primary shoe v. secondary shoe

[burnstransport]

Hi guys, I realize this is a simple question but I just can't seem to find the answer anywhere. I'm doing a brake shoe replacement on S-cam brakes using Meritor reman shoes. The cam is located in front of the axle, and I realize the primary shoe should go in the bottom position (first shoe past the cam in direction of wheel rotation). But which shoe is the primary? One shoe has thicker material than the other, does that make it the primary or secondary? Also I've noticed that on each shoe, one lining block is colored red on the edge. One shoe has the red lining closer to the cam, the other shoe has the red lining closer to the anchor. I think the red lining is a different frictiion material, but again I can find no information on whether that is the "leading" or "trailing" edge to the shoe. The shoe kit came with no information about primary or secondary. The Meritor brake service guide only mentions a difference between the two when shoes with electronic lining indicators are concerned.

Any suggestions?

[MACKS]

I never knew there was a difference..

[burnstransport]

I never knew there was a difference..

Neither did I until I went to put them on and took a closer look at them, holding them side by side. In the past I just threw them on the truck without second thought. Must be "new and improved", makes me feel "dumb and confused"

[MidniteMechanic]

There is no leading or trailing shoe, they are the same. The color on the edge along with the printing is simply for identification. How much difference is there in the thickness?

If it is alot it is possible they mixed Q and Q+ shoes in the same box. I was never impressed with they quality of Meritor reman shoes.

[DCR]

Not that it is the same today, but when I worked at my father's service station in the 60's there were primary and secondary brake shoes. The primary was the front shoe and the secondary was the back shoe of the two. There was a difference between the two. I think the primary was a bigger heavier brake shoe. My 2 cents worth for what it is worth.

[MACKS]

Not that it is the same today, but when I worked at my father's service station in the 60's there were primary and secondary brake shoes. The primary was the front shoe and the secondary was the back shoe of the two. There was a difference between the two. I think the primary was a bigger heavier brake shoe. My 2 cents worth for what it is worth.

Are you talking about class 8 trucks,been doing my own brakes for 25 years and this is the first time I ever heard of this!!

[burnstransport]

There is no leading or trailing shoe, they are the same. The color on the edge along with the printing is simply for identification. How much difference is there in the thickness?

If it is alot it is possible they mixed Q and Q+ shoes in the same box. I was never impressed with they quality of Meritor reman shoes.

The kit was supposed to be Q+ shoes, the difference is noticeable but not huge, prob 1/8" at most. I'm just trying to make sure they wear evenly so I can get the most mileage possible. The old ones wore down so they were pretty even across the length of the web's arc, makes it hard to match old shoes to the new ones.

[DCR]

Are you talking about class 8 trucks,been doing my own brakes for 25 years and this is the first time I ever heard of this!!

No, not trucks; automobile brakes. I left the gas station employment in 1970 after graduating from college and a lot has changed since then. I was just commenting that at one time there were primary and secondary brake shoes in response to Burnstransport question.

[rsb502]

I've been doing brake jobs on trucks and buses since I was in my early teens and I've never seen shoes that didn't match id take em back. The red paint on the edge denotes the lining material they used to be 551,555,557 linings now they're red, blue, green, etc..

[Maddog13407]

im a youngin and im pretty sure there is a primary and a secondary. on a few B61's an B42's tandem tractors i have worked on there is brake shoes with yellow on the edge and some with blue on the edge. last i knew the yellow was the primary and blue was secondary.

[felicello122]

New to me, you must have a mismatch in the box, happens alot with reman stuff, red indicates 23,000 lbs rating.

[TozziWelding]

Last time I checked all Q shoes were the same

[thomastractorsvc]

Way back in the mid 80's in VO-TECH I was taught about primary and secondary shoes see attached, this is from the Mack service manual read under cam brakes section.

Brake scan.pdf

[leversole]

My opinion is that is just a naming convention based on one brake being pulled tighter and the other pulled away from the drum, no difference in the shoes themselves...

[thomastractorsvc]

that's correct on cam style brakes the shoes are the same size and dimension for both primary and secondary, if they are not identical they are mismatched, the coloring is supposed to be the composite type/heavy duty/standard, I have seen different composites on the primary than on the secondary and maybe that is what he is talking about.

the hardware is also color coded, the blue springs are heavy duty

[burnstransport]

My main concern was that the red marking on the linings were on opposite ends of the shoes. One shoe had red marking closer to the anchor pin and the other shoe had red marking closer to the s-cam roller pin. So I was worried that maybe they were a combination lining and thus the one shoe would be primary and other shoe secondary. I've looked all over the Meritor website but they don't seem to indicate that they should be installed in any specific position so I've gone ahead and installed them without regard to primary or secondary shoe. Everyone's response here has reinforced my instinct that they should work OK however they're put on.

Thanks for the input everyone!