Afternoon all, I am thinking of polybushing the front suspension when I get to overhauling it and wondered about the pros and cons. Has anyone on here done this and what do you think of it. I believe the steering rack is a good candidate. Also can anyone recommend suppliers. Thanks

 

Generally I think that for the the rack bushings they are a must, and everywhere else should be avoided.

 

Brinny
If you are thinking about the top wishbone bushes, then there is no point. The top bushes OEM are an extremely good design, do not wear very fast, and are very easy to change anyway.
As to the bottom bushes, which on a V12 anyway, are a total pain to change, I cannot see the advantage of poly. I actually bought a set when I did my rebuild, forget the brand but a very high quality set, top brand. First they did not fit, as the "top hat" ends were too wide to fit between the wishbone and the subframe. Secondly I found out that they would not last nearly as long as the OEM Metalastics, thirdly they might well squeek! This latter can be held at bay by using special grease on assembly; BUT once the squeaking starts you have no option but to did-assemble to regrease. Some people have tapped the inside and grooved the outside of the poly so as to provide a few "valleys" for the grease to stay in, and this does work.
Having said all that, as long as genuine Metalastics are used, they will last for 10 years and maybe 25! There is no handling advantage and a likely increase in harshness. So my view is I do not think it is worth the bother.

 

Does the quality of the OEM style lower wishbone bushes vary?
I need to get some for my rebuild - The ones removed from the car did feel very soft & deteriorated & tore easily.

 

I'll say! Knowing no better I bought some own brand ones from a usually very good aftermarket supplier, and they fell apart in 3000 miles, not just a bit, completely, as the photo shows. Metalastic only. David Manners have them, for example.

 

That looks melted. I wonder if friction causes heating, as it can't turn freely.

 

Advice heeded. What about the steering rack?

 

My suggestion would be sports bushes for the rack. 2x CBC9107 and 1XCAC1635. These are fitted on my XJRS and l cannot fault the steering precision.

 

Absolutely 100% agree. JaguarSport bushes are still available, they are expensive (you need two one each side and one normal bush will do it) but last forever, give great feel and are not harsh.

 

No that is just the rubber material being unable to withstand the forces involved on corners. The bushes do not turn, the rubber is meant to be able to move, (ie give) the few degrees necessary without tearing, squashing out or delaminating.
What is VERY important is to tighten the nut on the pin ONLY when the car is on its wheels, then put in the split pin, so the wishbone is in its normal position.

 

I have poly in the upper front wishbone and I would avoid them, I will be removing them, rack bushing they work well.

 

Why? What brand are you using? I'm asking becasue I've installed poly uppers on many cars, including a few car for other drivers with good results. Conversely the OE upper front control arm bushes developed slop after a few thousand miles. Road conditions around here make quick work of them.

 

You're misunderstanding my point. Normal bushes are able to give (shear) to allow rotational movement of the arm. Poly ones are much stiffer, and hence might not shear, but rather might rotate in the outer diameter - creating lots of friction, and heat.

If they weren't rotating, they wouldn't squeek.

I have seen polyurethane get too hot and it looks just like that.

 

So the consensus is OEM metalastik for everything EXCEPT quality polybush for steering rack & anti-roll bar? What about the front subframe mounts?

 

Poly bushes do rotate, in the XJS lower wishbone application about the steel inner, totally agree they are apt to squeak.My collapsed ones were not poly, they were "OEM-style" non-OEM, non-metalastic, parts from a normally reputable supplier.

 

Pretty much, except I think the JaguarSport rack bushes, as mentioned by Baxtor above are even better. I have an idea, could be wrong, that Poly will not withstand any oil leaks that well. Certainly the correct heatshields are essential if you fit them, as heat will do them in. The subframe mountings, front and back: Metalastic too.

 

From Downunder, where the roads are unsealed, corrugated, large dust holes (Wombat nests), and generally Un-Jaguar style.

I use Poly on the rack and the sway bar "D ONLY.

Tried Poly on the top wishbones, NAH, too harsh for ME.

Metalastic only everywhere else. Genuine, even Dealer purchased (God forbid), but the amount of work to re-do, is just dumb.

I use rubber (Holden spec) for the sway bar links, Poly will cause the threaded section of the Hex pin to snap off.

I did use the OE "foamy" top shocker bushes originally, but they only lasted 2 trips to the Pub, so I staggered around at work and found suitably sized rubber top shocker bushes, Mitsubishi I think, and they have lasted 10 years, whoopee. Poly here CAN cause the shocker tower holes to crack out, OOPS.

Tail end: Genuine ONLY, no exceptions.

Trans mount centre "cotton reel", ONLY Poly.

Engine mounts, Rubber when and if needed, usually the LH side 3 to 1 for the RH side. First sign is the aircleaner tapping on the bonnet, LH mount split, again.

Other markets, better roads, different drivers, will all have their our specials, BUT, there is nothing wrong with the way it was made from the go get, apart from the rack mounts.

 

According to this chart, polyurethane gets the top rating for engine oil. But so does Nitrile, and some other synthetic rubbers.

Rubber Chemical Resistance, Rubber Chemical Compatibility, Page 5 - Mykin Inc

I don't know what kind of rubber Metalastic bushings use. Does anyone know?

 

Oil leaks on a V12, do they???????, mine dont.

Anyway, any oil leak from the engine should not reach the suspension, BUT, the 2 EXCEPTIONS are the trans cooler hoses above the alternator, and they will lubricate the alternator, and the inner lower wishbone Metalastic bushes, OOPS.

The LH side will get lubed from the "dunny brush" power steer cooler and its hoses, oops again.

Those oil lines are GONE on all mine, so no leaks, and the suspension is DRY.

Metalastic is a rubber compound and steel bushing. We see them on various makes of cars at work from time to time, and NOT unique to Jaguar at all.

The installation is very specific as far as final tightening of the pivot bolt/s. Get that wrong and they will last about 2 minutes.

 

I was going to order a complete poly kit, having seen a few videos of cars with the kit it rides properly compared to 40-year old OEM suspension but I might have to rethink this. Wasn't interested in retaining the boat-like handling but if poly is super harsh on the front end it may not be the best idea.

This got me thinking - has anyone ever heard of dual front shock absorbers for the XJS? I know it would probably be DIY or aftermarket thing not at all common.