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MG MGB Technical - Poly Bushings

I am considering replacing the stock rubber upper trunion bushings on my '72B (I replaced them last about 5 years ago) with poly bushings. I have already replaced the lower control arm bushings with V-8 bushings, and upgraded the roll bar to 5/8". So far I have been happy with the upgrades, but wanted the opinion of others if the switch to poly over rubber is worth the effort. The cost from Moss for poly bushings is relatively small, it is more of a question is it worth the effort. I realize poly should last a lot longer, but what are the side effects?
Joe

Joe-
Firmer bushings, such as those made from nylon, will reduce compressibility in the suspension component mounting points and make small steering inputs result in correspondingly small reactions in the steering. In other words, the steering will become more precise, but the greater reactivity will also demand that you pay closer attention to what you're doing. Unfortunately, because they're harder, you will feel more vibration emanating from the suspension and steering wheel, hear more road noise, and your hands will feel smaller pavement imperfections through the steering wheel. Hit a big pothole and you'll know it! Even worse, the greater transmission of these forces means that associated load-bearing components (Steering rack and column components, tie rods, ball joints, kingpins, swivel axle bushings, dampers, etc.) will wear more quickly. Hard bushings are also not only unnecessary for either the mountings or the attachment points of Stabilizer Bars, Panhard Rod ends, and Antitramp Bars as they offer no benefit in handling, but are actually undesirable as they will fail to damp out vibration and road shock. In reality, there are better options for increasing steering response while avoiding most of these drawbacks.
This is not to say that you should resign yourself to the use of rubber bushings. Rubber bushings wear rapidly and rot, polyurethane bushings take a long time to wear and never rot. Sadly, almost all of the aftermarket suppliers in the USA offer only the harder varieties, being either of the "Racing & Competition" or of the "Fast Road & Rally" type. In terms of their quality, some of these bushings are real "bargain basement" items. In my opinion, Superflex makes the best, and the price is quite reasonable for the quality of their product. They don't produce them in molds (a sure sign of an El Cheapo bushing), they start life as a solid rod that is actually precision machined to size and shape on computerized machines. As a result, they will slip-fit into place. This is not often the case with molded bushings. Sometimes you have to pound them into place with a mallet, which will result in their bores being distorted or compressed, which in turn will cause them to squeak. Superflex bushings are self-lubricating once installed. They even include stainless steel sleeves so that rust can't abrade them. If you want to purchase a softer set (like rubber) for use in a daily driver, go to http://www.racecar.co.uk/superflex/ and specify 80 Shore-A bushing material for the A-arm (wishbone) bushings and 90 Shore-A bushing material when you order the trunnion, leaf spring, and stabilizer bar bushings. Superflex makes bushings for 7/8", 3/4", 11/16", 5/8", and 9/16" stabilizer bars. I would recommend 70 Shore-A material for the crossmember pads.
Prior to fitting any suspension bushing, remove all dust, previous paint, old grease, or bushing residue from all of the surfaces that can come into contact with the bushing. Be sure that any original outer shell is not inadvertently left in place. This is a common mistake whenever an old rubber bushing has unbonded from its shell. Do not fit new bushings to worn, rusty, or distorted fittings. All such worn components must be replaced. When preparing to install a bushing, lightly coat both it and the contact surfaces with assembly lubricant (where supplied) prior to fitting. In a very cold climate, immersing high-interference fit bushings into boiling water can facilitate fitting. Insert the stainless steel tubes (where applicable) after the bushes are installed into their housing. Before the final tightening, all of the suspension arms must be at normal ride height. When replacing original components, ensure that all nuts and bolts are torqued to original manufacturer's specifications. Note that polyurethane bushings must not come into contact with alcohol-based solvents such as MEK, methanol, or methylated spirit.
Steve S.

Hi Steve,

What a wonderful, informed comment. Many thanks.

Peter
P L Hills

Is there a US supplier of the Superflex bushings?
D Enghauser

D,

There are actually two suppliers in the US:


http://bhive.tierranet.com/290SUPERPRO.htm

http://www.geocities.com/carorphanage/

Zach
Zach

Steve S. Where are you in Virginia? I am in Richmond.
D Enghauser

Joe,

i tried poly bushes and are on rubber ones again at the front. Same versions as you selected for your car too.

At the rear i will keep the poly bushes as it is a great advantage/improvement there, i think. With rubber in front and polys at the rear, the car handles very good and acurate, for my oppinion, it is an ideal setup for the B.

Ralph
Ralph

Ralph, I take it you didn't like the poly bushes in the front? Why? Whose bushes did you use in the front? I am doing a 1966 B roadster.
D Enghauser

I realise it might be heresy, but I don't understand all that Steve says about transmission of forces and increased wear.

As far as I recall there isn't any rubber between the steering and the road wheels except for the tyres so there cannot be any change in the transmitted force or any accelerated wear to the components.

The kinpgin et al sees the loads from the roadwheel and transfers some of them to the body via the bushes. Maybe I'm having a 'sunday evening moment', but I could see an argument that stiffer bushes decrease the amount of load 'transfered' but not that actually seen by the unsprung components. I'm not talking about vibration (what you can feel), but force which causes failure of components.

I'm not sure about the benefits of changing the centre mounts, but putting stiffer bushes in the anti-roll bar (sway bar?) definitely increases the effective stiffness of the bar. Same would apply to anti-tramp bars, although I could never see much point in those anyway!

Tell me I'm wrong...!

Neil

Neil Lock

D.,

i changed to the V8 bushes on both cars as i installed upgraded valves in the shocks of the GT (+30%) and Spax shocks on the roadster. The feeling of the stearing was more to my idea how it sould be with the V8 rubber bushes in front. At the rear poly bushes are a good inprovement and worth the money.

