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So in my RX7 FC project, all the buses are 30+ years old and are in need of replacement.
This car will be driven on the road so its fairly important that it doesn't rattle my teeth out, but I also need it to handle as well, so I'm looking for advice on which bushes I can replace with Polyurethane and which ones I should replace with OEM rubber.
I know this is all subjective, but I'd like the thoughts of people who've done this before.
Here's my current thinking:
Polyurethane:
Roll Bar Drop Links
Roll Bar bushes
Steering Rack Bushes
Toe Links / Lateral Rods
Camber Bar
OEM:
Subframe Bushings
All bushes in the front and rear arms
Top Mounts
Any others I've forgotten
The idea with this is that the stuff that absorbs the punishment from the road is standard rubber, and the stuff that takes up once you actually turn into the corner is done by the Polyurethane stuff.
Any thoughts?
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I've just swapped out most of the bushes on a Triumph 2000 for Super Pro Polybushes, the subframe ones are still rubber though. Also went for the harder compound ones.
To keep the ride soft though the shocks were renewed but just with new OEM ones, the spring rates were also kept the same.
If it were me I'd do the same for your RX7, performance bushes all around for arms, mounts, bars etc, subframe ones in new stock rubber and a well setup plush and progressive suspension setup rather than some harsh riding compromise.
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1987 Supercharged BMW R1150 Citroen 2cv Hillclimb Monster
1995 Renault Master Mk1 Race Transporter
1994 Mazda MX5 Mk1 / NA Road Going Class Hillclimber
1991 UMM Alter II Crew Cab OM606 SuperTurbo Diesel MegaUMM Overlander
1992 UMM Alter II Station Wagon
1980 UMM Cournil - survivor - resto project
1979 Lomax 224
2014 VW T5.1 Transporter Kombi Highline
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A well known car builder (Alan Lambert) once told me that if the car in question is known to eat certain bushes i.e. Cortina Void Bushes, then Poly them. This includes most drop links etc. but if you are changing the originals after 20/30 years of use, chances are OEM are more than adequate. If that's ok for him, then it's damn fine for me.
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Last Edit: Jun 6, 2018 9:10:24 GMT by SmokeEm
96 E320 W210 Wafter - on 18" split Mono's - Sold :-(
10 Kia Ceed Sportwagon - Our new daily
03 Import Forester STi - Sold
98 W140 CL500 AMG - Brutal weekend bruiser! Sold :-(
99 E240 S210 Barge - Now sold
02 Accord 2.0SE - wife's old daily - gone in PX
88 P100 2.9efi Custom - Sold
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I always swap the suspension ones for poly.
However.
The leaf spring bushes I returned to stock rubber type as it left the rear "snap happy".
It took away the predictability of the car and I hated that.
I've recently changed to single leaf type rear springs from multileaf and fitted poly again to see what occurs.
Also (because I fitted seriously better brakes) the front lower track control arm bushes were getting hammered fast.
A known cause of vibration in escorts.
The poly bushes didnt last much longer either so I have now fitted spherical joints there.
No vibration yet.
Just my experiences.
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mk2cossie
Club Retro Rides Member
Posts: 2,976 
Club RR Member Number: 77
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I've fitted a few types of poly bushes over the years, all with good results in firming up the suspension/chassis. The only exception being a dogbone mount on a diesel Leon, buthtat settled down after a few thousand miles  My old Ford is fully poly bushed, including the front and rear subframes. It stiffened the car up nicely, but not to the detriment of the comfy ride  And I would always recommend Superflex, they may be a tad more expensive than the other brands, but the quality and ease of fitment of them makes up for it  |
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ChasR
RR Helper
motivation
Posts: 10,199
Club RR Member Number: 170
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I've fitted a few types of poly bushes over the years, all with good results in firming up the suspension/chassis. The only exception being a dogbone mount on a diesel Leon, buthtat settled down after a few thousand miles My old Ford is fully poly bushed, including the front and rear subframes. It stiffened the car up nicely, but not to the detriment of the comfy ride And I would always recommend Superflex, they may be a tad more expensive than the other brands, but the quality and ease of fitment of them makes up for it This. SuperFlex/Pro bushes are good and keep ride comfort. Not many bushes can manage improvements in all areas |
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I’ve just bought a full 4Motion (Haldex) conversion for my B6 Passat. The entire rear end (top, bottom and spring arms, trailing arms and ARB, and diff mounts) are all Powerflex purple bushes. At the moment everything up front is OEM VW, am I expecting an interesting ride? I am running KW Variant 2 coilovers, and these ride better than standard.
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Cheers for the replies.
Well you've convinced me, I'll start with Polyurethane. (Which is handy as they're easier to fit) And then go back to rubber if I'm not happy afterwards.
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On the subject of poly bushes, can anyone clarify this thought one way or the other? It has to do with fitting poly bushes into suspension arms - let's say a front wishbone on a Viva, which has upper and lower wishbones, not a Macpherson strut arrangement.
