International MART Equipment Ltd.
1021 Pearl Crescent; Brentwood Bay, B.C.; V8M 1G2
Phone: (250) 544-1571 Fax: (250) 544-1591
Email: imel@shaw.ca

"If you have not heard about us is because our shoes do not squeal"

CAST IRON BRAKE SHOES

BACKGROUND

In the early 1960's the fabricated brake shoe was introduced in the transit industry in North America. Prior to this date, cast iron brake shoes were the standard in transit.

The design criteria, for the new fabricated shoe, which was to be thrown away after each reline, was to be light and inexpensive.

There have been some drastic changes in the bus design and operation since the early 60's:

1. Buses are much heavier - weights went from 20,000 lbs to over 25,000 lbs, which is an increase of over 25%. 2. Transit routes are faster - average speeds have been increasing gradually. 3. Loads are heavier - better schedule planning, suburban living and high costs of city parking create heavier passenger loads a peak times. 4. Road traffic is heavier - continuous stop-and-go. 5. Automatic transmissions are now the standard - there is no retardation in an automatic transmission compared to a standard transmission.

All the above five points directly create more work and load for the braking system. What stops the bus is the friction of the lining against the drum and the tires against the pavement.

Shortly after the introduction of the fabricated shoe, disk brakes became the standard in most light vehicles, consequently no major improvements or modifications have been done on the drum type brake components in the transit industry. On the other hand, thanks to the large research work done in car racing, tires for buses have improved considerably.

The fabricated shoe has not changed its design in the last 35 years.

THE PROBLEM

In spite of the heavier work loads, the performance of the fabricated shoe would have been quite acceptable, if it was not for the introduction of non-asbestos lining in the mid 80's. The use of asbestos as a brake lining fiber was discontinued.

The transit industry went in to major shock. All brake maintenance procedures had to be revamped; brake lining to drum clearances changed from vendor to vendor; brake lining life suffered; brake lining manufacturers kept on introducing new "mixes" in the search for a better combination, at the expense of the user. The change to non-asbestos lining was legislated and the manufacturers were not ready for it, nor had enough time to do proper testing of their product. The wake of this shock wave is still felt today, 15 years later.

THE SOLUTION

The asbestos lining was very flexible and used to conform to the fabricated shoe in spite of any deflections and/or distortions. The non-asbestos linings are made out of synthetic fibers such as kevlar and fiber glass; they are tough, or probably tougher, than the asbestos lining, but they are extremely brittle. Non-asbestos lining does not allow for deflection as it will crack.

Two other large problems were introduced with the non-asbestos lining: noise - a brittle lining will increase the braking noise, and, heat dissipation - heat tends to flow "in" the brake components, affecting the wheel bearings and the tire beads in contact with the wheel rims.

There have been many approaches in trying to solve the problems introduced by the use of non-asbestos brake lining. Some of them are:

1. Bonding lining on the shoes instead of bolting 2. Riveting lining on the shoes instead of bolting 3. Continuous welding of the fabricated shoe instead of a few spot welds 4. Use of steel backed lining 5. Cast iron brake shoes.

Of the above five solutions, none of them address all the problems introduced by the non-asbestos lining, except for the last one. This statement has been confirmed by several transit operators as they have "switched" to other possible solutions, when they find out that the original "solution" is not working. Number four, while very new and promising, is in the process of being evaluated but will not fix the problems caused by a badly distorted shoe.

The cast iron brake shoe will give the operator a true table, to bolt, rivet or bond lining to, without deforming due to stress of heat. By using a cast shoe the operator eliminates all the parameters introduced by the fabricated shoe into the brake equation, such as deformation, elongation, heat warping, etc., and can now, and only now, do a true and honest evaluation test of the brake lining.

International MART Equipment Ltd. (IMEL) has the solution and the experience, as it has been manufacturing and selling cast iron brake shoes for the transit industry since 1986. Please contact us!

THE ADVANTAGES OF A CAST SHOE

Some of the advantages of a cast shoe are:

1. Eliminates noise caused by brake shoes 2. Better heat dissipation 3. Table does not deform or distort 4. Much higher machining tolerances 5. Increased brake lining life 6. Written performance guarantee 7. Lowest price, if performance and life of the shoe is equated into the initial price

As most of the transit managers are very budget conscious, the focus of this discussion will be on item 7, Lowest price. The other six advantages, which are very hard to quantify, can be considered as bonus.

10 year warranty shoe

As mentioned above, the IMEL cast brake shoe is the lowest priced shoe in the market if performance is equated to the purchase price. The cast brake shoes are designed to be reusable and represent a long term investment, which must yield a return within the service life of the bus. If the purchase price of a cast shoe is divided by the warranty period, it will determine the cost per year of service or return on investment.



The above chart illustrates a typical break-even point when a fleet of 100 buses with fabricated brake shoes is retrofitted with IMEL brake cast iron shoes.

It has been assumed, for this example, that the fabricated shoes are replaced every reline (the fabricated shoe was designed as a “throw-away” at every reline), that the front shoes are relined once-a-year and the rear brakes are relined twice-a-year.

The cost of the cast shoes is higher at installation, but because they are warranted for 10 years, they will soon outlast any fabricated shoe in the market. The IMEL cast shoes will also eliminate noise, extend lining life, eliminate pulling and provide a much smoother and safer brake operation.

The difference in cost (distance between the two lines) at the 10 year mark indicates the net savings for the transit operator for retrofitting with IMEL cast shoes, which in this case is over $800,000 and the break-even point is around 1.5 years!

IMEL will be glad to work with transit properties, under no obligation, to prepare charts similar the ones above but specifically designed to their particular operation. Please, just give us a call or email us.

Transit Brake Shoe Specifications



Cross-over List



Please look up your OEM part number, cross it over to the IMEL part number, and contact us for a free estimate.

Brake Test Tool

This tool, designed and manufactured by IMEL, will assist you in evaluating the shoe table deflection within 0.001”.

Fabricated brake shoes deform in regular service; they were designed to be thrown away after each reline, but many transit properties try to re-use them. A large manufacturer in North America, which offers fabricated shoes in an exchange program, uses a 750 ton press to “coin” deformed fabricated shoes and restore them to their original configuration.

If the fabricated shoes deform in service, do they deform at the first brake application?, maybe the second?, or maybe the tenth? Nobody knows.

IMEL knows, and will guarantee that the cast brake shoes will not deform in service!

The Brake Test Tool is available from IMEL for $350.00 US funds, FOB our plant in Victoria. The full price of the Brake Test Tool will be refunded with the first order of 100 shoes.