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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.

Mounting the front springs on the TC chassis

29 Sep

In the August issue of TTT 2 we looked at modifying aftermarket front springs, including the desirability of bushing them at the front ‘eye’ and rounding off and chamfering the edges. This article looks at mounting the springs to the chassis and suggests a material specification for the shackle pins as well as giving dimensions of the pins and the bushes.

Quoting from the Instruction Manual, “The front ends of the springs are attached to the front end of the chassis by hardened steel suspension pins, which run directly in the spring eyes, being lubricated through grease gun nipples fitted in the outer ends”

At this point the reader may find it useful to look at a couple of photos to illustrate the text.


Photo 1: Chassis stamping for TC0750

The above photo serves two purposes. If you enlarge it you will be able to see that whoever was stamping the chassis numbers at Abingdon in May, 1946 must have had a momentary lack of concentration having not realised that he had already stamped all of the 0740s. The ‘4’ is just about visible “behind” the ‘5’, if you see what I mean.

However, the main point of the photo is to show the front mounting point for the spring. The hardened steel pin goes through the hole in the chassis dumb iron (or knuckle), through the spring ‘eye’ and screws into the threaded portion of the front chassis cross tube. The following photo (photo 2) shows the pin which has been passed through the spring eye. Note the tab washer which locates between the ‘nibs’ on the chassis front knuckle (see photo 1) with the other tab being bent over the ‘nut end’ of the pin.


Photo 2: Hardened steel pin and spring eye

A spare pin and tab washer (but not the grease nipple!) can be seen in the second photo; the pins I have are made from EN351 steel, case hardened and ground, the tab washers I keep have been laser cut and cost £0.70 each, compared with £3.60 each charged by MOSS Europe.

The diameter of the pin is ½” and the overall length is 3.569 inches. The pin should not be over tightened as it acts as a pivot for the spring.


Photo 3: Front spring rear shackle plates and shackle pin assembly


Photo 4: Tube in chassis that holds the top shackle pin along with its two bushes

The drawing of the rear shackle assembly above has been scanned from the TC Instruction Manual.

The suspension arrangement for the rear of the front spring is a little more involved, albeit, quite straightforward. If you refer to photo 3, the top shackle pin (shown without its bushes) is inserted (with its two bushes) through the tube in the chassis shown in photo 4. The bottom shackle pin is inserted (with its two bushes) through the ‘eye’ of the rear spring. The top and bottom shackle pins are then joined by shackle plates – one on the outside (as you look at the car) and one on the inside.

With the help of the photos above we can now put the jigsaw puzzle together. The front ‘eye’ of the spring is offered up to the space between the two sides of one of the chassis dumb irons, the tab washer is held in place with one of its tabs located between the ‘nibs’ at the side of the dumb iron and the pin is pushed (normally with a twisting action) through the hole in the tab washer, through the first side of the dumb iron, through the spring ‘eye’ and through the second side of the dumb iron until it locates the threaded insert of the front chassis cross tube from when it can be screwed in and tightened.


Photo 5: shackle pin and bushes inserted in the rear ‘eye’ of the front leaf spring – a spare shackle pin and 2 bushes also shown


Photo 6: The shackle plates

DIMENSIONS FOR FRONT SHACKLE PINS AND SUGGESTED MATERIAL SPECIFICATION

The overall length of the front shackle pins is 3.33 inches. The critical length is the measurement between the shoulders, which should be 1.75 inches. This leaves 1.58 inches for the threads on both sides of the pin, so 0.79 inches each side. Of the 0.79 inches, 0.615 is threaded (7/16 BSF) and 0.175 is left unthreaded (these latter two measurements are the best I could get and may be slightly different). The diameter of the pin between the shoulders is 0.5 inches and 0.434 inches at the unthreaded portion.

The pins I keep are made from EN19T. Originally they were lightly plated but mine aren’t – the manufacturer recommends a liberal application of grease or copper-slip before assembly.

