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Tailshaft Vibration??

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#1 ·
I've been having this constant battle with tailshaft vibration.

I was reading and old Performance Street car mag that has put an idea in my head.

The car :

XB Fairmont 5.8/C4 and 9" 4.11 gears

Every since I've had 4.11 gears I've had tailshaft vibration from about 3000rpm onwards. Smooth as hell below 3000rpm.

Got the shaft balanced @ G J drivelines in Dandenong. Not much has changed apart from the vibration is slighly less. So I guess the shaft was a little out of balance.

I am still getting vibration from 3000rpm up though. My car sits @ 3600rpm @ 100kph. It vibrates enough for the rear vision mirror on the windscreen to slide off its mounting.

Now in the mag they were talking about tailshaft flex due to the walls being too thin and the extra rpm the tailshaft is doing wit the 4.11's etc.

What are the chances this is my problem?? I am running 400-450hp @ the flywheel. I can't remember the vibrations when I had the 3.00 gears in the back.

The fix in the mag was to get a thicker custom built tailshaft.

Should add the car is lowered 2" all round. Rear with lowering blocks till I can get my grubby hands on a set of reset springs.

Brenden
 
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#3 ·
Unfortunately I doubt its my diff. As my diff is a whole 5000-7000k's old. As I had it reco'd. I am pretty sure it's tailshaft related as it feels to be at mid section of the car.

Brenden
 
#4 ·
SInce you mentioned it is lowered you might want to consider getting the pinion angle adjusted correctly. This will be the cause of your vibrations and you will end up with u-joint problems, first signs are the vibrations that you are reporting.

There is a way to fix this with lowered cars/trucks. if you used blocks then youcan get a angled block to correct the pinion angle and correct the issues with the U joint. I would suggest that if you do change to a 2" angled block that you replace the U-joint and yolk since you have probably screwed up the seals at minimum.

How do i know this. I have run and delt with and installed lowering kits on Trucks here in the states for years.
 
#6 ·
I don't think it's that either as the uni's are in perfect condition. I had the tailshaft out last week. The vibration didn't start till I changed from 3.00 to 4.11. Which increased the rpm the tailshaft was going. I've done 1000's of k's without breakage or hassle.

The car was lowered with the 2" block prior to the diff change.

Hey I am willing to give anything a try I have the Spring Car Nationals in Nov. I can't be bothered driving up there with it vibrating.

Anyone one got any idea where I'd get the wedge plate in Australia?

Brenden
 
#7 ·
I am still up the creek without a paddle on this issue.

Been to Pedders Dandenong, Peterway engine/tailshaft balancing Pakenham and a few truck suspension places (Dandeong/Hallam).

I can get the wedges easy enough but I've been old you can't just put them in as they will move.

They need to be bolted into the spring pack and welded so the don't move? I don't have a welder.

I've also been told that theres no point buying wedges unless you get the pinion angle measured first.

Theres another problem. Most truck places can measure the angle but wont touch a car. Finding a place that deals with cars that does this? Still looking.

Does anyone know anywhere in the Dandenong (Victoria) area that does this sort of stuff?

I just want to drop the car off and come back when the problems solved. I've blown $80 in fuel running in circles.

I am almost ready to rip the lowering blocks out and throw them through the window of where they were bought. More trouble than they are worth.

Pedders also stated that removing the blocks and resetting the leaf spring won't solve the problem.

This problems been a thorn in my side for roughly 1 year now.
 
#8 ·
You mention that the vibration occurs at a specific RPM . Is it road speed related or engine speed related. I have had clutches in the past that were out of balance due to missing springs etc that gave a vibration at a partucular engine speed. Also are you sure its not tyre or wheels out of balance. Its worth putting another pair of rims on the back just to be sure before you start spending dollars.
I have had rims that will balance up OK and still vibrate due to old tyres being out of round or hard. These werent cheap tyres either but they were 4 years old or so.
I would be a bit dubious about the pinion angle issue in a sedan. I can see where a lowered F truck might have a different pinion angle due to being lowered possibly 300 MM or so but with a sedan you would only be changing the relative height of the diff by 100 mm at the most.
You might be able to see if the tailshaft is out of true by jacking the vehicle and putting it in top gear at idle. I have spotted a bent tailshaft before by doing this but its probably not the safest thing to do. Its best to have the tailshaft turning fairly slowly so that you can see it "wobble".
 
#10 ·
You may think that as you've just had the diff rebuilt that the problem is not in the diff - sadly I have to tell you it IS. It is very common with FMX 9" diffs - I've been doing them for years.

The vibration is road speed related not engine speed related I can assure you. It occurred at between 90 and 110 and after 120 usually went away completely so if that sounds like what you've got then ...

Forget chasing driveline angles and pull the diff - you have to have the centre balanced - check your clutches first as they may have to be replaced as well even though you've only done 7,000km with them - they wear quickly with the vibration set up inside the diff centre.

I'm sorry I can't suggest anyone in Melb to do the work but Diff Trans Spares in Sydney used to do "mine" ie the Ford dealer I worked for at the time.
 
#11 ·
Vibration in the diff?

I've had the diff reco'd. When it was I replaced ;

a) crown and pinion gears
b) clutches
c) bearings

The diff is still very tight. The diffs 4.11 LSD. Its that tight some people mistake it for a minispool.

Diff never vibrated before. I'd rather take the car somewhere before spending shitloads. I've already spent $20,000 on the car this year paying people to rebuild stuff.

It vibrates from 70kph onwards on the speedo roughly 2000rpm. The vibration is very intermitent. Sometimes it vibrates very slightly (almost not noticable) and others it just thuds. The vibration doesn't go away. It starts about 70kph and continues right up to 240kph+.

Every place I've spoke to seems to think it's pinion angle related. My dad even thinks so. He's a mechanic and worked on trucks that had similar problems for years.

The tailshafts done roughly 2500k's since the last balance.

The reason I tend to agree that it's the pinion angle is the car is chopping out rear uni's @ a rate of one per month.

As for rims they're 13,500k's old and the tyres are 5000k's max. I get roughly 8000k's from tyres.

Brenden
 
#12 ·
Possibly your problem is twofold.An intermittant vibration may be tyre related.I have seen tyres balance up all right and then vibrate worse as they heat up.I would be trying another set of rear tyres.(borrow some?)Pinion angle error should not create an intermittant problem,however chopping out a particular uni generally indicates not enough working angle-pinion and tailshaft too close to a straight line.
 
#13 ·
Very fustrating I can assure you. When the uni's are new the problem isn't there till I do a very hard launch. Then the rearend torques up and bang vibrations back. Yet my mates car doesn't have the same problems but is only lowered 1 1/2".

I always replace both but it's getting a bit expensive and the cars lucky to do 2000k's per month.

Brenden
 
#14 ·
Someone above mentioned jacking the car up and having a look underneath it - I reckon thats a good start to give you some idea whats going on. I did it many times when setting up my combo. just be very careful that the car is secure. you might be able to rule out pinion angle by placing jack stands under the body of the car, and then gently lowering the diff, so that its weight causes it to hang below its usual position.

you said that replacing the uni's made the problem go away - is it possible that hard launchs are stuffing the uni's in some way?

anyway, good luck.
 
#15 ·
Just thought I'd let people know the outcome.

I've been playing around today and I spaced up the auto about 8mm. The vibration was reduced by more than 70%.


I am going to leave the spacer there for the moment and make sure the tailshaft is 100%. So up for a tailshaft balance and uni's.

Then if it's smooth I'll then rip out the spacer @ the auto and throw some 2 deg plates under the diff.

Brenden
 
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