Knocking from BMW carbon plate diff.

Knocking from BMW carbon plate diff.

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V84A

Original Poster:

3 posts

139 months

Sunday 12th August 2012
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I have recently bought my first Caterham, having thought about doing so for at least 10 years! The car is a Supersport ford sigma 1.6. It is only 9 months old. The guy who built it looks to me to have made a really nice job, but he is looking to change his career and become self employed so needed the capital. He tells me it came with a BMW diff. but that it whinnied really badly and Caterham replaced the original unit with the carbon plate diff. from the R500. This diff. doesn't whine, but it does clonk. I understand that it is not unusual to get a clonk form the take up of a little play as power is engaged however this is a different clonk from what I understand may be called transmission slap. This occurs most often when coming off the power, particularly slowing for speed bumps. It can get into quite a repetition of ( almost uncontrollable) on/ off clonks as you slow down and then speed up again. I wonder if anyone else has experienced this kind of diff. problem and whether it should be regarded as normal or acceptable? I have to say it is pretty annoying and marring what is otherwise a brilliant experience.

PINGUY

45 posts

158 months

Sunday 12th August 2012
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This short "Clonk" noise when accelerating/decelerating is normal, I have it on my current BMW diff and also on the previous one (both were/are with LSD Carbon plates).

The previous BMW Diff was just changed because of this "clonk" noise (I did not personaly complain about that "clonk" but my official CC Mechanik in Germany was the opinion that the free play (backlash) was too big, and changed under warranty the diff and all the transmission shafts....)

I could only see a very slight improvment after the change, if ever.

It's coming from all the backlash, in the diff and also in the transmission shafts.
There is probably nothing to do as you can see that my swap did not really change something.

Before, I had 2 FORD Diffs, they were very noisy at deceleration. The BMW is much better, but also not perfect, especially on the LSD one's, where CC has to open the diff, and is probably unable to set it up as good as in BMW transmission plant.

I also believe the CC 6-speed gearbox has far from perfect gear teeths definition or tolerances, especially the 5th, very noisy on deceleration (or at least much more noisy than the 6th is !)

PS: I have no noise in corners, the carbon plates diffs really solves what was an issue on the "non carbon LSD" BMW diffs


Edited by PINGUY on Sunday 12th August 21:49

Nicodema

259 posts

217 months

Sunday 12th August 2012
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A clonk is often attributed to the diff, but it is usually due to play in the tripod universal joints on the driveshafts (the half shafts that go from the diff to the wheels). So, this isn't the splines on the driveshafts, but the tripod wheels inside the UJ bodies being a bit slack in their slots.

Tripod joints are prone to this shunt, and some are worse than others. It might be worth getting CC to swap the driveshafts out, but unless they particularly bad there's no guarantee the new one would be better. TADTS kinda. That said, you could have a bad one. Try CC

Good luck

Martyn

Edited by Nicodema on Sunday 12th August 22:03

PINGUY

45 posts

158 months

Sunday 12th August 2012
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As said, my driveshafts were also changed, and the clonk remained nearly the same.
So probability is quite low that new one's will be any better than current one's.

Nicodema

259 posts

217 months

Sunday 12th August 2012
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Yeah, same here. Ours were changed over with the Sierra to BMW swap. The diff is super quite, but the driveline shunt from the UJs is the same and so is the gearbox "character". wink

Risky

167 posts

224 months

Sunday 12th August 2012
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Get along to your local Lotus 7 club meet and take someone for a ride to get a second opinion.

one eyed mick

1,189 posts

160 months

Monday 13th August 2012
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Remember you are sat at the side of the diff with no or very little sound proofing ,if those diffs were in a normal saloon I doubt you would hear them !!!

V84A

Original Poster:

3 posts

139 months

Monday 13th August 2012
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Thanks for all the information. What I didn't mention earlier (not wanting my first post to turn into a shaggy dog story!) is that I did take the Car to Caterham Midlands last week. That was interesting and informative but left me with more question than answers regarding the clonking, probably leading to my begging for help here!

