Polyurethane Bushes (At Last!)

14 Aug

Several months ago (it was either December last year or January this year) I gave a well known poly bush supplier all the data he needed to get a mould made to have some poly bushes produced.

From time to time I made the odd enquiry as to progress and frankly, was beginning to give up hope when the following reply came back to the latest e-mail enquiry:

“We should have some for you to look at next week”

True to his word the sample bushes duly arrived and here they are:

First a “history lesson”………..

For whatever reason – some say it was due to cost, others claim it was due to shortage of phosphor bronze after WW II – the excellent set-up used on Triple-M cars and the TA/TB whereby the rear end of the main leaf of each spring (front and rear spring) was located in slots in bronze trunnions, which were enclosed in housings – was discontinued in favour of shackle pins and rubber bushes.

The rubber bushes were made by ‘Harris Flex’ and were patented. I still have examples of these originals (which are rather the worse for 65 years of wear!) on TC0750 and these have proved to be invaluable in getting correct modern reproductions made.

The bush (one of a pair) which locates in a tube at the front of the TC chassis was ‘Harris Flex’ number CW8505. The part number given in the TC Factory Specification Book was 95050 “Shackle Bush -Top Ft. Sprg. Rear” (4 off). This part number was later given a BMC part number ACA5242 and this is the part number which appears in the TC Parts List.

The nominal diameter of this bush is 0.875” and the width inside the flange is 0.75”. Therefore, two of these bushes fit the tube in the front of the TC chassis. Two of these bushes also fit the rear spring eye of the TD/TF rear leaf spring as, at 11⁄2” the TD/TF leaf springs are wider that the 11⁄4” of the TA/B/C.

The bush (one of a pair) which locates in the spring eye of both front and rear springs on the TC was ‘Harris Flex’ number CW719. The part number given in the TC Factory Specification Book was 99557 and was described under the “Front Springs” heading as “Shackle Bush” (4 off) with an entry in the remarks column “Bottom – Frt. Spring, Rear” and under the “Rear Springs” heading as “Bush – shackle” (4 off) with an entry in the remarks column “Top – Rear Spring – Rear”.

The nominal diameter of this bush is 0.875” and the width inside the flange is 0.625”.Therefore, two of these bushes fit the rear eyes of the front and rear leaf springs on the TC.

One can deduce from the above that ‘Harris Flex’ bush numbers CW8505 and CW719 are essentially the same bushes, the only difference being the width of the bush, which is 0.75” and 0.625” respectively.

Fast forward to 2011 and if you look up the MOSS Europe catalogue you will find under the TA/B/C Front Suspension section, item number 45 “ACA5242”, which reads “Bush spring (standard)” and underneath there is a note which reads “Note: Lower bushes should be trimmed 5/8” shorter, prior to installation.”

The entry “Bush spring (standard)” refers to the rubber bushes, which retail at £0.55 each. The entry immediately below (still under item number 45) reads “280-625 BUSH, spring” and there is a note underneath which reads “Note: uprated polyurethane”

This bush retails at £8.15 (August 2011 price).

I have not yet agreed a final price for the bushes I am having made, but I would hope to sell them on a non-profit making basis for around half the price charged by MOSS Europe. This includes allowing for the recovery of the cost of having the mould made and assumes that this cost is recovered over 25 car sets (300 bushes) – so I need your support and would welcome expressions of interest!

I am not going to comment unfavourably on a commercially available bush I have inspected and measured but I make the following points about my bushes:

• the bushes I am having made are as close to the original as possible

• these bushes will be black (as original) and will have the correct wide flange at the ‘top hat’

• the bushes will be cut to size, so that they will be available in two sizes – one size for the front tube in the chassis of the TC and for the rear eye of the TD./TF leaf spring, and the other size for the rear eyes in the front and rear TC leaf springs.

Before returning to our “history lesson” I just wanted to pass comment on the note in the MOSS catalogue with reference to trimming the ACA5242 bush to fit the lower bushes i.e. the leaf spring eye. Instead of saying “Lower bushes should be trimmed 5/8” shorter” I think they should say that they should be trimmed so that the bush measures 5/8” – not 5/8” shorter.

Back to our “history lesson”………………..

The large bush (one of a pair) which locates on the large (bottom) shackle pin at the back of the rear spring location was ‘Harris Flex’ number CW8506. The part number in the TC Factory Specification Book was 99955 and was described under the “Rear Springs” heading as “Shackle Rubber, Btm. Rear Spring” (4 off). A “Washer” – material, “Hard Fibre”, part number 99956 was fitted between each pair of bushes and this was presumably to keep any moisture out.

Well that’s the end of the “history lesson”!

Just a couple more photos to show as follows:


Three of the original ‘Harris Flex’ bushes – the large one on the right is CW8506 and has picked up some rust from its housing.

The sample bushes fitted as a ‘mock up’. The sleeve at the top is there to replicate the chassis tube.

Finally, as I am writing this in the middle of August I would hope to have 100 of the TC chassis tube/TD and TF rear spring bushes and 200 of the TC front and rear leaf spring bushes available by the end of October. I shall also put in hand forthwith, arrangements for making a mould for the large bush pictured with the original bushes above.


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2 Responses to “Polyurethane Bushes (At Last!)”

  1. John McNarry 12. Sep, 2011 at 12:58 pm #

    In the last photo the thicker shackle is noticeable.. TC6338 for some unknown reason had shackles with no thickened portion. I added washers to tighten up the shackle sides to the spring eye bushes. Could you (someone) measure the thickness of the shackle or difference in thickness top and bottom.

    Thanks,
    John

    • JOHN JAMES 12. Sep, 2011 at 8:39 pm #

      John, The width of the leaf spring is 1.25 inches and the width of the chassis tube is 1.5 inches. Therefore to keep the shackle plates parallel, the thickness of the plate at the bottom needs to be an additional 0.125 inches (each side).

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