Drone from the back end

[Kevinrpayne]

Reading the subjects from others I may be suffering from similar ailments on the GT6 mk3 ( non roto) overdrive rear end

when I drive at constant speed I get a constant “der donk” noise that reduces considerably when accelerating. This to me suggests diff gear wear and backlash ?  Thoughts ?  It’s passed an Mot so I think they would have checked ujs and they were replaced a couple of years ago anyway and the prop is a refurbished unit 

ive thought about getting a replacement diff but I’m unsure of the ratio that I need to source and also where to get it refurbished ? I’ll do many things but don’t have the tools for this myself 

thanks kevin

[Pete Lewis]

its unlikely the pinion and crownwheel mesh and mounting distances have changed any problems with mesh whine or howlthey dont  klunk or knock

they only knockif you have lost a tooth 

backlash cannot be really detected its like 0.006 to 0.008 " and needs a DTI to measure 

any free play in the coupling will be the small crude differential gears  they rely on bronze cup and flat thrust washers , this does matter they only turn on corners at slow rotational speeds 

UJ 's  do klunk and knock you must examine all the outboard parts before you plunge into ££££s and the diff change , then find its not cured the problem 

so check out drive shafts and propshafts first even swap the oil from a ep90 to an ep140    always   do the easy first  but avoid thinking diff untill the other areas have been checked out 

Pete

[NonMember]

2 hours ago, Kevinrpayne said:

when I drive at constant speed I get a constant “der donk” noise that reduces considerably when accelerating.

That would be unlikely to be the diff. Much more likely a propshaft UJ or loose bolts on the flanges.

[JohnD]

See: https://www.canleyclassics.com/?archive=rear-end-noises

 

[Kevinrpayne]

Interesting replies thanks. 
I’ve checked out the canley site and mine is the reverse. It’s silent when accelerating but noisy when at steady speed

ill jack up again tonight and have a go at the ujss again  I did try but it all felt tight - what’s the best technique for testing them pls ? 
 

thanks Kevin

 

 

[Colin Lindsay]

20 minutes ago, Kevinrpayne said:

Interesting replies thanks. 
I’ve checked out the canley site and mine is the reverse. It’s silent when accelerating but noisy when at steady speed

Is it worse at low speed? My Gt6 diff used to whine at about 30mph, quite a noticeable noise, but this went away when the car went faster. I used EP140 oil from Paddocks and the drone never came back.

[Wagger]

It is virtually impossible to check the u/j's without uncoupling the flanges. Even then, it is hard to detect 'Play'.

Mine made no noise when accelerating either, just on the overrun when slowing down using engine braking. It was the drive shaft u/j's and I had to change them. Could detect nothing beforehand, even on the bench.

[Kevinrpayne]

Is there a drain plug on the rear diff. I’m not sure I’ve ever spotted it 

 

kevin

[Clive]

No (except really early diffs) but some people have drilled/tapped the case. There is another thread on here somewhere about it, just the past few days.