Drag Strut Bush Failure

[ukkid35]

At the beginning of the year I replaced the bushes with new rubber bushes from PartsForTVRs, formerly RG

They have failed already, whereas the previous bushes lasted at least 7 or 8 years

There's been no change to the way I have been using the car

I don't want to replace these with poly, so I've bought some more rubber bushes, but from a different supplier

What has your experience been?

[LLantrisant]

even nowadays metallastic bush quality could be quiet poor, i would say the drgstrount has been wrongly mounted.
wrongly? how?

the fixing nut of thestrut needs to be tightend only when the car sits back on its own wheels and the suspension has moved and settled.

if you tighten the nuts with wheels lifted, the pre-load on the rubber-bushes gets too much and they will tear-off.

this said: its the inner metal sleeve of the metallastic bush needs to be clamped properly between the chassis-brackets.

what also looks strange are the very bad welds of the brackets....even the welding-seams of TVR were sometimes not so fantastic....yours do really look like somebody has re-welded them..

Edited by LLantrisant on Monday 11th September 21:49

[ukkid35]

Good points, but not relevant in this case

I always lower the car, and settle the car, before tightening all suspension bolts

The welds are not visible as they are camouflaged by the very poorly applied POR15

I'll probably brush/peel it off and put another coat on sometime over the winter

I might even try spraying it on this time, although I doubt it will look any better

[spitfire4v8]

Why don't you want to use poly bushes ? It's one of the very few areas on a cerb where the polybush works brilliantly, virtually fit and forget and solves many of the brake judder issues that plague these cars (doesn't in itslff cause judder but a soft squidgy bush there exagerates it massively).

[paddy1970]

Rubber bushings are a softer material, providing a quieter, more comfortable ride. Polyurethane is much harder and more durable but leads to a stiffer ride and increased road noise.

The problem you described could arise from subpar quality of the rubber material, manufacturing defects, or inconsistent rubber composites could all contribute to the premature failure of the bush. Even reputable suppliers may sometimes experience issues with quality control.

[spitfire4v8]

paddy1970 said:

Rubber bushings are a softer material, providing a quieter, more comfortable ride. Polyurethane is much harder and more durable but leads to a stiffer ride and increased road noise.

That's maybe true for the vast majority of production car rubber bushes, but have you actually seen how much rubber is in a typical tvr bush? There's many lower shore poly bushes which are actually more compliant than the std tvr rubber bush (superflex for example make a range of shore hardness) . Also fitted and maintained correctly a poly bush is lower in rotational resistance than a bonded rubber bush, so ride quality often actually improves.

[ukkid35]

spitfire4v8 said:

Why don't you want to use poly bushes ? It's one of the very few areas on a cerb where the polybush works brilliantly, virtually fit and forget and solves many of the brake judder issues that plague these cars (doesn't in itself cause judder but a soft squidgy bush there exaggerates it massively).

I'm very circumspect about where I fit poly bushes

Generally I like to stick with rubber bushes, unless there's good reason not to, the obvious example being the rear diff bush, I also use them on the ARB mounts

However I'm not comfortable using them where the bush is designed to absorb some shock loading, because if they are absorbing less of the shock then something far more expensive is likely to be doing so

I will bear in mind what you are saying about the drag strut bushes, but since I've already bought some new rubber ones, I'm going to fit them first

Thankfully the only time I've ever experienced brake judder on my Cerb is after fitting brand new discs; the judder disappeared as soon as I put some used discs back on, the new ones clearly weren't balanced

[Jhonno]

paddy1970 said:

Rubber bushings are a softer material, providing a quieter, more comfortable ride. Polyurethane is much harder and more durable but leads to a stiffer ride and increased road noise.

Not entirely true.. Especially on smaller rubber bushes. Also the issue with "stiffer ride" from poly bushes comes from friction, not stiffness of material. You can also get various grades of rubber and poly bushes, some poly bushes are actually pretty soft.

