What size is my rear brake drum?

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Billy the average guy

Billy the average guy

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1974 Valiant Brougham /6 two door hardtop and all original parts.

Should be 9” (9x2) but the drum markings state max diameter 11.090”.

I measured the backing plate and its 12”. Inside diameter of drum is 11”.

Could the Brougham had some weird upgraded brakes? Even on a slant six? I need to know because it’s time to change the pads and springs etc.

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Well, if they are 11.090, then you have 11 inch brakes.
That's simple enough to figure out.
Then somebody along the line, swapped out the brakes, to eleven incher's.
 
Or you could go back to original? Junk everything you have now and go with the 9 inch. So it's 100% Mopar pure. :rolleyes:
 
Somebody changed more than the backing pates, shoes, drums on that car.
If you had everything stock, 9 inch drums, slant 6 engine, you still would have the small, 4 inch, small bolt pattern axle shafts, and wheels on that car, unless it was built as a DISC brake car.
What brakes are in front?
Disc, or Drum?
You have 4 1/2 inch bolt pattern wheels, on all 4 corners?
Or 4" in front 4 1/2" in the rear.
Lots get changed over, in 40+ year old cars.
 
No way 11" brakes on an a body from the factory but I'll defer to hemi71x.
11" drums on an A is way overkill unless you live on top of a mountain. And getting all that mass going is gonna slow you down especially with /6 power.
 
KosmicKuda said:
No way 11" brakes on an a body from the factory but I'll defer to hemi71x.
11" drums on an A is way overkill unless you live on top of a mountain. And getting all that mass going is gonna slow you down especially with /6 power.
Click to expand...

Well, in 1976 Ma Mopar made some A body police cars.
That package had 11 inch drum brakes in the rear, and a sway bar over the axle.
Very rare.
How many produced? Who knows? But not many.
Surviveability now, into 2019, not very many.
There are "rumored" to be some 76's made for the Mexican market to have 11 inchers in the rear, but i never found verifiable proof of that to be true.
Why Mexico, who knows?

I found this on the internet, but it really doesn't specify the rear brakes being 11 inch.
But somewhere i have a service manual; that stated they were, so that's what i'm going by.

In 1976, the Dart was offered with a police package, with production code A38. The A38 Dart had high-specification components and systems throughout, including a heavy-duty suspension with a rear sway bar, stronger leaf springs and firmer shock absorbers, larger brakes with semi-metallic front disc pads, maximum engine cooling, and high-capacity alternator and battery. The engines were Chrysler's 225 slant-six, 318 V8, and 360 cu in (5.9 L) LA V8 (220 H.P., with non-catalyst in 49-state models and a true dual exhaust; California models had a single exhaust with the catalytic converter) with an A727 TorqueFlite transmission. Police-specific equipment such as a calibrated speedometer ("certified" 120 mph), high-intensity dome light and wiring harness for a rooftop light bar were standard equipment and an A-pillar spotlight and push bars were optional. Production volume was low, with most A38 Darts going to the Los Angeles and Venturapolice departments in southern California. For the most part, police agencies preferred the larger intermediate Dodge Coronet or full-size Dodge Monaco.

Until i find, dig out, that manual, i'm going to step back on my reply in regards to the rear brakes.
Re reading the above, maybe it means 2,750 inch piston, caliper pistons over the 2.600 inch pistons, and 10 inch rear brakes versus 9 inch brakes.
Got me confused now.
Sorry if i got you confused, too.
 
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Totally agree with hemi71x. If it had 9” drums all around it should be a SBP car. But in ‘74 a lot of the slant 6 cars got disks up front, and if they did they were 5x4.5”. The 4 wheel drums were standard, but there were several option packages that would trigger the front disk option. My Duster was originally a slant 6 car, it came with front disks and was BBP all around. 10x2.5” rear drums, although if you have 10x2.5” BBP drums then the upgrade to 11x2.5” is easy, just replace the backing plates and drums.

As for the 11” brakes being overkill, I disagree. Maybe on a 100% stock car, but it you run more tire out back you can use more brakes to go with. I upgraded my Challenger to 11x2.5” drums and did exactly the same thing with my Duster, I’ve had 11x2.5” drums since I swapped the rear axle over to an 8 3/4. They work great!

Sounds to me like someone swapped out those rear brakes at some point. So much for “all original parts”! Probably should check what axle is in there too. If the brakes went to 11”, there’s a good chance that wasn’t the only thing that was swapped.
 
Did some more digging, and found this on allpar.com, in regards to the 76 a body car, police package.

Valiant pursuit cars with V8s used a wide 70 series police radial (with two plies of fabric cord and four full-width textile cord belts under the tread). The calibrated speedometer ran up to 120 mph rather than the usual 100 mph, while the power steering had a (desirable) firm-feel chuck and an oil cooler. The radiator was larger (22" with slant six, 26" with V8); heavy-duty brakes included front power discs with metallic linings and rear 10 x 2.5 inch drums with automatic adjusters. Interior trim was vinyl, in gold, green, or black, with heavy duty front cushion springs and air foam cushioning, and a full foam front seat-back.

Says the rears are 10 x 2 1/2 inch drums.
Then ya, bigger than 10 x 2 inch.
So, not 11 incher's then.
The other members reply is correct, in regards to no 11 inch.
My error.
 
hemi71x said:
Somebody changed more than the backing pates, shoes, drums on that car.
If you had everything stock, 9 inch drums, slant 6 engine, you still would have the small, 4 inch, small bolt pattern axle shafts, and wheels on that car, unless it was built as a DISC brake car.
What brakes are in front?
Disc, or Drum?
You have 4 1/2 inch bolt pattern wheels, on all 4 corners?
Or 4" in front 4 1/2" in the rear.
Lots get changed over, in 40+ year old cars.
Click to expand...
Front are manual disk brakes and I recently replaced pads with stock size. All four wheels were upgraded (by previous owner) to American Racing 14” in a 5 x 4.5” pattern.
 
