Rear spring eye bolt bushes.

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philthehill
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Rear spring eye bolt bushes.

Post by philthehill »

A modification for possible consideration.
The standard rubber bushes fitted to the Minor springs are in my opinion not up to the standard required for the application.
Poly bushes can be fitted but the best bush for the rear spring front eye which takes care of the spring for and aft location is the Metalastic bush. The bush used is the the J4 suspension bush Pt No: FMK5138 or FMK5137 which needs to be shortened to 44.4mm. The eye pin has the shoulder cut back to 1mm below the end face of the Metalastic bush to ensure that the shortened Metalastic bush is gripped tight. The Metalastic bush has the centre steel tube so cannot be crushed.
Below are two I did for the front eye of the rear springs fitted to my Minor.
Rear spring front eye bushing..JPG
Rear spring front eye bushing..JPG (1.59 MiB) Viewed 684 times
The rear eye of the spring and the chassis bushes can also be replaced with shortened Metalastic bushes.
Fitting the Metalastic bush to the rear spring eyes and chassis rail was a common mod way back before the advent of poly bushes.

Chipper
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Re: Rear spring eye bolt bushes.

Post by Chipper »

Seems like a good idea, and I remember seeing a similar idea mentioned in the MMOC Technical Tips manual, albeit for the front eyebolt bushes.

I have fitted poly bushes to the front eyebolts of my Traveller, but the rears are still on the original (albeit replaced a few years ago) rubber items; they are probably due for replacement again, I suspect...

What makes you think they're not up to the required standard?
Maurice, E. Kent
(1970 Traveller)
philthehill
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Re: Rear spring eye bolt bushes.

Post by philthehill »

I consider that the rubber bush is too soft a material to give good service. The bush needs to be at least 60 - 70 Shore 'A' hardness to get the best out of the bush.
Having now tried a genuine Shore 'A' durometer on a selection of rubber and poly bushes the standard BMC Minor rubber eye bolt bush is hard pushed to register 60 Shore 'A' hardness; with poly bushes ranging from 72 - 85+ Shore 'A' hardness.
The Shore 'A' hardness of poly bushes does vary according to supplier. The colour has no bearing on the hardness of the bush.
A bush with a hardness of 70 Shore 'A' is more than adequate for use on a Minor.

The modified Metalastic bush can be fitted to the front eye bolt.

jaekl
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Re: Rear spring eye bolt bushes.

Post by jaekl »

What ensures that the interface between the rubber and the eye of the spring does not rotate? Stock bushings are compressed so that the rubber is clamped to the inner and outer metal, which may increase the durometer of the rubber. The rubber flexes as the suspension moves. This changes when the bushing is poly. Now there is rotation between the bushing and the metal and most likely the inner one due to the associated leverage. Metalastic bushings require the inner tube to be clamped to prevent rotation with the flexing of the rubber to accommodate suspension movement. There is minimal retention force at the outer rubber to metal interface, just whatever interference there may be and still allow insertion. There are some metalastic bushings that have rubber flanges and are halves to be clamped together, but only the flanges might be compressed. I'm trying to understand how metalasltic bushings function and ruduceing the thickness of the rubber could limit the amount of flexing. This last point could be critical for the front eyebolt and the rear spring shackles where there can be significant rotation. I agree the relatively small diameter of the torsion bar pin drives it through the bushing rather quickly. The inner sleeve of the metalastic bushing improves that situation but now the rubber is thinner. Do I recall that Marinas used metalastic? We only had the 1.8L version over here which must be much heavier that a Minor.
philthehill
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Re: Rear spring eye bolt bushes.

Post by philthehill »