Suspension systems are complicated, poly bushes aren't always bad, or noticeably affect ride quality etc.

[SlimJim16v]

What about the crack in the arm?

[Jhonno]

SlimJim16v said:

What about the crack in the arm?

I think that is a shadow from the lap plate they have on them.

[ridds]

spitfire4v8 said:

Why don't you want to use poly bushes ? It's one of the very few areas on a cerb where the polybush works brilliantly, virtually fit and forget and solves many of the brake judder issues that plague these cars (doesn't in itslff cause judder but a soft squidgy bush there exagerates it massively).

This.

Poly here and on the Diff mounts. Rubber elsewhere imho.

The drag links take huge loads when driven hard, mainly braking.

[LLantrisant]

with very light cars, like lotus 7´s and their derivates or Sylva /Fisher the metallastic bushes were even parts of the suspension design:
(with sylva the rear trailing arms of the live-axles for example)

the restoring-force of the bush after beeing under load was used to assist the rebound of the supsension (coilovers)

Edited by LLantrisant on Thursday 14th September 20:53

[Jhonno]

LLantrisant said:

with very light cars, like lotus 7´s and their derivates or Sylva /Fisher the metallastic bushes were even parts of the suspension design:
(with sylva the rear trailing arms of the live-axles for example)

the resorting force of the bush after beeing under load was used to assis the rebound of the supsension (coilovers)

Generally the forces created by rubber bushes are very small though.

[LLantrisant]

https://forum.etypeuk.com/viewtopic.php?t=2212&amp...

a good read abut metalastik vs poly

[ukkid35]

So how does a Powerflex bush work in the drag strut?

Does it rotate on the inner sleeve?

Does it rotate within the drag strut? Or is it fixed?

If it's fixed, what is the correct way to fit it? Do you need a press (or vice)?

[Basil Brush]

ukkid35 said:

So how does a Powerflex bush work in the drag strut?

Does it rotate on the inner sleeve?

Does it rotate within the drag strut? Or is it fixed?

If it's fixed, what is the correct way to fit it? Do you need a press (or vice)?

It should be a tight push fit into the drag strut and rotate on the inner sleeve.

https://www.powerflex.co.uk/product-details/Front+...

[Jhonno]

Basil Brush said:

ukkid35 said:

So how does a Powerflex bush work in the drag strut?

Does it rotate on the inner sleeve?

Does it rotate within the drag strut? Or is it fixed?

If it's fixed, what is the correct way to fit it? Do you need a press (or vice)?

It should be a tight push fit into the drag strut and rotate on the inner sleeve.

https://www.powerflex.co.uk/product-details/Front+...

This.

Which is where poly bushes *can* reduce ride quality as they have friction vs. a frictionless rubber bush twisting. However, in the drag link application you will be very unlikely to notice a degradation.

[LLantrisant]

ukkid35 said:

So how does a Powerflex bush work in the drag strut?

Does it rotate on the inner sleeve?

Does it rotate within the drag strut? Or is it fixed?

If it's fixed, what is the correct way to fit it? Do you need a press (or vice)?

on all poly´s, as well as the metalastik, the inner sleeve is tightly clamped between the chassis-brackets.
therefore the sleeve is always longer*

while the metalastik is rubber vulcanized onto the sleeve, therefore the moevement of the strut /wishbone is fully going into the rubber (torsion), the poly is rotating over the sleeve, so with poly´s the sleeve is the pivoting-point.

• some wishbones /strut-eyelets are too wide or the poly´s not made in correct size for the application, so once the standard poly-bushes (which often come into 2 halfs) are fitted, they are wider than the inner sleeve and will fail.

Edited by LLantrisant on Friday 15th September 12:45

[mrniceguy351]

Are these the type of rubber bushes you have to remove with a blowtorch?

[ukkid35]

mrniceguy351 said:

Are these the type of rubber bushes you have to remove with a blowtorch?

I've replaced every bush on the car, the only one that is really tricky is the rear diff bush

I've not had to use a blowtorch once