Dramatic front wheel locking when braking.
 

Hi guys.

The brakes work fine (been tested on the rollers at SVA and MOT). But they seem to lock far too easy the front ones. Skidding along the road at low speed (around 20-30 MPH. Over dramatic.

The front brakes got 95% pass rate at the MOT.

Anybody else had this problem?

ah yes John I had the same issue. And at castle combe it was embarrasing locking up the front wheels every time i came up the the chicanes...!
The standard 1.6 FWD brake set up is not good enough for us with the heavier T16 engined 5EXis.

I immediately switched the rear callipers and discs for the larger rover (ZS?) set-up...which has helped a lot...but I reckon I will have to go larger again at the back to ensure better braking performance on the track (with an adjustable valve in-line).

Look at other lightweight mid-engined cars eg lotus elise...disc size at the back is the same at the front...etc...etc...MK1 Lotus Exige is a good example to follow as it has the same weight and distribution as our cars john...

HTH, John

I noticed this just driving around my driveway, and also could feel the fronts massively over-powering the rears on the 1.6 demo car I drove - the ground was slightly loose.

As John said, most mid engined cars of a similar proportion to the 5exi seem to have at least the same size rear discs.

Like the Elise, the VX220 also has the same discs front to rear, though different calipers. My friend finds his VX very prone to locking the fronts (well firing the abs), especially in the wet when you can't as easily gradually load up the fronts to get the grip.

My plan is to get through the SVA with whatever it takes, then up the size of the rears considerably, and control with a bias adjuster.

ah glad it's not nothing to do with what I have done.

I'm using the standard turbo brakes all round.

As an aside, my daily driver, which is a FWD hatch, has the same size disc front and rear......

The std rover brakes are designed to stop a much heavier car so can the bias be adjusted enough to cure this issue.

As I did not have a donor car I had to buy the Rover brakes new so would rather not throw away and start again.

there is no bias adjustment as fitted to your exi...
unfortunately those of us with the T16s and probably the Honda engines will find this issue soon enough...

I'll be designing in some bigger rear brakes soon I reckon.......:-(

is it not possible to add a brake proportioning valve into the brake line for the front brakes and reduce the pressure this way , leaving the rear at full pressure ?

Weight's not the only factor though, another key consideration is the rate at which you can put energy into the brakes, especially if you're going to track the car.

For the SVA, not totally clear. But I thought an adjustable brake system is not allowed. Not sure if it means adjustable while driving the car. Can't remember now. I can ask the SVA guy when I go back on the 12/7 ??

No valve for SVA as far as I'm aware. It makes sense to me that a valve is not allowed; I'm not sure if this is the reason, but they only test the car in one state, and if you can change the balance from what they test, how do they know it's still safe?

Adjustable bias valve if fitted has to be tested in its worst case setting i.e. full force to rear (a bit of a waste of time then) unless it is locked off so it can't be adjusted without special tools. This is usually taken to be welded or locked with a roll pin - lock nuts are not acceptable as they can be easily unlocked with a spanner.
Some people have gone to the trouble of cutting a roll pin in half so to the tester it looks like the adjuster is locked and theoretically they can't mess with the car and have to test it as presented but that seems pointless to me as the pin could just be drifted out after the test anyway.
In my case the adjuster is hidden away behind a panel which also prevents anyone fidling with it.

Yup! thats where mine will be aswell as an sva inspector is not allowed to take anything apart!!!

Yes, but he can ask for you to remove (within reason) panels etc for inspection as i found out when i took my last car for SVA.

Mike

Can't ask you to remove the dash and screen though can he??

I'm opting to fit a bias valve after the SVA (in 2011 at this rate! :) ), as I want the bias valve somewhere easily accessible for me / very obvious to the SVA tester.