Polyurethane or metalastic bushes?

ChrisC · Post by **ChrisC** » Mon Mar 07, 2011 12:57 pm

As part of my nut and bolt rebuild - I just fitted poly bushes to the front suspension but now I am doubting that I am doing the right thing because I am hearing too many stories of "squeaks". the last thing I want is to do is to strip the suspension apart again.

Reading this and various other forums - the chances of the bushes squeaking seems to be pretty high (although this appears to be because they did not fit properly as opposed to it being a particular trait).

So now is the right time to re-consider whether I should remove the poly and go back to metalastic

So to the Poll...
For those that have done this work - if you were in my position what would you do?

For clarity this is not a poll about any particular manufacturer of these units just a personal choice on whether you would fit them again or not.

If you prefer.... just drop me a PM...

Post by **Heuer** » Mon Mar 07, 2011 1:47 pm

Chris

My car has had poly bushes for the last 8 years but CMC are gradually replacing them with metalastic for two reasons - my creaking suspension and the rubber makes for a 'better' (in Jaguar's eyes) ride. If you are going to track day your car or go racing then poly bushes may be worthwhile but on a road car you are sacrificing some of the compliance Jaguar designed in. The advantage of poly bushes is they will last longer although mine are pretty knackered after 30,000 miles. The creaking can be eliminated by using the correct lubricant but several people report it returns after a while. Someone (Larry Wade?) fitted grease nipples to the poly bush housings so the lubricant could be replenished but when it gets to that stage I think 'upgrade's' have seriously got out of hand!

More info on lube's: http://polybushings.com/pages/bushinglube.html

Post by **1954Etype** » Mon Mar 07, 2011 1:57 pm

Chris, I have fitted poly bushes and have had no creaking so far (after about 7000 miles). On that basis, I would fit them again. Have just replaced the steering rack mounts with poly and it has sharpened up the steering without any of the negatives of solids.

PeterCrespin · Post by **PeterCrespin** » Tue Mar 08, 2011 5:13 pm

Rubber every time unless it was a track day or race car. Even then frankly, you'd have to be a driving God to get any overall benefit beyond the downsides. I suspect Messrs Hill, Salvadori et al in a Metalastik car would cream anybody on this forum in a polybush car, by miles.

The rubber bushes last effectively forever, in terms of a hobby car. If they break up in 30K then either they were tightened up with the suspension on full droop instead of mid-laden (far too common I bet), or they were craptastic parts. The only other explanation would be that the slight crumbling of the squashed/stretched visible rubber by the big washers was assumed to herald a disintegrating bush interior, where the rubber-in-torsion action really happens. It doesn't.

I just jumped in the E this morning after two trips in the D and it is sooo nice to drive that car. It's truly a Grand Tourer with classic Jaguar balance between ride and handling so why make it closer to a Big Healey? The car had Delrin bushes in when it was a V8 and they were horrible. Angus's car isn't that bad because poly is softer than Delrin, but there are much cheaper cars if you want a non-Jaguar ride.

Variety is the spice of life though. So as long as I always know someone with a polybush car to remind me how nice mine is, I'll be happy.

Pete

christopher storey · Post by **christopher storey** » Tue Mar 08, 2011 5:47 pm

I think there is some confusion about polybushes creeping in. The standard ones are broadly similar in functional attributes to the rubber ones . The ones which make your teeth rattle are the uprated ones which reduce the compliance in the suspension markedly, with the effects Peter Crespin speaks about. My FHC with standard grade polybushes feels no harsher than a standard rubber bushed car such as my OTS , and I am pretty sure they will see me out!

Post by **1954Etype** » Tue Mar 08, 2011 7:18 pm

Agreed Chris. (Just done 200 miles in mine today and haven't experienced a harsh ride Pete!)

Dave K · Post by **Dave K** » Tue Mar 08, 2011 7:33 pm

Polybushes no question.
I have had both Metalastic and Polybushes in mine and Poly are far better. Use the grease supplied with the bushes and they won't squeak. Like Angus I have done 9000 miles with the poly and never a squeak or a harsh ride.

I almost forgot to add it is important to set the suspension up using the links and set it in the mid laden position before cranking up the nuts or they will squeak. I know you have my links but if you don't then nip the nuts and fit the split pins, go for a 50 miles drive and then tighten up correctly.

