rear brakes locking up

[Gibbo]

On my corsa i have rear disk conversion. when i go to stop and press hard/ try and stop qwickly they lock up.but the front dont like you would expect.Even when i slow down fast useing gears and not put my foot as hard on the brakes they do the same and send me wide ways .anything i can do to stop this ?

[bazil]

Aye go back to drums lol

[autoworksnovasport]

get a bias adjuster inline

[Royston]

During braking weight is thrown forward, leaving the rear wheels light hence the lock up, you have also improved the braking capability on the rear, as suggested a bias valve may be needed

[Gibbo]

one of these http://www.ebay.co.uk/itm/Brake-Bias-Valves-/280847943565?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item4163d7878d ?

[autoworksnovasport]

yeah no nead to spend that amount though

[Gibbo]

were can i get a cheaper one from ?

[autoworksnovasport]

http://www.compbrake.com/brake-kits/brake-valves.html

try these

[mowgli]

a corsa has a load sensing valve under the back, why not just tweak it to suit.

[Gibbo]

thank you. rep + I will order one of these http://www.compbrake.com/brake-kits/brake-valves/bias-valve-without-unions-rotating-type.html

[Gibbo]

a corsa has a load sensing valve under the back, why not just tweak it to suit.
i forgot about them. dident know if they could be messed with?

[Novasport]

No doubt your Corsa is lowered so you have fooled the car into thinking it is carrying substantial weight. This will adjust the load sensing valve on the rear axle allowing the rear brakes to work harder. As said, adjust the valve accordingly and this should help. I would try this first before going to the trouble & expense of fitting a bias valve.

[mowgli]

if you remove the spring & fit an adjuster bolt, you will be able to tune it to suit.

i'm sure you could fit a bias control from a leading motorsport supplier...

[Stan Wrecked]

The brake lines run left front and right rear on a standard road car from the brake servo. This means you will need to change the brake lines to run one side of the servo to run the front brakes and the other side to run the rears. You can then fit a bias valve to reduce rear brake effort. If you dont do this then you will only reduce locking on one rear wheel. I would check the load compensator first, this could be stuck and is a commen fault. The valve adjusts when more weight is in the rear of the car to move bias backwards, ie when the boot is full and you have rear passengers. My track car locks the rears when the fuel tank is lower than 1/4 full. I get around this issue by keeping her full of fuel, about 40kg over the rear axel. Hope this helps

Stan

[mowgli]

stan, this is why i mentioned the load sensing valve, it is basically a 2 line bias valve.

what worries me now is that you need to put 40kg of fuel in to stop a cars brakes from locking up, adjust the valve for safety's sake at least.. and dropping 30kg from your car's weight is probably worth at least 1/2 second per lap, and that's before you've improved your brake balance, which will be worth even more time.

[Stuart]

http://stoptech.com/technical-support/technical-white-papers/proportioning-valves


Velly good read

[Stan Wrecked]

Hi mowgli
Im not running a valve on the rear brakes so unable to adjust. The car is a track car and is 722kg with half a tank of fuel so is very light and stiff as a board due to running coilovers and 888s. I would always say to check basics first then look at a bias valve as a last resort. I agree with your comment about balance but Ive only got about 80 bhp so looking for more power. My car is at Bogg brothers rolling road having the new Twin 40s jetted and balanced as we speak. Check out my build thread for updates all done on a shoe string ;)

[mowgli]

i used to work at a commercial veh. brake parts company. they had books with characteristic graphs in for various load sensing valves, which was handy if someone wanted bits for some obscure lorry or bus that was no longer available, we could match up an equivalent.. those old books were fascinating..
i really don't understand why car makers went away from load valves, apart from the cost implication... even the early mk1 astras had them, and externally adjustable rear brakes, so you never actually had brake trouble that took a lot of fixing.. then along came proportioning valves.....

[mowgli]

Hi mowgli
Im not running a valve on the rear brakes so unable to adjust. The car is a track car and is 722kg with half a tank of fuel so is very light and stiff as a board due to running coilovers and 888s. I would always say to check basics first then look at a bias valve as a last resort. I agree with your comment about balance but Ive only got about 80 bhp so looking for more power. My car is at Bogg brothers rolling road having the new Twin 40s jetted and balanced as we speak. Check out my build thread for updates all done on a shoe string ;)

stan, this is about corsa brakes. i just read your thread, you have good old nova brakes with the 256 front upgrade.. what valves are you running on the master cylinder? you should have 3/25 iirc..
also, the only reasons i can think that your rears are locking are that you have boiled up the fluid, or your rears are out of adjustment, so when you jump on the brakes, the rear cylinders move a lot further than they should before braking, and this takes the edge off the fronts. i used to suffer from this on my first nova, but a brilliant mechanic at where i worked showed me a proper old school trick he had done to his astramax.. you take the drums off, & measure just how far from the centre the adjuster is, then drill a 12mm hole in the face of the drum, then using a small allen key, you pull the pawl away from the adjuster and then adjust it up with a small straight screwdriver. then put the wheel back on & it covers the hole up.
99% of all nova brake issues can be blamed on the rears, the other 1% are the few left with 236 delco sliders.... lol

[Gibbo]

cheers all:thumb:.all sorted now. the load sensing valve was stuck.must have done it when i got the car, it was lowered around 110mm:tard: when i put the 60mm spring on must had stayed there:roll: