frans
Rover Rookie
Posts: 61 
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Post by frans on Oct 8, 2017 20:39:13 GMT
only 2 years ago both Y-bushes of the rear suspension blades were renewed and properly mounted. Now preparing for German TÜV (MOT) I lifted the car and discovered that the bushes on both sides were teared off. What went wrong??? Frans Attachments:
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Post by enigmas on Oct 8, 2017 23:36:00 GMT
only 2 years ago both Y-bushes of the rear suspension blades were renewed and properly mounted. Now preparing for German TÜV (MOT) I lifted the car and discovered that the bushes on both sides were teared off. What went wrong??? Frans My guess Frans is that a shear load was placed on the 'bushes'when they were fitted. Ideally there should be no shear loads when the car is sitting at rest on the ground. Suspension movement adds shear loads fore and aft to the bush. So at rest they should be setup for neutral 'shear' load. There will be compression loads (due to vehicle weight) but this another factor. You may have to slot the mounts to obtain a neutral shear load (at rest) on the bushes. The bushes will eventually take a set (develop a memory)...so ensure that once in place they are not moved again or disturbed. Changing a spring set alters things! PS. How did you lift the car ? (Hopefully by not jacking the car under the body so that the rear end hangs off the bushes) |
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frans
Rover Rookie
Posts: 61
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Post by frans on Oct 9, 2017 4:29:12 GMT
only 2 years ago both Y-bushes of the rear suspension blades were renewed and properly mounted. Now preparing for German TÜV (MOT) I lifted the car and discovered that the bushes on both sides were teared off. What went wrong??? Frans My guess Frans is that a shear load was placed on the 'bushes'when they were fitted. Ideally there should be no shear loads when the car is sitting at rest on the ground. Suspension movement adds shear loads fore and aft to the bush. So at rest they should be setup for neutral 'shear' load. There will be compression loads (due to vehicle weight) but this another factor. You may have to slot the mounts to obtain a neutral shear load (at rest) on the bushes. The bushes will eventually take a set (develop a memory)...so ensure that once in place they are not moved again or disturbed. Changing a spring set alters things! PS. How did you lift the car ? (Hopefully by not jacking the car under the body so that the rear end hangs off the bushes) |
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frans
Rover Rookie
Posts: 61
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Post by frans on Oct 9, 2017 4:32:02 GMT
My guess Frans is that a shear load was placed on the 'bushes'when they were fitted. Ideally there should be no shear loads when the car is sitting at rest on the ground. Suspension movement adds shear loads fore and aft to the bush. So at rest they should be setup for neutral 'shear' load. There will be compression loads (due to vehicle weight) but this another factor. You may have to slot the mounts to obtain a neutral shear load (at rest) on the bushes. The bushes will eventually take a set (develop a memory)...so ensure that once in place they are not moved again or disturbed. Changing a spring set alters things! PS. How did you lift the car ? (Hopefully by not jacking the car under the body so that the rear end hangs off the bushes) |
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frans
Rover Rookie
Posts: 61
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Post by frans on Oct 9, 2017 4:36:57 GMT
Many thanks for your recommendations! In particular the PS! I am afraid the car has been lifted under the body and obviously torn off the bushes! Must see how to lift the car and avoid this problem! Frans
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Post by Phil Nottingham on Oct 9, 2017 8:18:44 GMT
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Post by johnwp5bcoupe on Oct 9, 2017 9:14:10 GMT
Under the spring shackles Frans so you lift the car on the Axle
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Post by cyf on Oct 9, 2017 11:21:52 GMT
I have to take a look at mines because since the car is on the road again, I noticed a noise coming from the back not always, it's most audible a low speed when there's road imperfection or when accelerating.
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Post by cyf on Oct 9, 2017 17:22:02 GMT
You then mean that it's no more possible to get Y bushes that will last at least more than a few years?
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Deleted
Deleted Member
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Post by Deleted on Oct 10, 2017 9:59:01 GMT
The replacements aren't really fit for purpose and hardly good value at what seems a high price.Its possible to use engine mounts but they too seem of poor quality compared to those available some years ago and in most cases various mounts have been combined and turned into a 'one size fits all' mount so that the replacements aren't even the same size as the originals.
There are makers of rubber cotton reel type mounts in this country,I intend buying some one day. I started a conversation with one firm and they can supply mounts that might do the job in terms of strength and stiffness but only experiment will tell how long they last.
For what ever reason we can't match the durability of the originals,what a sad state of affairs.
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Deleted
Deleted Member
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Post by Deleted on Oct 10, 2017 10:56:31 GMT
Since posting I have found a mounting that I bought a while back.I'll test it to see what load it can take but of course only time will tell what the long term effects the altering compression/shear forces have on the rubber itself.
