Brake Caliper Factoids

[oemtech]

Here are a few facts about the Bosch/Workhorse brake caliper recall.

1. The 66MM/73MM calipers are used in many different applications. So, there may be potentially millions of them in use.
2. There are only 2 manufactures of phenolic brake pistons in the US.
   1. Kurz-Kasch, Inc
   2. Diemolding, Corp. (supplier to Bosch)
3. There are only 2 formulas for the phenolic coating.
   1. Durez 29502 Durez 29502.pdf
   2. Durez 29502B Durez 29502B.pdf
4. Diemolding, Corp. is aware of the recall and has not made any dimensional changes to the caliper piston size.
5. The phenolic formulas have not change in years. I got the data sheets here Molding Compounds - Data Sheets
6. The difference between the 2 phenolic compounds is the B version is more resistant to heat.
7. Brake pads are a large heat sink. The thinner they are the more heat is transferred to the calipers pistons via the backing plate. I have been told that it is as much as 150 to 200 degrees under hard braking.

So what do you get with the new calipers.

1. New casting with an increased bore. IE - proper clearance
2. Same size pistons with the B formula phenolic compound.
3. New high temp dust boots and seals.

For those that bought calipers from B & W you are ready have what Bosch/Workhorse are now supplying.

Initially B & W was selling the calipers for $100 per. The price was increased to $135 because B & W was selling them without a core charge. IE - No cores were returned for rebuild.

[CoastieSCPO]

Good stuff, Dale! Thanks. As Sergeant Joe Friday said, "just the facts"!

Bob

[Joe Gilbert]

I agree with the greater heat transfer on thinner pads however, In my case that does not explane why both front brakes started dragging. I had driven 43,000 miles with zero problems. I also have changed my DOT3 twice a year. On Oct. 1st I drove from NH to Allentown,PA with no brake problems. I than drove thru the city. Lots of 5MPH driving and sitting at red lights with the brakes on. After driving thru the city I got on I78 and immediately felt the brakes dragging. Not being one to stop on interstate highways I drove 6 miles before I coulod get off. Both front brakes were red hot. (This had a happy ending. See my post on "A good brake experence").

My point is that it was not heat which caused the brakes to drag though of course heat soon followed. My guess is that they didn't like sitting at so many lights with the brakes on????????

What do you think?

JoeG

[oemtech]

Quote:

Originally Posted by Joe Gilbert I agree with the greater heat transfer on thinner pads however, In my case that does not explane why both front brakes started dragging. I had driven 43,000 miles with zero problems. I also have changed my DOT3 twice a year. On Oct. 1st I drove from NH to Allentown,PA with no brake problems. I than drove thru the city. Lots of 5MPH driving and sitting at red lights with the brakes on. After driving thru the city I got on I78 and immediately felt the brakes dragging. Not being one to stop on interstate highways I drove 6 miles before I coulod get off. Both front brakes were red hot. (This had a happy ending. See my post on "A good brake experence"). My point is that it was not heat which caused the brakes to drag though of course heat soon followed. My guess is that they didn't like sitting at so many lights with the brakes on???????? What do you think? JoeG

Joe,

The point about thin pads is the amount of heat transferred to the caliper piston. The thinner the pad material more heat is transferred at a faster rate! That in itself is not the reason for the piston to stick. But, add that to the poor piston to bore clearance, the "low priced" phenolic coating, heavy braking with little cooling and you have the classic stuck brake caliper.

Ask yourself, how much heat is being transferred to the caliper when you are at a stop sign hold the coach with the brake?

[JCM]

Try rush hour traffic (Seattle) during a heavy rainstorm. That was my first adventure and I duplicated it the following year. Now I drive through Seattle on a Sunday morning - less traffic.

[Joe Gilbert]

I agree Oemy. Still I would have thought that mountain driving would be the worst case and I have done lots of that. I'm really glad to have all of this behind me/us.

JoeG

[Max Hubrich]

Oemy-

66mm equals a bore size of 2.598". Do you know the new bore size? How many thousands over this value?

I plan to buy my cores, and re-bore them.

[oemtech]

Max,

I don't have the spec's in hand. But, I will see if I can get them.