Rear drum brake backing plate questions.

[DAVEN1256]

I am going to have my differential gone through and while it's apart, sandblasted and painted. My backing plates are looking a little rough on the inside and I might be replacing them. I'll have a better idea of their condition after sandblasting.

Questions......

1) In all the photos I have seen of repro backing plates, none seem to have the 1" wide, 180 degree semi-circular plate spot welded to the rear lower half of the backing plate (outlined in red on my photo below.) Is it normal that repro plates do not come with this part? I wonder why they are not there? I wouldn't think the factory would have went through the effort of putting them there if they didn't serve a purpose. Maybe to help keep dirt and water out?

2) Every Camaro parts place that I have looked at repro plates, they cost about $63.00 each. That seems like a lot for what they are. I see you can get Dorman brand plates for '78 and later Camaros at the local auto parts store for $18.00 each. Dorman does not seem to have plates for 1st gen Camaros though. Does anyone know if 1st gen plates are out there more reasonable than $63.00 each?

3) Having almost no experience with rebuilding drum brakes, I have two questions about the areas on the backing plates that the shoes contact......There are three slightly raised areas on each side of the plate that the shoe contacts. (circled in red in the 2nd photo below).......As the shoes move back and forth, is it just metal to metal contact between the shoes and the plates or is something applied there to reduce friction?....These raised areas on my plates are a little rough and crusty right now. If sandblasting or sanding smooths them out, I would assume the plates would be OK to re-use. Any opinions on that?

Thanks........Dave

[janobyte]

Mine do not have the raised area you are refering to. They are original to the car. Smooth rear drum, if that means anything. If after blasting they look ok, might as well repaint and keep, imo.

Where the shoes make contact, I always smear a small amount of disc brake lube(slide pins,etc)...Permatax green.

[janobyte]

I'm waiting for my diff to come back from the shop. Called today cause I was out that way...mon or tues next week.

[Mike S]

 My guess is that plate is to help prevent water from entering the drum when driving through puddles. I checked both my '67's and they have that extra plate. One rear is a 3.07 open with an April 67 assembly date and the other is a 3.31 posi with a March 67 assembly date.

Mike

[bertfam]

All GM cars with drum brakes had the backing plate contact surfaces. They were there to keep the shoes in line with the drum contact surface and were to be lubricated with a thin coat of brake lube per figure 29 (see attached) of the Chassis Service Manual when a brake job was done.

Ed

[janobyte]

Sorry to confuse in my last reply, was talking about the raised ridge around the outer border not being on mine.

0424 12 bolt posi (68), Drum # 3841177

[janobyte]

I've read the inner surface received little if any paint. No plan and having judged, shot with Eastwood 2x satin.   

[janobyte]

Theses are actually in primer.

[janobyte]

My guess is that plate is to help prevent water from entering the drum when driving through puddles. I checked both my '67's and they have that extra plate. One rear is a 3.07 open with an April 67 assembly date and the other is a 3.31 posi with a March 67 assembly date.

Mike

Agree, my guess is removal was a cost saving measure. Where it's pennies x units produced. I will say these old plates are thicker then anything I've seen on newer vehicles...well 80's up. Don't know about the re-pops. Yours appear to be in pretty good shape.

[JKZ27]

Jano, in your backing plate rear view pic, it looks like there are dimples where the shield was spot welded on.

[janobyte]

Wow, good eyes. Went back out to check, and yes, evidence of the plates being present. Even a small grind scar by the weld. The who and why will remain a mystery.

[janobyte]

Pea gravel catchers.

[ko-lek-tor]

I did not read every reply completely, so if this has already been said, apologies. If I had backing plates that were not up to par, after blasting, then I would find another pair of GM backing plates. I have scads of them to dig through. Same plate as a 10 bolt and you can find those (10 bolt)rears subbing as jack stands they are so numerous. The thought of buying repop seems unnecessary.

[69Z28-RS]

I think the same backing plates and brakes (or very similar?) were used on the '72 and up 8.5" rears... which should be very common.

[bcmiller]

Yes I think the 8.5 axles used the same backing plates. I will try to check one this week.