Rear brake drum/shoe question?

[Jayru 17]

Hey Guys,

 

I'm going to be replacing the rear bearings/seals, and thought I'd rebuild/replace the rear drum brakes while I'm there.

 

Here's the issue. I'm confused as to what rear drum size i have.

 

There seems to be a 1 3/4" drum/shoe and a 2" drum/shoe option.

 

Problem is, i seem to have a 2" drum (aprox. 2 1/4" when measured on the inside brake shoe contact face), and 1 3/4" brake shoes (measured across the face of the shoe).

 

What should a 69 mustang (original 302 4 speed car) have?

 

Did the PO mix and match or something??

 

Help!

[very fat and very dumb 40]

Per the NPD catalog, page 61, you should have 10x1 3/4 on the rear. If it were me I'd go with 2".

[Jayru 17]

Per the NPD catalog, page 61, you should have 10x1 3/4 on the rear. If it were me I'd go with 2".

 

What would be involved to change? Is it as simple as getting larger shoes/drums, or do you need to swap axles/backing plates, etc.

[very fat and very dumb 40]

You can look at page 61 in the NPD catalog and see where the differences are. The backing plates and axles are the same. The only difference I see is the shoes, drums and hardware kit. You already have the drums so your almost there.

[Jayru 17]

You can look at page 61 in the NPD catalog and see where the differences are. The backing plates and axles are the same. The only difference I see is the shoes, drums and hardware kit. You already have the drums so your almost there.

 

NPD said, "sure, you can run 2" shoes from 1 3/4" if you just change the drums, everything else is the same." But after some research this doesn't seem to be correct.

 

The backing plate must be changed to accommodate the larger shoes (deeper offset of the backing plate). The drums have wiggle room to account for shoe movement, which is why i have a 2" or so drum with 1 3/4 shoes. The 2" shoes would have a 2 1/4 to 2 3/8" drum.

 

If i tried to put a 2" shoe on my 1 3/4" backing plate, the brake shoes would lock against the drum once they heated up! Because of the lack of wiggle room.

 

This is what i seem to have come up with after a few days of internet searching anyway.

 

I'm going to buy new 1 3/4" drums and see if they measure 2" - if so then the above statement would be right.

[very fat and very dumb 40]

"Problem is, i seem to have a 2" drum (aprox. 2 1/4" when measured on the inside brake shoe contact face), and 1 3/4" brake shoes (measured across the face of the shoe)."

 

"The 2" shoes would have a 2 1/4 to 2 3/8" drum."

 

 

 

You said that your drums measure 2 1/4 on the inside, based on the above info you should be good to run 2" shoes. I really don't think the backing plate is different, if it is I might be in trouble when my convertible is on the road this spring.

Edited December 1, 2010 by very fat and very dumb

[Burn 14]

Jayru, If you can come up with $500 you can upgrade to the MP Brakes 11" rear drums kit from CJ Pony Parts. They come with backing plate, all hardware and drums. From what I've read these are excellent and are as good, if not better, than 11" rear discs and will fit 14 and 15" stock wheels. Some new cars still come with rear drums and I think all 8 wheelers have drums!!!

For $600 you can buy a 11.625" rear BAER disc kit.

[Jayru 17]

Thanks for the info Burn!

 

Money's a bit tight with the holidays and all. Can't make that kind of commitment at the moment. I'm going to rebuild the stock stuff.

 

very fat and very dumb - Seems that i did have 1 3/4" drums afterall (which measure a bit larger than 2" total face). Went to NAPA today and compared them to the 1 3/4" and 2" drums/shoes. The 2" drums have a 2 3/8" face as i had suspected.

 

You were right that the 1 3/4 & 2" backing plates are the same. The 2" drum seems to have a different pitch on the face with less of a lip on the inside (compared to the 1 3/4") to compensate for the larger shoe, but the overall size dimensions are the same!

 

Going to install the 2" shoe/drum today.

[Jayru 17]

So now my rear brakes lock up under heavy braking!

 

Regular braking is fine and feels solid, but had to do a quick stop today to avoid a pothole and both rears completely locked up on me! As soon as you release the pedal the rears release.

 

I tried it several times after and it locks up everytime you hard or panic brake!

 

WTF!

 

What should I do?

[MikeStang 247]

Well when you brake normally your rear brakes always kick first, as is the case when you panic brake.

your rear brakes as well as your fronts should lock up when you stand on them hard, that is what they did back in the day, they didnt do the ABS thing, which i hate btw......I would suggest you loosten them off just a bit, maybe say a quarter of a turn, some times it takes a bit of playing with them to get them just like you want.....if you put it all back together right, you can loosten them off too much, then simply back up and apply the brakes....usualy will self adjust in about 100 yards or so if they are WAY out. As long as when you apply the brakes the rear of the car does not instantly drop then you are probably pretty close...just gotta play with it .

Mike

[Jayru 17]

Hi mike,

 

So are you saying that adjusting the rear brakes controls rear brake pressure as well as pedal travel?

 

I always thought adjusting the rear just controlled pedal travel (as the shoes had more or less distance to go before engaging). What your saying is by losening them it will put less pressure on the shoes stoping them from locking up?

 

I've been researching proportioning valve issues and rear brake pressures (and ajustable rear valves) for hours making my head spin! Is it as simple as losening the adjusters?

 

Just trying to see if I have your logic right.

 

until today, the car has actually never locked up on me (front or rear) since I've owned it (even under panic braking), this has me wondering if something was/is wrong elsehere like the prop valve.

[shelbyshelby 52]

You may want to double check to make sure the long shoes are in the rear and the short towards the front. Also, the rust preventive coating will cause lock up / grabbing if it was not removed with brake or carb cleaner.

[MikeStang 247]

Well basically loosening the adjusters will make it so that your rear brakes don't hit quite as hard and lock up, until you depress the pedal harder....just loosen the adjusters then install the wheel, and give it a spin by hand.....you should feel some drag, normally I set mine to where I spin the tire and it makes about a half revolution till it stops.....I have my brakes on, and don't have any lines hooked up, I can shoot a quick video for you if you would like me too so you can see about how well they need to be adjusted... On a side note a friends car has front and rear disks and you have to really stand up on the pedal to make it lock the wheels up, and then its questionable lol.

Adding an adjustable prop valve I don't think will help, from the factory these cars would lock all four tires up with no problem.

You can buy a brake pressure tester from summit for fairly cheep, it screws into the bleeded screw then you mash the pedal and have some one take the reading on the gauge....I want to say the front disks should have about 800psi, but I'm not totally sure that is right, I would have to look it up......could be the combo valve is stuck.....do some searching on how to center the valve.......have you bled the brakes yet? If not start at the rear pass side and then go rear driver and then front pass then front driver I usually bleed each wheel like 3 times, then do them one more time for good measure....if that don't do the trick you can use a vac pump and that usually always gets the air out, but I don't think you have and air in the lines issue.

I think its and adjustment issue

Also be sure the drums have been cleaned inside with some brake cleaner as mentioned above....sounds like the shoes are working like they should be but are just out of adjustment to me.

mIke

[Jayru 17]

Thanks guys for the suggestions.

 

I definitely didn't spray down the inside of the drum with brake cleaner. So i will pull them off, clean them, and readjust the brakes to see what happens.

 

We just got first snowfall last night and they salted the roads, so it looks like i won't be able to test it out till the spring :(

[MikeStang 247]

Ahh that sux, i would just try it in the driveway and maybe a mile or so down the road....i can usually tell if mine are right it the first 50 feet of driving LOL

Mike