Going for rear disks on an SD1

[Andy515666]

Hi guys

been quite a while since i was here last.... not sure if thats a good or a bad thing>!?!?!?!?

Was pondering the idea of replacing the rear drums to disks for my SD1.

Good idea/Bad idea/A lot of work/Not worth it?

The application is road purpose. FAST road but still just throwing the idea around.

[bones]

Hi,when i was looking at doing that to mine, i was told it would be wasted money ,so i didnt bother. I use mine for abit of fast road and drag racing,but i dont suppose this helps you much, rich

[Andy515666]

Hi Rich

Yeah thats what I thought but I have not really done any study to find out if its really worth while.

Just a set of good pads will do for now.

I will need to upgrade the brake master cylinder i suspect. Any advice on this????

[CastleMGBV8]

Andy,

I would agree with bones.

The rear brakes on most cars only contribute 20 - 30% of the breaking effort, so upgrading to rear discs isn't really necessary as you are unlikely to experience brake fade on the rear, so breaking performance will not be affected nor improved with a rear disc system.

Theres also the hassle of getting an effective handbrake system.

Kevin

[ramon alban]

pondering the idea of replacing the rear drums to disks for my SD1. Good idea/Bad idea/A lot of work/Not worth it? The application is road purpose. FAST road but still just throwing the idea around.

Hello Andy,

My first thought is "How fast is the road and is it similar to the ones we all drive on every day?". Probably so, in which case read on:

# Approx 70% of braking effort is applied to the fronts, with the rears just steadying the car.

# The brake balancing or pressure limiting valve divides the available energy between the front and rear brakes to prevent the rear wheels locking up before the fronts.

# Let's assume one simply changed/adjusted that valve to allow the rears to get more energy from the system? Upon normal enthusiastic braking (as opposed to emergency stops) the rears lock up, the car may go out of shape, definitely so if not in a straight line, and the preponderance of an accident (?) is quite high.

# I reckon that would be a No-No. What do you think?

# Lets say one put a more efficient system (discs?) on the rear that uses its normally typical 30% share of total energy much better.

# The fronts behave normally with their 70% share, but the rears break away too early - result, unstable braking again. Accidents waiting to happen?

# All this on our modern roads, infested with some incapable/ inexperienced drivers who do strange things without warning. At the same time the FAST ROAD brigade of very competent drivers, thee and me included I hope, are just hoping to hell we dont come across a dullard, but when we do, the last thing one needs is the rears locking up before the fronts, methinks?

# OK! One wants to be able to stop on a sixpence, and thats a good thing, then its a must, to uprate both fronts and rear brakes equally, I reckon, and that means fitting a more powerful set up-front.

# Indeed that may be all that is needed, as mentioned before, as the rears only really steady the car under heavy braking.

# There is another view! SD1 rear brakes are notoriously difficult to set up 100% tickety-boo and any braking system can be under-performing compared to the day it emerged from the factory, yet still get thro' an MOT.

# Perhaps all one needs is to review the current maintenance program, get the whole system 100% "Purfek" and then decide how much upgrade one needs.

Evverything needed is here:

http://www.vintagemodelairplane.com/pag ... ing01.html

[chodjinn]

I have a disc conversion on my SD1 axel.

Uses Sierra Cosworth calipers and Mercedes solid discs. Pretty simple swap by the look of things, and handbrake is sorted as the cossy caliper uses a cable. Can't remember if it uses special adapters or not (I didn't do the conversion).

[ged]

Hi All,

For normal every day driving a well maintained standard SD1 brake setup does the job. But if you like to occasionaly drive hard & fast through the twisty bits you will feel the benefit as the standard system does fade quite badly when hot. As Raymond has pointed out if you,re going to upgrade the rear you should also do the front.

I've got 305mm vented on the front & 265mm vented on the rear.

As for how hard is it to do. Well you have to find suitable discs & adapt them, then make mount's for the calipers, new brake pipes & handbrake cable. Cost would be quite expensive unless you have access to machinery. And finally will your standard wheels still fit.

After all that even though it was a pain in the a*** to do, they work well & look good.

