Diagnosing Differential or Drive shaft Clunk

Hi,
I have noticed over the past couple of days a more prominent clunk coming from the drivetrain when setting off from standstill or accelerating away after speed bumps. Quickly taking the foot off the gas also creates a bit of a clunk. This reduces a little when the car is warmed up, although could be my perception.

I recently replaced the near side drive shaft and inspected the other when changing a wheel bearing and they both seem in good order. I certainly can't feel any free play in them so fearing this could be the diff. After I jacked both wheels off the deck and when rolling them back and forward, I can also feel some play.

The car is a 130,000 mile 2001 AUA 1.4. I have recently changed the gearbox oil with the correct spec. The clutch has always had a fairly sharp bite since we purchased it at 35000 miles so fear the gearbox has not had the smoothest of lives. Only really noticed this when we picked up our second A2 recently and could compare the different feels.

Is there a definitive way of diagnosing a nadgered Diff?
If so, guessing it is easier to change the whole gearbox out rather than trying to open it up and repair.
Still very drivable at the moment and using it as a daily commuter so also considering the option of delaying the replacement option until it breaks properly.
What are you thoughts please?
Thank you!
 
Thank you Weetank for the dog bone idea. I'll have a look later. I'll try driving off with the bonnet off looking down to spot excessive movement of the engine and gear box.
Perhaps the rubber bushes get softer after I start driving and the harshness goes away?
 
Hi @b****rlugs ...the forum software doesn't allow your username to be fully displayed because it sees a supposedly naughty word!

The diagnostic process involves raising the front of the car, removing the undertray and then observing where rotation is delayed.

The two front wheels are attached to each other along the axle, with 5 distinct connections; the differential within the gearbox, the two inner CV joints and the two outer CV joints. With both front wheels off the ground, slowly start to turn one of the front wheels. In a brand new A2, the other front wheel will start to turn in the opposite direction immediately. If there is no wear to any of the 5 connections, there is no backlash between splines or toothed wheels, and the motion is transferred uninterruptedly to the opposite side of the car. If, however, there's some wear, you'll be able to turn one of the front wheels through a small angle before the opposite wheel starts to turn. This is likely to be the reality for most A2s, because they're all at least 15 years old and most have done a good few miles.
As you gently turn one of the front wheels forwards and then backwards, you need to observe the shafts and CV joints to establish where a majority of the slack is. For instance, if the casing of the inner CV on one side of the car turns in perfect synchronisation with the rotation of the road wheel on that same side, but the casing of the inner CV on the opposite side of the gearbox is delayed in its rotation, then we can conclude that the slack is in the differential. It's all about watching rotations on either side of the 5 points of connection along the axle.

I hope this helps.

Cheers,

Tom
 
As others have said the dog bone mount sounds like the most likely culprit.
Jumping to the wrong conclusion is easy. I had a situation where I was concerned about an unpleasant noise from the drive train. With the front raised I thought the noise was due to the diff as the amount of backlash seemed excessive and ‘cluncked’. The garage however diagnosed the wheel bearing. They were right, new bearing, problem solved.
The Moral being: don’t assume the worst, come to the forum and get the best advice there is!
 
Hi,
I have noticed over the past couple of days a more prominent clunk coming from the drivetrain when setting off from standstill or accelerating away after speed bumps. Quickly taking the foot off the gas also creates a bit of a clunk. This reduces a little when the car is warmed up, although could be my perception.

I recently replaced the near side drive shaft and inspected the other when changing a wheel bearing and they both seem in good order. I certainly can't feel any free play in them so fearing this could be the diff. After I jacked both wheels off the deck and when rolling them back and forward, I can also feel some play.

The car is a 130,000 mile 2001 AUA 1.4. I have recently changed the gearbox oil with the correct spec. The clutch has always had a fairly sharp bite since we purchased it at 35000 miles so fear the gearbox has not had the smoothest of lives. Only really noticed this when we picked up our second A2 recently and could compare the different feels.

Is there a definitive way of diagnosing a nadgered Diff?
If so, guessing it is easier to change the whole gearbox out rather than trying to open it up and repair.
Still very drivable at the moment and using it as a daily commuter so also considering the option of delaying the replacement option until it breaks properly.
What are you thoughts please?
Thank you!
Hi b****rlugs,
If yours is a 1.4 petrol it may be the same as the diesel in that the dogbone
mount has to be removed to get to the drain plug, as a result the dogbone may just need to be tightened to the correct torque.
hth
Keith
 
Thanks for all the replies and a very comprehensive one Tom! I have plenty to look at over the weekend, kids permitting! A weebley wobbley dog bone I am hoping would be easily identified with a good shove with a hand or pry bar? I certainly removed one end of the dogbone to get the oil out of the gearbox but almost sure I cranked it back on again. I did change one wheel bearing over the summer and have another replacement lying in wait for the near side to go, so prepared for most eventualities.
Yep the forum is a great resource! Thanks again all. I'll try and update when I get round to more diagnosis.
 
Inspired by this, as I have been thinking similar thoughts for a while, I replaced my dogbone mount this morning. Despite 190K miles the old one wasn't wrecked, but it was certainly more wobbly than the new one. Not driven it yet, but will check that later. I used the Febi part for a Polo, cost about £31 from eBay and delivered in a couple of days.
 
Well I'm pleased to report that it has made a significant difference - time and money well spent.

Andy, Excellent news on this development; I will take the credit for starting the thread!!!

I did not get to look under my car this weekend as kids kept me occupied, but I did get my wife to shuttle the car back and forward with the bonnet off to see if I could see significant movement. About 1cm movement forward and back of the engine hoist bracket near the coil was noted. Not sure whether this is normal, but with the geometry of the engine mounts, I would expect something similar at the bottom of the engine too, so definitely warrants a snoop down under.

Pse can you share a link on the Febi part you used?
Cheers
 
There are heaps availble but I chose this one because Febi are quality parts, price and delivery time. Others were as low as £27.

Thanks, I have a 1.4 petrol so will have to research further to find the right one. I have used febi and that seller before, no issues either way.
 
Well I finally got round to changing over the dog bone among other servicing jobs like oil change, brake bleed and winter tyres! Took it for a quick drive afterwards and what a difference it has made.
I used the Polo Febi part listed above and it was noticeably beefier when compared to the original item side by side.
Rubber portions seemed similar and distance between bolts the same. Giving the bush a tweak with a screwdriver showed how bad the original item had got after 130,000 miles and nearly 20 years; no wonder it was clunking and wish I had discovered the simple fix earlier.
Thanks @timmus, @Weetank2, @AndyP and @Sootywg for your help in diagnosis and link to the part.
Great job.........now for the starter motor squeal and other suspension knocks; neighbours prob do not need to know when every time I get up early to go to work.
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