Date: Tue, 19 Dec 1995
Subject: As promised: "Making Them Stop"
TRIPLE-M CARS: MAKING THEM STOP.
Mike Allison 10/95
Achieving proper and effective braking on MMM cars is all about reducing friction in the wrong places, which ensures the minimum effort in obtaining friction at right time. A disciplined approach should result in good brakes, but please, do remember that this is relative to the performance factors of the period in which the car was built... no way will the car stop like a modern servo-assisted disc brake system!
When driving a MMM car it should always be borne in mind that the style of driving in the thirties was quite different from the way people are taught now. Normally driving was done using the throttle only, and down shifting gears when descending steep hills. Brakes were only used for stopping in emergencies. When parking the car it is also wise not to lock on the parking brake, but to leave the car in gear, this will delay the over-stretching of the cables which results in poor braking performance.
How do we set the brakes up in the first place, however? As already indicated, we are aiming to reduce friction to a minimum, so the following points are carefully attended to:
1. Assure that all cables are running as freely as possible with no binding or kinks. Also make sure that cables are not fraying. Next insure that all pivot bushes have no sideways movement, but allow the camshafts to turn freely.
2. Assure that the hand lever and foot-pedal return to the "off" position quickly by the action of their return springs only.
3. Obtain and have bonded-on a soft lining to the shoes. Bonding is preferable to the original rivets as it always results in a concentric fit, and offers a small increase in effective lining area, which is useful. Furthermore, the linings are less likely to crack at the rivet holes if there are none!
4. Drums must be concentric to their 8" or 12" diameter, plus no more than 0.010". If the drums have been turned ("skimmed" in English!) they can be returned to original diameter by metal spraying with a suitable carbon steel, and then grinding to the correct diameter.
5. Use engineer's blue on the drum to check the contact of the shoe. I do this by adjusting the brake to a slight "rub" using the backplate adjuster nuts, and filing the high spots off the lining until a contact of 85% or better is achieved. Naturally if the linings contain asbestos, precautions should be taken not to breathe in the dust: a face mask should be always be worn when filing or grinding!
6. When the preliminary work is finished we can proceed with the final adjustments:
7. If you have got everything right, it should be possible to lock all four wheels simultaneously from 30 mph. Minor adjustments to each backplate adjuster will correct any faulty application.
8. It is essential to ensure that oil is prevented from entering the rear drums. To replace the original cork seals which are seldom effective, I press into the end of the axle case a small seal, an inch and one eighth OD, one inch ID and 0.125" thick, which I can supply from stock if you cannot get them locally. they are currently GBP6.59, but bulk discounts can be arranged. The end of the axle case will need machining to accept this seal, but once fitted these are most effective I have tried so far.
9. Rear axle failure is common with Triple M cars. Crown wheel (ring gear) & pinions are none too strong, but we are now able to supply new ones at a price. Axle half shafts are also known to fail, but I can supply stronger ones from stock, made in a 80/85 ton steel. . . the Magnette ones also fit TA through TC!
[Mike was very clear about having your drums be the right inside diameter, ie. no drum turning. Also, all this may just be academic, as you see in paragraph two, they never used the brakes anyway! Mike can be reached at: CRG Engineering, FAX +44 (0) 1491-874382]
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