are disc brake conversions bad ?

J

jason_is_here

Member
I was reading somewhere that some people say they're bad because the straight axle design.
Something about it puts twisting force on it ?
 
Regardless of brake system, your limiting factor will be the traction of the tires on the ground.
So, as many on the Barn will relate, the stock brakes do not need to be changed. I have kept my stock brakes and they will lock up the tires so changing to hydraulics of any flavor must have other considerations to factor in like changing the drivetrain.
 
Stock brakes in good condition are fine for driving at 45 MPH. If you drive faster, or with modern cars, or hilly country, you need a better brake. As stated by Bob C, all brakes tend to twist the axle but the A axle is plenty strong to handle that.
 
Yes I realize any brake would cause a twist but obviously some more so than others.


Ok doesn't sound like I'm gonna be causing any major issues by using them.


Thanks again
 
Jason, the twisting force is of course going to happen with whatever brakes you used but of course the stronger the brakes the more twist. The wishbone is there to take care of that and I’m certain they would be up to the task, if not they can be reinforced.
 
Some basic science here.....

So Model A brakes properly rebuilt do a wonderful job stopping it from 65-70 MPH. The limiting factor is the tire contact patch on the pavement.

The best you can do force wise is keep the braking force just below where the wheel locks up. Once it locks up the braking force is greatly reduced. Factory brakes have no problem locking the wheels when they are rebuilt properly.

So the forces are same for factory brakes or disk brakes cause no matter what the conditions. The limit is the tire on the road.

So obviously if you go to later tires you will get more force, but that still is not really a problem because the axle is way tougher then braking force as the force of a pot hole at 30 MPH is likely way more.

The A does not need different brakes it needs properly rebuilt brakes. A properly rebuilt car running 60 MPH will do fine stopping with properly rebuilt brakes.

Doing brakes on the A is not cheap, easy or fast. It also requires special tools and like most of the A, Attention to details. I find most people cant do them right.
 
A few comments: Disk brakes are not available for a stock Model A. So going to disk brakes means changing out a lot more than just the brakes. Most Model A's are not driven hard enough to need disk brakes. Lots of people like to keep their car as tock as possible, or at least looking stock, so disk brakes are not for them.

The advantage of disk brakes is fade resistance. So if you are coming down Pikes Peak you can ride the brakes all the way down without having to worry about the brakes fading.

Regarding tires: If you want to keep the stock size wheels, the best you can do is go to radial tires, which grip the road better. The larger tires, I am thinking 16 inch wheels, are better on dry roads, but will have a greater tendency to hydroplane on flooded roads.
 
jason_is_here said:
Yes I realize any brake would cause a twist but obviously some more so than others.


Ok doesn't sound like I'm gonna be causing any major issues by using them.


Thanks again
Click to expand...

Disc brakes or drum, the twisting will be the same unless you use stickier tyres, then the sky is the limit but who wants to drive a hot rod???
 
Trust the Frank
 

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jeepguy1948 said:
I want to drive a hot rod....
Click to expand...

I love my Model A, but like you, sometimes I like to drive a hot rod
And sometimes...it's hard to decide which one
 

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There are a lot of hot rods running around with disk brakes on straight axles. And they work just fine.

But, on a stock Model A ? That just ain't right ! If the brakes have been installed and adjusted correctly the brakes will lock up if wanted up to about 40 mph. I've had to do it a number of times.
 
I did not complete my train of thought yesterday.
Kevin in NJ picked up my train of thought. Since the limit to the forces put into the axle is based on the traction of the tire on the road, it doesn't matter what type of brake you use to apply the stopping force. Many hot rods use disc brakes with modern tires on original or (worse for twist) 4" dropped axles. The only twist concern I have heard comes from using radius rods with tube axles.
NKaminar, there are disc brakes for stock model A's, sort of. They are hydraulic and, I think, require later model spindles but Mike Hoskins outside of KC, MO is putting together a disc brake kit for use with stock Model A wheels right now.
The advantage of the disc brakes is the higher performance, the disadvantages include the looks and the loss of originality.
To each his own. Jason, it is your car, build it the way you want to. Model A's are not an endangered species.
 
It's not about locking up the wheels, it's about fading, and almost anything is an improvement over stock 'A' brakes. Come down Pikes Peak and you'll find out what it is like.
 
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