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MG Midget and Sprite Technical - Polybushes-just fitted and thinking of removing!

Hi guys

Recent MOT work gave me a chance to change my inner wishbone bushes for polybushes (and yes, it was not much fun to get the old rubber ones out).

New polybushes were easy to fit and drive with no problems. However when I look at the suspension arm in motion I lose confidence in the whole polybush design concept. My patchy reasoning goes as follows:

-A standard rubber wishbone bush clamps up tight with no rotation. The joint movement is simply the torsion of the rubber. There is no rotation and no wear between parts.

-Polybushes are stiff enough that torsion doesn't work, so the motion comes from the rotation of the bush around inner steel tube or the tube around the mounting bolt. This rotation must mean that the edge flanges of the polybush are rubbing against something (either the wishbone, the chassis bracket or both). Surely this rotation means that without regular lubrication I will get squeaks or wear on the rubbing surfaces?

Am I looking at this correctly? The polybush manufacturers don't seem to help themselves by disagreeing about whether lubricant is even required. I have also experienced problems with top trunnion polybushes that simply 'oozed' around the mounting washers so I am pretty much out of patience with them.

Lots of people report great improvements with polybushes, so am I missing something? I am on the verge of pulling out my new polybushes and going back to rubber....

Thanks for any thoughts
Martin
martinf

I think there is a special grease you have to coat the poly bushing with...

Weather you use the orginal rubber or the poly, it dosnt excuse you of MG maintance and alot of it...you will still need to spend 1 hour for every 3000 to 5000 miles with a grease gun, oil gun (early rack) bearing gease, and top up armstrong oil, ect ect.

But I think the black orginal rubber is fine esp on street use, its been used for 50 years, you just have to replace it out every 2-3 years

thats the great thing about these cars... they are SOOooo tunable...some guys like reg armstrong shocks others like the peter cardwell, others like the F/L...some love the ribby, some like the ford 9 and others the datsun...webbers vs SU, 1.25 su vs 1.5 su, ect ect. its just the nature of the car and the owners taste and desires

So I dont think its odd that there are some (yeah your probably the only one...LOL) that would perfer the black rubber over the red poly.

Im glade we dont all dont have to like the samething, with no choices... there wouldnt be a need for this site if that ever happens

Prop
Prop

I'm running poly bushes; have been for years, and they're fine.

As for grease on the lower arm bushes, my thought is that since there are steel sleeves over the pins that actually take the rotation, grease is essential.

For other poly bushes, say at the rear spring shackles, it may not be that big an issue, since there's so little actual rotation there. I'll let more experienced voices weigh in... my thought is that I'd use grease just to be on the safe side, but only if said grease wasn't injurious to the bushing material.

But above all, when torquing up any suspension components, whether rubber or poly, be sure you just run them up finger-tight and lower the car to apply full load to the suspension before doing them up to final torque. Otherwise, you run the risk of applying a heavy twist to the poly/rubber while the car's simply sitting at rest, and they'll fail prematurely.

Cheers, and best of luck,

-:G:-
Gryf Ketcherside

Gryfs thread is exacly the way I understand it, I have read that grease on the rear spring shackel area, and those flat pieces...keeps out moisture and in doing so... The Rust Bunnies.
Prop

Like most of us, I'm no stranger to a grease gun! I just never had to worry about the inner wishbone bushes before.

Prop makes an interesting point about changing the old-style rubber bushes regularly. I know this is the generally held opinion, so is this because the repro-parts are lousy quality? My daily drivers (modern stuff) would go 100k before I even thought about rubber bush failure, and I don't treat them any gentler than my midget. Perhaps it is sloppy suspension locating mechanisms putting our bushes under more stress than a modern car?

Anyway...back to my polybush musings:

A bit more research is making me think there might be 2 types of polybush out there, one where the inner sleeve is bonded to the bush (so it works in torsion only, just like a rubber bush) and the type I have with a rotating sleeve arrangement. (This rotating design seems to be the norm from Autobush, MGBHive and MGOC).

With this second type (rotating bush/separate sleeve) I just don't see it as a good wishbone bush (despite it obviously working fine for other people). Surely the bush's flange rotation has to be a source of wear or stiction or plain old squeaks? It will be rotating against the suspension arm or the chassis bracket with every bump. Could it be stiction that makes the suspension suddenly feel firmer?

The wishbone mounting brackets are pretty thin even on a solid car, so I don't really fancy a bush/grease/grit combo going to work on them as the bush rotates. This is why I think I might stick to polybushes in places where they have very limited rotational movement.

Interestingly I agree totally with Gryf's point about only clamping things up once the car is fully settled, but I think this is only really an issue with a torsion type of bush. The polybushes I have tried (MGBHive Blue and MGOC yellow) both just rotate with the arm so there is no chance of deforming them by tightening them at the wrong angle.