In a standard rubber bush, the centre sleeve is bonded to the outer rubber and, in some places, to an outer steel sleeve. These are an interference fit, the central bolt is tightened up with the weight on the car and the only movement of the arm is through the "give" in the rubber - that is, it does not pivot around the bolt, the centre sleeve does not (or should not) move at all.
On a poly bush, the centre isn't bonded to the poly, or at least it isn't in the Superflex ones I've used. So I tighten the bolt in the same way, so that the centre sleeve doesn't turn. But because it isn't bonded to the rest of the bush, surely that means the whole thing pivots around the sleeve, and allows much more rotation than using a standard bush?
I imagine that the way I drive my cars (very gently) probably means that I don't see any difference, but for those fitting poly for handling purposes, surely increased movement is not a good thing? Or am I missing something?
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On the original Viva bushes the rubber is only bonded to the central tube and not the outer case, we got the original Vauxhall engineering drawing to get some made, going back to poly bushes I have always tried to avoid them personally as I think they tend to move the stress and forces to different positions on the mounting points which can cause stress fractures, I have seen it happen on the Viva HB/HC range, just my opinion and I'm always happy to be educated!!
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mk2cossie
Club Retro Rides Member
Posts: 2,976
Club RR Member Number: 77
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On the subject of poly bushes, can anyone clarify this thought one way or the other? It has to do with fitting poly bushes into suspension arms - let's say a front wishbone on a Viva, which has upper and lower wishbones, not a Macpherson strut arrangement. In a standard rubber bush, the centre sleeve is bonded to the outer rubber and, in some places, to an outer steel sleeve. These are an interference fit, the central bolt is tightened up with the weight on the car and the only movement of the arm is through the "give" in the rubber - that is, it does not pivot around the bolt, the centre sleeve does not (or should not) move at all. On a poly bush, the centre isn't bonded to the poly, or at least it isn't in the Superflex ones I've used. So I tighten the bolt in the same way, so that the centre sleeve doesn't turn. But because it isn't bonded to the rest of the bush, surely that means the whole thing pivots around the sleeve, and allows much more rotation than using a standard bush? I imagine that the way I drive my cars (very gently) probably means that I don't see any difference, but for those fitting poly for handling purposes, surely increased movement is not a good thing? Or am I missing something? essentially yes, what you have there is correct. The way I see it is that although there is not bond between the bush and sleeve on poly bushes, there is a certain amount of friction at least. That and the fact that the suspension spring rate is freer to do its job means that the non bonded bush isnt as much of a difference as you expect. Although there will always be certain causes like gtviva has mentioned  |
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ChasR
RR Helper
motivation
Posts: 10,199
Club RR Member Number: 170
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It's not that simple regarding where is best.
SuperPro will design a bush differently to PowerFlex for the application, and vice versa. For me as a rule:
-If the genuine dealer bush isn't available then go Poly with someone decent like SuperFlex/Pro. Otherwise, stick with the dealer bushes. The OE branded bushes IME are now becoming more hit and miss.
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I use poly where i can for the simple reason that most come in 2 parts with a central seperate sleeve, which makes pressing them in a joy compared to a metal sleeved standard bush, and no preload needs to be set due to the separate central sleeve. My time and ease of fitment is worth the extra cost.
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Jun 15, 2018 21:18:04 GMT
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On the subject of poly bushes, can anyone clarify this thought one way or the other? It has to do with fitting poly bushes into suspension arms - let's say a front wishbone on a Viva, which has upper and lower wishbones, not a Macpherson strut arrangement. In a standard rubber bush, the centre sleeve is bonded to the outer rubber and, in some places, to an outer steel sleeve. These are an interference fit, the central bolt is tightened up with the weight on the car and the only movement of the arm is through the "give" in the rubber - that is, it does not pivot around the bolt, the centre sleeve does not (or should not) move at all. On a poly bush, the centre isn't bonded to the poly, or at least it isn't in the Superflex ones I've used. So I tighten the bolt in the same way, so that the centre sleeve doesn't turn. But because it isn't bonded to the rest of the bush, surely that means the whole thing pivots around the sleeve, and allows much more rotation than using a standard bush? It does indeed, which is why generally polybushes are detrimental to ride and handling unless very carefully engineered and fitted, or the OE rubbers have known problems. Because they rotate like a bearing they introduce a lot of friction and stiction to the system that wasn't there before, so the low speed damping suffers and becomes very inconsistant. Often they feel better out of the box simply because you're replacing knackered old bushes, and sometimes the bush sticking slightly on small inputs basically makes the suspension feel higher sprung so the car feels more responsive. In much the same way that replacing your springs with solid bar would make it feel more responsive, there are better ways. I won't use polyurethane for rotating bushes unless I absolutely have to, rubber, bearings, rose joints, fine, but only poly if I need it to have some flex and rubber won't give me enough travel. |
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ChasR
RR Helper
motivation
Posts: 10,199
Club RR Member Number: 170
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Jun 18, 2018 16:56:15 GMT
