I'm picking ur brains really guys.
I've got a v2 sti type ra track car and I took it out for the first at oulton park recently and was getting a vibration only on slowing down at around 3500 revs when I had the dccd in any of the locked positions.
If the dccd was set to the fully open Position I didn't experience any vibration.
The car has a rear diff lock down kit, hardrace gearbox & engine mounts plus pitchstop and is fully Polly bushed all round.
Would any of the above mods produce this vibration at these revs? At all other revs/speeds there is no vibration at all.
The car ran faultless all day and the vibration didn't change in anyway.
Hope u can help!
Thanks Tim.

 

You shouldn't need to use much lock, if any, when when on track really - even people doing straight line drag strip stuff only lock it for launch and then turn it off.

The grinding snatching vibration is probably just the locked centre diff fighting as you slow down - at higher speed the forces just scrub the tyres instead. Try manoeuvring in a circle at slow speed with lock on and, if the car doesn't stall, it'll sound like a bag of spanners - lift the handbrake slightly to open the diffs or turn the lock off and it'll roll freely and quietly again. Try it on the road with the diff fully open and see if the vibration is still there. If not, then that's what it is. If it's still there, then you may need to investigate further but i'm fairly sure that's what it 'll be.

On track if its dry I would have it fully open or, at most, just below the second orange if it's a bit slippy. More lock = more understeer generally.

I have 500bhp going through a dccd and it spends 99% of the time fully open as all I wanted really was the RWD bias.

By the way the noise sounds bad but it doesn't really do anything bad.

Cheers

 

Hi fat boy,

Cheers for the detailed reply, the vibration is ony there when the diff is used in any of the locked postions and disappears when fully open like you say.
I was running it pretty locked up at the trackday just before christmas as it was bloody cold, damp and slippy, but ur right in the fact that it did encourage understeer.

Im hoping that it is just vibration caused from having the diffs locked up and nothing more serious.

Ive also checked the rear diff to make sure it is correct by having the rear cover off, so ive ruled that one out.

What are you running 500bhp in? Bet thats a handfull. Thought my old stripped classic was fast enough at 326 lol.

Thanks again Tim.

 

p1 here mate. Nippy at 500 but more on its way

 

Right guys im still struggling with this drive train/ vibration noise.

Ive replaced the propshaft centre bearing which has made no difference, double checked propshaft joints, triple checked diff / gearbox ratio and everything seems ok.

The car has a v4 type r gearbox and r160 4.444 rear diff at the moment and before that it had the original type ra gearbox and diff.
With both of these combinations the car has had the same noise so im presuming that its not g/box or diff related, but I could be wrong.

Ive had the cars up on ramps and jacked the wheels up and ran it in gear up and down the rev range whilst a friend listened with a stethoscope underneath for anything unusual.
There was a slight grumble from the rear diff but nothing major and this didn't change no matter what position the dccd was in so it shouldn't be that.

So im at a loss really, im hoping that its just coming from the car been very stiff with everything uprated, suspension,mounts,bushes, diff lock down etc and the car is just transmitting noise at certain revs with the dccd locked.

Thanks again Tim.

 

I had a bit of vibration at a certain rpm on my blob, it turned out to be the rear uj where the prop meets the rear diff. I dropped it down one day and grabbed the end and moved it about and it was very rough to move and could feel the little spindles as you rotated it back and forth, may be worth a look

Edit:- just seen you've looked at them

 

I'll have another check just to be sure, thanks for the input. :-)

 

Right guys a quick update, removed lock down kit/bolts and took it for a run and the noise is still there, so that's ruled that out.
Next im thinking is the propshaft out of balance/ had a knock??
Tim.