10"drums front and 9"drums rear, what master Cylinder use?

-
Miguel Castro

Miguel Castro

Well-Known Member
Joined
Jan 17, 2019
Messages
47
Reaction score
49
Location
Ciudad de México
Hi guys, finally i bought my first car last december, a Plymouth duster 1974. The car have 10" drums on front and 9" drums rear but the master cylinder looks like an disk/drum configuration.
The braking performance feels fine to me but the drums of all wheels need to be replaced, they pass the maximum diameter permised.

Can i stay with this master cylinder or i need to replace it with the correct one?, i think is the Raybestos number part MC36338

It´s ok that my front drum size was 10" size? Attach photos below (proportional valve to)

i don´t wanna die.

IMG_20181220_100647777_HDR.jpg


IMG_20181220_100834472.jpg


IMG_20190106_114100969.jpg


IMG_20190106_114117241.jpg


IMG_20190107_093816191.jpg


IMG_20190107_093852844.jpg


IMG_20190112_091420602_HDR.jpg
 
The larger reservoir is built into the disc/drum master cylinders because the larger piston volume of the brake calipers requires more fluid as the brake pads wear. If it stopped fine before, I wouldn't worry about it.
 
That's an interesting mix of brake components.
Was the car made sale in US, or Mexico?

Yes. The Master Cylinder is for a disk/drum system.
Depending on the casting number, it might even be somewhat rare!
In addition to the larger reseviour for the front pistons, a disk brake master cylinder will not have a residual valve in the rear outlet (for the front brakes).
Around 1975-76 Chrysler started using 'expanders' in the drum brake wheel cylinders instead of residual valves in the outlets.

Rear brakes you show are using an automatic adjuster system the Chrysler stopped using in 1969. To purchase parts, and to adjust the shoes, reference 1968 and earlier.

If you want to see what the master cylinder was originally used for, check the tables out in the article linked.
Brad goes by "Mastershake" on Mopart. He's made some updates and corrections since it originally came out but still a good starting point.
http://www.moparts.org/Tech/MoparAction/Master_Cylinder.pdf

A picture of residual valve is shown on this page.
1970 Chrysler Imperial Hydraulic Brake Service Guide from the Master Technicians Service Conference Session 274
 
Last edited:
Miguel Castro said:
(proportional valve to)
Click to expand...
That's just a distribution block with the safety switch.
A disk/drum system would have a either a seperate proportioning valve further along the frame rail toward the rear brakes.
or a distribution block combining the proportion valve and safety switch. Its got a bigger bottom to fit the proportioning valve in, so that's not what you have there.

A car with drums on all four will not have a proportioning valve.

Cutaway of the safety switch from the same pamphlet as above.
upload_2019-2-24_23-56-31-png.png
 
sounds like somebody swapped the whole rear axle assembly and just kept the 9 inch brake stuff that was on it (6 cylinder car). I presume that it has a 7 1/4 inch rear? If so I can ship you the whole 10 inch brake assembly to match your front brakes off a 7 1/4 inch rear end that I pulled from my 70 Dart (going to a 8 3/4 rear axle). I'd do it for $50 plus the shipping. If you are interested PM me.

Chrysler certainly never sold a car with mismatched brakes like that and for good reason...
 
I would try it just as it is, but would test the brakes hard to make sure the back stays in the back. But knowing those 9 inchers originally barely stopped skinny 13 inch tires, I don't see a problem. Pick someplace with lots of room, no traffic and some lightly sanded patches. Work up to skidding the front tires at something like 15 mph and see what happens, then a lil faster. If at any time the back skids first, you will need: a proportioning valve, or smaller rear wheel cylinders, or bigger front wheel cylinders,or bigger rear tires; whatever is easiest or cheapest. If the rear skids first, it will spin you out or could put you into a bad situation.
 
Last edited:
str12-340 said:
sounds like somebody swapped the whole rear axle assembly and just kept the 9 inch brake stuff that was on it (6 cylinder car). I presume that it has a 7 1/4 inch rear? If so I can ship you the whole 10 inch brake assembly to match your front brakes off a 7 1/4 inch rear end that I pulled from my 70 Dart (going to a 8 3/4 rear axle). I'd do it for $50 plus the shipping. If you are interested PM me.

Chrysler certainly never sold a car with mismatched brakes like that and for good reason...
Click to expand...

Thanks, i gonna make a decision on this days. And yes, i think is a 7.25 differential.
 