Dave

Post by **Heuer** » Tue Mar 08, 2011 7:35 pm

There seems to be three grades of Polybush:

For the E-Type 'Performance' (Red) and 'Comfort' (Black) are available. I assume the black ones are the same as the blue but more visually pleasing on a classic car.

sulzeruk · Post by **sulzeruk** » Wed Mar 09, 2011 2:05 pm

I have a full set of the blue Polys to put in my series 2. I run them in my Elan with no squeaks or harshness. I think a lot is dependant on the quality of the bush themselves. I always go for the proper Polys as others can be a bit variable in the quality department,
Alasdair

PeterCrespin · Post by **PeterCrespin** » Thu Mar 10, 2011 2:19 pm

Erm, if you are not getting more precise suspension/steering/handling from having stiffer pivot points, what is the point of spending a penny on Poly?

Poly is fine when used to stiffen things up - my contention is that it's just not worth the trade-off having a stiffer ride on a road car, but everyone's view is different, which is fine.

Logic suggests, however, that if you *don't* get a stiffer ride you aren't getting any steering improvements either. You can't have it both ways and claim better steering with no worsening of ride compliance and NVH, since the former comes from the latter. QED.

So we have three options:
Option 1: sharp handling / less compliant ride = Race spec
Option 2: Normal (great) handling, OEM (great) ride = Road spec
Option 3: Half and half = Compromise spec

There is no 4th option: improved sharper handling / no deterioration in ride. That would be an engineering impossibility. Anyone claiming same is operating in the subjective realm, not dispassionate objectivity. My view is that if you want Option 2 you are wasting money on Poly and OEM bushes are fine. If you want Option 1 you're hapy to have the trade-off and changing what an E-type is about, but it's your car so have at it. You are still subject to being blown away by a hot driver on standard bushes, so the ultimate benefit from your harsher ride seems 'moot' to put it politely. Chris certainly doesn't soundl ike he was necessarily sold on the idea, let alone the squeaking issue (avoidable).

But then apart from durometer tests on compound deflection, or chassis tests for suspension behaviour (which none of us can do for ourselves) there are no quantitative data for us to analyse. So there is just as much scope for entertaining and totally subjective banter with this as with anything. Of which this post is merely one more example....

Even back-to-back tests jumping in an out of each other's cars wouldn't prove much, since there are so many other variables. But hey, I'm not a Poly seller so I don't mind which way the debate goes - at least Chris had had a range of views.

Post by **Heuer** » Thu Mar 10, 2011 2:36 pm

Nicely summarised Pete!

Having gradually moved from Polybushes to OEM I can attest that my car is no slower through corners than before but NVT has noticeably reduced (specifically by my wife) making the car more enjoyable to drive.

PeterCrespin · Post by **PeterCrespin** » Thu Mar 10, 2011 3:18 pm

We did a tour of Europe in my S3 OTS but my wife moaned a lot about comfort and was very reluctant to get in the car again. Result? I bought a hard-as-nails D-type :-)

Now my Series 2 on OEM bushes has won her over and she has remarked how good the ride is and is a frequent passenger. Whether this is good or bad depends on the timing, but I have another D-type anyway.

That one is for sale incidentally if anyone wants to see it at Stoneleigh, or save me the trip. Reason for sale is I'm getting a third Lynx-clone D-type custom built by Zealia's Brian Wilkinson, to include live rear axle and some original D-type panels.

I'll post it in For Sale and Wanted

Tony · Post by **Tony** » Thu Mar 10, 2011 7:19 pm

I do not know what my car has but I could not ask for a better ride. On the basis I cannot see any blue, red or orange around the suspension area, I presume I am on the normal rubber bushes.
What they will be like after 50,000 miles I do not know but I suspect I will not be around to worry.

38E · Post by **38E** » Thu Mar 10, 2011 8:38 pm

The Metalastic type of rubber bushing for pivoting applications has to be one of the most major advances in automotive suspension design, along with top and bottom ball joints for steering instead of king pins etc.

No moving parts to wear plus the rubber assists the suspension compliance (which the poly bushing does not).

One of the most common comments by people riding in my car for the first time is surprise at the supple ride it provides.