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Post by velvet on Oct 11, 2017 18:05:23 GMT
I used some engine mounts when i sorted my bushes out and that was 1989.   |
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Post by Phil Nottingham on Oct 11, 2017 18:45:00 GMT
I used some engine mounts when i sorted my bushes out and that was 1989. So did I but the rubber these days is just not the same - this applies to new cars too. Bushes are considered consumable like disk pads/tyres etc with a short end life |
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Post by enigmas on Oct 11, 2017 21:51:13 GMT
I'm not convinced about that Phil. Poor quality rubber is more the product of the boutique reproduction industry than modern chemistry. It simply doesn't have the big stick of leverage imposed on it by the large scale auto manufacturers to ensure a quality product is produced. Our 1998 Mitsibushi Lancer coupe that has covered 270,000 kilometres, still has its original radiator hoses, engine mounts, etc, etc, (oh...it does have new sway bar bushes!) and a set of tyres that will seemingly not wear out. Companies in Oz like Mackay Rubber...just down the road from me, still manufacture quality components for major industries including the Defence Dept to Military specifications. |
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Post by Warwick on Oct 12, 2017 3:15:49 GMT
I've made my thoughts on this known before.
From an engineering point of view, the Contrasonic shackle is a ridiculous thing. It's being asked to do what no-one else has asked of a block of rubber. It has to endure both compression and very high shearing forces, back and forth. An engine or gearbox mount of a similar size only has to sustain reasonably constant compression, and absorb vibration. Most of them even include devices that actually prevent them being subjected to anything but small shear forces. The Contrasonic shackle was developed by Metalastic, and as far as I'm aware, only ever used on the P5 and an experimental Leyland gas turbine truck. It would have required a very different rubber formulation to survive in its intended service.
This is pure speculation on my part. Just a guess. This is what I think probably happened.
The P5 was Rover's first monocoque body.
No longer could they rely on rubber vibration isolation between the chassis and the body.
The only isolation possible on monocoque bodies was at the suspension.
Rover was obsessed with silence and smoothness. That was the nature of their clientele. Why else would you go to all the expense and trouble of adding the heavy, rubber-isolated, front subframe? People who have replaced failed old rubber subframe mounts with solid cylinders of aluminium have found no difference to ride smoothness or vibration.
But that's not so easy to do at the rear without sacrificing boot space. (The floor would probably need to be higher). The Citroen GS has a rear subframe that carries the suspension and petrol tank. It can be dropped down and removed as a complete assembly. But it's a much smaller, lighter car.
It's easy to rubber isolate the front end of a leaf spring, but thick rubbers bushes at the rear end would make a leaf spring's rear shackle a very large and cumbersome thing.
Maybe Rover approached Metalastic for an alternative to a conventional shackle, or perhaps it was the other way around.
There is a very good chance that it was designed specifically for Rover, and that non-standard rubber formulation was necessary. It wasn't just a matter of using the same formulation used in engine mounts.
P5 owners were probably not the sort of people who ventured far off the good roads. Most of the cars probably spent their time 'wafting' around city streets. The Contrasonic shackle clearly worked, and survived the probably less than strenuous service it was required to perform.
Interestingly, no other manufacturer went down that path. Probably because a well-designed leaf-sprung rear suspension with conventional shackles gives an equally good ride. The only way to do better is with coils or hydropneumatic spheres.
So I suspect that the use of the front subframe and Contrasonic rear shackles was as much about marketing as anything else.
Rover was very particular about silence and smoothness, as were their customers.
They had belatedly made the change from the veteran era chassis and body combination to modern monocoque design.
They needed some way of assuring their customers that, after finally changing to the modern body construction methods introduced years earlier by the mass-market manufacturers who built cars for the peasants, they were not sacrificing any of their legendary silence and smoothness. They could point to these extra features that set them apart from the common monocoque cars.
To support my argument, I offer another example.
Not that many years after the P5 was introduced, Toyota made its first move from being a mass producer of small cars, to one offering a large car aimed much further up market. How were they going to convince people in that market to buy a large Japanese car and pay a lot more for it than for a similar sized car from their usual competitors? Simple. Put a mirror on the showroom floor and let the prospective customer see the refinement underneath. The first Toyota Crown was built on a separate chassis with rubber isolation between it and the separate body. Did it make much difference to ride and quietness? Not really. It was a selling feature. I worked with a guy about 35 years ago who had been a Toyota dealership salesman in the 1960s. He told me how effective this was at convincing potential buyers that the Crown was a serious contender in the mid-range luxury market.
Regardless of whether the original Metalastic rubber 'recipe' has been lost in time or not, or if some of the ingredients are no longer permitted, a current day manufacturer of a Contrasonic replacement (or rebuild) will be limited to using today's rubber formulation intended for engine mounts and similar components. The manufacturing process of moulding and bonding liquid rubber to a steel substrate could only be effectively done by the manufacturer of engine mounts. And they will be restricted to using their standard engine mount formulation. It is just not economically feasible to do it any other way. If all the Rover car clubs in the world banded together and ordered a job lot of say 2,000 units, it would probably still not be enough to interest a manufacturer at a price we thought reasonable, and many of the finished units would sit on shelves around the world for years before being sold.
