overrun noise is nothing I have ever heard from my diff. If that noise is there in my car, I've never noticed it, I usually drive the car for a few kilometres each time after annual maintenance without earplugs in to check for unusual noises. If it is an inherent noise, do you think it is being amplified by another problem such as metal-to-metal contact due to clearance issues or a bad bush? In my car I have a small amount of whine on overrun that resonates more in 4th gear than other gears, but nothing like your "rrrrrh" sort of sound.

[ChrisC]

Most of the noises sound fine to me, but there is a noise I don't like.   As you said, sound like CW and P, but I guess if it was CW and P it would be there all the time.    Have you got access to a chassis ear to prove the location of the noise?

[ScottR400D]

Hi James. I couldn't be definitive on whether or not it's being amplified, there's always a chance. There were no issues removing it from the frame and none of the metalastic bushes were disturbed at all. Under power, on slight lift off, its at least as good as its ever been, possibly better. I've never noticed any whines, just this chatter, now on full overrun.

I've ordered a quart of the 75w140 Redline. For £20 and 1/2 an hour's work I might as well try it out.

Have they changed the recommendation now then? When did that happen? I also see the latest manual advises 85Nm for wheel nuts not the 75Nm they used to and what I've always used.

A moving target, isnt it? 

[ScottR400D]

Chris. Yes it does sound like CW and P and in my experience that could be there on overrun, when there isn't so much load on the assembly and not under acceleration.

What do you mean a chassis ear? I have a mechanic's stethoscope but I'd need someone to use it in the car when I'm driving. You can't replicate the noise when not moving.

Having said all that, the noise has always been there it's now just louder and at a different point of loading. Only the diff has been disturbed significantly and it sounds clear when sat in the car that that is where it emanates. 

[aerobod - near CYYC]

Yes, the only oil they now sell on the Caterham site is Motul 75w140: https://caterhamparts.co.uk/160-differential-oil

There was some documentation somewhere a while ago that indicated that switch.

I find that there is always inconsistency in the documented torques, with a lack of cleanup in documents of old values, sometimes leading to more than one value for the same bolt in the same guide. In that case I go and look up the default torque for a given grade of bolt of the same size and decide what I think the best value should be.

[ScottR400D]

In answer to John's earlier question, yes, I did send this sound file to Phil.

He basically said its something to do with the fact that the 2.0 and 2.3 Duratecs are tilted forward at an angle of 1.5 degrees and its a characteristic with those engines, it's not the LSD.

I can't understand why that would be but in any case it doesn't answer my question of why it's so much louder etc, now, than it was.

 

 

 

[aerobod - near CYYC]

Would that tilt and the fact that the diff has been removed and may be in a slightly different position perhaps point to the propshaft and UJs?

[ScottR400D]

Maybe but how? I think the gist of that was that the prop and this angle somehow excited this noise on the CW and P. 

 

[aerobod - near CYYC]

One of the causes of overrun driveline noise is the diff pinion not being parallel to the front yoke, normally when the diff nose is too low. If the engine is rotated front down, then the rear will be lifted, perhaps causing this condition, on the other hand in our cars it may be too high, too.

I would check the rear gearbox mount for position, tightness and gearbox clearance and see if there is any noticeable play in the UJs. Not sure why your car would be noisier than others, but if it is an inherent noise it may be amplified due to contact or an unfortunate combination of tolerances in your car that leads to a stronger resonance than in other cars.

Also might be worth slackening the diff and diff carrier bolts and rotating the diff as far as possible within the confines of the mounting holes to move the nose slightly and see if that changes the intensity of the overrun sound.

[ChrisC]

A chassis ear is a electric stethoscope which allows you to drive and listen to the noise at the same time, if you know someone in the trade you might be able to borrow one.  

I once had a noise I could only hear on track day videos of my car, the noise came while changing gear, so it is possible the noise is only there when recording. 

Working on the assumption it's the prop angle thing, have you changed the diff spacers?  

[Shortshift]

Just a wild thought, given the comments about diff alignment.  Would it be worth rotating the propshaft through 180 degrees (relative to the diff input flange) and assessing that?  (I'm assuming that a 90 degree twist is not possible).  I know it shouldn't make any difference, but stranger things have happened...

James

[ScottR400D]

OK, I see where we're going.

I didn't remove any of the spacers, the mounting bracket was left in at all times and the main, long bolt was never loosened.

The two 1/2" bolts that hold the bracket in to the chassis were eased to allow clearance for the diff flange, but not removed, so the spacers there weren't altered.

The long top bolt that holds the diff to the bracket was removed and the two 1/2" bolts that hold the diff to the bracket lower down were too.

The diff is a very nice fit into the bracket laterally, no spacers, just a nice sliding fit and I would have thought it would remain central on tightening. 

