BEWARE - More Prothane Suspension Bushing Failures

I posted last year about failure of the Prothane polyurethane bushings on the upper control arms on my Series 2 E-type. This week, I noticed that 2 of the front anti-roll bar link bushing were gone! Just the steel liner remained. The D-bushings were partial disintegrated too. I can’t understand what went wrong with these. I’ve got about 1,000 miles on these. Moss sells this brand for E-types. Never again. Went back with standard rubber bushings.

That’s never happened to the brand CJ sells. The worst I can say is that they can squeak if you don’t use copious thick ptfe grease. Disintegrating like that makes me think those are vulnerable to heat or oil.

I’ve been selling polyurethane bushings for Jaguars for about 25 years. Shop use, retail, and sales to shops and retail users. Some of the Jaguar shops bought hundreds over the decades. I can’t recall a single warranty.

None of them were Prothane. Are there bad reports on the brand or is this a
more isolated issue?

Mark,

Have you reported this to the vendor? It may not get you any compensation but might save someone else from the “no one’s ever reported a problem before” line, though probably not…

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No, but I guess I should. The worst part is the rework effort to disassemble everything to put rubber parts back in. If the lower control arm bushing go, I’ll have to unspring the torsion bars…not fun!

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Please report your problem. I have done this before with other components and the vendors took it seriously. If you say nothing the vendor can’t fix the problem.

Paul

The ones that failed were not exposed to either heat or oil. The first failure was before the restoration job was complete.

I’m guessing it was a isolated “bad batch” problem, since Moss Motors sell this brand. I just got lucky… :cold_face:

I’m trying to inform them, but I’m having technical problems.

Wrong material for the job. As you can see, it’s quite brittle when cold.
kind regards
Marek

I had one Polybush lower control arm disintegrate like this after just a couple miles after rebuild. All the others were fine, or at least have been for the 25 miles or so since. It practically crumbled like sawdust. I reported it to SNG Barratt who I purchased the kit from, and polybush directly. Neither would do anything for me since the kit sat on my shelf for a year before installing as these things go. I had to buy a new individual bushing. I picked a polybush to match, but I’m weary of them for sure. Like Mark, was really annoyed to have to disassemble so shortly after rebuild. Original rubber held up better after 50 years.

Greg, what is the appeal of PU bushings?
I’ll say up-front that is a loaded question as I’ve been bench-testing and comparing PU and rubber bushings for a year or more, so far without finding a compelling argument in favor of PU.

I agree there is no compelling reason when there are high quality versions of each available. On some of the Jaguar bushes, the only available rubber bushes are unacceptable such as the lower bushes for E-Types and XJ Series1-3.
I cringe when people want an entire poly kit or something like the upper A-Arm bushes for E Series 3 or XJ Series 1-3, where the OE bushes are incredibly good. When people ask, I will give them my opinion. Some people tell me what they want because they read it on the internet or marketing material.

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Thanks for the detail.

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Right… if and when you are SURE that you’re getting true OEM bushings rather than an el-cheapo sold as “OEM”.

On the XJ sedans and XJSs the OEM supplier was “Metalastic”. Not sure about E-types.

Cheers
DD

I’ve found some of the after-market parts have slightly different dimensions for the inner sleeve, perhaps a metric near-equivalent of the original. I’ll search out some numbers and post them for others to add, correct or comment.

Who currently sells OEM E type upper lower wishbone bushes…especially as the “original” manufacturer no longer exists…the trade name has been purchased…the usual suppliers have after market or PU options as far as i can tell…Steve

When I 1st bought my s3e the bushes were shot, bought a Polybush Kit 25 (for V12 e-types), couldn’t believe how bad it was. My take on this:

Jaguar’s S3 design: Upper wishbone bushes were stiffer, for control. Lower wishbone bushes softer, for impact absorption. Such different stiffness is good, when on the ragged edge you don’t want the point of control jumping about, irrelevant to us these days but not in the days when “sports car” was about more than just the look.

Rubber bushes, there are no sliding surfaces. The outer diameter is clamped to the frame, cannot rotate, the inner diameter is bonded to a metal sleeve that is clamped to the axle, must rotate. Between these, rotational movement is by torsional flexing of the rubber. Axial movement is similarly possible, by shear loading the rubber between the outer diameter (fixed to the frame) and the inner diameter (fixed to the axle). To enable this, and also to enable the bush to rotate as above, the inner metal sleeve needs to be a smidgin longer than the elastomeric.

PU does not have the same flex/stretch as rubber; it’s a molecular structural thing. So, to accommodate the same physical movement as a rubber bush, a PU bush has to be designed differently. Otherwise, if you are simply replacing the rubber with PU of the same dimensions, you may have to limit the movement; is why, way back when PU bush upgrades 1st became a thing, the fine print was for stiffer suspensions.