When the Metalastic bushes are fitted to the rear spring eyes especially the front eye of the rear spring the angle of rotation realised by the spring eye is quite small. Therefore there is little rotational force generated that has to be resisted by the Metalastic bush rubber. There is a little more angle of rotation at the rear spring eye and chassis mount but not sufficient to cause concern.
When fitted to the Minor front suspension eye bolt the Metalastic bush rubber has to rotate through a larger angle but still does not give way or slip within the eye.
The Metalastic bush when fitted to the Austin J4 inner wishbone pivot points rotates through a larger angle than the Minor spring eye and about the same angle of rotation as when fitted to the Minor front suspension eye bolt.
The J4 Metalastic front suspension bush is a proven application as is when fitted to the Minor eye bolt and rear leaf spring eyes.
The Morris Marina/Ital has a Metalastic bush fitted at the inner end of the lower front suspension arm though the eye bolt is fitted vertically into the chassis rail.
Both the J4 suspension pivot Metalastic bushes and Marina/Ital eye bolt Metalastic bushes do not have an outer metal sleeve, the rubber part of the bush is an interference fit in the eye and suspension arm. The inner metal sleeve is stopped from rotating by being clamped between the pieces of the suspension arm.
Below (2nd picture) is a dismantled front suspension for the Minor utilising Marina/Ital components and the shortened Austin J4 Metalastic bush.
The thick and thin arms are Marina/Ital. The eye bolt is Minor. The tie bar rear fixing is Marina/Ital.
The Marina/Ital arms are the same length as the Minor but the eye bolt pin does not have the stepped shoulder as per the Minor eye bolt pin.
The Austin J4 Metalastic bush is shortened to the same length as the Marina/Ital Metalastic bush and the shortened bush is clamped between the rear shoulder of the Marina/Ital eye bolt pin and the inner face of the thin suspension arm. The Marina/Ital eye bolt pin is splined into the thick suspension arm which helps resist the bush turning.
Below - assembled.
Marina eye bolt 2.JPG
Marina eye bolt 2.JPG (1.33 MiB) Viewed 515 times
Marina eye bolt con 1.JPG
Marina eye bolt con 1.JPG (1.22 MiB) Viewed 526 times

jaekl
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Re: Rear spring eye bolt bushes.

Post by jaekl »

Yes, the front mounting of rear spring has very little movement. The stock rubber bushings hold up fairly well and even the shackle ones survive better than the torsion eyebolt because it's easier to clamp them closer to the neutral (not twisted) position. Back to the front, I think you said the rubber part of the metalastic bushing is pressed into the eyebolt AND engages the splines of the Marina cast suspension arm. However, there is relative rotation between those two surfaces, so I don't think you wanted to state that. Without a doubt the inner metal tube facilitates the assembly procedure in regards to keeping the rubber in the neutral state until tightened (clamped) with the suspension in the static position. Trying to do that with the stock rubber one was more wishful thinking than actually being successful.

In regards to the need for the outer surface of the rubber part to not rotate, I forgot about the role gravity will play. That will help keep the rubber in place. I don't see a problem when used on the rear springs. However, I do feel the reduction of rubber thickness due to the addition of the inner metal sleeve may over stress the rubber. (for the torsion bare eyebolt application) I would think the outer diameter of a metalastic bushing needs to be larger than the the diameter of full rubber bushing it replaces. Poly bushings (bearings) are a good solution without the need to change any components.

Going back to the stock design, it has its problems. Just a quick analysis reveals that the front eyebolt bushings are either way over stressed or the rear spring bushings are way under stressed. The same bushing is used in all location yet the lighter load on the rear suspension is carrier through twice as many bushings with much less flexing required. The rear shackles have a bit more movement but also less load than the front of the spring. Add the problems of properly assembling the eyebolt bushings, it's obvious they were doomed. As mentioned the ease of assembly to prevent preloaded rubber may be enough to make metalastic bushings feasible for the eyebolt, On the other hand poly bushings still have a relatively small diameter pin bearing onto the poly. Do you have any observations on the long term performance of poly versus metalastic in the higher stress front eyebolt application? It appears I've ramble back and forth hear, but I think it comes down to that last question.

There is a different issue with metalastic bushings but will not be a problem for the eyebolt but may be a problem for the front of the rear springs. Over years the metal sleeve and through bolt can rust making disassembly extremely difficult when the inner bolt MUST be removed in order to separate the components.
philthehill
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Re: Rear spring eye bolt bushes.

Post by philthehill »

To clarify:-
The Metalastic bush does not engage with the splines of the Marina thick arm. The metal tube of the bush is held tight between the head of the Marina eye bolt pin which is splined and which fits into the Marina thick arm. The rubber part of the bush does not come into contact with the head of the splined pin (or the inner face of the thin front arm).

The outer diameter of the Marina eye bolt bush is much larger but using the smaller diameter J4 bush in the Minor eye bolt does not cause any problems.

Over the years I have used various bushings for the eye bolt and spring eyes but the BMC rubber eye bolt in my opinion is the one to avoid for the reasons already quoted above.

To reiterate the above - the Austin J4 used the Metalastic bush in its independent front suspension in the same way/style and same location as when fitted latterly to the Minor. I am not aware that the J4 of ever having problems with suspension bushes.

As regards seizure of the bolt/pin going through the centre of the bush - yes it could happen but care in assembly could minimise the seizure issue. I would not recommend greasing the bolt/pin as that could compromise the ability to secure the Metalastic bush centre tube.

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