Drum brake width?
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Posting Guru
Joined: Apr 2005
Posts: 1,155
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From: Sweden (Fagersta)
Drum brake width?
Ok guys
In the rear the stock drom brakes are 11" in dia and 1 3/4" wide.
If I switch to a 9" rear with 11" dia and 2 1/2" wide
Would that effect the brake distribution? Brake torque front vs Brake torque rear?
According to my schoolbook the formulas for calculating the brake force (friction force) between drum and shoe, does not include the width of the shoe/drum interface as a parameter.
However i understand that the size (width) would increase the effect that the drums can handle without fading (i.e temperature rise) as the brake effect (energy over time) would be dstributed over a larger surface.
The larger surface would also increase cooling.
Sooooooo:
Will the width effect the brake distribution? Brake torque front vs Brake torque rear?
In the rear the stock drom brakes are 11" in dia and 1 3/4" wide.
If I switch to a 9" rear with 11" dia and 2 1/2" wide
Would that effect the brake distribution? Brake torque front vs Brake torque rear?
According to my schoolbook the formulas for calculating the brake force (friction force) between drum and shoe, does not include the width of the shoe/drum interface as a parameter.
However i understand that the size (width) would increase the effect that the drums can handle without fading (i.e temperature rise) as the brake effect (energy over time) would be dstributed over a larger surface.
The larger surface would also increase cooling.
Sooooooo:
Will the width effect the brake distribution? Brake torque front vs Brake torque rear?
Hotshot
Joined: Oct 2009
Posts: 16,135
Likes: 4,735
From: Burbank, WA
Obviously, as you stated, the larger the friction area, the better the braking force will be. Ford increased the brake size in 1968 because trucks got heavier and able to carry larger loads, and needed better braking. You will have better brakes with the larger shoes. Safe to assume you will notice a difference, but not to the extent to have ill effects. I don't have school books or an engineering degree to back up the opinion, but I have driven a truck with stock front drums and the bigger brakes like you're asking about with a newer 9" in the rear.
Thread Starter
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Posting Guru
Joined: Apr 2005
Posts: 1,155
Likes: 7
From: Sweden (Fagersta)
Well that´s my point.
Larger friction area DOES NOT mean larger friction force.
To increase friction force one haveto increase the slave cylinder force, or the friction coefficient. or Both
Increasing slave cylinder force can be done by increasing the cylinder diameter.
What I meant with more efficient brakes is that the larger brakes can handle more heat without fadeing. Not necessarly higher friction forces.
Larger friction area DOES NOT mean larger friction force.
To increase friction force one haveto increase the slave cylinder force, or the friction coefficient. or Both
Increasing slave cylinder force can be done by increasing the cylinder diameter.
What I meant with more efficient brakes is that the larger brakes can handle more heat without fadeing. Not necessarly higher friction forces.
Laughing Gas
Joined: Jun 2011
Posts: 1,041
Likes: 53
From: Sterling CO
I swapped a 1948 (stock) dana 41 for a 1972 ford 9".
so bigger brakes (as you mention), bigger wheel cylinders (I believe by 1/16" ).
There is no noticeable driveability change at all. That said, subjectively I would say my old worn out 1948 brakes are not as good condition as my "basically new" 1972 setup (I picked the absolute best looking set in the junkyard). It's still balanced, you don't have premature rear lockup issues or anything.
I drove it that way for about 500 miles, then got a new master cylinder (front leak, and a rebuild kit was more expensive than swapping to a dual master). I changed to a 10-1485, and again with that no premature lockup or any other issues. I tested both on pavement and gravel.
so bigger brakes (as you mention), bigger wheel cylinders (I believe by 1/16" ).
There is no noticeable driveability change at all. That said, subjectively I would say my old worn out 1948 brakes are not as good condition as my "basically new" 1972 setup (I picked the absolute best looking set in the junkyard). It's still balanced, you don't have premature rear lockup issues or anything.
I drove it that way for about 500 miles, then got a new master cylinder (front leak, and a rebuild kit was more expensive than swapping to a dual master). I changed to a 10-1485, and again with that no premature lockup or any other issues. I tested both on pavement and gravel.
Thread Starter
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Posting Guru
Joined: Apr 2005
Posts: 1,155
Likes: 7
From: Sweden (Fagersta)
I swapped a 1948 (stock) dana 41 for a 1972 ford 9".
so bigger brakes (as you mention), bigger wheel cylinders (I believe by 1/16" ).
There is no noticeable driveability change at all. That said, subjectively I would say my old worn out 1948 brakes are not as good condition as my "basically new" 1972 setup (I picked the absolute best looking set in the junkyard). It's still balanced, you don't have premature rear lockup issues or anything.
I drove it that way for about 500 miles, then got a new master cylinder (front leak, and a rebuild kit was more expensive than swapping to a dual master). I changed to a 10-1485, and again with that no premature lockup or any other issues. I tested both on pavement and gravel.
so bigger brakes (as you mention), bigger wheel cylinders (I believe by 1/16" ).
There is no noticeable driveability change at all. That said, subjectively I would say my old worn out 1948 brakes are not as good condition as my "basically new" 1972 setup (I picked the absolute best looking set in the junkyard). It's still balanced, you don't have premature rear lockup issues or anything.
I drove it that way for about 500 miles, then got a new master cylinder (front leak, and a rebuild kit was more expensive than swapping to a dual master). I changed to a 10-1485, and again with that no premature lockup or any other issues. I tested both on pavement and gravel.
Laughing Gas
Joined: Jun 2011
Posts: 1,041
Likes: 53
From: Sterling CO
For the record, everything locks up on ice (I just remembered Jim is in Sweden) :P
And my fronts are still original setup drum, and still about half worn, I did not replace all the front parts.
And my fronts are still original setup drum, and still about half worn, I did not replace all the front parts.
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