Prop shaft problems

[trunt]

Recently I have been experiencing a clunk on takeup. I really don't think its the Diff itself as I have replaced the shims, the play is not excessive and its quiet. Initially it was only when I take off in 1st gear after I have been in reverse, maybe if I lift off and accelerate hard in 1st or second gear but nothing in 3/4 i.e it needs torque. I'm on new CV driveshafts so surely they are OK.

I have been chasing this for months first thoughts were that the diff or suspension was moving, as that's what it feels/sounds like. it does not happen with braking, only power so suspension was quickly eliminated. I checked the rear diff mounts, which are new, the security of the 4 diff extension to crossmember bolts, and carefully looked for cracks in the extension, nothing.. The front suspension mounts, all new all good. some bolts tightened a little but none made any difference. The issue has steadily worsened but its still only with torque.

My attention went to the propshaft, sometimes the clunk/clang has a ringing note, like hitting a propshaft but what I feel did not in my mind shout propshaft. I checked it and greased the splines However as it has worsened I am now even getting an occasional clicking sound, I worked out the frequency at 6mph (5/6 per second or so) and that says its absolutely coming from the propshaft.. time to do it..

So my question is.. can the propshaft cause such a large clunk that I can feel in the seat without a hint of vibration at speed? I'm absolutely going to replace the UJ's but what about the spline? could that cause it? Any other experiences out there that I can check for whilst I have the car in the air?

Terry "Should have replaced the UJ's when I had the chance!"

[NeilR]

All I could suggest is thoroughly clean all the grease of the spline (both halves) and see if you have any free play.
There should be very little.

[sujitroy]

I was planning to have two manual shafts rebalanced. the spines were shot. I couldn't tell. but the specialist could. no harm taking out out and have it looked out.

[Lingen]

Terry.
Put it in first gear (or "P"if it is an automatic), and then get someone to rock the car backwards and forwards while you watch all the U/Js / CVJs.. You should be able to see at once where the slack is.
It can be done lying under the car, but if you have a co operative local workshop with a four poster lift, it will be a lot easier.
Mike.

[trunt]

Terry.
Put it in first gear (or "P"if it is an automatic), and then get someone to rock the car backwards and forwards while you watch all the U/Js / CVJs.. You should be able to see at once where the slack is.
It can be done lying under the car, but if you have a co operative local workshop with a four poster lift, it will be a lot easier.
Mike.

Yes tried that - I'm afraid it needs more torque than that to happen.. It sets.. and once its set you can drive clunk free (if you avoid sudden lift offs in 1st or 2nd gear) then you can stop and take off again clunk free. It needs reverse or a lot of engine braking to "unset"

Though maybe now that the condition has worsened??? I'll try again..

[trunt]

Yes just did that again and now I can hear something.. need help.. text son-in-law!!

meanwhile.. where's that Gopro!

[Lingen]

Terry.
I agree with you that something with that much slack would be likely to cause vibration if it was on the propshaft. Could it perhaps be a woodruff key/stub axle failing on one of the rear hubs?
Mike.

[jbuckl]

Most drivetrain lash I’ve seen was caused by wear at the diff. (Apart from extreme propshaft U.J. wear)
Thats been attended to as mentioned.
all that’s left to check is splines, u/js or bearings.
time taken to check is usually greater than time to fix though, sometimes.

[trunt]

Most drivetrain lash I’ve seen was caused by wear at the diff. (Apart from extreme propshaft U.J. wear)
Thats been attended to as mentioned.
all that’s left to check is splines, u/js or bearings.
time taken to check is usually greater than time to fix though, sometimes.

Well you got me thinking... As you may detect I really cannot imagine that the clunk is from the propshaft, Ok its clicking and I just rocked it and yes there is the tiniest amount of play in the front one so its getting new joints ..but this is far more noise than I can imagine, I can sometimes feel it in my seat.

I went right back and thought about it, and it occurred to me that when I refurbished my spare diff I separated the inner driveshafts to replace the seals.... but did I fully tighten the nuts?? cant remember doing it, which is not to say I did not - I'm usually pretty good at such things, but it was a couple of months between assembly and install and its difficult to secure them to get the torque on the nut, maybe I hoped to do it once on the car? I did re-check the input flange nut but not those..

I think they are certainly worth a check... Thanks!

[trunt]

One thing I learned over years of giving and receiving Tech support was that the answer is usually in your head but it sometimes takes another person to make you redirect your thinking and stop missing the important item that cracks the problem.. The important Item was those inner driveshaft nuts.. I tightened them as best I could and I guess planned to check the torque on install.. and 3 months later forgot.. then proceeded to skip those nuts every time I mentally mapped the drivechain.. How the heck I managed to think to check the input flange but not those beats me! New CV driveshafts.. not that! but the drive flanges are not new.. and I had messed with them

Thanks Mike and Julian.. you got me on the right track.. Mike with the keyword "woodruff key" not on the hub as I have Splines there now but they are in the drive flanges! Julian with the check splines etc..

The nuts were not exactly loose but certainly not torqued all the way to specs.. I took it out this morning and Bingo, no clunk!

[jbuckl]

Really good to have feedback. Thanks.
Be warey of drive flanges & rear drive shafts that were separated with excessive force e.g. a big hydraulic press which can distort the flange & overstress the shaft. A puller is less harmful for separation force.

[trunt]

Ok on that, yes I was lucky and by bolting them together back to back one cracked quite easily, the other came off with a regular puller, no drama. I do have a concern that the month or two of looseness could have damaged the woodruff key or the taper so do plan to have a spare pair of output shafts ready with new seals for next time I have the car up on jack stands, probably when I do the prop shaft as it started clicking again today.. I also have a good quality diff extension bearing to go in as well, I had installed a cheap one before finding out about them.... what the heck..in for a penny in for a few grand!