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MG MGB Technical - bushes 'A ' arms

On another thread, i have been kindly given advise about the wheel bearings. I now should say why I made such a mistake, what had distracted me! Under the title suspension rebuild, you will recall my adventure. Rebuilding over several weeks. The car was finally back on the floor, on its own weight when I noticed one of the 'A'frame bushes looking cracked around the edge? These are urathane, supplied but the local mg specialists.'What', I thought, let's check all of them. ALL cracked! BLast! So, my mind was in overdrive now, I have got to get these off again, and determine what has happened. Could I take one arm off at a time with the aid of 3 jacks? Yes, its possible and I still had in its packet un-used standard rubber bushes, with the steel sleeve in the middle, ( the urathane ones did not have a sleeve.) I pressed in all the rubber bushes into the arms one by one. Got the whole job done in a day, then in the rush did not check the wheel bearing adjustment, that was the other thread. But what happened to the urathane bushes? will try to post a foto later. I did coat all nuts an bolts with WAXOIL, on the instructions of the can, it said one can thin with White Spirit, if it has gone thick, or in cold weather. I did not have white spirit , but mineral Turpentine, could this have dissociated the urathane? But if so, then, surely it would not have resisted oil, water, fuel, tar which might all be possible under a car? Or was it the fact that I tightened the nuts on the 'A' frame shafts, before the car was on the floor, at its correct ride height? But, this last, the large washers come to sit on a shoulder, not continually 'squeeze' the bush? My bet is that the bushes did not like the twist they must have been subjected to once lowering the vehicle. The only way I could have avoided this was to have lubricated the inner shaft and the 'A' arm housing so that the bush moved under its own tension?But there were no instructions with the kit. Am I right or wrong? Academic now, since I now have the original rubber bushes on,and they actually feel stiffer. But it was a dam nuisance. Mike
J.M. Doust

"turpentine" is distilled from pine tree sap.
"Mineral turpentine" is lots cheaper and is AKA "paint thinner", or properly "VM&P naptha" (Varnish maker's and painter's), known as "white spirits" in British influenced places. All of these are really mixtures of Stoddard Solvent with other napthas, which are most of the stuff between kerosene/paraffin and gasoline/petrol.

I have been waiting for years to hear about urethane bushes disintegrating; you are the first. No prizes! These materials are used in metal forming operations where they are deformed under extreme pressure to unbelievable degrees, and they return to original shape with no problem. This means the cracks are evidence of chemical deterioration of the urethane. I had numerous pieces of urethane of differing characteristics from various sources, which I found to be extremely useful as tools or raw material. Over about 20-25 years, they have all disintegrated at different rates. Some just got weak/brittle, others turned into lumps of ever decreasing size. Some fell apart a year or so after purchase from large industrial suppliers, hence presumably not too old; others lasted 20 years and had been found in scrapyards etc, age unknown. So, I have been expecting reports of urethane bushing failures.

PS: check my comments re your wheel bearings!

FR Millmore

Thanks FRM, again a wealth of knowledge and information.I will experiment with the remains, see if I can find out what happened. Maybe tackfully approach the manufacturers? Mike
J.M. Doust

Just a heads up to other Aussies reading this thread.

White Spirit as sold here is NOT the same as mineral Turpentine. It is highly flammable. Often referred to as dry-cleaning fluid. Be very careful with it!!

John Minchin

I do not like using solid bushings on the street, as it is unecessary and they will eventually wear.

Use the MGB GT V8 Metalastic bushes and they will be firmer than stock, will never allow play and will last for years.
Bill Spohn

Bill. Here in the Arizona desert, the V-8 bushings last a few years, then the rubber begins to crack. (Several cars in this test.) So far, the poly bushings seem to be holding up for over three years with no signs of problems. (But, only a single vehicle and I will be taking a close look at it as I prepare it for our winter driving season.)

I wonder how much the general lowering of quality control/inspection standards, due to a world wide depression, is affecting the quality of parts available over the last several years?

Les Bengtson

Along the lines then of bushings, when, if at all does one use solid engine mounts? Some pages of the 'hot' car magazines show solid engine mounts for various cars, to stop movement, torque motion etc. But it must be awfully noisy.Ultimately, cracks must appear. I suppose for race use, full helmets, ear plugs etc it is bearable. Then again, I suppose any movement of the engine other that to generate and transmit power is wasted energy? Mike
J.M. Doust

Great thread as I was just about to post on this topic. Took my Bgt in for an oil change and noted that the V8 bushings were not only failed (less than 5 years since I put them in) but one is nearly totally gone and the one side is actually lower on the bracket. (I think I found where my vibration is coming from)

Obviously, I need to replace these and was looking at the poly bushings. Just wondering if there are any tricks to installing them? Do they need to be pressed in?