Ok then, you got yourself a disc brake, 6 cylinder car, by factory build.
Former owner put on some aftermarket wheels, and upped the rear brakes to 11 inch.
Easy, peasy, thing to do.
 
Thanks for the replies from all! After a long time delaying 2 years and finally fighting with lock lugs (missing key) I found myself scratching my head when I expected small 9” drums under the wheels and then saw these big things.
So what parts do I replace with? I plan on ordering online. Do I look at B or E body V8 brakes? Any particular model? The drums I removed had Chrysler logo embedded in the cast iron.
 
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Well I'll tell you this.
Look at the parking brake "levers" the that brake shoe attaches onto.
First see if the shoe is held on with a "pin" and a bendable horseshoe clip, or the lever just goes into the shoe, by a "slot" in the shoe.
That will be the difference in what shoes that you buy.
The pin type was used throughout the 60's, 70's, and the slot type the 80's, 90's. 00's.
Ya look at shoes for B and E body's if you got pin type shoes, or slot, look at vans, trucks.
Look up 2 1/2 X 11 inch shoes.
If your doing wheel cylinders too, they most likely will be 15/16 diameter, as that's the most common, used, wheel cylinder size for the 2 1/2 inch brakes.

Parking Brake Levers 009 (Small).JPG
 
72bluNblu said:
Totally agree with hemi71x. If it had 9” drums all around it should be a SBP car. But in ‘74 a lot of the slant 6 cars got disks up front, and if they did they were 5x4.5”. The 4 wheel drums were standard, but there were several option packages that would trigger the front disk option. My Duster was originally a slant 6 car, it came with front disks and was BBP all around. 10x2.5” rear drums, although if you have 10x2.5” BBP drums then the upgrade to 11x2.5” is easy, just replace the backing plates and drums.

As for the 11” brakes being overkill, I disagree. Maybe on a 100% stock car, but it you run more tire out back you can use more brakes to go with. I upgraded my Challenger to 11x2.5” drums and did exactly the same thing with my Duster, I’ve had 11x2.5” drums since I swapped the rear axle over to an 8 3/4. They work great!

Sounds to me like someone swapped out those rear brakes at some point. So much for “all original parts”! Probably should check what axle is in there too. If the brakes went to 11”, there’s a good chance that wasn’t the only thing that was swapped.
Click to expand...
Good point about the axle. I’ll check that next.
 
hemi71x said:
Well I'll tell you this.
Look at the parking brake "levers" the that brake shoe attaches onto.
First see if the shoe is held on with a "pin" and a bendable horseshoe clip, or the lever just goes into the shoe, by a "slot" in the shoe.
That will be the difference in what shoes that you buy.
The pin type was used throughout the 60's, 70's, and the slot type the 80's, 90's. 00's.
Ya look at shoes for B and E body's if you got pin type shoes, or slot, look at vans, trucks.
Look up 2 1/2 X 11 inch shoes.
If your doing wheel cylinders too, they most likely will be 15/16 diameter, as that's the most common, used, wheel cylinder size for the 2 1/2 inch brakes.

View attachment 1715333588
Click to expand...
Just checked. They’re pins.
 
Most of the shoes available now come with provisions for either pins or slots. The last couple sets of 11x2.5’s I bought came with the pins in a bag. If you have pin type you install the pins (the holes are drilled already), if you have the slotted type then you just use the slots and leave the pins out.

Huh, 8 1/4 too. Well that could have been factory. Decoding the fender tag or build sheet could be interesting!
 
72bluNblu said:
Most of the shoes available now come with provisions for either pins or slots. The last couple sets of 11x2.5’s I bought came with the pins in a bag. If you have pin type you install the pins (the holes are drilled already), if you have the slotted type then you just use the slots and leave the pins out.

Huh, 8 1/4 too. Well that could have been factory. Decoding the fender tag or build sheet could be interesting!
Click to expand...
Well then, you sent me to brake shoe college here tonight.
Didn't know they made the shoes "universal" in the way of pin, or slot.
Been a long time since i bought brake shoes.
 
why you would ever downsize your rear brakes would be a mystery to me! Bet this thing stops great! Rebuild the 11s and let 'er rip!
 
hemi71x said:
Well then, you sent me to brake shoe college here tonight.
Didn't know they made the shoes "universal" in the way of pin, or slot.
Been a long time since i bought brake shoes.
Click to expand...

Well hey! After all the stuff I’ve learned from you it’s nice to be able to give something back!

I dunno when it started, or if they’re all like that. I just know that the last few sets of shoes I bought in 11x2.5” were universal, they could be set up either way. The originals I’ve seen definitely weren’t all like that. But considering that most of the shoes are likely made by only one or two factories and then branded after that there’s a decent chance most of them are universal now.

Here you go. The loaded backing plate is pin only. The set of shoes next to it is set up for both, you can see the round hole is in the same place as the pin on the loaded plate. The slots are present as well.

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Info for that particular set of shoes. I'd include a picture of the pins they're supposed to come with, but I guess that's why there were a closeout at RockAuto! :rolleyes:
IMG_6258.jpeg
 
Follow up: When I finally got 11 x 2 1/2 inch shoes, and struggled installing, and bruising that left thumb with several spring retractions, I discovered the correct size brakes are 11” x 2”. Live snd learn. Will be posting 11 x 2.5” shoes for sale.
 
The triangular shaped hole with the half moon cut-out pictured in this thread will accept either hook or pin type parking brake levers.

The self adjuster saddle/secondary spring mounts to the lower, round hole.
 
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