New tire sound(s)

[Pomorza]

Hey guys

Today I invested in a set of new tires. 215/70R14 in the rear and the stock 195/70R14s in the front. Car drives great but I've noticed that when I decelerate I get a thud thud thud sound from the rear passenger's side. The best way I can describe it is it sounds like I'm crossing a bridge. (and hitting the spacers on the bridge once in a while). The tires don't rub.

Three things that I've thought of at the moment. One, for some reason they used different lugs on the one tire. don't know why, but it could maybe make a difference. Secondly, the struts on the rear are gone, literally I don't think they "absorb" any kind of impact anymore. They are leaking fairly badly and make noise. Thirdly, the rear tires are misalligned. They are pointed inwards towards the front of the car. If you look at them from the top, they are about 2-5 degrees pointed inwards.

Any ideas.

Thanks greatly

Jan

Happy 4th to everyone.

[mlc240z]

Bad tire?

Might have belt separation internally.

[Gary in NJ]

Bad tire?

Might have belt separation internally.

Assuming that nothing else has changed, that's what I was thinking. Swap the rear tires and see if the noise moves to the left.

[d240zx2]

You may have some "burping" going on in the strut, too. If they're leaking as badly as you describe, air has supplanted the oil and you may be hearing air getting by the seal.

Just a thought...

[Zedyone_kenobi]

I was not aware that the Z's could adjust toe in the rear?

Before you start blaming anything else, I would recommend a new set of struts, and replacing your bushings in the rear end. Under braking or decel the weight transfers to the front of the car to some degree, leaving the rear suspension somewhat unloaded. It may be enough to upset something. Just a thought.

It is hard to diagnose something when you have known rear suspension bits that are shot. I would recommend parking her and fixing the bits that are worn or tired.

[Carl Beck]

I'd pull one lug from each rear wheel - and check to see that they are the same length. If you use too long a lug on an aluminum wheel it will hit the rear drum before it actually clamps the wheel to the hub/drum.

Better to be sure..

FWIW,

Carl B.

[Pomorza]

Thanks guys for all your input.

I drove on the tires for a good hour last night to wear them in a bit. The noise only occurs when I decelerate or brake so I'm leaning more towards the suspension or lugs rather than a bad tire. (as wouldn't the sound be continuous if there belt was bad inside?).

I sadly can't stop driving the car as it is my daily driver. I try not to drive it much as the suspension is in dire need of repair but when I have to I really have no other choice.

Thanks again

Jan

[Smokey]

Check around the wheel well opening front to back, and top to bottom, and inside out. With the suspension so bad in the rear, you will be getting more movement front to rear than you would normally. This is supported by the toe issue you mentioned. When you are decellerating or braking, the diff will put a load on the wheels in a different direction then when its under power. This could be shifting the wheels and causing them to come in contact with some part of the body. You will notice scrub marks if this is the case. The tires you are using are both wider and taller than what was there before which would support why the new tires caused you to hear the noise. The smaller tires wouldn't be big enough to make contact.

It might also be your U-joints on the rear axle going bad. The extra mass of the bigger tire could have put week joints over the edge. They would make a knocking sound under different loads similar to a CV joint in a front drive car when turning.

[Inf]

I had the same symptoms before with a front tire. Turned out the tire was coming apart on the inside. It had one part that was slightly out of round, and I only noticed the lump while rolling the tire along the garage floor with my hand sliding on top.

The whump-whump-whump only showed up at low speeds, like when rolling up to a stop sign.

At least dismount the suspect wheel, and do some close examination of the tire.

[Pomorza]

Check around the wheel well opening front to back, and top to bottom, and inside out. With the suspension so bad in the rear, you will be getting more movement front to rear than you would normally. This is supported by the toe issue you mentioned. When you are decellerating or braking, the diff will put a load on the wheels in a different direction then when its under power. This could be shifting the wheels and causing them to come in contact with some part of the body. You will notice scrub marks if this is the case. The tires you are using are both wider and taller than what was there before which would support why the new tires caused you to hear the noise. The smaller tires wouldn't be big enough to make contact.

It might also be your U-joints on the rear axle going bad. The extra mass of the bigger tire could have put week joints over the edge. They would make a knocking sound under different loads similar to a CV joint in a front drive car when turning.

Thanks for the advise.

I went out for another drive today to see if the sound was there. It was but only after a few minutes of driving over 35mph. I took a look at the tires and suspension and I'm in dire need of new struts in the rear. They are in horrid shape.

By u joints on the rear axle I'm assume you mean the half shaft u joints? The drive shaft has brand spanking new u-joins (actually the whole thing is new).

Thanks again guys

Jan

[Smokey]

Yes, I am talking about the half shafts. Didn't even think about the actual drive shaft, although that could also cause some thumping. Since you have new U-joints there, that should be just fine.

I thought of a test that you could do to see if you have enough slop in the rear end to cause excessive movement. With the car in gear and the parking brake set, you and a buddy get behind the Z and start pushing it in a rocking motion. While the car is rocking, you should not see any front to back movement on the rear wheels relative to the fender openings. Then try the same trick with the parking brake off. With the car in gear, you should still have a lot of resistance to the rocking motion. If you hear clunking, it is likely your half shaft U-joints.

[Pomorza]

Guys you are going to fall over this. Apparently my mechanic, who I've been going to for years, was no aware (or forgot) that I have staggered rims. (that is one is 1" wider than the other). Well to my amazement (and fright) I found that the rear has one thin rim (driver side) and one wide rim (passenger side) on. The tires are the same size (215/70/R14) but the rims are not. Assuming that the wider rim is heavier (which it is) I found the problem.

I'm going to avoid driving at all costs until this can be fixed as a weight difference can really mess with the diffy and really pretty much everything else back there.

Thanks guys for all your help

Jan