2018 Diff clunk

[Limitless]

I have a 2018 420r and mine is the same especially at low speed and hard lock. Oakmere have looked into this and queried this with Caterham. The reply was, more or les "they all do that" and it will get worse. Before I bought mine I took out a 420r and s, they both did it though not quite as bad as mine.

When 'pressing on' there are no clunks or knocks at all.

Minty, it does play with your mind a fair bit, but as long as it doesn't fall to bits after the warranty just enjoy!

 

[Tigger]

I’ve not trawled through all the previous posts but in my own case the clunk under torque was due to the diff knocking on the dedion tube. In the end I filed off some of the aluminium ‘vanes’ on the back of the diff which gave enough clearance. Since then no clunk.

tim

 

[ChrisC]

One easy and minor thing to check is the screws holding the plywood floor aren’t fowling the diff / carrier.  One of mine touched the diff, which meant I was left with two options move the screw or (and what I did) file down the screw so it cleared, its only a self tapper. 

For what its worth, my opinion is the noises you have are normal.   As far as I can tell all the knocks are coming when the car is on very light throttle and the speed is more of less constant, i.e. the engine is not accelerating or decelerating the car.   

I bet you will find examples that make more noise, and some make less.   I suspect this is because the BMW diff is modified for the Caterham.  Significant amounts of metal are removed from the original BMW casting, and I assume this means the diff is stripped before that machining takes place.   Then it’s reassembled with either the open or titan LSD internals by the Caterham supplier.    How much care and attention to detail that’s applied to this reassembly is the real question.   Although not faulty, I.e. within Caterham’s acceptance criteria, I suspect a noisy diff rebuilt by a specialist can be improved.

[CtrMint]

Thanks all for the input, most appreciated.  I'll try and respond to all.

Anthony 
I don't believe my boot floor is loose, if you recall I needed to sort the fuel sender and during that process lifted both the wooden and aluminium section.  I've replaced some of the self tappers with very small allen head bolts and nylocs, so I'm pretty sure it's fine.  I will check though.

Limitless, 
Your experience does sound similar to mine.  When you've got the throttle under a good amount of pressure you can't hear it.
But you are correct it does play on your mind when pushing on.  I just have this fear it's going to let go in some way and lock the rear end up.  The outcome doesn't bear thinking about.
I always find Oakmere fantastic, but given your experience, I'm not sure a costly ferry trip and time away is going to be fruitful.  CC seemed to be dismissive.

Tigger,
That's worrying, surely the dedion repeatedly hitting the side of the diff is going to cause some form of structural fatigue over a prolonged period and ultimately cause the tube to fail.  Did you mention it to CC?  How did you spot the contact?  did you see marks on the tube?  I'll certainly want to check this.

ChrisC.
As mentioned to Anthony I have replaced the screws but will double check.  With respect to it being normal and some are worse some are better, sadly you might be correct.  I find it very disappointing though.  Don't get me wrong I know there is going to be a degree of noise from the diff given the design of the chassis and the manner in which the diff is mounted   It is an inherent factor in the design of the car, so totally understood.  But what you are saying is the diff supplier is constructing the diffs with very wide tolerances and subsequently it's luck of the draw whether you get something which is pleasant and something like mine.  An R pack doesn't make the car a track only race car and CC should be mindful they are still producing a recreational vehicle.  If the diff can be built to an appropriate spec, and we know it can, then it should and consistently.  If I'd have received a crappy paint finish should it be accepted?  The car would still be painted, it wouldn't matter on a race car,  similarly, a noisy diff wouldn't matter on a race car.  but I doubt there would be any debate over crappy paint on a road car etc.    I'm not trying to be flippant but trying to illustrate why I feel a little consistency is justified. 

 

I guess in summary, as per my agreement with Limitless it's difficult to accept from a safety perspective.  You're left thinking is this noise really correct, did CC really intend for a road car to operate in this fashion.  I do have some experience of competition plated LSDs having been involved rallying here on the Isle of Man. Listening to a clonking diff on a road section or backing out of service isn't new to me.  So I am surprised CC would fit something comparable if not more noisy to a road car.
If it does boil down to my diff being built in a manner which makes it noisier, I certainly don't feel I should foot a rebuild cost to obtain something more tolerable for road use, especially if there are identical spec cars with acceptable diffs etc. 

It's a bit of a shame, I've really been bitten by the 7, if it's dry I'm out in the car, it's costing me a  fortune in fuel.  As a comparison I've owned my Exige since 2014 and in that time only done 5k miles, I've had the 7 on the road since March and it's already done 2300 miles.  I've learnt to accept the unique handbuilt issues like the dash vibrations, rubbing cam cover and various other minor issues, but this diff knock is so loud and relentless its pretty hard to tolerate.  I need to solve it, it is wearing.

As an aside, I've ordered some of the Motul diff oil from Opie and intend to change the oil as soon as possible.  I'm doing this out of curiosity, see if there's anything which can be concluded from the oil.

 

[Tom_Arundel]

I know this may not apply to your LSD but when I built mine with an open Sierra diff. 10 years ago the diff was so noisy that you could hear is a quarter of a mile away across Bruntingthorpe! Needless to say I took it out and back to Caterham who gave me another with no questions asked. Th replacement was almost a noisy as the first, so I decided to change things...First I turned the crown wheel bearings in 3 notches....that`s better....another 3 notches ...much better....changed the oil to Redline heavy...    almost silent...no whine...no clunks...no worries!  Its done 32,000 miles since ....so things can be improved.

 

[anthonym]

Is there anything in the boot? (I have no experience of that condition, as in empty). Anyway when I said boot I just meant « not the diff » . Whatever it is I can see it’s very frustrating. If the boot is empty, remove the floor and test on the road. Vibrations do odd things. Might also change the sound evidence you hear.

[Jim 123]

Random thoughts that might be worth checking, some of these are long shots.....  Check security of the gearbox to mounting plate fixing bolts and box properly seated into mount.  Box mount the right way round. Is LH gearbox casing well clear of LH chassis lower longitudinal.  Propshaft u/j's OK and fully greased. No excess play in splines gearbox to prop.  Propshaft to diff flange bolts all secure and OK. Routing, clearance and security of handbrake cables. Loose hanging multi plug connectors touching rear chassis or body skins. Hood strap buckles contacting with fuel filler cover inside boot.  A frame the right way up.  Braided rear brake hose not touching.  Inserts fitted in upper damper mounts.

[sjl1]

This does sound completely normal from my experiences. Current 360r with bmw titan diff is very noisy and whines. Have just finished carpeting the rear bulkhead and boot using 6mm neoprene sound absorber behind carpets. It hasn't eliminated noise but much reduced it, quite pleased with results.

i think the best way to stop the noise bothering you is to drive it like you stole it

[CtrMint]

There's nothing in the boot apart from an emergency woolly hat for when it gets cold and of course the washer bottle but that's secured.  I will double check the boot but I'm very doubtful it's something loose given it takes little momentum to create a disproportionately loud clonk.  You'd need metal on metal with reasonable force, say if I tapped the chassis hard with a socket, I can't see that happening with anything in the boot and being slightly loose etc.   I will try though.

Jim, you'll have to excuse my lack of knowledge with some of the terminology you've used.  I have been around all the bolts that I can get at, ie the ones which face down plus the prop shaft flange bolts.  Everything seems secure also Oakmere have looked at the car during the service and so I hope would have flagged any build errors, plus they did find one of the engine mount bolts not sufficiently tight, the one which holds the earth connection.  I suspect the probably checked others too.

Clearance on the LH side is low, very low although its hard to tell how tight due to the volume of the silver padding  Caterham installed down the tunnel.  I've greased the UJs, they've also slung plenty round the chassis.  

There is some play in the prop into the back of the gearbox, is it too much I don't know.  I didn't pack loads of grease on the splines during install. just enough to ensure smooth fitment.  Should I have packed it in?

Handbrake and other cables, again not being dismissive but it's a good old bang I just can't see those components generating the sort of deep tone which is involved.

As I write I recall I have tested the car over bumpy ground out of gear, basically coasting, sure there are a few noises, the usual stuff, but not this knock/clung.  So it is doubtful it is a loose component etc

Having listened to it for 2000 miles, I'm convinced its the noise I can generate in the video I originally posted. (

).  The tone and harshness are just right.  Plus the other night when I commented it sounded like a Gatling gun, it was identical, I could do it at will.  I'm pretty convinced of this.

Given I produced the sound in the aforementioned video by jacking the car up and rotating a wheel back and forth, is it reasonable to conclude its either the diff internals ( and expected depending on your point of view) or prop shaft to gearbox interface?  I say this as the amount of force required to generate the noise (by hand) wouldn't be sufficient to create play in the interface between the prop and diff if the related bolts were loose.

Or am I talking rubbish (due to inexperience).

 

[ChrisC]

This is a long shot because its not diff related, but my car had terrible rattle from the rear because of the combination of pads and new (non Ford reconditioned) rear calliper.   I had Delphi pads due to having 4 pot calipers at the front.   It was easy to diagnose, the rattle would stop when braking, and you could feel the outer pad had play in the caliper event through the wheel, with the handbrake off.  I only started having the problem when my leaking rear calipers where replaced under warranty, with post 2017 spec items (as fitted to your car).   I changed pads and anti rattle springs without success.  Eventually a simple tweak of the spring on the pad sorted my noise. 