KEEPING THE SHACKLE PINS PARALLEL

The tube in the chassis which takes the top shackle pin measures 1.5 inches across (and is 0.875 inches in diameter), however the rear ‘eye’ of the leaf spring which carries the bottom shackle pin is only 1.25 inches across. To keep the shackle plates parallel a 0.125 inch ‘washer’ is brazed to one end of the shackle pin (see photo 6). It would have been helpful when taking photo 6 to have placed the shackle pins the other way around so that the thicker ends were at the bottom (as they are when fitted to the car). Sorry about this!

THE SHACKLE PIN BUSHES

The original bushes were made by Harris Flex and were patented. A couple of these original bushes, which were removed from TC0750 are shown in the photo below.

There are two different part numbers for these rubber bushes:

ACA 5242 (a BMC part number, I believe) is the bush (one of a pair) which goes through the tube in the chassis (see photo 4). The Harris Flex part number is CW8505. Part number 99557 is the bush (one of a pair) which goes through the rear ‘eye’ of the leaf spring and is used for the rear ‘eye’ of both front and rear leaf springs. The Harris Flex part number is CW719.

The chassis tube bushes should measure 0.75 inches in length from inside the flange – the thickness of the flange should measure 0.125 inches. The spring ‘eye’ bushes should measure 0.625 inches in length from inside the flange – the flange (thickness) should measure 0.125 inches.

Bushes are available commercially both in rubber (the original spec for these bushes) and in polyurethane. Polyurethane is the way to go, since I am told that the rubber bushes “do not last five minutes”. As long as I can get a favourable price, I am going to have moulds made for these bushes and also for the large bush on the lower shackle pin at the rear. An added bonus is that ACA 5242 fits the rear ‘eye’ on the rear TD/TF leaf spring.

© JOHN JAMES September 2010

Front Leaf Springs on the TC

2 Jun

The title of this article is specific to the TC but the application is generic to front leaf springs on the beam axle cars.

The original front springs on the TC were made by Brockhouse Berry of Manchester. Fortunately, TC0750 (‘The Vicar’s Car’) still has the original front (and rear) springs, so it has been possible to examine them really well.

The first observation is “they don’t make ‘em these days like they used to!” Take a look at the rear of the spring which takes the bush and shackle pin:

Notice how the ‘eye’ is formed in the original spring (‘eye’ on right) compared with the modern manufactured spring. The ‘eye’ of the original spring is perfectly round; modern replacements can be out of round.

Now take a look at the front ‘eyes’. Admittedly this is not the best of ‘shots’ but I can assure you that the ‘eye’ on the right (which happens to be a re-manufactured J2 spring) is distorted, whilst the ‘eye’ of the spring on the left (from TC0750) is round:

The other obvious difference is in the finish to the ends of the leafs. Modern re-manufactured spring leafs are cut square at each end so that there is a tendency for the leafs to “dig in” to each other as they slide. The leafs on the original springs are very nicely rounded and chamfered to avoid this happening.

So where does this leave the beam axle owner who wants some good quality springs?

Well, you can ask some questions of your spring supplier. You can ask what material has been used for their manufacture. EN45, a silicon-manganese-carbon alloy steel, is a recommended steel for suspension springs. You can also ask where they have been made. If the ‘eyes’ on your springs are out of round, particularly the front ‘eye’ so that the front pin is not a good fit in the ‘eye’, you have every right to send them back and get a refund.

A recent project which I have been involved in with Eric Worpe has been arranging for the manufacture of new front main leafs for the TC. Eric has been very much the driving force behind this project and has done most of the work.

We figured that if ‘out of round’ is an issue with modern replacement springs, then wouldn’t it be a good idea to get the front ‘eyes’ made oversize 5/8” instead of ½” internal diameter so that a bronze bush could be pressed in and reamed to the standard ½” standard size?

