Steering, Suspension, & Brakes

tips, technology, tools and techniques related to non-driveline mechanical components

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dlwharleyman
David Winn

(2 posts)

Registered:
11/20/2017 10:44PM

Main British Car:


Stay with rear drum brakes or go to disc? Upgrade front disc brakes?
Posted by: dlwharleyman
Date: May 25, 2018 12:34PM

My 74 Jensen Healey has a Ford 9 inch rear end. I'm not sure if it has the original healey drum brakes or has the Ford drum brakes. It has the original front disc brakes. Just wondering if it's worth it to change over to rear disc brakes and are there kits to do this? Saw a video on the installation of a disc kit, but the installer had to do a fair amount of fabrication and welding to the kit to get it to fit correctly. Also, since the car has a TPI 350 should I consider upgrading the front disc brakes?


rficalora
Rob Ficalora
Willis, TX
(2541 posts)

Registered:
10/24/2007 02:46PM

Main British Car:
'76 MGB w/CB front, Sebring rear, early metal dash Ford 302

authors avatar
Re: Stay with rear drum brakes or go to disc? Upgrade front disc brakes?
Posted by: rficalora
Date: May 25, 2018 09:28PM

You probably have the Ford drums. Can't imagine anyone putting MG drum brakes on a 9" Ford.

As for whether to switch to disc, depends on what you want and how you drive. Some will disagree, but braking needs really aren't dependant on horsepower. It takes the same braking force to slow down a 2500 pound mass from speed X to 0 no matter how fast the mass got to X or how long it has been at that speed.

So, if you can lock up your brakes and don't experience brake fade, big brake kits for the front or switching the back to disc is not really going to buy you anything. But, if you can't lock them up (and they're working correctly) or do a lot of corner carving at speed and are experiencing brake fade an upgrade would be in order.

Another reason to upgrade is if you just like the look and want to. I fall in this bucket. No real need, but wanted discs to show thru my wheels rather than drums.

Whether you keep your existing or switch to big front &/or rear discs, Google how to check brake bias and how to adjust it. You don't want the back brakes locking up 1st as that'll cause the the rear end to come around you pretty quickly!

Lastly, depending on what master cylinder you have, switching to rear discs might require you to add residual pressure valves or even install a bigger master cylinder. Reason is calipers require more brake fluid volume than drum brake wheel cylinders.


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5655 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: Stay with rear drum brakes or go to disc? Upgrade front disc brakes?
Posted by: BlownMGB-V8
Date: May 26, 2018 02:55PM

"braking needs really aren't dependant on horsepower."

Yeah, I do disagree since it's a power-in/power-out formula. Ordinarily correct but by shortening the time to speed as well as increasing top speed, cooldown time is truncated and can lead to brake fade. Not in every case clearly but it can under repetitive braking conditions. (Like competition)

Jim


rficalora
Rob Ficalora
Willis, TX
(2541 posts)

Registered:
10/24/2007 02:46PM

Main British Car:
'76 MGB w/CB front, Sebring rear, early metal dash Ford 302

authors avatar
Re: Stay with rear drum brakes or go to disc? Upgrade front disc brakes?
Posted by: rficalora
Date: May 26, 2018 04:47PM

"cooldown time is truncated and can lead to brake fade"

Right. Not directly related to HP; rather, to driving habits. For the average street driver, stock brakes are plenty and won't experience brake fade. But that's why I said "or do a lot of corner carving at speed and are experiencing brake fade an upgrade would be in order". I also allowed for extra driveline weight with "but, if you can't lock them up (and they're working correctly).

I think we agree vehicle weight and driving style are the primary factors affecting whether an upgrade is needed on our cars.


88v8
Ivor Duarte
Gloucestershire UK
(609 posts)

Registered:
02/11/2010 04:29AM

Main British Car:
1974 Land Rover Lightweight V8

Re: Stay with rear drum brakes or go to disc? Upgrade front disc brakes?
Posted by: 88v8
Date: May 29, 2018 04:46AM

The fronts do 80% of the work, so upgrading the rears will usually give little perceptible improvement**

If you want to make the drums look cooler - Google finned drums for Ford 9"

Ivor

** unless you spend a lot of time going backwards. Spike Milligan was into going backwards
[www.youtube.com]


DiDueColpi
Fred Key
West coast - Canada
(1259 posts)

Registered:
05/14/2010 03:06AM

Main British Car:
What if the Hokey Pokey really is what it's all about?

authors avatar
Re: Stay with rear drum brakes or go to disc? Upgrade front disc brakes?
Posted by: DiDueColpi
Date: May 30, 2018 12:13AM

Past experience has taught me to "Ixnay on the akebray"
But I'm a slow learner. So here goes.

Common sense says that the vehicle has to stop. And they all do .....eventually.

Bigger brakes are not always better, generally they add unwanted unsprung weight, rotational drag and added inertia to the rotating wheel mass.

The bigger the brake gets the more power that is needed to deal with it. Whether you are speeding up slowing down or turning it all creates heat that is lost power.
Shock tuning, spring rates, brake bias, alignment specs, master cylinder choice and on and on. All need to be rethought with a change in brake size.

Ideally the smallest brake package that will get the job done would be the best choice.
But that's not how it works out in the real world.
First you need to convert whatever velocity the vehicle has into heat, generally multiple times. And you need to consider the tire size and contact patch. Do the brakes match the available traction?

Once you get that down you should be fine.......unless you have a bigass motor.
What if you mash the fun pedal? Can you stop the car?

In the econo car world. Hamster breath can overpower the motor. So the rules are different. You need to deal with the mass of the vehicle.

My hot rod math says that the brakes need to be bigger than the motor.
Our cars are usually a little more endowed in the hp department.
So in our world the engine will generally dictate what kind of braking system you use.
And show boating counts as well, so there's that too.

To me, if you are unsure, go bigger. You may not have the perfect setup for your car, but you will still be around to have the discussion.

To get back to the original question, assuming that you have the original 9" brakes you should be fine. A disc conversion will look cute but won't really buy you anything.
The Jensen fronts however are not up to the task and should be upgraded yesterday.
I don't have a clue as to what is available to you in that regard, but I would make it my mission to find out.

If you can't stop ....don't start!

Live like you mean it.
Fred


geezer
Charles Durning
Magee, MS
(45 posts)

Registered:
11/16/2017 01:16PM

Main British Car:
1974 MGB, 1967 Morris Minor

authors avatar
Re: Stay with rear drum brakes or go to disc? Upgrade front disc brakes?
Posted by: geezer
Date: May 30, 2018 12:04PM

Well I switched my 74 BGT to rear disc. That was a huge improvement in braking performance. I will definitely do it again on my next car. Heck I even have 4 wheel disc brakes on my Morris Minor. Time and money well spent. Nothing better than good modern brakes on an old car.



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