2018 Diff clunk

[ScottR400D]

I tend to agree with Tazio. I’ve heard nothing that would bother me. 

I noticed soon after building my R400D 4 years ago that after a run, if I rolled the car it in the garage it would clunk like that but not when cold. There’s a fair bit of backlash in the diff, just like the OP’s. 

To be honest I haven’t thought about it or looked at it since. Several track days and thousands of miles later it still all works..........

I find a lot of noises can be cured by earplugs! 

 

[Jim 123]

Mark re #20 to possibly help settle you down as it's unlikely you can find another LSD to check from the IoM.

Whilst it's not the most tech investigation, what about eliminating the upstream driveline tolerances as much as possible and measure the clunk to clunk rotation of the diff flange with the back wheels locked (handbrake).  If you have a dial gauge all the better, and Im sure some other LSD owners on this posting would give you comparative readings from their cars.

 

 

[John Vine]

I find a lot of noises can be cured by earplugs! 

Oh yes.  Essential in an R400D, and a wise precaution in any 7.  Without earplugs, mine sounds like a metal biscuit tin full of assorted spanners, nuts, bolts and washers, being shaken vigorously.  After 50K miles, I've got used to it. 

JV

[CtrMint]

Thanks all for your help.

I suppose it might be worth me expanding on my thoughts further to explain where I am with this, or at least my thinking.

I suspect there is nothing wrong and it's simply how the diff is, however I am slightly paranoid over it.  Partly because I've not had the car PBC with a CC/Dealer although a local specialist did review the car and of course it's passed its SVA.  Sadly the earliest I can get the car in at Oakmere is the 30th April.

If there was an issue and I made it worse by driving the car would CC have an issue over a warranty claim etc?  I'm therefore trying to make every effort to avoid such an issue and end up with a bill for a new diff or argument over one!

That's the logic...

So any vetting or confirmation the diff is sound would be helpful.

I drove this car last summer too, it's diff was so quiet in comparison, that's not helping the paranoia 

https://www.oakmeremotorgroup.co.uk/used/cars/caterham-seven-620s-310bhp-20-new-car-new-car

https://www.caterham7diaries.com/420r/not-so-intimidating

Jim,  I believe the majority of local cars, certainly those down at our local specialist were imperial, so I'm assuming the diffs are likely to be Ford and thus different in characteristics.  I don't have a dial gauge, but I'm all for learning new skills so made it's something I should invest in?

[7 wonders of the world]

 

Mark is new to our small cars he was probably not aware of the tight tunnel to gearbox clearances etc, and having been supplied with a prop on my last car that had the wrong pitch splines in the nose so they were a p!ss fit on the mainshaft, and again seen the same on the centre plate splines on more than one occasion these are valid areas for checking.

Metal to metal knocks are not a design feature and the source needs locating, 

A straight cut or semi heli box will whine - but this is a design characteristic, but not a hypoid final drive, I read on here far too often that a final drive whine is considered acceptable..... it's not !, it's down to how its been assembled.

And a ZF LSD with the correct oil, inside a correctly built final drive should be silent......... mine is..... 

[Jim 123]

Mark in my experience with a kit build you will have no issue whatsoever with Caterham regarding warranty. I cannot speak more positively about them. Maybe talk to CC, as I'd suspect that at this stage with a brand new car they will want you to get a lot more miles on the clock to bed everything down.  There are dozens of components in a new car that influence driveline shunt and they need to be worked over miles to achieve their design intent. 

[ChrisC]

I had a gearbox that need repair under kit warranty.  CC allowed me to drive until the end of the year before the warranty repair was carried out.   That said I was able to avoid the problem, by avoiding high revs. 

Also are you comparing apples with apples? its my understanding the 620 still uses the Ford Sierra diff, where as the 420 uses the BMW.

[John Vine]

its my understanding the 620 still uses the Ford Sierra diff, where as the 420 uses the BMW.

That's my understanding too.  (Something about the BMW diff not being able to handle the torque?)

JV

[CtrMint]

Are you saying my prop maybe the wrong part/spec? 

[Tazio]

Stop looking for problems, get in the bloody car and drive it...and stay off here for a while, you are continually thinking the worse, its just a car, use it, you have a warranty, if it breaks get it fixed. Simples.

[p.mole1]

I think it is normal with certain types of LSD's 

[CtrMint]

well, I've been out all afternoon in it, I've got approximately 270miles on the clock now.  It is a blast, very frustrating keeping it below 4k though.

It's moving off, reversing and low-speed manoeuvring that's the worse, the whole thing sounds so loose.  At speed it's fine, I've hit 85 mph a number of times and it feels planted with no undue noise.