I assumed that the holes in the bracket would be a reasonably close fit on the bolt shanks, no reason why they wouldn't be, its a plain shank, but there could be some play. The top bolt holding the diff to bracket certainly was a close fit, I can't see any movement there.

It wouldn't be hard to loosen the front bolt and see if it moved up with a jack, I'll look at that before i change the oil and see if there's anything there.

Can't get at it for a day or two but I'll let you know if anything works.

Thanks again for your interest, its appreciated.

Peter. (Scott's the surname!!) 

[ScottR400D]

Ahh, James! I've thought of that but, for the life of me, can't see how it would affect anything.

The flange is connected to the pinion, so you'd be moving the prop position relative to it, but unless its out of shape somehow I can't see what difference it can make. 90 degree is possible, there're 4 holes in the flanges.

Also, as far as the CW and P are concerned, the pinion teeth constantly mesh with different CW teeth, don't they, it being an odd ratio. I.e if it was 2:1 the any pinion tooth would mesh with the same CW teeth twice in every turn of the CW. But at 3.62 it changes all the time.

If you could change the relative positions of the two prop UJs, maybe, but of course you can't.

 

[7 wonders of the world]

worth also checking the prop has been made correctly and the yokes re in the correct plane... wont be the first one I've seen 90 degrees out.

 

[ScottR400D]

I’ve been doing a little research and now understand what James meant earlier about the pinion being parallel to the front yoke. 

So, as I see it, whatever angle the engine and box are sitting at, the diff pinion shaft should be at the same angle. There can be some difference in height of the centre lines of the box and pinion but they need to be parallel.

I should be able to measure the angle the block is at and there are flat machined areas on the diff that are parallel to the pinion so I should be able to check that too. It doesn’t matter what angle I read as long as they’re the same.   

i know the flat spots are parallel to the pinion because I used them for the fixture I made to refit the diff. When the diff is sat flat on them the pinion flange is vertical. 

Does that make sense? Anyone agree it’s worth a check?

[Billy.Whizz]

ChrisC, thanks for your input, my car will never be taken shopping and will certainly be driven hard at certain times, I have driven a caterham before and am looking forward to owning one. I am just concerned about the LSD problems a lot of owners are having and what the alternative is and cost if I should need to rebuild or replace mine.

[ChrisC]

There are owners that have had problem, and there owners that have had no problems.  I know the spec changed in the plate material, what age car are you looking at?

[Billy.Whizz]

New 420R, ready April 2021.

[ChrisC]

So it will have the sintrax plate differential, a change made in recent years by Caterham from carbon,   I have been warned by the production manager at Caterham that the sintrax diffs are noisy but more reliable than the carbon plates.   

I am not worried about my diff, in my 420R. 

[ScottR400D]

#84 James. 

On further thought about the alignment of the UJs, which I now understand, it made me wonder if CC actually align the diff differently in Duratec cars compared with Sigma engined cars, which, in theory, they should if one of them is inclined.  

I can find no evidence that they do, which could be an issue for many cars to begin with. 

Then again, I’ve found nothing official to say the Duratec is inclined. How is that achieved if it is?

 

[Shortshift]

Jumping in on #95 (though I know it was Aerobod James you were asking). 

I'd be very surprised if the diff is positioned differently for Duratec cars - in fact, I'd wager that it isn't.  And the gearbox tail mount, engine mounts and mount pick-up points on the chassis frame are all common - but the brackets between block and mounting rubber are engine-type specific.  So if the Duratec is inclined at 1 degree nose down, I'd say this is where that is achieved - on the block to rubber brackets.

Must say - I have not heard of that before, though.  Fascinating - is there a source for the information?

James
 

[ScottR400D]

#94. Is that correct Chris?

I understood that CC still use the same Titan diff which Titan now fit with sintered steel plates following the failures with carbon plates.

Haven’t heard of a Sintrax diff before. 

 

 

[ChrisC]

Sintrax is Titans name for the sintered steel plates, so you are correct.  Sorry I was using marketing speak from their website. 

For reference https://titanexpress.co.uk/collections/drivetrain/products/bmw-168-lsd

[ScottR400D]

Interesting. I didn’t realise they still offered the carbon plates at all. Talking to Phil the other week they’ve been a significant problem. 

He did also say the sintered were noisier but that they’re stronger.

 

 

[ScottR400D]

#96

I would agree with all that James. It was Phil at RRT told me the engines were canted, I’d not heard before, though I’ve heard of issues with bonnet interference. 

There’s so much rumour and unsupported stuff about it’s hard to know what’s true and not. 

Anyway, everyone who’s heard the noise now thinks it’s totally abnormal and not acceptable so I now need to check everything to just pin it down to the CWP, which is what I think it is and go from there.