02 XC70 Momentary noise at 15 mph

[tesavage]

Hi,

I'm a fairly new Volvo owner, having picked up an '02 last fall, currently at 104k miles. I have a few questions about it but I'll start with one to which I couldn't find any reference with the Search.

The car makes a momentary crunching noise at exactly 15 mph the first and only first time it hits 15 mph after starting the engine. The noise seems to be coming from below the pedal box in the vicinity of the trans and angle gear - this makes me a bit nervous. The only other time it will make noise is when exercising the AWD, which seems to work as it should. Any thoughts?

Some more info - the angle gear is dry and not leaking. The viscous coupling is leaking a bit and I haven't yet tested the turning force. The car has no other driveline noise and has new mounts and is smooth and serene until 77 mph, when a vibration sets in; I plan on pulling the driveshaft to address that soon. This is my first AWD car and I'm finding that I have more than a little to learn.

Thanks for any input,
Tom
'02 XC70 104k
'98 MB S420 240k

[howardc64]

The car makes a momentary crunching noise at exactly 15 mph the first and only first time it hits 15 mph after starting the engine. The noise seems to be coming from below the pedal box in the vicinity of the trans and angle gear - this makes me a bit nervous. The only other time it will make noise is when exercising the AWD, which seems to work as it should. Any thoughts?


You are probably hearing the the ABS module activating itself when going forward after ignition. You will hear it only once per start when going forward. Happens on all these cars so no worries.

But you said you also hear it when AWD is being exercised. Actually, there are no sounds when AWD is being exercised. The viscous coupling simply locks up when it detects different rotations between the rear wheels and the propeller shaft. The only other sound I know of is when ABS is functioning. I've always thought when the ABS is pumping the brakes, it sounds like something is broken :)



The viscous coupling is leaking a bit and I haven't yet tested the turning force.

Leaky VC is usually the leaky pinion seal on the Final Drive (the real differential in Volvo speak). This seals the VC's output shaft entering the FD. Just replaced mine recently. If you pull the propeller shaft (driveshaft in Volvo speak), its pretty easy to get the VC off and change this seal. Left my notes on this job here

http://www.freewebs.com/howardsvolvos/driveline.htm#882323515

If you pull the prop shaft, might want to regrease the front CV joint on the shaft. If the joint is bad, replace it. Left notes on this here

http://www.freewebs.com/howardsvolvos/driveline.htm#874378164

Congrats on the purchase and its great to see you doing some research for the upkeep on this car. European cars needs a little work around 100k miles to keep them running for the next 100k miles. You probably already know this from your 98 MB :)

[RockitShip]

You are probably hearing the the ABS module activating itself when going forward after ignition.

Howard, I keep thinking it's his angle gear sleeve/collar. Mine made a similar crunching noise, although only once o twice, until I replaced it.
He should see if the prop shaft is spinning.

[howardc64]

Howard, I keep thinking it's his angle gear sleeve/collar. Mine made a similar crunching noise, although only once o twice, until I replaced it.
He should see if the prop shaft is spinning.

Good point, if the sound is distinct from the ABS module activation and appears more than once... It might point to this weak spot.

[tesavage]

You are probably hearing the the ABS module activating itself when going forward after ignition. You will hear it only once per start when going forward. Happens on all these cars so no worries.

But you said you also hear it when AWD is being exercised. Actually, there are no sounds when AWD is being exercised. The viscous coupling simply locks up when it detects different rotations between the rear wheels and the propeller shaft. The only other sound I know of is when ABS is functioning. I've always thought when the ABS is pumping the brakes, it sounds like something is broken :)

Thanks for the input, guys. It looks like the noise is in fact the ABS module. I just pulled the ABS fuse and went for a drive - no noise! It is however the most fearsome ABS module noise I've ever heard (but I'm new to Volvos...). My first thought was also the angle gear but the noise just seemed too consistent to be a broken mechanical piece. The noise isn't so much when the AWD is working per se, but when I'm being a hooligan in the snow and it detects slip and the little light comes on in the dash, which makes sense.


Leaky VC is usually the leaky pinion seal on the Final Drive (the real differential in Volvo speak). This seals the VC's output shaft entering the FD. Just replaced mine recently. If you pull the propeller shaft (driveshaft in Volvo speak), its pretty easy to get the VC off and change this seal. Left my notes on this job here

http://www.freewebs.com/howardsvolvos/driveline.htm#882323515

If you pull the prop shaft, might want to regrease the front CV joint on the shaft. If the joint is bad, replace it. Left notes on this here

http://www.freewebs.com/howardsvolvos/driveline.htm#874378164

Wow, excellent write up, thanks!


Congrats on the purchase and its great to see you doing some research for the upkeep on this car. European cars needs a little work around 100k miles to keep them running for the next 100k miles. You probably already know this from your 98 MB :)

All too well. Things get really interesting when you go for that third 100k miles...

Thanks again,
Tom
'02 XC70 104k
'98 MB S420 240k

[tesavage]

You are probably hearing the the ABS module activating itself when going forward after ignition. You will hear it only once per start when going forward. Happens on all these cars so no worries.

But you said you also hear it when AWD is being exercised. Actually, there are no sounds when AWD is being exercised. The viscous coupling simply locks up when it detects different rotations between the rear wheels and the propeller shaft. The only other sound I know of is when ABS is functioning. I've always thought when the ABS is pumping the brakes, it sounds like something is broken :)

Thanks for the input, guys. Sorry about the delayed response; my first try didn't go through. It is in fact the ABS module - I pulled the fuse and went for a drive and no noise! It is however the most fearsome ABS module I've ever heard (but I'm new to Volvos...) My first thought was also the angle gear as the noise reminds me of a missed shift, but it is too consistent to be a broken mechanical piece. I guess it doesn't happen when the AWD is working per se, but more like when I'm being a hooligan in the snow and it detects wheelspin, which makes sense.


Leaky VC is usually the leaky pinion seal on the Final Drive (the real differential in Volvo speak). This seals the VC's output shaft entering the FD. Just replaced mine recently. If you pull the propeller shaft (driveshaft in Volvo speak), its pretty easy to get the VC off and change this seal. Left my notes on this job here

http://www.freewebs.com/howardsvolvos/driveline.htm#882323515

If you pull the prop shaft, might want to regrease the front CV joint on the shaft. If the joint is bad, replace it. Left notes on this here

http://www.freewebs.com/howardsvolvos/driveline.htm#874378164

Wow, excellent resource. Thanks!


Congrats on the purchase and its great to see you doing some research for the upkeep on this car. European cars needs a little work around 100k miles to keep them running for the next 100k miles. You probably already know this from your 98 MB :)

All too well. Things get especially interesting when you go for that third 100k...

Thanks again,
Tom
'02 XC70 104k
'98 MB S420 240k