I took the car for a general check over, 1000 mile service, and a tweak around with the pedals (being 6'5" and needing as much help as I can get, leg room wise). I spent time with a very helpful mechanic. I was particularly reassured in that he talked me out of rushing into spending money unnecessarily and when we were discussing the clonking noise from the back axle (whilst the car was on a ramp) he said that it was most likely to be the take up in the necessary play in the diff. It seemed like a reasonable explanation and certainly with the wheels off the ground it was possible to turn the axle and witness the play. It seemed quite a bit to me but when we tried a few other cars in the workshop they were much the same. He also pointed out that any noise would be accentuated by the bare metal and lack of sound proofing and one's close proximity to the axle. He did, however, want to take the car on the road and when he came back he thought the noise was actually play in the universal joints so he put the car back on the ramp and checked those but they seemed to be Ok. At this point he was a bit puzzled and asked another mechanic for a second opinion. After a further test drive the second mechanic said the noise we were hearing was normal from the BMW diff. I have to say it was apparent from the first mechanic's reaction that he was surprised and I could tell he was a bit uncomfortable reporting back to me that it was perfectly normal.

At this point the things that make sense to me are that Caterhams by nature of the lack of sound deadening and the fact that you are sat inches away from the diff. are likely to be noisy (certainly by comparison to most others cars one might drive). I also understand that a element of play in the diff. may be necessary and this may lead to an element of clonk on take up. What doesn't sit comfortably with me is excessive clonking. I can't help think that if what I am experiencing is normal (the mechanic I mentioned agreed that the excessive clonking is pretty irritating)that CC would not want to resolve it, particularly if this diff. is the one they put on their flagship R500.

I am wondering what to do. Certainly the suggestion of a second opinion from a Lotus 7 club veteran does sound like a good idea but I am conscious that the car will soon be coming up to 12 months old (it was registered late in October but being a self build the bits were received somewhat earlier, September I think) so I am thinking that if anything were to happen under a warranty then time might be short.....

2slo

1,998 posts

166 months

Tuesday 14th August 2012
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I think the search engine on here is still knackered so I'll post this again for the OP's benefit. My car had one of the first BMW LSDs when it was built in early 2011. From new it clonked on lock, on gearchanges and the whine it made meant earplugs were a necessity. After discussion with CC, Midlands took it back in and agreed that it was worse than it should be and swapped it for a new BMW LSD under warranty. The replacement, although certainly not silent (you wouldn't expect it to be) was a lot better, it didn't clonk on lock, it didn't bang nearly as much on gearchanges and the whine is still there but subdued to the point that short blats don't require ear plugs.
Lots of discussion on here and blatchat about this very same issue, it comes down to where do you draw the line as to what is too loud and how much knocking is too much? Difficult without a point of reference but I found CC were fine with listening to my concerns and they did swap the unit straight away after road testing it.
I don't know where abouts you are but if you are anywhere near Durham you're welcome to come out in mine and hear what it sounds like for comparison.

V84A

Original Poster:

3 posts

139 months

Wednesday 15th August 2012
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Thanks for the further information. I am beginning to think that clonking is fairly normal given the things I am reading and that perhaps what I am experiencing is not unusual. Many thanks also for the offer to try yours as a point of reference, I live in Yorkshire so not a million miles away. Having been out in it a couple more times I am now thinking that the exhaust note, whilst impressive and head turning initially, is also wearing on more than a short blast and that I might look to get some kind of headset (with intercom) to block out the noise and make it possible to chat more easily to my 12 year old navigator. That might solve both the ringing ears and clonking noise!

On the subject of headphones with intercom, has anyone tried that? It seems there are such things designed for aviation but they are expensive.

pipnjones

111 posts

148 months

Wednesday 15th August 2012
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So there seem to be about 7 places in the drive train that contribute to this sort of undesired noise/whine/other and the only option is to go to Caterham and hope that the replacement part is slightly better machined that the current part? This isn't terribly sustainable.

Are there any Companies out there offering replacement parts that have been properly made/assembled? Even if the parts were slightly more expensive, I would expect a market if the word got round that the parts were better made and reduced noise, vibration, etc?