I was thinking that it should be possible to do one side of the A at a time. Do you have some instructions on how you did it?
Bruce Cunha

The Poly bushes are really quite easy to push in, as they mostly come as two parts with a shoulder. I am just a little suspicious of them now. A motor engineer who looked over the MG when I first got it, for certification purposes, said precisely this; he would not go to poly because they will not last long? My thought then, was, well the car will never do high milage, so it may still last, in relative terms. What got me was they did not last even for one kilometer! I am still thinking chemical breakdown. As for the rubber bushes, I made a 'home' inserter out of a long threaded bar and some hollow steel tubing. The tubes have to be same dia internal as the bush, and need to sit onto the edge of the bush housing. The threaded rod passes thru the hollow tube, the bush, the housing at the other end is a shorter piece of same hollow tube. a couple of big washers and nut are placed onto the threaded rod. Centralise everything and start to tighten. The bush will compress and move, Oh, put some lubricant on the inside of the tube and bush housing washing up liquid as an example. The tube or sleeve prevents the rubber bush from squidging out and maintains its travel. The little tube length at the other end of the housing allows the pressed bush to overshoot the housing a little as most bushes do. works well. Mike
J.M. Doust

JM, there are two types of poly A-arm bushings on the market. The cheaper kind that are merely a piece of polyurethane, and the good ones which have a stainless steel sleeve inside them.

The cheap kind mimic the original rubber design which is meant to be compressed in place, and flexes torsionally as the A-arms move up and down. Problem is, the polyurethane does not compress nor flex as rubber does, so you end up with the bushing rotating on the pivot. This pivot was never meant to act as a pivoting surface and after all these years it will be especially rough and corroded. This tears up the bushings in short order.

The better type of bushing uses the machined smooth inner sleeve as a pivot surface. The sleeve itself is clamped down by the large washer (make sure you install them the right way 'round) rendering it immobile. The poly bushing can then rotate on this smooth surface as teh A-arms move up and down. This type of bushing should last many years if not forever. I personally use Superflex on my cars but there are other brands out there that use the inner stainless sleeve as well.

I agree with Bill about solid bushings on the street. MG used them in the pre-war days but changed to rubber on street cars for good reason.

As for solid engine mounts, there is no good reason for that whatsoever. My '25 Ford has solid mountings. Come by for a ride sometime and watch the wings vibrate as you drive down the road. ;)
Steve S

I thought so Steve! Bruce, the changing of the bushes on the A arms, by tackling one side at a time, actually turned out to be relatively easy. Jack up the car as usual, at the front crossmember, then place axle stands under the chassis rails just behind the front wheels. Having the wheel nuts loose, take the wheels off. Now, with a scissor jack, placed under the spring pan take some load off not much. undo the sway arm, both sides and you can push this up. Now you have only one spring pan nut and bolt to undo, and the King pin bolt. I had the King pin nut on the front side ( don't know if this is correct.) so Just took the nut off, now the front A arm came off. The scissor jack still supporting the spring pan. You can take the arm to the workshop, or whatever to change the bush. And yes Stephen I must have had the cheap poly bush, no steel sleeve! When these present now new rubber ones 'bite the dust', I might try poly again with sleeves! The rear A arm can be dealt with, in the same manner. But be sure to have the front A arm back otherwise there is only the jack supporting the spring pan and spring.I have a telescopic conversion so the mounting plate for the lower shock-absorber attaches to he spring pan here undo these and push the absorber up out of the way( it will slowly move down again, but easy to push up.)Tricky thing with the back one, is having to withdraw the whole King pin bolt. Mine was new so un-seased. Lining up the-holes after took two scissor jacks to 'finely tune' the access to bolt holes. But I completed in a day. Mike
J.M. Doust


Did you order your superflex from England or did you find a supplier here in the US?
Bruce Cunha

Reckon Bruce has just proved that the parts thieves have screwed up the V8 bushes too! I've never seen any failures of these, but they were all bought long ago.

Alternatively, if the large flat washers were not correctly located on the pivot shoulders, then the bushes were not correctly compressed, and failure is likely or inevitable. Note that the washers supplied recently are not correct, and cannot be fitted properly. I use the old ones, or machine the holes until they do fit on the shoulder.

FR Millmore

FR. Well, I will hold off on making any comment on actual V8 bushings from one of the reputable suppliers. The ones installed came off e-bay.
"Genuine MGB V8 bushings"

The old saying "you get what you pay for" should be tattooed on my forehead.

I want to go with the superflex so I avoid not knowing I have good bushings.
Bruce Cunha

"reputable suppliers"
Problem one is that if there are any reputable suppliers, they are hard to identify.

"you get what you pay for"
Problem two is that you frequently do not get what you pay for.

I've had ones from big M that had to be drilled through to fit on the pivot shaft. After that they did seem OK, but I've lost track of the car so I don't know about longevity.

So far, the ones from TRF have been OK.
And I used to bitch about the prices for the real Rover ones! But I paid it, and wish I still could.

FR Millmore

Bruce, the last US supplier who carried them went out of business a few years ago. I believe I bought my last set from MechSpec on eBay.
Steve Simmons

So Superflex would be he way to go next time? Mike
J.M. Doust

I have been on the Superflex site in England. Does not appear that they have any problem in shipping to the US

I also see that Summit racing lists poly bushings for the B.

Very big difference in price, so I have to wonder on the summit ones.
Bruce Cunha

The available US bushes are probably Energy Suspension, made for Cobra replicas and other kit cars. Should be OK, decent company, but I have no experience.

FR Millmore

Just about to purchase my poly bushings. Anyone have experience with the MOSS bushings? How have they held up?
Bruce Cunha

This thread was discussed between 24/10/2011 and 24/11/2011

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