Poly Bush Installation On Rear (outer) A Arms

[mark030358]

Gents,
Bought some poly bushes from Millers for my rear suspension (actually for all the car). I received a little drawing saying that it might be required to file down the mounting surfaces where the bolts pass through to 132mm. As mine are 137mm end to end I am reluctant to do this just yet.

Has any one fitted the Millers bushes to the outer A Arms? they are "T" shaped and if so did you file down/machine the castings?

thanks in advance
MArk

[lotusanglia1965]

Hi! yes ,i thought it odd too. we fitted polybushes on s4 at work,took both uprights to be milled to correct dimension-didn't fancy filing that much off. all gone back together ok. advice would be check,measure,check and measure again to satisfy yourself it's correct before machining,every car seems to be slightly different!
Martin

[mark030358]

MArtin,
From which part of the upright did you mill the metal from? The inner surfaces? Outer surfaces or both?

Where did you fit the stainless washers? did you fit them to all faces? inner faces or just the outer faces?

Any help appreciated.

Why not modify the bush and steel insert?

cheers
Mark

[miked]

Mark,

I have jut done my S4 all round with the Miller bought bushes. (more advice if you want it about the front)

I filed my alloy housings in situ to the dimension that Susan sent. I used engineers blue and a bolt with a nut and washer. I kept blueing the washer to ensure I kept at 90 degrees to the bolt hole.

I measured everything (both sides) and then worked out how much I was to take off each (outside, front and rear). You do not touch inside, no point. You are making clerance to fit the washers/bush top hat. It took a couple of hours each side.

I made some washers out of stainless plate and put them in between the housing and the top hat of the bush. The washer is there to create a large surface as the casting of the housing is a bit small and would chew up the poly.

To fit the washer you need a friend with a bar to lever the gap apart to push the washers in. These are going to be snug as the late Mick was stopping the front to rear movement by introducing the top hat part and the shoulder to lean on. If they were not tight it would be a pointless exerercise.

As said above I have some good advice for the front as people have locked their wish bones by incorrect installation.

mike

[Hamish Coutts]

Mike,

I am rebushing my +2, starting at the front and working my way to the rear. I have just started and am currently doing the lower trunions.

I would really appreciate any advice/war stories that you have.

Regards,

Hamish.

:unsure:

[miked]

Hamish

I had my problems due to using none lotus lower bones. The top bone were fine but this is worthy of note incase dims alter. The M Miller bushes fit great and the washers that Susan supplied. My problem arose when I discover that the inner bores of the non lotus bones were about 18-20 thous smaller than the Lotus ones. This causes the bush to migrate side ways and then they are proud of the crush tube. When you tighten them with the washers and the grease, the washer clamp the poly and you are rigid.

I had the lower bone bored out to the size of the Lotus ones. All then went together nicely. They do say about removing the powder coating etc. Believe it as reduction in the bone bore will make you poly migrate. The only way it can go is sideways.

I would remove your dampers and build up without them and then you can swing on the pivot points to ensure thay are not nipped. Get some plain nuts than you can take them on and off.

One other subtlety is the top ball joint. Others may disagree about caster angle etc. When I built up the top bone I found that the two bolt that nipped the ball joint caused quite a clamp action on the poly bushes (yes, I did check them for distortion). I tried to get slim washer either side to very slightly space them off. It was so subtle that I settled for just one washer between the rear of the ball joint and the bone on each bolt. This may be me being an "old tart" about the movement of the top bones and looking for two much freedom. I will check this when I haved put some miles on and remove these washer if they do not apprear to clamp any more. I think they may come out as the top hat poly bit that goes against the inner washer actually start to work the poly and find a natural position.

I was somewhat paranoid about the horror stories of locked up suspension.

please email and I will chat on the phone if you need more info'.

Mike.

[Hamish Coutts]

Mike,

Thanks a lot for the information.

I managed to do the N/S lower trunion bushes and all the anti-roll bar (sway bar) bushes last night without too much trouble. So far so good. It's amazing how much the old rubber bushes deteriorate, some were virtually non existant - just a gooey mess with oil. The back bushes are more intimidating but it's nice to know that I can contact you for advice if need be. Thanks.

I've also got a set of new Spyder front wishbones and am fitting them as part of the exercise. They look far better and much more robust that the originals.

The car has got to handle much better after all this!

Regards,

Hamish.

