Prop shaftl vs bevel gear vs viscous coupling

[johngxc]

My prop shaft has been on the bench for a month, and I'm still wondering how to diagnose the origin of my mysterious shudder problem. The low speed (5-25 mph) shudder vanished with removal of the prop shaft, but all the prop shaft bearings appear to be OK (the front bearing was replaced about a year ago).

I have been unable to locate any way to test the VC, or the bevel gear. It looks like my only options are to:

1. Send the prop shaft to Colo. Driveshaft for testing. Assuming it comes back OK, then

2. Replace the VC (I'm thinking this is more likely to be bad than the bevel gear - no leaking fluid from either). This seems like a _very expensive_ way to diagnose the problem.

I've been completely unable to locate any way to test these components - any clues? I simply don't trust the dealer, in the absence of any formal means to test components.

Advice, experiences, or insights???

[JRL]

Huh?
You removed it and the shuddering stopped
You found the problem stopped
You are now aware what is needed to fix it.

Why the heck are you obsessing about others parts on the car?

[hogie50]

I defer to JRL as he has way more experience on these than I will ever get.

I agree with him on having the prop/driveshaft checked and balanced first.

Also check the output shaft from the Angle Box for movement in the bearing, and the 'nose' bearing in the Torque tube (mine collapsed) and finally the support bush at the front of the torque tube housing. All simple visual tests. I have been wrong before (well actually several times) but I'd put my money on the drive-shaft as JRL says.

There is a way of testing the torque tube and it has been posted elsewhere on this forum. It is not a method I would dare use (or my local Volvo dealer when asked) but it does exist. Good Luck!

[Space]

There is a way to test the VC and the freewheel. Search on Mathew's site. It is easy enough.

[johngxc]

Thanks for advice. JRL - I'm obsessing since (1) front prop shaft CV joint was replaced last year, and (2) all the prop shaft bearings/seals look fine. There might be some _minor_ binding in the real CV joint, but only when I rotate it at the maximum angle. I pried off the cover and the grease is intact and no burnt smell.

Before removing prop shaft, I was also sure this was the issue. But not I'm not so certain.

Also looking for post on Matthew's site for testing VC - all I've found is:

... viscous coupling (jack up one front wheel, put a torque wrench on the center nut, and make sure it doesn't turn up to the specified torque).

I think I saw the 'specified torque' was 50 lbs but not sure.

[JRL]

I'll say this one last time, I'm almost 99% sure a bad VC does not Shudder.
(I've learned never to say 100% anymore)!
If you're shuddering on turns, this is a classic bad PROPSHAFT

(For the record, you do not have front propshafts, you have front AXLES)

[johngxc]

Many thanks. I'll follow your advice -- my next move will be to take the prop shaft to Colorado Driveshaft for testing. It'll probably take a couple weeks to resolve but I'll post the outcome.

Out of curiosity, why does a shudder on turning indicate a prop shaft? I would have expected noises/shudder on turning to indicate a problem with e.g. a bevel gear, differential or something that accommodates of different wheel path lengths.

[johngxc]

Took the prop shaft to Colorado Driveshaft yesterday. Took Dave all of about 15 seconds to identify a problem with the center universal joint that I had missed (despite repeated examination by me and some of my friends). He also noted that it sounded like the center carrier bearing would soon have have failed - it's not binding and seal is fully intact, but it didn't sound right. Good reason to go to an expert - I would not (did not) note anything unusual about that one either.

Dave also noted that he thinks it's rarely worthwhile to replace the universal joint on the front of the prop shaft (which is what I did 15,000 miles ago - a $425 repair). In his experience, the bearings on the prop shaft seem to be designed so more than one frequently fails at about the same time. A rebuilt prop shaft is about $450, so in my case it would have cost about $175 more for parts to replace the entire shaft rather than one joint, but presumably labor would have been less since it's easier to replace the entire unit than to remove and press on another joint. I haven't installed the new prop shaft yet but will be very surprised if this doesn't solve my problem.

[v2k]

Took the prop shaft to Colorado Driveshaft yesterday. Took Dave all of about 15 seconds to identify a problem with the center universal joint that I had missed (despite repeated examination by me and some of my friends). He also noted that it sounded like the center carrier bearing would soon have have failed - it's not binding and seal is fully intact, but it didn't sound right. Good reason to go to an expert - I would not (did not) note anything unusual about that one either.

Samething happen to my driveshaft. I got it replace it with a new one by the dealer but the mechanic forgot to take note where the longest balancing bolt (between the drive shaft and the viscous coupling) position it was, and he end up replacing with same length screws. Since that time I have quite noticeable and annoying vibration at the rear of the drive shaft. I went few times back to my Volvo dealers, and they are not able to fix the problem.

Does someone know how to balance the drive shaft & viscous coupling? Is there any documentation on it?

[cattlecar]

There is a procedure where the spinning in-car driveshaft is cleaned at front and rear and then run car on lift at 45-50 and bring a grease pencil slowly near the driveshaft and mark the high point caused by the imbalance throwing the dshaft off center. Now use a longer bolt 180 degrees opposite your grease pencil mark. Then you repeat the rotating test and mark again if not balanced in first try. Check front, rear, and center.
The tech did the right thing as new driveshafts are not supposed to use the balancing bolts from old as the new shaft may be balanced or if not the old location may make any imbalance worse if in the wrong spot.

I was able to buy hex 8mm x 1.25 cap screws from a local bolt supply for .72 to 1.08 each to have to balance mine. It seems to me that 50 mm is the std length and I got 2 each of 55, 60, and 65 MM long to have on hand.