Nothing wrong with rubber bushes on a properly designed suspension. The original Lotus Elan had them too and would run rings, handling-wise, around an E type.

christopher storey · Post by **christopher storey** » Thu Mar 10, 2011 11:20 pm

Metalastik when they were genuinely available were first class. Few of the bushes are now genuine metalastik ( unless you can obtain NOS from Jaguar dealers)but are modern replacements . The quality of rubber parts now is generally vastly inferior to that of 40 years ago , the hysteresis and other attributes often being radically different from the originals. Furthermore, rubber is highly susceptible to degradation from ultraviolet radiation , and this is why so many bushes show clear signs of crazing and cracking. Polybushes are not subject to this type of degradation, nor in general are they so subject to tearing under shear forces . The suspension on an E ( or indeed any IRS Jaguar of the 1961-1986 era ) is about as sophisticated as you can get, and it is this which accounts for the exceptional ride/handling compromise irrespective of the type of bushes that are used

38E · Post by **38E** » Thu Mar 10, 2011 11:47 pm

I must be misunderstanding the whole concept of poly bushes then. What shear forces are present that might cause a polyurethane bushing to tear? I thought they just rotated on the bolt or a metal sleeve or whatever. Isn't that how they work, and why they creak?

I'm not sure why there should be a problem obtaining decent bonded rubber bushes these days since just about every vehicle on the road uses them. The Metalastik company was of course taken over by a Swedish operation over 10 years ago so maybe the current offerings by the usuals for Jaguar replacements have a more oriental origin.

christopher storey · Post by **christopher storey** » Fri Mar 11, 2011 10:28 am

Clive : my understanding is that they do not work by rotation of, or around, the securing bolts. The whole point of flexible suspension bushes is to provide a degree of compliance by allowing the bush to flex in different directions and not be absolutely solid. Thus by way of example , the radius arm large bushes flex each time the lower rear wishbone rises or falls - a classic shear motion. The radius arm small bushes do the same and in addition both these sets of bushes provide a small measure of both lateral and fore and aft compliance, allowing the suspension to "lead" under braking and "trail" under acceleration without promoting rear wheel steering except to the most minute degree . The same , in principle, applies to the front suspension bushes, the rack mountings, etc

PeterCrespin · Post by **PeterCrespin** » Fri Mar 11, 2011 1:47 pm

christopher storey wrote:rubber is highly susceptible to degradation from ultraviolet radiation

Which is zero problem since UV doesn't reach the working rubber deep inside the forged steel suspension arm... Even the 'exposed' radius arm bushes are out of UV's way, unless you parked over a glass disco floor with UV uplighters I suppose.

The bushes work as rubber in torsion, which is a superb corrosion-free way of arranging suspension pivots in the worst areas for corrosion damage - the undercarriage. Before they were invented it was bushes or and needle rollers, with lots of lubrication and mainetenance needed. I'm guessing the vast majority of cars from the last forty years have gone to the scrap yard still wearing the bushes they left the factory with.

The range of movement is not huge if you use a narrow cylinder of rubber like on the E-type wishbones, which is why you need to tighten at mid-laden. Since front wishbone polybushes don't act in torsion there's no issue with tightening at mid-laden AFAIK - they just rotate anyhow. The rubber for wishbone bushes is pretty low-tech and I have not heard of anybody's bushes failing very quickly if assembled correctly. Trelleborg are still around and making Metalastik stuff I think, which is not expensive, but my pattern rubber ones are fine anyhow.

The pressed-in shock absorber or radius arm bushes would flex but I think Chris was only referring to the fronts? Very little torsion on the shocks or radius arm bushes - they are mostly compression loadings and fail by the eye pulling to the edge of the bush when the high-load part of the rubber is eventually crushed.

christopher storey · Post by **christopher storey** » Fri Mar 11, 2011 2:02 pm

Pete : the horizontal radius arm bushes are in shear,the small vertical ones in torsion ( which is of course in itself a shearing motion ). Incidentally, UV radiation is reflected off almost all surfaces so that even the underside of a car receives a fair amount unless the car is kept indoors

Post by **Heuer** » Fri Mar 11, 2011 2:04 pm

christopher storey wrote: ............ the horizontal radius arm bushes are in shear,the small vertical ones in torsion ( which is of course in itself a shearing motion ).

And the reason the Polybushes squeak!

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Polyurethane or metalastic bushes?

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