PS they would also make a noise when the wheel was rocked back and forth, but not to the same extent, do your same test as per the video, but put you finger on the outer rear pads

[ScottR400D]

1) It’s the diff. 

2) Get better earplugs.

3) They all do it. 

4) You can get it rebuilt but it won’t be significantly quieter for long if at all.

5) Stop trying to make it replicate the noise. 

6) Get better earplugs  

7) Learn to drive the car in a way that minimises the noise, it is quite possible.

8) Get better ear plugs. 

 

[CtrMint]

Thanks for the input Scott, but from my own limited experience they don’t all do it, and I feel mine is on the extreme side, so I’m looking for a sensible route forward to improve the road experience. I want to enjoy the car on a Sunday drive with the wife without it sounding like the arse end is falling out each time I lift slightly.  I would also had mine is so bad it’s impossible to prevent through better driving as the smallest lift generates sufficient slack to cause the knock.

All, is it possible I wasn’t sufficiently generous when greasing the prop in the back of the gearbox? I’m not experienced on this sort of stuff, but would putting lashings of grease on the splines help?  Could that interface magnify the noise?

[anthonym]

How about a chat with Phil at Road & Race Transmissions? 44 (0)1959 525 105

https://www.rrtransmissions.com/

He has supported me and my cars for years, and many other owners of course.

[CtrMint]

Thanks for that Anthony!

Either way, there is some fascinating information about differentials on their website which makes for excellent learning https://www.rrtransmissions.com/lsdstore/lsd-comparison  

[anthonym]

How about attaching an external mic to the go pro and putting it by the diff, to get clear evidence? Maybe remove part of the boot floor for easy access.. these noises are very slippery as regards where they Come from

edit: you could alternatively attach (duck tape) a cheap dictaphone down there, might be less hassle and cost than a gopro ext mic adapter

[7 wonders of the world]

Or for a silent final drive speak to Steve here - 

https://www.tracsport.com/

 

[Roadsport06]

Sounds like your diff. Mine is a nice quiet LSD done by Steve at SPC

[Jim 123]

Would you consider getting the car on stands with wheels off and running the drivetrain? Obviously with appropriate care about rotating parts, but it might settle you down about the exact source of your concern.

It looks like this issue is probably one that is going to be pretty impossible to define based on written exchanges.

[CtrMint]

My plan is to get the car up on stands this week so I can certainly give it a go.  Should I support the dedion tube so the drive shafts/wheels are at their normal articulation before applying drive?

My reason to jack the car up was to have a really good listen, see if I can identify anything, I'm personally curious about the prop to gearbox, as mentioned previously I wasn't heavy with the grease. There is probably nothing in it, but again I'm desperately trying to learn as much as I can.  

I was considering undoing the diff to prop bolts and rotating the prop by hand.  If the noise is still there, it would indicate the gearbox/prop interface.  If the noise isn't present then it's in the diff or other similarly rearward components.

[Tigger]

Would be worth putting a piece of plastacine on the back of the diff to see if it’s knocking the dedion tube.

[ScottR400D]

I still think you’re over reacting. 

Not that much grease is needed on the prop nose into the gearbox. If there’s enough slack there to cause the noise you describe, which sounds exactly like mine has always been, grease would soon be driven out, if it made any difference at all. 

If you really can’t live with it have one of the experts set it up, there are many reports of just short term improvements that way but some say they’ve had lasting benefit.

Just a point on your comment that the smallest lift causes enough slack to create the noise; IME that’s exactly when it’s worst, a very light lift at low medium revs and that’s exactly what I try to avoid and I’ve long since stopped noticing the chatter.

 

 

[ScottR400D]

Regarding the reference to Phil at RRT, he was quoted on here some years ago as saying:

”but as Phil said, " due to the very nature of the car, how they are built and the power to weight ratio it's never going to be silent so it's a case of learning to live with it"

Another post at the same time:

“Hmm, the above comments don't compare with my experience so far. New R400 collected yesterday, warned by one of the mechanics to expect some diff noise due to carbon plates in the diff. Clonking and banging on any kind of lock and at motorway speed with the half hood on driving home, the diff whine drowned out the engine noise. Shame I don't have a point of reference to compare. The noisiest diff I've heard in any car to date.”

These quotes are from 2011 but not much has changed. 

[anthonym]

dup

[anthonym]

yes always good in a 7 never use a light foot.. ;-)

[ScottR400D]

If you think how a diff is constructed, especially with an LSD, holding it lightly I loaded either way is the optimum situation for noise and, I expect, wear. 

If I’m at a speed where a very light throttle is needed in, say, 6th and there’s chatter I change down to maintain a bit of load.