[Andy515666]

pondering the idea of replacing the rear drums to disks for my SD1. Good idea/Bad idea/A lot of work/Not worth it? The application is road purpose. FAST road but still just throwing the idea around.

Hello Andy,

My first thought is "How fast is the road and is it similar to the ones we all drive on every day?". Probably so, in which case read on:

# Approx 70% of braking effort is applied to the fronts, with the rears just steadying the car.

# The brake balancing or pressure limiting valve divides the available energy between the front and rear brakes to prevent the rear wheels locking up before the fronts.

# Let's assume one simply changed/adjusted that valve to allow the rears to get more energy from the system? Upon normal enthusiastic braking (as opposed to emergency stops) the rears lock up, the car may go out of shape, definitely so if not in a straight line, and the preponderance of an accident (?) is quite high.

# I reckon that would be a No-No. What do you think?

# Lets say one put a more efficient system (discs?) on the rear that uses its normally typical 30% share of total energy much better.

# The fronts behave normally with their 70% share, but the rears break away too early - result, unstable braking again. Accidents waiting to happen?

# All this on our modern roads, infested with some incapable/ inexperienced drivers who do strange things without warning. At the same time the FAST ROAD brigade of very competent drivers, thee and me included I hope, are just hoping to hell we dont come across a dullard, but when we do, the last thing one needs is the rears locking up before the fronts, methinks?

# OK! One wants to be able to stop on a sixpence, and thats a good thing, then its a must, to uprate both fronts and rear brakes equally, I reckon, and that means fitting a more powerful set up-front.

# Indeed that may be all that is needed, as mentioned before, as the rears only really steady the car under heavy braking.

# There is another view! SD1 rear brakes are notoriously difficult to set up 100% tickety-boo and any braking system can be under-performing compared to the day it emerged from the factory, yet still get thro' an MOT.

# Perhaps all one needs is to review the current maintenance program, get the whole system 100% "Purfek" and then decide how much upgrade one needs.

Evverything needed is here:

http://www.vintagemodelairplane.com/pag ... ing01.html

Woah!!!! Thats some pretty good info Ramon.
Think i will just stick with the current set up.
Have upgraded the front disks to slotted with 4 pot callipers so was just toying with the rear.
Too much work and for what purpose is the main question I am asking myself.

Always good to get the answers from the forum. Ive missed not being around here!

Andy

[bones]

i fitted jag front brakes and calipers to the front of mine, ive heard of some putting grooves on the rear drum to help abit, rich

[topcatcustom]

Can you get alloy finned drums? You can get them for classic mini's and are very light and disperse heat very quickly!

[Robrover]

I considered fitting rear discs but was told not to bother and use Jag dics upfront. But I wanted to keep my 14 inch Minilites, and the Jag brakes won't fit under these.

So instead I use Vitesse dics and calipers, braided hoses, green stuff pads. The car is also relatively light with fibreglass bonnet, bumpers, rear hatch with perspex screen, etc so it's not too heavy to stop. Seems to work ok for normal road use.

Some Buicks form the 60/70s used finned alloy rear drums (similar to the Minifin ones).

[john 215]

Hi,
Carrying out a rear disc conversion for my TR7 V8 at the moment, as you all know the five speed seven axle is basically an SD1 axle shortened and the half shafts are 4 stud fixing rather than 5, a couple of pictures-



And yes it is in my conservatory, its great being divorced Old master cylinder temp fitted to test for leaks ect!



Taken whilst mocking up



Cheers John

[topcatcustom]

How do you sort out getting the driveshafts shortened when you cut the axle down?

[Basil]

Easily done.
Rover 820 calipers (rear)
BMW 520 Discs need machineing.
Brackets I have a box of them.

So long ago since I did it cant remember wether it needed a brake pressure reduction valve.

Is it worth it. depends how often your drums need adjusting, and wether you do track days.

Jag brakes were a definate advantage, on front.

Cheers David

[john 215]

Hi,
A lot of conversions on TR7's (basically the same axle) use Rover 800 calipers. They end up hanging down at about '5 oclock' because of shock mount gets in the way! Unfortunatley cant use the BMW discs as only 4 stud on the Triumph. Mine are Maestro / Montego front discs with minor rework to get them to fit over half shaft flange.
Cheers John