Differentials - can cause car to shake?

Hey all

My car, when it reaches about 25 MPH in any gear, begins to vibrate horrendously. My mechanic says its a worn differential and that I would basically have to rebuild the entire car front to back to fix it.

HOWEVER...I looked in my Toyota service manual and the Haynes manual and neither has "vibration" as a possible symptom for differential problems.

AND...we just had the driveshaft replaced, and this was not happening with the old driveshaft. The mechanic swears the driveshaft is straight and not causing any vibration. I think its bent slightly at the center support bearing.

My question is this - can the differential really be a source of car-shaking vibration, or is this a driveshaft problem? We also just had the motor mounts and transmission mount replaced. My car is a 1985 Corolla SR5 5-Speed.

Thanks!

BTW - My mechanic is the one that recommended we get the driveshaft replaced in the first place.

IMHO you are correct. Differential problems may result in clicking or rumbling noises and sometimes mild vibration, but a horrendous vibration at low road speed is likely a driveshaft

The car does make a rumbling noise. However, the vibration is especially strange because it is completely absent until about 22-25 MPH and then suddenly appears in full.

if the differencal was not working properly, the wheels would fight each other during turn(or going straght if the wheels are missmatched) i could imagine depending on the suspention set-up this would cause wheel hop.

this may help: http://www.saturnfans.com/photos/showphoto.php/photo/15886/

how do you feel about running the car in drive with the drive tires jacked off the ground?

you need a new mechanic.

if it is a diff problem (which is probably isnt) there is no way you would need to get the car rebuilt front to back. at least ask him what he thinks is worn in the diff.

My mechanic told me I would need the entire car rebuilt because, he said, "there's vibrations coming from your engine, transmission, wheel bearings, and suspension too."

Personally, I suspect he's saying this to cover his tracks, because he was the one to advise me to get the driveshaft replaced initially.

UPDATE - I jacked the rear axle off the ground and ran the car through the gears. Rumbling and vibration at around 25 MPH, as before, can't tell where its coming from. One wheel sometimes spins faster than the other. No noticable noise coming from the differential. Just changed the differential fluid with no results.

One wheel sometimes spins faster than the other.

thats normal. sorta. its nothing to worry about unless its a large difference in speed(check for draging brakes)

if the noise is still there with the wheels of the ground i doubt its the diff

AND...we just had the driveshaft replaced, and this was not happening with the old driveshaft. The mechanic swears the driveshaft is straight and not causing any vibration. I think its bent slightly at the center support bearing.


Ok I just want to clarify this before I go further. Your saying here that the vibration didn't happen before with the old driveshaft? Now with the new one the vibration is evident? Am I interpreting this correctly or was the vibration still evident in the old driveshaft?

You interpreted it correctly. The vibration began with the new driveshaft. The mechanic insists its the differential and that "the old driveshaft was absorbing its vibrations, now that the new one is rigid it is transmitting it."

Um, right.

maybe you should go to another mechanic and have him check the driveshaft straighness, balance, driveline angle, and driveline phasing. (i think thats right, i'm more of a FWD kindda guy)

You interpreted it correctly. The vibration began with the new driveshaft. The mechanic insists its the differential and that "the old driveshaft was absorbing its vibrations, now that the new one is rigid it is transmitting it."

Um, right.

It sounds like the new driveshaft wasn't balanced correctly. I would go to another mechanic and have it checked out. Out of curiosity if you could, have a different mechanic check out the diff (this will let you know how honest this other mechanic really is).

Trying to bring in to another mechanic tomorrow, hopefully he'll be able to figure things out...

You had the drive shaft replaced, but did you have the U-Joints replaced? This sounds like it could be the problem. When the needle bearings inside the U-Joint go bad, they start to sieze. This causes them to lock up. Put some speed behind it and now it makes for a pretty bad shake. U-Joints can go bad almost instantaneously. May be the mechanic thought the driveshaft was out of balance so decided to replace it? My guess... (good news: A U-Joint should only be about $20)


P.S. Usually when a rear end goes out it makes a LOUD noise on top of the vibration. Also, the noise should be loud when the differential is under full and minimal load. If it makes the noise when you're turning, one of the spider gears is dead. If it makes its noise under load, the main bearing took a dump. (Causing the pinion gear to bind on the ring gear)

BRAIN THOUGHT--Durr... May be when the replaced your old drive shaft they A. Didn't have it balanced or B. If they did put new U-joints on, perhaps a needle bearing or two fell out (very easy to do) this could cause some troubles...

The U-joints were *supposed* to have been replaced. If they were or not, that I dont know. They looked new when I poked around under there, and they had absolutely no play in them when I turned them by hand.

It does make some noise, but it isn't noticable from under the car - only from inside.

I am now beginning to think that FWD may not be so bad...CV axles are so much cheaper than this driveshaft...

you're not going to get play out of them, the only way you could determine if they are functioning properly is if you disconnect one end of the the U-joints from the drive shaft or differential and try to move it by hand. If you have to hit it with a hammer to move it, thats bad. you should be able to freely turn it with your hand...

I'd definitely be in a shop that can service your driveshaft, check it for straightness and balance and check the U joints. It definitely sounds like your driveshaft is the problem.

Oh yeah, and don't go back to that mechanic, except to get your old driveshaft back.