general layout of front wishbone fixing points and polybushes

[Sportster-Green]

today i got my front axle parts back from powder-coating and passivating.

during assembling i noticed the following:

1. the upper wishbone is not clamped between chassis brackets
2. the polybushes marlin fitted to the car are not correct.

why?

a polybush works as follows:


the inner sleeve is clamped between the chassis-brackets and the ploybush is rotating around the sleeve
as my poly´s are even longer than the sleeve this doesn´t happen on my car. a longer sleeve or shorter poly´s wold cure that...but only on the lower wishbone!!

even if i would have the correct length of sleeve, on the upper wishbone it wouldnt work as they arent clamped between chassis brackets.

i have checked several www-pictures of different sportster models....on none of the cars the upper wishbone is clamped between brackets.

so the pivot point is always on the long bolt passing through the chassis-tower or even the bolt rototes into the chassis.

any wishbone eye, ploybushed or even fitted with balljoints need to be clamped between brackets that the pivot-point is play-free between bush and sleeve or inner-eye to outer-case of a balljoint

using the bolt as pivot point will never work play free, will weaken the bolt etc...


what are your opinions / comments?


IMG_20141218_155807_555.jpg
IMG_20141218_155824_043.jpg


the bushes fitted are 53mm wide, the sleeve is 51mm

i tried shortening the bushes on my lathe..but the material is too soft.

[andyf]

Re: general layout of front wishbone fixing points and polybushes

Can you include a picture of the normal mounting? It's difficult to visualise what you think the problem is without it.

[Sportster-Green]

Re: general layout of front wishbone fixing points and polybushes

with the upper wishbone, the marlin design looks, imo, wrong:

any bush needs to be fixed between 2 brackets. for the upper wishbone there is the chassis tower, a long bolt, a fixing nut on each side..thats it...the chassis tower acts like bracket on the inner side of the bush..but on the outside??

checking several www pictures it seems that on most marlins the inner sleeve is not longer than the bush, means for the lower wishbone the side-walls of the bushes are rubbing against the chassis brackets...which is not correct.



DSC04398.jpg

[andyf]

Re: general layout of front wishbone fixing points and polybushes

I would agree that it doesn't look right. The closest thing I've dealt with is a F2 stockcar and in that case the rose joint fitted in a bracket rather than just on one side. Having said that on my rally car the rose joint at the wheel end of the track control arm was only supported on one side leaving the bolt to take the load and I never had any problems with it, in fact when the co-driver had a go at driving he managed to take the front wheel off when he hit a barrier and it ripped the rose joint out of the end of the track control arm and the bolt securing the other end to the upright was fine. The sleeve might be shorter to ensure that there is a clamping force on the bush.

[Sportster-Green]

Re: general layout of front wishbone fixing points and polybushes

the pictured design is common on ALL sportsters...so wrong on all cars?

a polybush MUST rotate on the sleeve, therefore the bush needs to be shorter than the sleeve, or vice versa...the sleeve needs to be longer!! said that...on most www pictures of people fitting poly´s the sleeve is too short because the bush-manufacturer, especically the cheapish ones, are using a wrong design.

a polybush nor any other bush or balljoint is designed to give any sideways damping when clamped between 2 brackets. the PU material is giving the damping, but this happens between the sleeve and the bush...not on the side, at the brackets.

under no circumstances the PU-material should be in contact with the chassis brackets.

look here...anyother similar design as marlin, its a royal sabre...same front upper-wishbone fixing....

http://www.madabout-kitcars.com/forum/showthread.php?t=3824&page=3

[andyf]

Re: general layout of front wishbone fixing points and polybushes

I'm inclined to agree with your comment about the the bushes. Why not just change the sleeves and then all should be well.

[cameronfurnival]

Re: general layout of front wishbone fixing points and polybushes

The rubber bushings on most cars consist of a larger steel sleeve, with a smaller steel sleeve inside for the mounting bolt, held in place with rubber that was cast in place. The sleeve is fixed in the component (in this case the shock top eye), and the inner tube held tight by the mounting bolt. As the arm moves, the rubber material gives to the shear forces, allowing smooth movement of the component. Aftermarket polyurethane bushings are completely different than the rubber bushings they replace. Instead of deforming, the polyurethane forms a friction-surface that slides around the steel suspension member or mounting point. So as long as the inner sleeve (with the bolt through it) is held in place tightly then everything should be ok as long as the poly is not being gripped by the brackets? Does it look like this was originally designed for rubber bushes?

[andyf]

Re: general layout of front wishbone fixing points and polybushes

From the pictures it looks to me like the poly would be gripped by the washers on each side so either the poly is rotating inside the outer shell that's part of the arm or the bolt is rotating in the tube where it goes through the chassis member. Either way it sounds like the sleeve should be replaced with a longer one, unless we can find the original designer and get their view on how it should work.

[Sportster-Green]

Re: general layout of front wishbone fixing points and polybushes

sure the inner sleeve is too short...thats what i already told in the opening post.

considering i would have longer sleeves, what happens on the upper wishbone?

the sleeves are not clamped between anything, as inside there is the chassis tower, outside is nothing...or is my thinking wrong?

[Sportster-Green]

Re: general layout of front wishbone fixing points and polybushes

by the way: where do i get longer sleeves...as i think the bush manufacturer has its standard sizes and nothing else?

i even dont know the manufacturer...the bushes are lateraly marked with 770 and 65 on the surface which sits inside the wishbone...

65 could be the hardness in shore.

[copperleaves11]

Re: general layout of front wishbone fixing points and polybushes

The sleeves should be clamped to the face of the chassis tower with a large washer each side and the bushes rotate around the clamped sleeves. David

[Mike]

Re: general layout of front wishbone fixing points and polybushes

sure the inner sleeve is too short...thats what i already told in the opening post.

considering i would have longer sleeves, what happens on the upper wishbone?

the sleeves are not clamped between anything, as inside there is the chassis tower, outside is nothing...or is my thinking wrong?

Why do you think the outer face is not clamped.....?
The inner face can only clamp against the strut through the force generated by the washer/nut on the outer face. It is this washer/nut that is making the clamp.

The solution to your issue is very simple: add spacer tube washers of the same I/D and O/D as your bush tube. I guess you still have the tubes from the original bushes? - cut them into spacers to the length you require: you can then tighten up the nut/washer and your polybush sleeves will be held tightly in position.

[Sportster-Green]

Re: general layout of front wishbone fixing points and polybushes

the pictured bushes are the original bushes as used by marlin when the car was built in their factory.

i will now try removing 1.5mm material on the outer colar of the PU bushes, so the metal-sleeve will be visible.

in case this will not work out, i will add some spacers

[Sportster-Green]

Re: general layout of front wishbone fixing points and polybushes

was in my garage and narrowed the PU bushes...test fitted them to the upper wishbones and test-fitted also the wihsbones to the car.

indeed the marlin construction is fine, as long as the metal-sleeve protudes out of the PU bush


longer sleeves wouldnt be possible as the lower wishbone brackets have exactly the same width as the actual sleeve.

means narrowing the PU bush was the right way!!

[CABRIOBOB]

Re: general layout of front wishbone fixing points and polybushes

On the Lotus cars wishbone suspension with same design after fitting the wishbones you leave the pivot bolts loose then you either jack up each corner of the car or set the car on the ground with wheels fitted, bounce the car so the suspension settles then tighten the wishbone to chassis pivot bolts. As this uses the fixed bush system part of the suspension. If you tighten the pivot bolts when the car is jacked under the chassis and the wishbones are hanging down you will destroy the bushes as the travel rotation in the bush will be to much.