ES3 upper wishbone mounts: CAC9295. I note SNGB currently sell (genuine and aftermarket) versions of the original design as well as a different design they are marketing as “uprated” which is a Polybush P/N 31Y, same as what is included in a Polybush Kit 25.

The original design imo is superb, cannot be beat, the perfect upper wishbone bush. Arguably it is not a bush at all, it’s a sleeve bearing with coated metal (self lubricated) radial and axial bearing surfaces; the meagre amount of rubber “sprayed” on the outside is merely for bedding purpose. Provides virtually free rotation and virtually zero axial movement.

In comparison the PU alternative, SNGB’s “uprated”, imo couldn’t be worse. To evaluate a bush I consider, what is the movement (radial and axial) that is required and how is this movement provided? The polybush 31Y design is basically the same as an ordinary “cotton-reel” rubber bush, except the elastomeric is PU that is only 6 mm thick which therefore, for full suspension travel, would need to elongate (torsionally twist) a lot more that the ~25% that PU can accommodate. The bush (inner sleeve) is compressed between two large steel washers, ie:

The torque required to rotate the inner sleeve against the washers is a lot less than the torque required to twist the PU. So that’s what happens; rotational movement is by the washers grinding against the ends of the inner sleeve, usually accompanied up some metal-on-metal squeaking in protest. Imo, PU doesn’t squeak. If bushes squeak its metal-on-metal, there is a problem.

Jaguars lower wishbone bushes, C8673. Imo nowhere near as perfect as the uppers. Conventional rubber “cotton reel” type bushes, sandwiched between washers C15376 and C3693/1. For inexplicable reason the inner sleeves are shorter than the elastomeric. Consequence is the flanges of the bush are compressed/clamped very tightly between the stationary bush housing and the rotating washers, with the result that the flanges shear off.

Polybush 31C are offered as uprated versions of these C8673 lower wishbone bushes. The design appears to be dimensionally the same as the original rubber C8673, including the inner sleeve being shorter than the elastomeric, as a consequence they have the same failure mode; Ted’s photo (post #10) is an example. Such failure is more likely with Polybush 31C bushes compared to the oem rubber bushes: The Polybush elongate more than the oem rubber when pressed into the housing. A consequence, depending on how this was accommodated, can be that the washers may not bear against the inner sleeve at all, the only movement interface is between the rotating washers and the stationary elastomeric flange, in which case the flanges will shear off extremely quickly.

“Depending on how this was accommodated”: Installing these bushes can be difficult, due to the extent that the bush elastomeric elongates when it is pressed into the housing. An oft tried solution is to leave out the front (non thrust) C15376 washer. Still the flanges shear off, this time due to the sculptured shape of the wishbone lever (C3201) providing recess into which the elastomeric flange then expands and is “keyed”, again forcing it to be sheared off.

Imo the best available solution for the lower wishbone bushes is the PU “top hat” design (two halves of a cotton reel) with an inner sleeve that is not bonded to the elastomeric. There is no requirement for the elastomeric to distort (twist), instead the PU forms the bearing surface within which the sleeve rotates, i.e. it is effectively an elastomeric sleeve bearing and is a solution that can only work with PU, not possible with rubber. The PU is also ideal bearing surface for the face washers to turn against, here is pic of one of mine; note that for such as these, the length of the inner sleeve is still critical:

Massive overgeneralisation about polyurethanes (“PU”) there and you need to rewrite that and refer to the specific “prothane” compound in question.

There is also nothing mentioned about how these were manufactured. The properties will vary depending on whether this is done under vacuum or not, the curing temperature and the curing time. The same basic rubber PU rubber resin can be made to have a wide variety of shore hardness by mixing in additives and “solid” suspension parts are totally different from “rubber” suspension parts, but they are both PU resins, as are PU resins that mimic glass and ABS plastic.

The mold temperature is also a variable you can play with and is critical for making thin sectioned parts. Temperature is also is important when making dimension critical components as all resin shrink, so making them in a temperature controlled oven enables them to be made “oversize” when hot, but correctly sized when cured and cold. Two different manufacturers are unlikely to be using exactly the same PU compounds or the same process, so talking about “Prothane failures” is very different from talking about all polyesters and all polyurethanes. You need to look at the datasheet for the specific PU compound before coming to any conclusions.

That’s just my take on this after twenty years in the rapid prototyping business.

kind regards
Marek

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Good description on the E S3 upper bushes. The one thing to add is those are the same as XJ Series 1-3 and XJS upper bushes. XJ40 uppers are also the same part number up to VIN 594575. Extremely good design and one you never want to exchange for any poly bush.