[CtrMint]

Guys,

The knock from diff is continuing to be a point of frustration, it's just relentless, the only time I don't experience those on off noises is when it's being driven relatively hard.  Plus having driven other 7s (mainly recent dealer stock), most before my own purchase I've never come across a car as bad as mine.

I shot some video last night from the roll bar using a GoPro, using the mic on the GoPro, my intention wasn't to film the noise, however during editing, I noticed how pronounced it actually is.  Plus when you take into account engine, road, and wind noise its pretty bad.  You also feel the bad ones through the chassis too.

I wondered if I could garner your views on it.

I've annotated the worst or severe noises, however, if you listen closely there are more knocks occuring than those I've denoted.

Thoughs? is it really typical for BMW diff to sound like this?

 

[Tazio]

Are you sure that's the diff, I only have experience of ZF slipper diffs, and they sound so different than that

[CtrMint]

With my limited knowledge, it sounds like it's coming from the rear and around the diff and it also sounds similar to the video I posted in #6.

What else could it be?

 

[Jim 123]

Given what can be heard on the video, and if you feel it sometimes through the chassis could it be driveline shunt.

You may want to try the following to see if it replicates. Find a slice of road with a very gentle uphill incline, keep your foot off the clutch in 1st gear, and let the car slow down to almost a stall on a trailing throttle.  Then attempt to increase speed by throttle to only just below walking pace and no more and hold that speed.

[CtrMint]

Will need to give that a go.  Might also be worth commenting its also vicious when reversing.

[Collidog]

I get the same noise when reversing up my sloped driveway and shunting around to point car in right direction for blat. Seems to be related to clutch control as has been suggested by Jim123

Don’t notice it out on open road

I’ve always thought these cars sound like an Austin 1100 in terms of the creaks and knocks. Not surprising with the similar minimalistic construction the two cars share with respect to lack of sound-deadening and lack of sound-attenuated cabin etc

 

[anthonym]

Diff mounting bolts, probably 19mm 

[CtrMint]

I've been out for around 2 hours, another tank of fuel, had lots of fun.  I did fit in some testing though.

I've tried Jim's suggestion repeatedly but it didn't generate anything which I'd consider untoward.

I did find if I drove at low speed, (I think) ~15-20mph in second gear, in a straight line, and gently pulsed on and off the throttle I could get create the knock at will and quite loud.  It sounds like a Gatling gun from an old western.  Unfortunately, the GoPro had gone flat before I found this, so will need to record that tomorrow evening if the weather holds.

It's pretty bad low-speed cornering too.

Anthony, I'm not following your comment?  Are you suggesting a bolt isn't sufficiently tight?

[anthonym]

 Just let me check something, my apologies I missed your video at #11. Whatever it is it’s not loose diff bolts. 

 

Previously I wrote this, now retracted:

Yes - terrible clunks and it was the two bolts (or nuts) holding the diff to the chassis (?)19mm in my case. The more you describe the more it sounds like it. Very disconcerting to drive. In any case the two lower forward diff bolts, whatever they connect to. Check them all of course, but these lower front ones seem to be the ones that come loose. I suppose you could characterise it as like very bad backlash, especially on torque reversal.

and if the car doesn’t feel like it should be driven, trust  your instincts. Fear can be useful, I find.

 

p.s. Or I suppose, anything else in the drive train, like gearbox mountings (two bolts into a cross plate) and  a B to get at.

but then you write this:

It's moving off, reversing and low-speed manoeuvring that's the worse, the whole thing sounds so loose

Which just sounds like the usual graunchy LSD 

Methinks if it’s ok at 85 then it’s not loose nuts.... when I had my problem I’d not have dared go that quick.

[Roadsport06]

Anthonym - is yours a BMW diff you are referring to or a Sierra?

[anthonym]

My #46 now retracted and this one after seeing

and now

That’s from the diff?

I’m not so sure. Sounds like a loose boot floor ... something like that. I just cannot see the noise at #11 causing the noises at #38. No torque reversal for a start. Any relation to road surface bumps or other body movement?

 

 

 

 

previously I wrote:

I don’t know. The problem seems universal looking at a BC search. 

R 500 K so I guess not a BMW

actually the first hit in that search is BMW diff bolts

[anthonym]

My posts at #46 and #48 completely revised after seeing both videos.

[Tazio]

My super clunky ZF slipper shunts and is noisy going on and off power , but unlike yours it makes no knocking when cornering, and to my ears, the noise you are experiencing seems too 'light'to be the diff internals, I would expand my search.