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On the subject of poly bushes, can anyone clarify this thought one way or the other? It has to do with fitting poly bushes into suspension arms - let's say a front wishbone on a Viva, which has upper and lower wishbones, not a Macpherson strut arrangement. In a standard rubber bush, the centre sleeve is bonded to the outer rubber and, in some places, to an outer steel sleeve. These are an interference fit, the central bolt is tightened up with the weight on the car and the only movement of the arm is through the "give" in the rubber - that is, it does not pivot around the bolt, the centre sleeve does not (or should not) move at all. On a poly bush, the centre isn't bonded to the poly, or at least it isn't in the Superflex ones I've used. So I tighten the bolt in the same way, so that the centre sleeve doesn't turn. But because it isn't bonded to the rest of the bush, surely that means the whole thing pivots around the sleeve, and allows much more rotation than using a standard bush? It does indeed, which is why generally polybushes are detrimental to ride and handling unless very carefully engineered and fitted, or the OE rubbers have known problems. Because they rotate like a bearing they introduce a lot of friction and stiction to the system that wasn't there before, so the low speed damping suffers and becomes very inconsistant. Often they feel better out of the box simply because you're replacing knackered old bushes, and sometimes the bush sticking slightly on small inputs basically makes the suspension feel higher sprung so the car feels more responsive. In much the same way that replacing your springs with solid bar would make it feel more responsive, there are better ways. I won't use polyurethane for rotating bushes unless I absolutely have to, rubber, bearings, rose joints, fine, but only poly if I need it to have some flex and rubber won't give me enough travel. I was under the impression the shore rating, design (taking compressing loads, preload etc.) of the bush would make a poly bush work, which IMHO alot of bush manufacturers don't do. I know on my MGB that when I changed the rear shackle bushes from new rubber to new poly (SuperFlex) it felt like a limo ride in comparison to before; the rear end felt solid much to my surprise previously. |
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Jun 19, 2018 10:00:51 GMT
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No matter what you do to itm you can't avoid the fact that you've introduced a lot more friction and stiction into the system than a flexing bush has, because you now have a rotating bearing - even F1 uses flexing joints that work like a normal road car rubber bush, rather than bearings, where they can.
You can reduce it massively with decent designs, waisted side pads, grease knurling, grooves to allow microflex, etc, but you can't get away from it, it's inherent in using the material as a bearing rather than a bush.
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Jun 19, 2018 18:01:36 GMT
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PolyBushes like all replacement / upgrade components come in a varying range of hardness and from experience quality !!
There are a few companies around i would never dream of using again and some i have had great products from.
I stumbled across a company in Luton that custom make bushes and hoses for just about anything.
I wont plug them nor will i belittle the cheap nasty bush manufacturers.
Happy to pm if you have not purchased yet. Considering how long the OE bushes have lasted, is there no way of obtaining OE bushes ?
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ChasR
RR Helper
motivation
Posts: 10,199
Club RR Member Number: 170
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Jun 19, 2018 22:23:55 GMT
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For Mazdas there are potentially. The dealers however are an absolute pain to deal with, or at least my local two were; I think luckyseven had a similar experience with the ones near him. Not even Alfa are as bad to my surprise! With my MX-5 I was lucky as you can get genuine parts from Autolink or MX-5 parts, generally cheaper than the dealer for a change and with much quicker delivery! I think the biggest issue will be if Mazda even make them now for such a rare car. There's alot to say about dealers but considering BMW, Porsche and to a certain event Mercedes & Peugeot relatively help out the older scene, both in terms of sourcing that parts and in a number of cases being reasonable, it's surprising to see Mazda not really give a damn. If someone like MX-5 Parts exists in the RX-7 world you are laughing. |
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luckyseven
Posted a lot
Owning sneering dismissive pedantry since 1970
Posts: 3,839
Club RR Member Number: 45
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Jun 20, 2018 14:23:16 GMT
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Yeah, Mazda main dealers are almost indescribably atrocious.
Racing Beat or Atkins Rotary are probably your best bet if OE is your thing. I had superb results with Energy Suspension bushes on my RX-7 which although poly don't seem obsessed with racetrack levels of rock'ardness and work well in the real world too
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kitch
Part of things
Counting his chickens
Posts: 157
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Jun 20, 2018 14:50:38 GMT
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In my experience, poly bushes don't affect NVH (Noise Vibration Harshness) all that much.
I recomissioned an AX GT a year or two ago, which had 250k miles on the clock! Needless to say most of the bushes were shagged! I replaced everything on the front end with Powerflex, with with OEM replacement dampers & springs etc. It rode beautifully, with no loss in refinement over standard parts.
I also fit a lot of TVRs I refurbish at work with Powerflex. They drive better than original.
The only area I'd be wary of is engine mounts. Poly engine mounts are a totally different story, because they're normally void bushes from the factory. Replace that with a solid lump of poly (or rubber, for that matter) and you know all about it! That said, you've got a rotary. They're so smooth I doubt you'll notice!
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