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Brake Bias

7.3K views 20 replies 6 participants last post by  NuttyS  
#1 ·
Hope this is the right place for this.

I've been looking on the forum for information as to how I can change the brake bias on my MX5 MK1, as I have, without doing enough research, fitted 4 pot callipers on the front, not the cleverest thing to do I have found out. I only use my car for track days. can someone guide me in the right direction please.
 
#3 ·
^ I second that. Kozy's brake calculator is the nuts. You can fit mk2.5 calipers in the rear, they have bigger pistons so put more force at the rear brakes, you can also fit the larger "sport discs" and carriers if you need to.
 
#4 ·
Thanks to both for that advice, I finally found two threads 'Removing the prop valve, no rear proportioning' and 'Removing brake proportion valve on MK2 NB' both instructive the first thread has an excellent picture at the bottom of page three.

I've now removed the valve, quite an easy op. For anybody else wanting to do the same here's what I did for what it is worth.

Rather than drain the brake fluid, squeeze a small plastic container well wrapped in paper towel beneath the 22mm bolt head at the drivers end of the proportion valve, unscrew the bolt (very little fluid escaped but shall still bleed the brakes) pull the spring out with a magnet, you'll just be able to see the valve stem grab this with a pair of long nosed pliers and pop the bolt back in not forgetting the washer, job done. Shan't know the result of this until I'm on track again early August.
 
#6 ·
G-Bob on here did the 'prop valve gutting' to his NB and had issues with the rubber bit of the bolt leaking. I had a spare NA one with the solid bolt which I believe solved the problem for him.
 
#8 · (Edited by Moderator)
Is your 22mm bolt the solid one, or the rubber plug one? Some have found the rubber plug one to leak with the added pressure.
Solid. I'd read about the problem with the rubber plug ones but they are on later models than mine, I understand that the bolts are not interchangeable but the whole unit is.

The main thing is did it do the job? I can't test mine properly until I get on track next month, very frustrating!!
 
#9 ·
I wasn't aware of the rubber plug versions and their leaking problems. Will bear that in mind when advising that mod in future.

OP, did you check your setup in the calculator before removing the valve? It doesn't suit all cars as it can generate too much rear bias on cars with sticky trackday tyres, but is generally OK for cars wearing normal everyday road tyres.
 
#10 · (Edited by Moderator)
Thank you Kosy for your advice, not being very technically minded I'm struggling a little with the calculator and may end up in a suck it and see situation, worse come to worse I'll fit a bias valve. I'm just using up a set of Toyo R1Rs then I'm onto Nankang NS-2R medium, so nothing that sticky.
 
#15 ·
OK I just checked the setup the 280mm Wilwood kit with 35mm pistons is actually a perfect match for the stock 1.8 front brakes so it doesn't actually add any front bias.

You should be fine with that setup, just exercise caution when threshold braking on a hot dry day as the rear tyres will be much closer to locking up than a stock car.
 
#16 ·
I sprint and autosolo in my 1994 1.8 eunos with ABS. I use list 1a tyres (michelin PS3) and yellow stuff pads with standard brake disks and calipers would it be worth doing the proportioning valve delete keeping everything else the same ?
 
#17 ·
OK I just checked the setup the 280mm Wilwood kit with 35mm pistons is actually a perfect match for the stock 1.8 front brakes so it doesn't actually add any front bias.

You should be fine with that setup, just exercise caution when threshold braking on a hot dry day as the rear tyres will be much closer to locking up than a stock car.
Thanks Kozy, you have been a great help and put my mind at rest and I have been having a play with your calculator and once I put my mind to it I found it easy to use. I'm old school and must try harder.

Thanks again,

Mike.
 
#18 ·
I sprint and autosolo in my 1994 1.8 eunos with ABS. I use list 1a tyres (michelin PS3) and yellow stuff pads with standard brake disks and calipers would it be worth doing the proportioning valve delete keeping everything else the same ?
Sounds similar to my setup, the prop delete would be a good mod for you. I logged an increase of braking G from 0.8 to about 0.95 with this mod, the same sort of increase you'd expect going to R888s!

As an additional bonus it also makes the ABS far less intrusive, because all four wheels slow down at the same rate it doesn't detect slip until a wheel is actually slipping. Mine literally only kicks in now on full bore emergency stops if I'm braking on bumpy/muddy roads.

Not sure how long I've been running this now but must be coming on 2 years, driven hard in all weather on road, autotests and track and I don't have a bad word to say about it, it's bloody brilliant.
 
#19 ·
OK I just checked the setup the 280mm Wilwood kit with 35mm pistons is actually a perfect match for the stock 1.8 front brakes so it doesn't actually add any front bias.

You should be fine with that setup, just exercise caution when threshold braking on a hot dry day as the rear tyres will be much closer to locking up than a stock car.
Thanks Kozy, you have been a great help and put my mind at rest and I have been having a play with your calculator and once I put my mind to it I found it easy to use. I'm old school and must try harder.

Thanks again,

Mike.
No worries, I love this kind of stuff. :)
 
#20 ·
I sprint and autosolo in my 1994 1.8 eunos with ABS. I use list 1a tyres (michelin PS3) and yellow stuff pads with standard brake disks and calipers would it be worth doing the proportioning valve delete keeping everything else the same ?
Sounds similar to my setup, the prop delete would be a good mod for you. I logged an increase of braking G from 0.8 to about 0.95 with this mod, the same sort of increase you'd expect going to R888s!

As an additional bonus it also makes the ABS far less intrusive, because all four wheels slow down at the same rate it doesn't detect slip until a wheel is actually slipping. Mine literally only kicks in now on full bore emergency stops if I'm braking on bumpy/muddy roads.

Not sure how long I've been running this now but must be coming on 2 years, driven hard in all weather on road, autotests and track and I don't have a bad word to say about it, it's bloody brilliant.
Nice one Kozy, apologies for the hijack Nuttys, I will add prop valve delete to the list of mods :)
 
#21 ·
I sprint and autosolo in my 1994 1.8 eunos with ABS. I use list 1a tyres (michelin PS3) and yellow stuff pads with standard brake disks and calipers would it be worth doing the proportioning valve delete keeping everything else the same ?
Sounds similar to my setup, the prop delete would be a good mod for you. I logged an increase of braking G from 0.8 to about 0.95 with this mod, the same sort of increase you'd expect going to R888s!

As an additional bonus it also makes the ABS far less intrusive, because all four wheels slow down at the same rate it doesn't detect slip until a wheel is actually slipping. Mine literally only kicks in now on full bore emergency stops if I'm braking on bumpy/muddy roads.

Not sure how long I've been running this now but must be coming on 2 years, driven hard in all weather on road, autotests and track and I don't have a bad word to say about it, it's bloody brilliant.
Nice one Kozy, apologies for the hijack Nuttys, I will add prop valve delete to the list of mods :)
No apologies needed the more info the better, I'm sure this will be of help to others, learned a lot myself and you are certainly better off asking before doing as I didn't.