My rear end's knocking ?

[SJL]

Have just finished building a 1.6K roadsport and have been running it in over last couple of weeks since March registration. Just starting to notice a knocking sound from rear end on gear changes and am worried that its a dodgy driveshaft or something. Its already had the diff replaced at the post build check (original was very noisy) so doubt its that - I remember similar knocking on way to its post build check. I'm pretty confident its not the suspension bushes etc since these were fully torqued up OK and checked out OK by Caterham.

 

Its definitely somthing taking up the slack in the driveline on gear changes (especially spirited ones) - is this normal and am I being paranoid - any ideas ?

 

Also I experience a bad jolt when either rear wheel is unloaded due to a bad bump in road - feels like dampers fully unloading - again is this normal and if so is there anything I can do to reduce it - I have to keep slowing down for all the bad bumps in SE Londons roads.

[Andrew Russell]

Check the main hub centre nut to driveshaft. This has to be very tight indeed...can't recall correct torque, but a lot! Any degree of free play here will translate into a knock on take-up of drive.

 

Well, it worked on mine!

 

Andrew

[SJL]

Yes I have already checked them - still torqued up to 200 foot pounds ! This is what made me suspect the drive shaft ?

[Peter Carmichael]

Limited slip diffs make quite a noise when pootling, but by the sounds of it, your probolem is worse when giving it the beans. It might be that your dampers are topping out - how did you set the ride height? Is it on adjustable platforms? Are you on standard springs?

[SJL]

Running standard diff and standard springs

[millsn]

Does sound like your dampers topping out. Not sure what the solution is - is your ride height set at about 155 mm from the bottom of the rear wheelarch?

 

Nigel Mills - 2.0 Zetec carbs

[SJL]

Ride height is about right - dampers are topping out on fast bumps - is this normal ?

My thoughts were that I hadn't compressed suspension enough before torquing up the bushes - although I did put a lot of weight in the car before doing this ?

 

Does anyone have any more ideas on the clonks during changes please ?

[Russ D]

Have owned a couple of Caterhams now and both do the loud clunking when changing gear. It is related to the diff, the LSD being even worse with other strange noises. I think it is something to do with the way it is mounted to the chassis (not isolated enough) and not supported in the correct places. Own a W*******D using the same unit and no noise from that, but mounted totally different.

Have played about with the crownwheel to pinion clearance on an old unit and this will eliminate alot of the noise (not advised) as may reduce life.

Normally gets worse as the unit becomes hot, haven't tried using any thicker oil yet.

Russ

[millsn]

Your clonks during changes could be down to something loose - have you checkd thast your gearbox is bolted to the brace under the tunnel? Is your ngine bolted to the chassis - sounds silly but numerous people I know have forgooten at some time or other myself being one.

 

Nigel Mills - 2.0 Zetec carbs