2slo

1,998 posts

166 months

Wednesday 15th August 2012
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/\ unless as in the OPs case and mine the car is under warranty so there's only one place to take it!

jason61c

5,978 posts

173 months

Friday 17th August 2012
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What does caterham do to the bmw diff unit? I built a car with a bmw lsd(not a caterham but another kit car) and the diff was smooth and silent. Why is this unit have so many niggles?

evotell

138 posts

137 months

Saturday 4th April 2015
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I find it interesting that Caterham say that this clonking is normal. I have just finished building a Sigma Roadsport for one of my customers and the diff is silent, (I mean NO noise) So according to CC this is NOT normal. I find it hard to believe that BMW would make a diff that is so badly machined that some clonk and some dont. The BMW diff on my Supersport doesn't wine but the back lash is dreadful. Next winter it come out and goes to Phil at Road & Race Transmissions, mean while its another box of ear plugs.

anonymous-user

53 months

Saturday 27th June 2015
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evotell said:
I find it interesting that Caterham say that this clonking is normal. I have just finished building a Sigma Roadsport for one of my customers and the diff is silent, (I mean NO noise) So according to CC this is NOT normal. I find it hard to believe that BMW would make a diff that is so badly machined that some clonk and some dont. The BMW diff on my Supersport doesn't wine but the back lash is dreadful. Next winter it come out and goes to Phil at Road & Race Transmissions, mean while its another box of ear plugs.
I completed the build of my R400 in April. Since then it's been like wading through treacle trying to get a Z number, get it IVA'd and finally registered, but today I recovered my V5 and have been out for my first drive!

There isn't much noise from the diff but there does seem to be a lot of play. It's no issue on a reasonable road but I live down a fairly bumpy lane. The first few hundred yards I had to almost stop twice to stop kangarooing, though to be fair, the 4th time I was managing to get down the lane with little 'clonking'.

On the road, it seems OK under acceleration or if you lift off fully, but if you just slowly lift off the throttle the backlash does make itself heard.

Are we saying this is, if not normal, quite common?


downsman

1,099 posts

155 months

Sunday 28th June 2015
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If it is quiet, and the kangarooing is your only problem, then leave it as it is.
A light car like a Seven with very responsive accelerator pedal is always going to easy to kangaroo on a bumpy road as any tiny foot movement with a bump becomes amplified.

The play may well not be due entirely to the diff, the gearbox, prop and CV joints will also have some movement.

Also, I have found with my Seven that there was a feeling of excessive backlash going from fully off the throttle to back on which I attributed to the diff.
However, after some experimenting, I found that there was no noticeable backlash if I rev the engine in a lower gear and then partially lift and reapply the throttle.
In the end I decided that it is an issue with fuel cutting off on a closed throttle and a hesitation when it is opened again. Now I know about it, I seem to drive around the problem and don't notice it.

DCL

1,215 posts

178 months

Sunday 28th June 2015
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It can be difficult for new owners to accept that 'new' cars behave like this, but it is part of the Seven's character, and soon you'll be completely accepting, if no oblivious, to it all. The whole transmission train is held in place with very thin metalastic bushes that just wouldn't be used in a modern car today. But being part of the mechanical symphony can be a very inclusive experience once you've become accustomed to it.



Edited by DCL on Sunday 28th June 12:01

anonymous-user

53 months

Friday 3rd July 2015
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downsman said:
If it is quiet, and the kangarooing is your only problem, then leave it as it is.
A light car like a Seven with very responsive accelerator pedal is always going to easy to kangaroo on a bumpy road as any tiny foot movement with a bump becomes amplified.

The play may well not be due entirely to the diff, the gearbox, prop and CV joints will also have some movement.

Also, I have found with my Seven that there was a feeling of excessive backlash going from fully off the throttle to back on which I attributed to the diff.
However, after some experimenting, I found that there was no noticeable backlash if I rev the engine in a lower gear and then partially lift and reapply the throttle.
In the end I decided that it is an issue with fuel cutting off on a closed throttle and a hesitation when it is opened again. Now I know about it, I seem to drive around the problem and don't notice it.
I've been thinking about your last comment re. accelerating in a lower gear and lifting off etc.

If I accelerate and lift off altogether, or lift off quite a lot, there is some noise but it's not at all bad. When the noise is worst is with a very light lift, I.e just feathering the throttle. Then there is quite a lot of backlash rattle, for want of a better term.

That's all OK, as you say it's easy to drive around. What's a bit harder is, e.g. when you're 'cruising' along at a steady 60, say, and the road begins a decline. As the effect of the decline lifts the load on the engine, it rattles again. This, of course is the same as a very light lift, except that it's less manageable unless one simply speeds up down the slope!