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Has anybody succesfully balanced a drive shaft on a 940 (DIY)?

Boulder Dash

New member
Joined
Nov 7, 2020
Location
Denmark
I got this 1992 940 sedan, which was originally a 2.3 NA automatic, but was converted to a 2.3 turbo including the associated M90 gearbox by the previous owner. I bought the car as a running project, and have fixed most of the problems the car was having.
The car did have a rumbling noise as well as a felt imbalance when driving faster than 30 mph and peaking around 50 mph. I started out balancing the wheels and aligning the front wheels of the car, which helped a little bit, but but both problems persisted in some form.
The rumbling noise seemed to come from the right front of the car, but the wheel bearings seemed okay when rotating them with by hand.
I then raised the car into the air, and had a helper rev the car with the transmission engaged, and the rumble seemed to originate from the center bearing. I also checked the universal joint which both seemed okay. I then removed the drive shaft, and replaced the center bearing, while being very careful to mark the drives on the ends as well as the splines where the two halves merge. After assembling the car the problem was even worse, especially the imbalance. I know I triple checked the markings before assembly, so I?m pretty sure everything as assembled correctly, which puzzles me a lot. The bearing was bad, so at least it wasn?t a complete waste of time.
After having thought about this a little, I?m pretty sure the former owner did only swap the front drive shaft together with the M90 gearbox and reusing the rear drive shaft, they don?t to be in the same condition when looking at them, which I guess is not really perfect, as the drive shafts a dynamically balanced as a complete unit from the factory afaIk.
So today I called local shop who specializes in, among others, drive shaft balancing, and they quoted me north of $200 for the balancing if I deliver it to them. That?s probably twice as much as a used complete driveshaft (both halves) would run me.
I then tried researching whether you could try and balance the drive shaft ourself, and of course there are people doing this online (using hose clamps) , but whether it is a feasible solution I?m not really sure.
But hey, this is Tbricks, so if anybody has tried (and hopefully succeeded) it would be here :)
So any tips or tricks before I cash out on either another used drive shaft or on having my hybrid drive shaft balanced professionally?
 
Years ago I did a crude hose clamp with washers as weights balance. It was on a '69 Dodge Polara, when we had the car on the lift you could see that it wasn't straight, played around a little and it worked. It was at the shop that I worked at in 1973, It wasn't skill it was luck.
 
$200 is cheap for work at a driveline shop, they usually start at $350 to do anything for you.

DriveshaftOrientation.jpg
 
Are you sure the drive shaft is still assembled properly? In other words, are the j-joints still in phase with each other? If not, the drive shaft will create a vibration.
 
Are you sure the drive shaft is still assembled properly? In other words, are the j-joints still in phase with each other? If not, the drive shaft will create a vibration.
I think, but I?ll have to check again. The car has been put in the corner for the last couple of months, so maybe it is time for forgiveness :lol:
I do remember at least one of the bolts and nuts holding the drive shaft to the gearbox flange was not looking very OEM, so maybe that alone might upset the balance at little.
I also read about the need for spacing the center bearing carrier, so might try that as well as replacing the two u-joints as I have them lying around anyway. Another thing that might be worth checking would apparently be the tail shaft bushing, but I?m not entirely sure that they are also present on the M90 manual transmissions, or only on the AW?s.
 
I have mixed-and-matched driveshaft halves a million times without ever having a problem, including an M90 swap into a 940 that had an auto. There are little arrows stamped on each half, in addition to a dot of paint. Make sure those line up.
 
Might be worth checking the giubo at the front of the driveshaft where it mates to the transmission.

I have a 97? 940 M90 front half and 93 940 AW71 rear half in my car like shoestring said. Had reservations at first but it is vibration free up to probably faster than you can go in a non turbo 940.

Not sure how you'd balance a two piece driveshaft with a slip yoke as an assembly so most likely the halves are balanced individually at the factory. I can't imagine you'd get very far balancing it yourself, unless you're very lucky.
 
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