Car shudders on deceleration at 110kph+, diff strap too loose?

[monkeyman]

Hi all,

I have been searching through the forums and have been reading a lot about diff mounts. I crawled under my car to have a look and noticed the diff strap for the first time. It has a fair bit of slack. Should it be like this? It is still in one piece.

What my car does is vibrate or shudder when I let the accelerator go, but only if I am up around 110kph or more. I know my uni joints are good and the ball joints are good (had them checked twice). Drive shaft is balanced. The gear box is very unhealthy right now (but that's another story), but the shuddering doesn't change much regardless of the gear I am in, whether the clutch is in, or whether I am in neutral.

From what I have read I will look more closely at the diff mount, but what is the diff strap supposed to do? Protect from further damage if the diff mount fails, or hold the diff snout down firmly (in which case I wouldn't expect any slack)?

Thanks,

Eric

[doradox]

I'd have those U-joints checked again. Take the shafts off the car to do so. No play AND free movement in all directions. A bad joint can feel "tight" or "good" on the car but you can't check for smooth operation on the car. On decel the diff nose tends to be forced downward so the strap is not doing anything. Is the fit between the driveshaft and trans tailshaft bushing good?

Steve

[monkeyman]

Thanks for your reply. It can't be the strap as you mentioned, not during deceleration. My gearbox started giving trouble around the same time I noticed the vibration and I am getting my original 5-speed rebuilt. Once I have changed it over, I will look at it again. If it still vibrates I will do as you say and get the drive-shafts off for a better look at the uni joints.

Thanks for the help,

Eric

[AggieZ]

I suspect the U-joints as well. The easiest way to check the U-joints is to get up to about 4500rpm and pump the accelerator (no brake afterwords). If you have a 'banging', then your likely have a bad U-joint(s). If you find a bad U-joint(s), then replace them all.

Also, you might have bad wheel bearings. If you find that your problem is bad bearings, replace then all.

For saftey, you need to find the problem and correct it.

[monkeyman]

This thread is now pretty old, but I found my problem and thought I would post in case it helps anyone down the track.

The shuddering/vibration had slowly gotten worse.

I had my rebuilt gearbox put in and while I was at it, I replaced all the universal joints. No joy.

I have ordered new rear wheel bearings and diff mount from Nissan. They have delivered them all except for two bearings that have an ETA of 30 December!

In the mean time I have replaced my old tyres and voila! The vibration has gone!

It was my old tyres. I just took the Z for a 8500km drive across Australia and I expect the old tyres didn't wear too evenly.

I didn't expect the tyres initially because it would only happen on decelleration and at high speed.

Well there you have it. I will still change the rear wheel bearings and diff mount when all the parts finally come in.