We ordered some SAE 660 bronze to make the bushes and five pairs of TC front main leafs. The chosen spring maker (Brost Forge, Unit 7, 149 Roman Way, LONDON N7 8XH – Telephone 020 7607 2311) has been in the business for a good number of years and has a working proprietor.

We also ordered a pair of complete front springs and these have been used as demonstration springs for this article.

At this juncture it is worth pointing out that the fitting of replacement main leafs is not worth it and certainly not recommended if the rest of your leafs are badly worn or sagging.

You will have noted my use of the plural “leafs”. Yes, I know that the plural of “leaf” is “leaves”, but this does not ring true to me in the context of leaf springs. Yes, I can sweep up leaves from the trees in the Autumn (the Fall) but I cannot lay out “leaves” of a leaf spring to photograph them.

One more piece of information before I forget; Brost Forge has a good size drawing of a TC front spring and also one of the original front springs from TC0750 to act as a reference.

Many new springs come bound up with paint, which has seeped in between the leafs and dried up solid. This alters the dynamic characteristics of the spring, resulting in an even harder ride and increased stress on the suspension. This should be rectified as follows:

We start by dismantling the spring; you’ll need to carry out this task whether or not you buy a new spring with oversize front ‘eye’ from Brost Forge. That is to say, if you buy a new spring, it needs to come apart – or if you are using your old spring it also needs to come apart to fit the replacement main leaf. The photo below shows the spring in the vice and the clips being bent back:

The next task is to run a 16mm HSS Co. milling cutter through the eye of the oversize scroll of the main leaf, truing it up to accept the press fit of the bush. Care must be taken to avoid opening out the spring eye by choosing the cutter direction to be the same as the ‘eye’s’ scroll:

It is now time to make the bronze bush and the top two ‘shots’ (overleaf) show it being made using the lathe. The bush is made to have an interference fit in the ‘eye’s’ scroll of about 0.4mm, so an outside diameter of 16.4mm (+0.1mm. -0.0mm) should be aimed for.

Then the bush needs to be pressed into the ‘eye’ of the oversize leaf, where it should deform to the shape of the scroll and then reamed to suit the fit of the front pin (1/2”):

Work can start on the leafs. The first operation is to round off the square ends and form a small bevel on the upper contact surface of each leaf:

When the work with the angle grinder has been completed and all the square ends have been nicely rounded they can be painted with Galvafroid (a zinc based paint) as in the photo below. This is a messy job, but well worth the time spent as the leafs will now be protected from rust:

The edges of the leafs and the flat areas of the leafs (where they do not overlap) can be painted with some black paint (see photo below):

It is nearly time to put the spring back together, However, before so doing it’s necessary to carry out one more task. If you thought that painting the leafs with Galvafroid was messy, this is a pig of a job! You need to coat between the leafs with a mixture of graphite and silicon grease or waxoil; reassemble the spring leafs and bend over the clamps, making sure that the dimples are in alignment. The graphite lubricates the springs, whilst the silicon grease/waxoil prevents water washing away the graphite mixture.

After assembly of the springs, force some of the mixture of graphite and silicon/waxoil into any gaps between the spring leafs. Some plastic gloves should be worn as graphite is truly messy stuff.

The photo at the top of the next column shows the task almost complete with the spring clips being bent back over. I found that it was a lot harder to bend the spring clips back over than it was to bend them back in the first place.

Note in the photo above the use of tie wraps to “clamp” the springs whilst the clips are being bent back over – whatever did we do before tie wraps came on the scene?

The final two photographs show a close up of the bushed ‘eye’ and the completed pair of springs.

At the time of writing there is one pair of bushed main leafs remaining at £65 the pair plus carriage (approx. £8 including insurance). If demand is there we could probably look to supplying another five (5) pairs. Enquiries please to John James (0117 986 4224).

Due to the amount of work involved we will not be supplying complete springs.