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I have an NB8A track day car in which I have just upgraded the brakes, front and rear, to the "big brakes" of the NB8B. However, I have left the brake master cylinder unaltered. At Winton on the weekend, I was locking up the rear brakes when I had to do anything like hard braking (and really not that hard).

Is there a mismatch between master cylinder and the front and rear brakes? That is, is the braking system applying too much force to the rear brakes, or do I have some other problem?

You've added 5% bigger front rotors and 10% bigger rear rotors, but still using the same NB8A bias, hence the rears lock first.

Easiest is probably just adding an adjustable bias valve into the line and adjust it to suit.
Wilwood ones are around $80 I think..

I'm guessing you upgraded calipers but forgot about the BPV. If i recall correct the brake proportioning valve was different between the NB8B and NA8/NB8a (but someone else may want to confirm).

As the above user said, Wilwood would be a good option if you didn't need the OEM route.

Garido wrote:I'm guessing you upgraded calipers but forgot about the BPV. If i recall correct the brake proportioning valve was different between the NB8B and NA8/NB8a (but someone else may want to confirm).

the brake proportioning valve in the NB8A line is replaced with just a straight through union on the NB8B, as the proportioning is done via the ABS unit.

As for Rascal!

If you are going to install a manual proportioning valve make sure you remove the OEM prop valve. 100% brake pressure to the front wheels and the rear circuit going through the manual prop valve. This removes the knee point and allows complete control of the rear circuit.

rascal wrote:

Garido wrote:I'm guessing you upgraded calipers but forgot about the BPV. If i recall correct the brake proportioning valve was different between the NB8B and NA8/NB8a (but someone else may want to confirm).

the brake proportioning valve in the NB8A line is replaced with just a straight through union on the NB8B, as the proportioning is done via the ABS unit.

That's interesting. So does this mean the NB8A with ABS also features the same setup? Haven't seen many 8a's optioned with ABS?

If you do go for a proportioning valve I have a FM/Wilwood one for sale (brand new/never used).

As others have mentioned, proportioning valve should fix your problem.

Interestingly, I have NB8B brakes with na6 master, full rear bias via proportioning valve and I still lock the fronts first.

Garido wrote:That's interesting. So does this mean the NB8A with ABS also features the same setup? Haven't seen many 8a's optioned with ABS?

Pretty sure ABS wasnt an option on NB8A in australian cars, other than the 10AE (and heritage?) where it was standard.

Phillbert wrote: I still lock the fronts first.

What tyres? Remember tyres are what make you stop, the brakes apply the force. If you are locking the fronts then it could be tyre or pad related not brakes. I had a very similar problem, changed tyres problem gone (plus was faster)

rascal wrote:

Garido wrote:That's interesting. So does this mean the NB8A with ABS also features the same setup? Haven't seen many 8a's optioned with ABS?

Pretty sure ABS wasnt an option on NB8A in australian cars, other than the 10AE (and heritage?) where it was standard.

Perhaps the ones I saw were 10AE (don't remember if they had Shiny wheels though).

Magpie wrote:

Phillbert wrote: I still lock the fronts first.

What tyres? Remember tyres are what make you stop, the brakes apply the force. If you are locking the fronts then it could be tyre or pad related not brakes. I had a very similar problem, changed tyres problem gone (plus was faster)

Thanks for the feedback! They are 195 Hankook RS3 all round. Back when I was testing the tyres were cold and from memory my front alignment wasnt great (it had a fair bit of toe out). I havent locked them up on the track yet. What tyres were you running before/after?

I was using FZ201 then went to AD08R's

Are you running the same pad compound front and back?
Have you confirmed the brake calipers in the rear have been adjusted correctly?

Also, I'll take this opportunity to unashamedly post this:


And, if you DO decide to go this route:
http://beavismotorsport.com/store/performance/wilwood-brake-proportioning-valve-kit-for-mazda-mx-4-na-nb-89-05.html