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Severe vibration on decel


Dan_Austin

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This started as an annoying vibration between 50 and 65 miles an hour.

I had about 800 miles on new tires so, I took it in for a rebalance,

but the shop claimed they were not far out of balance. The vibration

was completely absent below 50 and and above 65.

 

I searched the forums and found reports that a bad u-joint was a common

cause of this problem. Since I had no reason to believe I the u-joints

had ever been replaced, I put a new set in. I don't usually like to

diagnose by replacement, but 35 years seemed like a fair run.

 

The new joints did not solve the vibration or the ever present clunk.

 

I had already installed new springs, struts, poly bushing and an RT

mount about 3,000 miles ealier. I checked that everything was still

torqued to spec and that nothing was showing signs of unusual wear.

 

On my evening commute home the behaviour changed. While under load

the vibration remains annoying, but nothing more intense than a wheel

that is slightly out of balance, but as soon as I lift off the throttle,

the intensity feels like it doubles or more. It now feels like a belt

seperation, but only while not under load between 50 and 70.

 

I've looked for a definative test to check the wheel bearings, but come

up short. Swapping the rear wheel bearings is one task I think I would

rather avoid unless I absolutely knew it needed to be done.

 

I plan to ask the tire shop to check for a belt seperation and to rotate

the tires, but I do not have high hopes.

 

Any hints on tests to confirm or eliminate the wheel bearings or diff as

the problem would be appreciated.

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And/or it could be the front diff mount. Under accel it pushes up against the retaining strap and that deadens any vibration. Under decel the diff pushed down on the mount and the cross member transmitting all the vibration into the car.

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I could have sworn I had the year in the post, but that's what I get for

editing and re-editing to try and get it right.

 

The car is a 1976. The originally felt like it was originating from the

right rear. The decel vibration is so severe that it can be felt through

the floor, seats and steering wheel. If a belt seperation does not convey

the nature of the vibration, picture driving over cobble stones, or highway

rumble strips (only more violent).

 

I installed a Ron Taylor mount close to 5000 miles ago, so no straps or original

mounts to let go. I also should mention that braking does not alter the

intensity, which I would expect it to if the issue was in a wheel bearing.

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From my experience,

when you feel it in the body of the vehicle, or the seat backs shake,

and you feel it in the seat of your pants, it's drive shaft/rear drive axel related.

Bad/stiff u joint. Bent drive shaft/axel. Shifting differential/shaft angle?

Rotational balance issue.(anything rotating)

Road Force

tire balancing is STRONGLY suggested. A tire can balance

good dynamicaly, but when the "force of the road" is applied, vibrations can occur. Bad tire/ stacking of radial runouts.

 

 

There was a Sienna mini van that went through the shop, no one could fix the vibration.They swapped axels (fwd), tires/wheels, etc,etc.

They even put a FWD transmission in it. :o

The shop foreman FINALY asked me to take a ride and give him my opinion.

I found an aftermarket rear brake drum had been recently installed at an outside shop.

I put it on the tire balancer...8 ounces out :o

 

The hub hole was not concentric with the casting. A new factory drum fixed the vibration.

 

Make sure your wheels are CENTERED on the axel.

Edited by jasper
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I had the tire shop check for belt seperation and balance

today. The tires are in fine shape. I had them rotate the

tires at the same time. On the way home I made sure to

get it up to the problem speed, and confirmed that the

balance did not fix it, and that rotating did not relocate

the problem.

 

Next up will be to see if the driveshaft or halfshafts have

thrown a weight. The halfshafts did have their wieghts when

I replaced the u-joints back in November, after the initial

vibration problem started. I don't particularly notice the

vibration through the shifter, so I am doubtful the driveshaft

is the culprit. I also would not expect an out of balance shaft

to cause the asymmetric vibration.

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I hate to admit to being one of 'those guys', as I do try to fully

diagnose issues with me Z before asking, but I have egg on my face

for this one.

 

I check all bolts when the initial vibration started and found nothing

out of spec or loose.

 

This morning I checked again, and found one missing driveshaft bolt, one

with the nut backed off to the end of the bolt and two that were just more

than finger tight.

 

Replace the missing bolt and tightened the others, and now there is no

vibration under load or coast.

 

The upside of being a twit in this case is that I received approval to

overhaul the diff, so I picked up a 200SX R200 and ordered an OBX.

All bolts will get new lock washers and locktight when the new pumpkin

goes in.

 

Sorry for the noise...

Edited by Dan_Austin
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I hate to admit to being one of 'those guys', as I do try to fully

diagnose issues with me Z before asking, but I have egg on my face

for this one.

 

I check all bolts when the initial vibration started and found nothing

out of spec or loose.

 

This morning I checked again, and found one missing driveshaft bolt, one

with the nut backed off to the end of the bolt and two that were just more

than finger tight.

 

Replace the missing bolt and tightened the others, and now there is no

vibration under load or coast.

 

The upside of being a twit in the case is that I received approval to

overhaul the diff, so I picked up a 200SX R200 and ordered an OBX.

All bolts will get new lock washers and locktight when the new pumpkin

goes in.

 

Sorry for the noise...

 

 

I wouldn't consider your thread "noise" this thread will be good for guy's down the road that search for vibration issues. I know by seeing this thread I will for sure double check all my drivetrain bolts before I drive it.

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  • 1 year later...

Kinda old but instead of making a new one i will bring this one back.

 

recently bought a z and i'm daily driving it now. i have the exact same problem with mine as stated in the original post. I have a pretty good all over car vibration from 55MPH up under acceleration and deceleration. but nothing when i'm just cruising under power. so another words if i accelerate from 55 or completely let of the gas above 55 i get the vibration. if i'm cruising at say 70 i have nothing as long as i don't accel or decel.

 

I looked under the car and the only thing i could find was the yoke that goes into the tranny has significant play up and down. i thought for sure it was a u joint as i had this problem on my truck and found all my drive shaft u joints completely shot. when i look all my driveshaft and half shaft u joint looked good with no play. the diff is securely mounted.

 

Is there a bearing in the tail housing of the tranny that could be worn out causing this? easy to fix? way off base? what else could it be. i dont want to tear into it until i'm relatively sure what it is.

 

If i grab the driveshaft right behind the ujoint i can move the shaft up and down and side to side maybe 1/8 inch. total. bad????

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What tranny? I have a t-5

I am dealing with a similiar situation and I don't know enough about trannys to know if my end play is okay or not. I'm going to take it to a tranny shop and have them look at it.

 

As far as other possibilties, you said you looked under neath your car, I hope that was with wrench in hand. Not preaching here, but I just got egg in my face like Dan did because I found out a clunk was caused by a loose diff mounting bolt. Couldn't tell by looking, but it was almost two turns loose-and it made a lot of noise.

 

Keep us updated.

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