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98 V70 XC AWD thunks!

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Old Jun 10th, 2013, 21:10   #1
bingus666
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Question 98 V70 XC AWD thunks!

So cruising along & coming to a turn or roundabout, I slow down & turn... then "CLUNK" like a metal hammer hitting underneath... only happens when I slow down to take roundabout or signal turn...

so after hours of thrawling I came across this in an Hamerican site:

Thunk:
A thunk is defined as a loud "thunk" or "bang" that you can physically feel come up through the bottom of the car. Like it is being hit with a hammer. Typical symptom is when moving from park to Drive or reverse to drive or drive to reverse. When you are in motion all will be as normal and there will be no noises except when you come to a stop and start again. Upon starting again you are likely to get the thunk.
Probable Cause and Diagnosis:
It is highly likely it is the mounting bushing on the front of the viscous coupler. Here is what happens. The rubber bushing itself will look good. There will be no evidence of side to side movement. What you won't realize or be able to spot initially is that the bushing has separated from the steel carrier. When you put the car in gear and the drive train engages, as it torks the VC, the VC rides up over the rubber bushing and hits the bottom of the car making a "bang" or "thunk". This won't come on particularly slowly, from the 1st hint of a thunk, to a full blown bang will only take a few drives. To verify this is the case there are a few things to do and look for.


My prob is: what is viscous coupler? I think this is the US terminology but I've no idea what this is... basically I need to find out part number & the fix!

Anyone got any ideas?

cheers, bingus666
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Old Jun 13th, 2013, 18:39   #2
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Quote:
Originally Posted by bingus666 View Post
So cruising along & coming to a turn or roundabout, I slow down & turn... then "CLUNK" like a metal hammer hitting underneath... only happens when I slow down to take roundabout or signal turn...

so after hours of thrawling I came across this in an Hamerican site:

Thunk:
A thunk is defined as a loud "thunk" or "bang" that you can physically feel come up through the bottom of the car. Like it is being hit with a hammer. Typical symptom is when moving from park to Drive or reverse to drive or drive to reverse. When you are in motion all will be as normal and there will be no noises except when you come to a stop and start again. Upon starting again you are likely to get the thunk.
Probable Cause and Diagnosis:
It is highly likely it is the mounting bushing on the front of the viscous coupler. Here is what happens. The rubber bushing itself will look good. There will be no evidence of side to side movement. What you won't realize or be able to spot initially is that the bushing has separated from the steel carrier. When you put the car in gear and the drive train engages, as it torks the VC, the VC rides up over the rubber bushing and hits the bottom of the car making a "bang" or "thunk". This won't come on particularly slowly, from the 1st hint of a thunk, to a full blown bang will only take a few drives. To verify this is the case there are a few things to do and look for.


My prob is: what is viscous coupler? I think this is the US terminology but I've no idea what this is... basically I need to find out part number & the fix!

Anyone got any ideas?

cheers, bingus666
Dude i'll email you the schematic in a min
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Old Jun 17th, 2013, 14:48   #3
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Did Bren help you out?

The VC is a part that is largely responsible for the distribution of torque from front/rear - its located at the rear of the prop shaft. Its oil inside becomes thicker/thinner depending on what the front wheels/rear wheels are doing, and can adjust the torque sent to the rear axle from the engine using this viscosity.

Its a few bolts to remove, but you need to disconnect the driveshaft first - you'll need a good allen key (6mm I think) to shift the bolts - and the help of an assistant wouldn't go amiss.
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Old Jul 7th, 2013, 11:02   #4
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do you have an autobox?
it could be that or the solenoids in it - mine does it.
or check your gearbox mountings. not sure what they are like on the Mk1 v70, but mine needed replacing on my Mk2 v70xc
both the top one and the little bottom one.
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Old Jul 7th, 2013, 23:33   #5
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Hi there....


There is a bush on the side of the casting of the Viscous Coupling, sometimes this is the problem, it allows the casting to hit the body causing the thunk....


Worth a look
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Old Aug 14th, 2013, 22:12   #6
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Default thunks a million

so since then I've removed the prop shaft - bye bye thunks for now but also bye bye AWD
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Last edited by bingus666; Aug 14th, 2013 at 22:30. Reason: typo
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Old Aug 14th, 2013, 22:17   #7
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I hope you mean prop shaft!
Removing the crankshaft will still cure your problem but only because you wouldn't be able to move ;-)

Sounds like your problem is somewhere from the gearbox backwards then...
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