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Drum Brake Upgrade

A

AlabamaDan

NAXJA Forum User
Location
Heart of Dixie
Now, before some of you guys say just upgrade to disc brakes, I'm looking for a simplier upgrade until that rear axle swap comes along. Ok, here goes...

I've heard that Dodge truck guys replace the dodge wheel cylinder with a 1 ton GM wheel cylinder. It's got a slightly larger bore diameter and it will put more pressure on the shoes against the drums when you hit the pedal stopping faster. For $12 is seems like a good upgrade.

Is there such an upgrade for the XJ drum brakes?
 
What brakes do you have now? It seems to me that changing to 9" drums is a huge difference in braking power over the 10" drums

-Ron
 
Zuki said:
Ron;244412734]It seems to me that changing to 9" drums is a huge difference in braking power over the 10" drums

-Ron
Click to expand...
Really? How' that work?

EDIT: Sorry about screwing up the quote bit. Don't know how I did that.
 
The 10" drums have shoes that are only 1 3/4" wide. The 9" drums have shoes that are 2.5" wide. The surface area is larger on the 9" brakes, and provides more braking power.

I have seen people upgrade the masters on inferior brake systems. It's a waste of time and effort because in the long run, you have not addressed the root of the problem.

-Ron
 
This is incorrect. The 10 inch drums have about 7% more mating surface than the 9 inch. We checked this out long when this was still the XJ Forum, measuring actual contact area of the shoes.

Fred
 
mopar cop cars had factory 10 and 11 inch drums from the factory, which will bolt on most cherokees and comanches with minimal mods, and i have first hand knowledge that the 10 inchers will stop a 3200 lb., 10.40 drag car just fine without a parachute. I'd think they'd be fine for our cherokees for all the more they do. and my half ton dodge pickup has 10" drums on the back, and they will lock the rears up at will.
 
Fred said:
This is incorrect. The 10 inch drums have about 7% more mating surface than the 9 inch. We checked this out long when this was still the XJ Forum, measuring actual contact area of the shoes.

Fred
Click to expand...

I find it hard to grasp that a shoe that is 3/4 wider and only a bit shorter has 7% less total area, but the mind does play tricks. I have both sets of shoes in the garage. It sounds like a learning opportunity ;)

From a seat of the pants experience aspect, the 9" drums outperform the 10" brakes. The 98' will lock the 31's up tight, but the 86' or 85' never would.

-Ron

Edit: These are the shoe area measurments:
10" Small shoe: 16.19"; Large shoe: 19.25" TTL=35.44
9" Small shoe: 15.31; Large shoe: 21.88" TTL=37.19
 
Last edited:
I was unaware of 10" XJ drums, other than on the D44... I'm pretty sure XJ D44 drum brakes are 10"x2.5".
 
Read in a the old thread a member replaced the rear wheel cylinders with a set from a 84 amc eagle, if i am not mistaken and braking was greatly improved. larger wheel cylinder!
 
Just buy two sets of shoes and put the other two longer ones on in place of the two shorter ones. You end up with a significant amount more braking surface. I did this and could feel a big difference.
 
Zuki-Ron said:
I find it hard to grasp that a shoe that is 3/4 wider and only a bit shorter has 7% less total area, but the mind does play tricks. I have both sets of shoes in the garage. It sounds like a learning opportunity ;)

From a seat of the pants experience aspect, the 9" drums outperform the 10" brakes. The 98' will lock the 31's up tight, but the 86' or 85' never would.

-Ron

Edit: These are the shoe area measurments:
10" Small shoe: 16.19"; Large shoe: 19.25" TTL=35.44
9" Small shoe: 15.31; Large shoe: 21.88" TTL=37.19
Click to expand...

did the 86, 85 have the single diaphram booster? where the 98 has the dual diaphram booster
 
AlabamaDan said:
Now, before some of you guys say just upgrade to disc brakes, I'm looking for a simplier upgrade until that rear axle swap comes along. Ok, here goes...

I've heard that Dodge truck guys replace the dodge wheel cylinder with a 1 ton GM wheel cylinder. It's got a slightly larger bore diameter and it will put more pressure on the shoes against the drums when you hit the pedal stopping faster. For $12 is seems like a good upgrade.

Is there such an upgrade for the XJ drum brakes?
Click to expand...

dont know about the brake cylinder upgrade, but swapping out the single diaphram booster to a dual diaphram booster is a coomon upgrade.

what year is your xj?
 
Mine is an 88. So swapping to a dual booster from a single. I had no idea mine were single.

As for using the larger shoe on both sides, I wonder why they don't come like that?
 
Yes, but usually in the automotive world if it came like that, it was for a reason. Drum brakes with a floating adjuster are self-energizing. When the car is going forward and you apply the brakes, the wheel cylinder pushes both shoes out to contact the drum. When the front shoe contacts the drum, it tends to rotate with the drum. The rotational force is transferred through the adjuster link to the rear shoe. So now the rear shoe is being forced against the drum by the wheel cylinder and the front shoe. Because the rear shoe is doing more "work", it needs to be longer because it is doing a larger percent of the stopping. It also evens out the wear, as the rear shoe would wear out quicker if it were the same size since it is doing more braking than the front shoe.
 
Last edited:
Zuki-Ron said:
What brakes do you have now? It seems to me that changing to 9" drums is a huge difference in braking power over the 10" drums

-Ron
Click to expand...

Not sure what axle is being used, but the D44/Non C-Clip D35's use a 10" by 2 1/2 wide drum surface. I can lock up 35's with em. I also have a 97 booster and master cylinder installed as well.

I Did the prop valve mod, not very freeway safe, wouldn't recommend for a daily driver.
 
matchrocket said:
Not sure what axle is being used, but the D44/Non C-Clip D35's use a 10" by 2 1/2 wide drum surface. I can lock up 35's with em. I also have a 97 booster and master cylinder installed as well.

I Did the prop valve mod, not very freeway safe, wouldn't recommend for a daily driver.
Click to expand...

my 89 non c-clip d35 has 10 x 1.75 shoes.
 
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