AJ/FormS said:
I would try it just as it is, but would test the brakes hard to make sure the back stays in the back. But knowing those 9 inchers originally barely stopped skinny 13 inch tires, I don't see a problem. Pick someplace with lots of room, no traffic and some lightly sanded patches. Work up to skidding the front tires at something like 15 mph and see what happens, then a lil faster. If at any time the back skids first, you will need: a proportioning valve, or smaller rear wheel cylinders, or bigger front wheel cylinders,or bigger rear tires; whatever is easiest or cheapest. If the rear skids first, it will spin you out or could put you into a bad situation.
Click to expand...

For the moment the brakes work fine, i think, is my first car and the difference between the corolla in home and this are abysmal. But your advice sounds good, maybe can try in some parking.
 
Yes, first verify what you have.
Front and rear drum brakes.
You can figure out the diameter from the maximum size allowed for cutting.
It will be marked someplace on the drum casting. Either where the shop manual shows or where I added a second arrow are common locations.
upload_2019-2-27_10-8-54.png


If that is not readable, then measure the inside diameter.
Also measure the width of the shoes.
 
It's a 7 1/4

By the way, from your pictures it looks like one of your front brake hoses is rubbing against the shock. If it wears through you will lose your front brakes. A few minutes now might save you a world of headache later...
 
str12-340 said:
It's a 7 1/4

By the way, from your pictures it looks like one of your front brake hoses is rubbing against the shock. If it wears through you will lose your front brakes. A few minutes now might save you a world of headache later...
Click to expand...


Thanks for the advice, im using the car only weekends around my neighborhood.

Tonight i gonna check the correct size of the front drum and the bolt pattern to buy the new ones and the correct master cylinder for drums + drums.

i bought the new 9" rear drums last week (2941R raybestos), if the front drum size is 10" i gonna buy the raybestos mc36338 master cylinder and use that configuration, 10" front and 9" rear. Just for the time to take me find all the rear brake parts necesary to make a 10" rear swap.

I need to change the K frame too, my steering bar is almost rubbing with the oil pan, have new engine mounts, transmission mount, and a used k frame in better shape that mine.

IMG_20181220_100159597_HDR.jpg


IMG_20181220_100445500.jpg
 
Well, i dont have a 9"drum in back, always was a 10" drum set, unfortunately now I have to find who buys me the drums of 9 " I ordered online. Rookie mistake.

Anyway, today was a productive day, i think. New brake hoses has installed (i found they in autozone), bought the correct oil seal for the shaft and found the Timken bearing. The wheel cylinder that i ordered with the drums are smaller (for 9" drums), so autozone helped me again. (thanks autozone).

So, for the moment it's all. I have to find the 10" drum brakes (rear and front) and sell the 9"drums.

The Timken bearing was LM48548A with cup LM48511A. The collar have no brand. Other option was a japanese brand, KOYO.

About my axle, it's a 7.25?

IMG_20190305_143347023.jpg


IMG_20190305_143535091.jpg


IMG_20190305_143632822.jpg


IMG_20190305_143640194.jpg


IMG_20190305_143650306.jpg


IMG_20190305_160556855.jpg


IMG_20190305_160626881.jpg


IMG_20190305_163919067.jpg
 
Miguel Castro said:
Well, i dont have a 9"drum in back, always was a 10" drum set, unfortunately now I have to find who buys me the drums of 9 " I ordered online. Rookie mistake.
Click to expand...

Miguel Castro said:
So, for the moment it's all. I have to find the 10" drum brakes (rear and front) and sell the 9"drums.
Click to expand...

I think what you mean to say is written the other way here: The car has 10" drum brakes. But you need some of the parts, including the drums. First check the width. Its may be the wider rear drums, so check. Look at the shoes for the number stamped on them. Assuming they fit, that's another way to figure it out.

The rear brake hose is too short! It can't be under that much strain every time the car is lifted. There needs to be a gentle curve even at full extension,
The right rear brake line should be attached tight to the axle housing. If there's no clips welded to the housing, make a retaining clip that will be held by one of the differential cover bolts. Sorry I can't ID the diff. I'm sure someone here can.

Miguel Castro said:
The Timken bearing was LM48548A with cup LM48511A.
Click to expand...
Might be able to look that up. That's the hard way. Usually they are sold here by Set numbers.
 
You must log in or register to reply here.
-

Back
Top