Rear drums overheating switch to disks etc.

[groutledge]

Does anybody have any comments on this...

 

Last Monday I had a track day at Donington with my 160bhp live axle. I am currently running EBC grooved and vented disks on the front with 4 pot Wilwood cailpers and greenstuff pads. The rear is standrad Ital drums with Green stuff shoes, wheels are weller steel, tyres Yoko 21/32Rs.

 

While the green stuff pads give a good feel and retardation they tend to break up under heat in fact by the end of the day my rear shoes which where nearly new where shot on one side, fronts aren't a problem as they are vented and very understressed anyway.

 

For the time being i've stuck the caterham shoes back in the rear.

 

I spoke to Sejoc ( EBC supplier ) about this and he said they had the same problem with the mighty mini race cars so they "cross drilled" the drums. This involved drilling rows of countersunk holes around the drum friction surface. This is supposed to get rid of the dust and also let the heat out.

 

Any body got any comments on this or have any other ideas on rear brake cooling. EBC do a disc brake conversion for live axles using a VW caliper and an in line bias valve but this is £450+fitting and VAT and seeing as I may have to uprate the axle, ( which is already a strengthened SPC item with a quaiffe lsd ), to an atlas or Ford it may be a waste of money.

 

I'd like to make the drums work as they should be more than enough for a live axle.

 

Any ideas chaps, get those opinions rolling!!

 

Graham

[I.Mupferit]

Graham,

With the uprated fronts you have I am surprised the rear drums are apparently taking so much of the load, I have not previously heard of such a problem. As they seem to be generating so much heat would it be worth trying the Redstuff shoes? Although they would probably not be too good for road use, but maybe with a bias valve?

A slight digression, but you say your axle is a strengthened SPC item. Apart from the LSD, what exactly have they done to strengthen it? I only ask because I have a live axle car with over 190 bhp which I tend to feed VERY carefully through the drive line - given the horror stories we keep hearing about the Ital axle. I agree with your opinion of the EBC grooved discs and Greenstuff pads at the front having just fitted a set myself, they are really excellent.

 

Brent

 

[StewartG]

I would have thought with the rear drums working this hard the brake balance must be so rear biased as to make the thing scarey. It's a problem with the seven's open front wheel layout that front brakes run a lot cooler than rears. This makes the back brakes more efficient and leads to rear lock up. The solution is usually bigger front brakes so maybe your EBC discs and Wilwood calipers aren't giving the desired increase in front retardation for some reason. Have you bled them properly? As a second thought I wonder why you said the rear shoes were nearly worn out on one side this in itself sounds suspicious surely equal wear is expected.

 

Edited by - stewartg on 6 Mar 2001 23:45:27

[flick]

Concerning the rear brake wear being uneven on the live axle car, A good place to start is to remove the drums and check to make sure the wheel cylinder is free to slide as this is very important in this setup.

 

The wheel cylinder has only one piston and the force is distributed via the piston sliding on the back plate, If this is seized up you will only get brake effect on on shoe.

 

Also check to make sure the piston is not seized in the side that is not wearing out the shoe's

 

Regards

Flick

[R2D2]

I imagine that the Green Stuff pads may be an organic material and one of the reasons that disc are grooved and cross-drilled is to allow the removal of the gas that is produced when these new materials become hot. It could be that if there is a build up of gas it could have an insulating effect that may not help.

 

It is surprising that you are having this problem because if you have only converted the front brakes the rears should be being used less.

I am fairly sure that you must have some type of rear brake problem and I think I would start by checking the complete function of the rear brakes.

 

I have seen figures quoted that upgrading front brakes can reduce rear brake effort to as little as 26%. I don't know what he balance for a standard Caterham is but 64/36 is fairly typical for road cars.

 

I think that the subject of brake balance is quite interesting and SPA sell an instrument to measure and log changes of brake balance and it would be good to see what effect changing balance had on stopping distances and lap times.

 

 

[groutledge]

Thanks for the replies chaps. The rear shoes did not actually wear out but instead broke up on one side with chunks of the friction material breaking away. I think the problem with greenstuff pads/shoes is that they are quite soft and susceptible to heat (I'm not the first to experience this problem!). Up to this point the brakes where working perfectly.

 

I tend to stand on brakes quite hard and late as I am used to a Sport 190 Elise which has Pagid equiped race brakes. These are horrendously expensive £120+ for a set of pads but will take just about any amount of abuse you can throw at them!, perhaps i should adjust my driving style :)

 

Sejoc are currently cross drilling a set of brake drums for me now and I'll let you know how I get on with them, i must say they are very freindly and helpfull chaps!. If it works and stands up to the abuse I'll go back to using.

greenstuff rear shoes as they have a better feel and retardation to the mintex. If this still fails I stick with Mintex as they are OK once they are up to temp...

 

The theory is that the holes with cool the drums and also clear any dust and gas from the friction surfaces, I don't see why it shouldn't work as it does for discs!. I may also try drilling the back plate and feed cold air through the drums via a brake cooling ducts, but first things first.....

 

It may also be because i am using steel wheels and these don't get rid of the heat as quick as alloys, anybody have any facts on this?

 

 

As for the rear axle I don't think it's sepcifically strengthened in any way maybe higher grade drive shafts thats all.

Graham