Ralph
Ralph

Steve S. I will be replacing the front and rear bushings on a 79B this year. Even the V-8 bushings do not hold up well here in Arizona--very dry and very hot weather seems to cause them to degrade quickly.

The recommendations you make do not mention any specific model year. Do the recommendations hold true for all model years, or do you set up the CB and RB cars differently?

Thanks, Les
Les Bengtson

Neil

I am with you - surely if a greater proportion of the force is transmitted to the crossmember/damper then there is less available to transmit to the steering!

In my experience the issue with rubber bushes is that they deform unevenly and allow the kingpin and lower A frame to get out of alignment - soft polybushes will do the same - only frequent replacement or the use of harder bushes will mitigate this. This is why the V8 bush is so successful, it is a much stronger design and less prone to misalignment while retaining the rubber core that provides the flexibility and noise absorbing benefits. It certainly provides better location than the two top hat style poly bushes!

The same is true of the rear - and I would never bother replacing the front eye bush, it is a really strong item.

I can't help feeling that the whole polybush issue is a "go faster" goody that makes money - I reckon that a new set of rubber bushes including the V8 A frame bushes is the best option.
Chris at Octarine Services

Les-
The principles are the same, so the bushings and pads should be the same.
Steve S.

Steve. Many thanks. I will use them when I do the rebuild on the LE. The 68GT has stock bushings with the V-8 upgrade. The 79 roadster is being rebuilt using the "red" bushings from Moss. This, combined with your recommendations for the LE should give me a better idea of how the cars will handle (79 roadster to 79 LE roadster) and an idea as to how well the various parts will last (the GT's stock parts vs the poly parts on the other cars).

Thanks, again, for taking the time to let me know a starting point on which to base my researches.

Les
Les Bengtson

Neil-
You said "As far as I recall there isn't any rubber between the steering and the road wheels except for the tyres.....". There are rubber bushings at the top trunnion, the bottom of the swivel pin and at both attachment points of the lower wishbone arms. By absorbing energy, they prevent it from being transmitted elsewhere.
Steve S.

Quite. Rubber bushings give you quietness and comfort but fractionally delayed response as opposed to the sharper turn-in but more noise and harshness of harder bushings. Except at the highest level it is rather pointless, as long as any given car is consistent one simply learns the turn-in characteristics and drives it accordingly. Changing to a car with different characteristics may give you problems if you drive it at full-tilt without learning its characteristics first. Journalists opinions about one car have a fraction sharper turn-in that another are utterly irrelevant to anyone driving the same car to work every day, on more than one level.
Paul Hunt 2

Steve, Paul,
The load transmitted through the suspension is the same, regardless of the bushing material. Ask Sir Isaac Newton if you want a third opinion. The amount of compression in the bush is less with a stiffer bushing, hence the improved response; and the damping characteristics are different hence the different feel. But poly bushings will not wear out your steering column!
Neil
Neil

Steve, I have removed the old rubber bushings that I installed about 5 years ago. Have the purple poly Super Pro, and decided to order new bolts due to the fact there was a lot of wear on the old bolts and bushings. My question, on the poly bushing package, they said to clean up the metal surfaces. I have a sort of red/tan paint when you get inside my suspension where the bushings rest, it is a little chipped and rough, would you sand down and polish the surface with a Dremel?
Joe

Neil-
I agree that, as you said, that "The load transmitted through the suspension is the same", but the bushings do have a thrust-damping part that they play. When using hard bushings it is not wear on the steering column that is the worry, but long-term wear to the ball joints, the rack and the pinion gear, as well as the nylon seats at the inner end of the tie rods. Sudden, outright failure of these components is highly unlikely unless they are of defective manufacture, but longevity is always desirable.

Joe-
I use emery cloth to clean them up, then apply lithium grease between the stainless steel sleeve and the shaft.

Steve S.

I purchased bushes from Autobush (on the web) they are not on the car yet but look very good,and they have a sale on mgb bushes at the moment! very cheap!
Dave Lowe

wear on ball joints in an MGB? Ahhh, nope
Richard Morris

Richard,

Ahhh, yup - in the track rod ends!
Chris at Octarine Services

Joe,

For what its worth, I replaced the bushings on my 72B coilover suspension with Delrin bushings. When I removed the rubber bushings some were badly worn - especially the lower ones. I think there may be more response feel in the steering - its not a huge difference. I know the Delrin will hold up better.
Christian

How do Moss's Prothane Polyurethane bushings compare with those from Autobush and Superflex? Pricing from Moss and Autobush (special price including freight)are similar. Autobush special is good until end of Feb.
D Enghauser

What shore rating in poly bushes would be comparable to stock rubber ones? I'm getting ready to do a full replacement in my '67 GT and was planning to use the V8 setup. From what I can see, the only V8 bushing available is the lower arms. It's been so long I don't remember... were the rest the same between standard and V8 cars? If so, I may go with the equivalent poly, since the current crop of rubber bushings does not last very long.
Steve Simmons

Christian,

If by 'Delrin' you mean nylon, as in Nylatron, then they really are to be avoided on a road car - at least one running standard type suspension. They have no compliance whatsoever, not meant to have. If you don't fit them absolutely right they break. You'll need stiff nuts or lock nuts on the rear shackles and rear spring eye bush.

And your teeth will fall out.

Neil
Neil

Neil,

Delrin is a different material than Nylatron although they do have fairly similar physical characteristics. The bushings were machined for a very good fit. Although I stated above I did not notice much difference in handling I really did not have much to drive the car before I put it away for the winter. I am using them on my coil over suspension so I will likely need to adjust the Gaz shocks.
Christian

This thread was discussed between 13/01/2007 and 03/02/2007

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