Thrust Arm Bushes - Redux.

I've posted many times on the issue of the thrust arms on the E31 causing apparent brake judder and vague steering. I have just done another couple of cars recently with bushes worthy of pics and posting.
For any newbie's, the thrust arms are the rear arms with the downward pointing balljoints at the bottom of the front suspension. The bushes are very well known to fail, but in a manner that is generally not possible to see visually, and in fact one has just passed a stringent MOT with TOTALLY failed bushes.
These bushes can cause a resonance in the front suspension/steering that is usually diagnosed as warped discs but can set off a violent shudder just by hitting a bump, initially when cornering.
There are a number of replacement choices, replacement oil filled E31 items, soft E32 7-Series ones, E34 M5 heavy duty bushes or solid polyurethane bushes.
Of these, I would only EVER consider the M5 or poly bushes. I feel so strongly about this, I would even replace these bushes if fitting a brand new arm with the stock E31 bushes fitted.
When installing these bushes there is a pre-load procedure that Must be applied or the new bushes can fail within 5000m!

FITTING OF BUSHES
Jack and support both sides of the front of the car, remove both front wheels.

Slacken nut and bolt holding the inner front Aluminium Track Control Arm, undo and remover the nut and bolt holding the Rear Thrust Arm to the chassis.

Undo outer thrust arm ball joint and remove Thrust Arm to allow removal of bush.

If outer ball joint is too tight to remove Thrust Arm, entire assembly can be removed by disconnecting steering arm, 3 bolts from under shock absorber and previously loosened front control arm bolt

.Once old Thrust Arm bush has been replaced; re-assemble removed parts but DO NOT TIGHTEN inner control arm bolts.

Loosely refit Thrust Arm nut and bolt.

PRELOAD PROCEDURE

The front suspension MUST BE COMPRESSED with the weight of the car BEFORE the inner track control arm and thrust arm bolts are tightened. This can easily be done in one of two ways:

1) Jack the front suspension up with a small floor jack under the front shock absorber until it supports the weight of the car, and then tighten the bolts

OR

2) Re-fit road wheels, lower car to the ground and either drive the car up on ramps or using a pit, tighten the bolts with the weight of the car fully on its wheels.

I would then recommend the tracking is checked/re-adjusted to parallel.

Pics below show the following;

1. Comparison between E31 (right) and M5 solid bushes. 31122226528
2. Failed oil filled E31 bush
3. Failed CSi bush, at just 64000m has lost all its oil and even dried out. Passed MOT.
4.Visibly failed, torn E31 bush
5. Solid Poly bush kit.

Dont overlook these bushes, they give all sorts of issues and as long as you have access to a press, are a fairly straight forward DIY job.

8Tech.

Would be pleased to look at them for you but we have 3 CSi's here at the moment so will not be able to take a look for a week or so.

If you are performance driving orientated I would go for the poly bushes, otherwise, go for the M5. Once fitted, the poly bushes will only take about an hour to change both sides, reckon on about 3 hours for the M5 bushes.

Please PM me for my address and prices.

Regards, 8Tech.

Yes, there were some design oversights in the Grunts bushings which I believe have been designed out of the bushes I fit.

I sent a set to a guy in the US who does very high mileage, over unmade roads, in poor conditions and also tracks his car and he has fitted the bushes in an attempt to destroy them. So far so good and here is his report.

Here is the kind report submitted by Thomas.

I have put about 2000 miles on the bushings and the ride and handling are great. I am not comparing this vehicle to any other I am only noting that the slop that I felt from the bushings that had clearly failed is gone and the car holds very well in turns at speed whether they are long sweeping at freeway speeds or quick hard turns pushing out.

The process for replacing was limited by my experience with the car but the manuals provided in the past by Wuffer and others are plenty to keep even the most poorly trained novice on the right path.

I removed the front wheels with the car supported on Jack Stands and the Tires under the vehicle as a safety precaution.

Removed the three bolts holding the lower plate



Loosened the ball joint on the arm where it attaches to the plate

Removed the three bolts holding the lower plate on and
While this was loose I removed the bolt holding the bushing end to the frame.



Disassembly was met with a large initial challenge of breaking free the ball joint pins from the lower plate. I used the fork and a little leverage and they popped out with out too much trouble but it would have been much more easy and more comfortable if I had the proper tool available.

One of the bushings was clearly torn and though I always thought the ride was smooth we have to remember I was comparing it to an 89 Mustang with 240,000 miles on its original equipment. My daughters called it the roller coaster.



Bushing removal is not done easy without the proper tools this step took a little while as I had to line up the machine shop in town that does all of the boat propellers. He was pretty sure that there would be some issue with placing car parts in the press finally I got him to agree to take a look and give me a quote on the price. 10 minutes later the bushes were out and he laughed at his hesitation. No Charge!



We popped the new poly bushes right in without any issue or lube required.





We put in the sleeves with the lube provided and then placed the washers on either side to make a bush sandwich.







Slipped the arm back into place and turned the bolt in by hand. (do not tighten yet)

Next we placed the ball joint pin back through the plate and put the three retaining bolts in by hand.

We then jacked the wheel up to preload the suspension



We looked up the appropriate torque in the manual (purposefully left out of this presentation so as to be sure that I do not inadvertently give bad info.) and using a manual torque wrench - the manual specified that all of the fasteners we removed shall be tightened to specified torque with the suspension under normal load.



We tightened the three retaining bolts on the lower plate, the nut for the ball joint under the plate and the bolt through the bushing.

Rinse and Repeat put the wheels back on and took her out for a drive.
_________________
Once fitted, it is a simple 15 min task to replace these bushes as no press is required and it can all be done in situ. IMO, stock or even M5 bushes will only give their best service for 30,000m so if you needed to renew the poly bushes at this interval, they still give a better performance for that time and are only a 15 min job to renew, not a 2-3 hour job. You can even swap them to a new arm if you need to replace a balljoint.

8Tech.

Zitat von EddBud;54057

Were can I purchase these bushings?

www.phoenixmotorsport.co.uk

in the UK/International

www.wuffer.net

in N America.

Zitat von ukzero;54064

I'm sure it's been asked before, but......

Polyurethane bushes have been around for years, giving equal or better performance, are more simple in construction, thus cheaper to design and manufacture than the complex fluid filled item used on the thrust arms on BMW's.
Why haven't BMW used them?

Cost, availability and marketing. Polyurethane, as a raw material is about ten times the cost of rubber plus it is more expensive and slower to process. Car manufacturers buy a lot of components. If Ford decided to use polyurethane bushes in their range of cars they would need to find a supplier capable of making literally millions of bushes a year. There is no company in the world (even POWERFLEX) who could make those sort of quantities. Cars are all about marketing. As long as the standard rubber bushes work without serious failure for two or three years then the manufacturer is happy. Would fitting of polyurethane bushes make you buy one car in preference to another make? Probably not.

Yes, that is the initial signs of failing thrust arm bushes.