During my working life I've spent a lot of time in rubber industry companies. Tyre factories. Rubber hose, engine mounts, industrial belting, etc. Goodyear, Dunlop, Olympic, Bridgestone, Mackay Rubber, and a company that specializes in preparing rubber formulations for those industries. The hoppers, blending mixers and mills that prepare the powdered rubber blends for melting and moulding are huge and the process is highly automated. We are very lucky that some smaller firms are still prepared to do small runs of new or rebuilt Contrasonic shackles at an affordable price, even if they are forced to use the current day engine mount formulation.
But, as I said at the beginning. From an engineering point of view, they really are a terrible and unnecessary design.
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Post by Phil Nottingham on Oct 12, 2017 13:42:00 GMT
The contrasonics on our 72 saloon look to be original and still OK at 174k miles! They may have been replaced in its 1st 15 years but I doubt it.
The Wadhams Y bushes on our 1964 Coupe have been on since 1997 and 50K miles and still look OK
I still have a pair of NOS I bought 10 years ago for £10 which will be used as & when required as a pair
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Deleted
Deleted Member
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Post by Deleted on Oct 13, 2017 9:09:26 GMT
Apart from the insulation from vibration aspect the contrasonic bushes altered the spring rate. (probably not enough to make any real difference)
I had a few hours playing with the mount I found,Its about the same size as the engine mounts others have used to replace the Y mounts. In the rovers case it is at an angle so under shear and compression,I tested the one I have loaded under shear but I could only test it to 150Kilo. I intend making up a dummy rover rear end using an old Y unit and a 8 ton digger as a load with a five ton jack.
On a more sensible level,I have asked the maker for the technical specs.
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Post by petervdvelde on Oct 13, 2017 12:16:51 GMT
Every time i go to the MOT test, the same mechanic always makes a remark about this silly construction but i never had problems with sheared mountings so its can't be too bad although it looks silly.
Some time ago i had a look at these mountings and thought it should be possible to make a shackle construction for this without modifying the body.
If you make a V-shaped brackets which can be attached to the body and weld a piece of pipe to this bracket for the shackle rubber bushes and make another bracket which bold on the springs with also such a pipe for the shackle rubbers then you should be oke.
Depending on the length of the shackles, this bracket could be fitted to the top or bottom of the spring.
I looked at Land Rover parts as some have leaf springs with shackles. The pipe where the rubber bushes go in has a critical dimension and could be difficult to find but one could buy some Land rover chassis repair pieces and buy bushes and shackles as Land Rover parts are very cheap and in identical weight region as our Rovers.
I will look into that deeper ones my Y-bushes fail. i won't be buying new ones.
Peter
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Post by cyf on Oct 13, 2017 17:30:21 GMT
very interesting as ever
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stef
Rover Rookie
Posts: 45
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Post by stef on Oct 14, 2017 8:25:31 GMT
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Post by Warwick on Oct 14, 2017 10:26:24 GMT
Apart from the insulation from vibration aspect the contrasonic bushes altered the spring rate. (probably not enough to make any real difference).... Another task that's best left to a component well designed for the job .... the hydraulic shock absorber. ... Some time ago I had a look at these mountings and thought it should be possible to make a shackle construction for this without modifying the body. .... Peter, you might find this old post of Vince's interesting. roverp5.proboards.com/thread/6160Scroll down through the photos. |
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Post by johnwp5bcoupe on Oct 14, 2017 15:12:19 GMT
My only concern using shackles would be axle windup? may need anti tramp bars?
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Post by petervdvelde on Oct 14, 2017 21:25:16 GMT
Apart from the insulation from vibration aspect the contrasonic bushes altered the spring rate. (probably not enough to make any real difference).... Another task that's best left to a component well designed for the job .... the hydraulic shock absorber. ... Some time ago I had a look at these mountings and thought it should be possible to make a shackle construction for this without modifying the body. .... Peter, you might find this old post of Vince's interesting. roverp5.proboards.com/thread/6160Scroll down through the photos. Thanks Warwick, I remembered that thread but this involved modifying the body by welding a plpe into the the "chassis" and cutting off the the brackets for the Y-bushes. i guess it should be possible to make a reversible system using the shackles.Peter |
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Post by Warwick on Oct 15, 2017 1:09:06 GMT
My only concern using shackles would be axle windup? may need anti tramp bars? You're probably right John. Many of these cars will be driven very differently these days from the way they were when they were current models. Can't imagine a 1960s chauffeur or bank manager doing anything that would be likely to induce axle trap. |
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Post by djm16 on Oct 15, 2017 3:46:45 GMT
"Can't imagine a 1960s chauffeur or bank manager doing anything that would be likely to induce axle trap."
Then you should watch "The Man Who Haunted Himself".
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