[type26owner]

Feel obligated to warn you of a potentially dangerous suspension problem caused by the poly bushings binding. If they introduce too much stiction then when cornering at 10/10s they will not allow the tire to be loaded gradually as the car rolls into the turn. By making that car body rolling motion into a jerking one the tires can be instantly overloaded and loose all the grip suddenly causing a SNAP OVERSTEER which may not be recoverable. It's very, very dangerous to have the suspension do this. Not a single car manufacturer uses these damn things. Ask yourself why? Do your homework, the facts are posted out there on the web!

BTW, polyurethane has the same friction coefficient as brake pads. That's a clue.

[miked]

Keith,

I do not know about the friction co efficient. Are you sure about this. Can you Point us at the site. It was my ignorant belief that these were going to move more freely against the washers and the crush tubes. It seems odd that every performance car magazine and company has them all over their pages. Can you please elaborate as I thought I was doing well by getting rid of the poor quality rubbers that perish and allow all manner of movement.


Mike

[type26owner]

Hi Mike,
Yeah, sure. I'm in between meetings at the moment so it'll have be later on this evening though.

Here's just one of many sites which tells the truth about the poly junk bushings.
<a href='http://www.elephantracing.com/techtopic/polyurethanefriction.htm' target='_blank'>http://www.elephantracing.com/techtopic/po...anefriction.htm</a>

My son doesn't remember this but we put them on his 4000+ pound 70 Plymouth GTX. It destroyed the handling. We spent the next weekend removing them and putting the rubber bushings back in. A lesson well learned is a painful one!

[berni29]

Hi

For my 10 pence worth I used polybushes all round on my plus 2 for a few years befor crashing while driving at 11/10ths. I liked them and did not experience any binding problems. Having said that I used a fair bit of copper grease when I fitted them. They are a tightish fit though and I guess that it is possible for them to stick.

I read the article and I do not buy the weight of the car on the bushes bit because the weight of the car is not on the bushes, but the springs and suspension legs. Under cornering, acceleration, and braking yes though. I am not sure about the harshness factor either.

Its a good and valid point to raise though. Maybe its worth checking regularly.

I am not an engineer or mechanic, but can usually make sense of what I can see.

Berni

[type26owner]

Lubricating will make the problem go away okay. Applying a grease while doing the installation is great for awhile. Depends on the fit how long it will last. If it's an interference fit then the grease will be squeezed outta there in matter of days. That's what happened on my son's car. The suspension didn't have grease fittings at those locations since they were intended to have rubber bushings there and not require any grease.

[type26owner]

I always find it's better to understand a mechanism BEFORE making modifications to it. Have you thought through all the 6 degrees of freedom aspects of the loading which the Chapman Strut is subjected too? Do you understand the engineering aspects of the tire you're using well enough in order to actually optimize it's performance or are you just guessing? IIRC, Carroll Smith states 80% of the performance envelope is the tire alone. You have 20% more to gain if you're able to tweak the forces acting upon the tire. It gets tricky from here because of all the variables and the complicated way they couple (interact). The Chapman Strut is a brilliant solution yet simple. It might be interesting to discuss it and see it from the inside.

Has anyone tried modeling the Chapman Strut in Lotus Engineering's newly introduced suspension software called SHARK or any other modeler? They have a free demo version which is useful I gather. I'd like to know what the compliance of the lower strut bushings does under braking. Does it allow the toe to go to zero? Has anyone tried doing a high speed threshhold braking in a straight line with your hands off the steering wheel with the poly bushings. Does it track in a straight line? I can state on my car outfitted with rubber bushings it does track almost straight ahead. Actually it tracks slightly off to the left since I'm sitting on that side. With a passenger it does track true.

[berni29]

Hi Again

I must say that I do not think all that hard about it. I agree with you about the tyres. Modern tyres let a shopping trolley (eg Citroen AX) corner like it's glued to the road. I would personally avoid using a modern performance tyre on my plus 2. I think that a standard tyre (of the right size for a plus 2) like the kind that you find fitted to a plain Nissan Almera (for example) performs fine, and allows the slippage that is in keeping with the way that the car should handle.

As far as the bushes go, part of the attraction is the fit and forget and non deterioration factor, which if you need to grease them doesn't hold as much weight. How about some sort of low friction washer? You have to fit steel ones between them anyway. Can you get teflon coated washers? Or thin stainless steel ones? How about copper?

Berni

[type26owner]

Berni,
If you've already driven the car at 11/10s then why in the hell would you not want a performance tire to do that with so it's somewhat safer? That logic escapes me!!!!!

BTW, if you goto the websites of the polyurethane manufactureres they mention in the fine print that some types of the poly should not be allowed to get wet. It swells by just a smidge but enough to possibly bind the suspension.