[nednil8]

Hi I have a clunk in my 91 Sierra whenever I change gear, or apply sudden power. It feels like something is shifting underneath. I've checked all the transfercase and gearbox mounts but may have missed something. So any other ideas of what the problem could be? and solutions?

Cheers,
Linden

[alien]

Uni joints?

[nednil8]

Is there anyway to check what condition there in?

[Gwagensteve]

Chock the wheels and put the car in neutral. Grab the flange and the driveshaft and try and twist them. Also try and push the driveshaft up and down at the transfer and rear diff. ANY play is unacceptable. Don't just check the rear driveshaft, check the jackshaft too - this spins 40% faster than the trap driveshaft so the unis don't always last that long.

Also check for more than 10-15mm of rotational play on the rear pinion - it could be due to failing pinion bearings.

Your car has a fair bit of lift (if it's the one in your avatar)- this will shorten uni life.

Steve.

[nednil8]

Thanks for that. Yeah it does have a bit of lift, so I think changing the uni's is probably a good idea anyway.

Cheers for the reply, I'll try what you said.

[jono165]

Also check the slip joint in the driveshaft, if its got no grease in it or worn out it will clunk.

[nednil8]

Thanks mate. The only up and down movement in the driveshaft was at the transfer case end and that seemed to be from inside, rather than the uni, however, this was very minimal. Other than that I couldn't see any unusual movement. The rotational play in the rear pinion seemed right. If I was to change the Uni's is it a job for a workshop or could I do it myself? Note: I don't have a press.

To inspect the slip joint am I required to remove the driveshaft?

Cheers

[alien]

Slip joint wear is easy - just push on one half and see if it moves around. It'd need to be VERY sloppy to make clunking noises though!

Are you sure all your mounts are OK? Could be a hairline crack somewhere.. you'll know if it's tcase by holding the tcase stick while driving - it shouldn't move. If a mount is broken it really cranks around =)

Have you checked all your U-bolts are done up tight???

[nednil8]

Cheers mate, I'll do a more thorough check of the mounts tomorrow. I'll have to check the U-bolts actually as I did drop a leaf from the packs recently so they may not be tightened enough.

Cheers

[whincup]

nednil8 wrote:

Cheers mate, I'll do a more thorough check of the mounts tomorrow. I'll have to check the U-bolts actually as I did drop a leaf from the packs recently so they may not be tightened enough.

Cheers

double check there was enough thread too, the nut may have tightened on the u bolt itself where the thread ends, rather than tightening on the base. simple solution would be a thick washer.

[nednil8]

I checked the u-bolts and they are all good. I redid the Uni test and I'm fairly certain that is the problem. It is the joint on the jackshaft going to the tranfer I believe. Next question is are all the uni joints the same? I have seen that they come in sets of two, does it matter what shaft they go on?

Cheers

[Gwagensteve]

All the unis are the same throughout the driveline.

Steve.