Which way does the diff 'turn' under acceleration?

[Barreti]

A bit of an odd question I know, but I might have found the source of a clunk on acceleration but it will be a couple of days before I can fix and test it.

When you accelerate, the diff will attempt to twist under the torque.
Which side will be trying to lift - Nearside or Offside?

I'm hoping the answer is Nearside.

[Sardonicus]

The O/S will try to twist upwards Ian

[jesfirth]

A common problem is often the front brackets where they bolt to the diff. If the bolts are even a tiny bit loose the diff moves under acceleration and lift off and the bolt hole in the plate enlarges over time hence the clonk. the only solution is to replace the bracket. My clonk was the o/s bracket.

o/s is easier to get at - no fuel pump in the way

[Mr2Mike]

The diff will try to rotate the same way as the propshaft (clockwise looking from front to rear) and will also try to rotate in the opposite direction to the rear wheels. The driveshaft torque reaction is much higher (by a factor of the diff ratio) than the propshaft,

[Barreti]

Aha, thick sod I was confusing OS with NS because I was picturing the car from the back!

I think I might have found it then.

There are 2 cap head bolts holding the diff to each side bracket.
I found the top bolt had no spring washer and nut attached so the OS bracket was only securely bolted on by the bottom bolt

I can see a slight shiny bit at the very top of the thread, so my guess is the torque was lifting the diff slightly under acceleration and it would settle back on the bolt so it didn't clunk under deceleration.

Sounds plausible ?

[Sardonicus]

Barreti said:

Aha, thick sod I was confusing OS with NS because I was picturing the car from the back!

I think I might have found it then.

There are 2 cap head bolts holding the diff to each side bracket.
I found the top bolt had no spring washer and nut attached so the OS bracket was only securely bolted on by the bottom bolt

I can see a slight shiny bit at the very top of the thread, so my guess is the torque was lifting the diff slightly under acceleration and it would settle back on the bolt so it didn't clunk under deceleration.

Sounds plausible ?

Yes, polished/shiny witness marks are always a good sign of movement something amiss

[Barreti]

Thanks everyone.

I'll have to drop the exhaust to get a ratchet onto the cap head so it will be a couple of days before I can confirm I've got it, but I've been chasing this for 2 years on and off so it will be a relief if this is it.
I was starting to think I might have to pull the diff out

[jesfirth]

the only problem you may have is that the hole in the bracket will have enlarged so you may still have some movement even with the bolt tight. mine did that and I had to replace the bracket. they are only £40 though.

[Barreti]

Thanks Jes, I’ll bear it in mind if I can still hear anything.

[Barreti]

Good news everyone. Not only has the clunk gone but the test drive was on the way to the garage for an MOT which it passed with just 2 advisories

1. Tyres are getting a bit worn but they are still legal and it looks like the front tracking needs doing (again)
2. Emissions

So I'll be hunting for new tyres this winter and I will finally have to get my finger out and get a tweaked ECU chip now I have a spare ECU and see if that gives me better emissions - or at least helps with the eye watering richness.

[Sardonicus]

Barreti said:

Good news everyone. Not only has the clunk gone but the test drive was on the way to the garage for an MOT which it passed with just 2 advisories

1. Tyres are getting a bit worn but they are still legal and it looks like the front tracking needs doing (again)
2. Emissions

So I'll be hunting for new tyres this winter and I will finally have to get my finger out and get a tweaked ECU chip now I have a spare ECU and see if that gives me better emissions - or at least helps with the eye watering richness.

Ian dont leave the richness too long as you will suffer bore wash dilute your engine oil and fk up your cam & lifters, bearings, bores, rings the lot, witnessed this many times farewell to the clunk however