Has anyone suffered the noise, stiction or wear issues that I describe above?

martinf

You should never tighten up the bolts against bushes.

What you are doing if removing the bushes efficiency to work.

Using thread lock you can nip up the bolts leaving your suspension components free to move up and down with very little effort (not loose though)

You will find doing this that your suspension is allowed to work at its best and how it is designed to work. No resistance should come from seized bushes or dry rubber/poly.

The difference can be seen by the amount of grip that can be found by the rear tyres when everything has been bolted together in this way.

Poly bushes will squeak, so be liberal with the application of the grease supplied.

Hope that helps

Pete
PeterJMoore

Hi Pete

Maybe this is the fundamental difference with polybushes because I thought an 'old-style' rubber torsion bush was designed to be help tight so it can't rotate. The movement would only be the torsion or strech of the rubbber (this being why you only tighten them up in their normal settled position).

From the feedback here, it seems that polybushes work fine if they are free to rotate against the suspension components. I still think this is a bad idea on a rotating joint like an inner a-arm, but I have absolutely no expertise to back up this suspicion!

On the issue of tightening the bolts up, on the wishbone inner bushes (and the top trunnion iirc) aren't we prevented from overtightening by the shoulders on the bolts? Don't we just tighten them snug to the bolt shoulders?
martinf

I personally have never tightened up against bushes to that extent.

The reason is that your suspension control should be done entirely by the items designed to do so - ie shocks and springs. Bushes are there to allow a moving surface in the same way bearings are in your engine, if you over tighten the bolts in your engine you end up with bearing problems despite them not being directly connected (if you get what i mean)
PeterJMoore

My personal opinion why the rubber bushing break down ... is becauce of the rubber is not compatable with motor oil.

Ive never had any issue with my suspension rusting do to all the oil thrown about, So I think the bushing are probably made in china and and just desolve with oil contamination and heat.


Im guessing the rubber used is natural from the rubber tree and not petroleum based, like the poly is is ( well synthised from anyway )
Prop

>>> My personal opinion why the rubber bushing break down ... is becauce of the rubber is not compatable with motor oil. <<<

Up front, perhaps, but at the rear you can still get perished bushes - mainly due to moisture getting between the shackle pins and bushes and causing corrosion that eventually grinds the bushes away until metal meets metal. At least that's what I found when I rebushed my rear springs years ago.

-:G:-
Gryf Ketcherside

Great observation gryf... Im a beliver
Prop

Martin, I'm going to add my tuppence worth to this discussion. I've been running nylatron bushings in my lower A frames and upper trunion joint for 12 years now without any problems. They don't have sleeves, just allow the bolts to rotate inside the bushing. The nylatron material has a self lubricating property, so no additional lubrication is needed. The plus for me was much lower maintenance and very precise handling. When I turn the steering wheel there is no delay as rubber suspension bushings compress and absorb the loads, the input to the tires is instant and very predictable. I personally like that precision and was willing to live with the slightly harsher ride qualities of the car. As Prop said, either change the rubber bushes every few years or use a modern material such as nylatron or polyurethane and basically never have to worry about them again. I have polyurethane bushings on the anti sway bar and end links, no wear in them for 12 years either. I installed poly bushings in the rear spring hangers and my anti tramp bars last year and am more than pleased with the increased control in the rear from the tighter bushings.
If you use the grease provided by the manufacturer and install them according to the instructions provided you shouldn't have any problems and I think in the end you'll grow to appreciate the increased response in the handling.
Bill Young

Thanks guys. I guess since the polybushes are fitted(and I can now whip out the a-arms without too much trouble) I'll give them a go.

I want a 'tight' handling car and have plenty of tracktime on bikes so have no real concern about ride quality (or even bush lifespan for that matter). My only concerns are regarding squeaks and wear on the mounting surfaces from the polybush rubbing as it rotates.

Interestingly, I just found this article which explains my thoughts much better than I managed to express them!

http://www.netbug.net/blogmichael/?p=103
martinf

Interesting reading in that link Martin!

I was especially curious about all of the complaints folks have had about noise when using polyurethane bushings because I've been using them for years, with no lubricant, with no problems. It is apparent that there are different durometers, and probably different materials, being used by various suppliers, and maybe even some suppliers use different stuff in different years that they make them, so that even though we all think we are talking about the same thing, we really are not!

The urethane bushings I used in my car felt roughly the same durometer to my rubber ones, so maybe that is why my experience was less problematic than some other folks? I wasn't looking to make my car ride harsher, just be less of a difference on hot days.

