why do you grind down rear backing plates and drums?

J

jnunez1955

Member
Im learning about installing hydraulic brakes on a Model A axle....but im really curious on to why must you grind 1/8th of an inch off both the backing plate and drum....i understand its for clearence, but i want to know the difference in the model a rearend vs the earlier v8 rear end.

is it the axle or the axle housing that is tapered in closer?
has anyone tried swapping the housing onto a model a 3rd member?
what options do i have to keep the stock rear without grinding anything down?
 
On a V-8 Rear End, The axle sticks out just a little further relative to the backing plate mounting flange then a Model A.

There is also a tapered shim that can be used which will space the drum out a little if you do not want to relieve the backing plate and drum.

Chris
 
Last edited:
CWPASADENA said:
On a V-8 Rear End, The axle sticks out just a little further relative to the backing plate mounting flange then a Model A.

There is also a tapered shim that can be used which will space the drum out a little if you do not want to relieve the backing plate and drum.

Chris
Click to expand...


thanks for the tip...i figure 1/8 off the drum and plate...so a total of 1/4.
where can you buy the shims? any negatives to it?
 
jnunez1955 said:
thanks for the tip...i figure 1/8 off the drum and plate...so a total of 1/4.
where can you buy the shims? any negatives to it?
Click to expand...

I don't think axle shims are a good thing as less of the axle key will go into the hub. I'd grind 3/16 off the drum, 1/8 off the backing plate rim and chamfer the edge of the brake shoe. My website shows the surgery required. Don't forget to buy some of the support rings for the wheels as 40/49 drums don't have the ridge needed for model A wheels. They are part 5199-8 $22.50 each at Sacramento Vintage Ford. They also have a lot of the other parts you need. Warning, the 40/46 brake hoses are too short, you need a longer ones.

http://members.fortunecity.com/pjsauber/HydraulicBrakes.htm

I actually think a better idea is to remove the drum from the hub, insert an aluminum spacer instead of all the grinding, and then installing longer studs. I haven't done this route myself. But that is what Dave Wilton does for his bendix backing plates. I'm currently installing some bendix plates on the rear of my 28RPU.

Remove the drum from the hub, insert an aluminum spacer instead of all the grinding, and then installing longer studs.
You dont have to remove any from the outer edge of the backing plates,
you dont have to remove any of the outer edge of the drum,
you dont have to grind away any of the shoes.
You dont have to rotate the backing plate to funny angles.
Take out the lug studs.
Separate the hub and drum
Position the backing plate so the wheel cylinder clears the spring hanger and is in the upright position.
Mount the hub properly.
Calculate the distance the drum needs to be moved out to fit properly.
Make a spacer to fill that space.
Install new longer studs
 
Last edited:
jnunez1955 said:
also, so the axle is the difference?
is the axle housings between the model a and later v8 the same length?
Click to expand...

The Model A and the Early '32 used the same axles.

I do not think there is a problem when fitting Hydraulic brakes onto 'Early '32 Housings so it sounds like the early '32 axle housing itself is a little shorter then a Model A (from the inside gasket surface to the backing plate mounting surface).

I never thought about it before.

Chris
 
mrtexas said:
I don't think axle shims are a good thing as less of the axle key will go into the hub. I'd grind 3/16 off the drum, 1/8 off the backing plate rim and chamfer the edge of the brake shoe. My website shows the surgery required. Don't forget to buy some of the support rings for the wheels as 40/49 drums don't have the ridge needed for model A wheels. They are part 5199-8 $22.50 each at Sacramento Vintage Ford. They also have a lot of the other parts you need. Warning, the 40/46 brake hoses are too short, you need a longer ones.

http://members.fortunecity.com/pjsauber/HydraulicBrakes.htm

I actually think a better idea is to remove the drum from the hub, insert an aluminum spacer instead of all the grinding, and then installing longer studs. I haven't done this route myself. But that is what Dave Wilton does for his bendix backing plates. I'm currently installing some bendix plates on the rear of my 28RPU.

Remove the drum from the hub, insert an aluminum spacer instead of all the grinding, and then installing longer studs.
You dont have to remove any from the outer edge of the backing plates,
you dont have to remove any of the outer edge of the drum,
you dont have to grind away any of the shoes.
You dont have to rotate the backing plate to funny angles.
Take out the lug studs.
Separate the hub and drum
Position the backing plate so the wheel cylinder clears the spring hanger and is in the upright position.
Mount the hub properly.
Calculate the distance the drum needs to be moved out to fit properly.
Make a spacer to fill that space.
Install new longer studs
Click to expand...



Yes, ive kept up with your entire website dealing with your Model A.
i was actually thinking a wheel spacer (they usually use push the rim farther from the drum) will work but instead pushing the drum father from the hub.
thanks for tips.
also, i know that you added the "Model A modern style backing plate from MT Auto Products of California"

 i dont know if you know, but 1948-56 f1 backing plates are self adjusting also and a lot cheaper then the MT stuff....actually from 1948-52
you can use the entire front brake set up including the spindle's because it had the same kingpin size for the model a axles.
and, if you use the backing plates from the 1948-56 f1/f100 (f1 only because i think f100 53-56 went to a larger kingpin dia. but still retained the same backing plate)

but there 11" brakes.
if you wanted the 12" brakes, you would want the f2 1948-56 ( alot of people use for the buick finned drum conversion.)

also all the internal brake parts from 1948-1966 i think are the same
so if you wanted to take your f1 backing plates and install later self adjusting kit on it...it will work great.
.

 
I have a set of those 11" drums with bendix backing plates. They were represented as from a 40 Ford and didn't return them because the postage wasn't worth it as I only paid about $100.

The ones I have are not self adjusting and they won't work on model A or 35 Ford wheels either. The front brake hose you need is SBH1001. I bought mine from a local parts house.
 
You must log in or register to reply here.
Back
Top