In my case, I rebuilt the fr and rr suspension with all new "OE" rubber (back in '93 or so), and drove it like that for a few years, in all weather, and the only complaint I had was that it got pretty sloppy on hot days, and after a few years of driving. So, I swapped them out for these black, "similar to rubber" ones I am talking about and the handling was roughly the same as before, but did not degrade over time, or at high temperatures. I wish there was some way to better quantify these parts so that others could benefit but at this time all I can say is that they are black, (somewhat) squishy like rubber, but definitely made of urethane (shiny, smooth), and are still as good as new after 15+ years of driving (took them out this year to check!).

Norm "lucky one" Kerr

PS: Nylon bushings (hard like a piece of smooth wood) would probably make the ride as harsh as a wooden ox cart, and I can't imagine driving a car with nylon on a public street, but I have seen folks use that term somewhat interchageably with urethane (really?)!


Norm Kerr

Norm, in this instance the bushings are indeed Nylon. Nylatron is a plastic that combines nylon and molybdenum disulfide which acts as a lubricant. They are very hard, no "give" in them at all and the ride is harsh when you hit something like a pot hole or a tar strip because there is no deflection in the A arm, just what the tires can give. Ride over bumps isn't really affected that much as the shocks and springs really control that, it's just the sharp irregularities in the road surface that get transmitted into the chassis. It's really not bad, I've driven the car many thousands of miles now wihtout any undue discomfort or problems. I do run a wide tire (205) at around 28psi for highway use so they are soft enough to absorb some of the harshness that smaller tires at higher pressure would not.
Bill Young

Interesting to see the harder bushes clearly work for a lot of people. Can anyone who runs nylatron or polybush on their inner arms tell me which side of the bush flange is taking the rotation when the arm moves up and down? (ie does it rotate against the wishbone arm or against the body bracket?). When it rotates does it do it nice and smoothly or does it jerk/release due to friction?

I would speculate that those people whose nylatron or polybushes rotate on the wishbone side have a nice silent ride (smooth metal and probably greased) while those whose bushes rotate against the body bracket (old, pitted and painted metal) might get a squeak.

Just a theory I guess, but it would explain why some people love 'em and some hate them.


Interestingly, on my desk in front of me I have the following inner wishbone and top trunnion bushes:

-MGBHive blue poly
-MGOC yellow
-Superflex trunnion bushes
-and finally a set of plan old black rubber from MGOC.

They all feel pretty much the same in terms of stiffness, except for the black plan old MGOC top trunnion rubber bush which improved by having a washer bonded into its outside surface.
Hardly scientific I know and no account for longevity, but I had imagined the difference in stiffness would be obvious (as I am sure it would be with nylatron).
martinf

I've only ever used the OE bushes on my frogeye but did consider some harder bushes in the late 1980s. At the time I think only the nylatron bushes were available and the advice from a few people that had tried nylatron for road use was don't!, unless you wanted to shake the fillings out of your teeth. I didn't try them as the car was a daily driver. Interesting to note the differing opinions.
David Billington

I installed red poly bushings last winter...no regrets at all!

They're a little bit solid feeling in cold weather when I first take off, but after a few miles they become more compliant.

Poly bushings, a 3/4" sway bar & rebuilt shocks from Peter Caldwell TOTALLY transformed my little car's handling.

The poly bushings were first, they tightened up the handling so nicely, I just kept going with the rest of the improvements.

No problems, no complaints...I would personally recommend them & not second guess the choice!

Dave :)
Dave Rhine ('78 1500)

I prevoiusly had yellow, fasr road 'Performance urethane' (yellow) bush sets fitted all round to replace the standard rubber

I later replaced the yellow ones with Super-Flex

I much prefer the Super-Flex (purplish-blue) in my personal opinion and suiting my personal style and type of driving

The yellow ones, to me, made the car feel a little too stiff, harsh and jigally (no I'm not too technical)

So I'd guess the red, race, ones would be even stiffer, harsh feeling
Nigel Atkins

This is a very interesting discussion. I was advised to install rubber bushings in the front. I reluctantly followed that advise because so many of the new rubber parts simply break down in a year or two, but I did it anyway because I respect the person that gave me the advise, and they are not very difficult to replace.
In the rear I used the red poly kit from Moss. Two reasons, I want to compare them and they are more work to replace. They seem to be as pliable as rubber but I don't like the red color. Since the color comes from a dye that is added to the mix why red?
tomshobby

I ran nylatron bushes all round on my roadgoing midget in the early nineties which gave a very firm ride but very predctablwe handling - would n't even consdier it niow with the condition of the roads these days.
l snowdon

Tom

you might give this a go...Ive used it several times ...50/50 it will work well or it wont, no middle ground IMo

http://www.krylon.com/products/fusion_for_plastic/
Prop

This thread was discussed between 11/10/2010 and 17/10/2010

MG Midget and Sprite Technical index

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