Brake options

[PW@Woodsport]

I was told at my last MOT the car's braking was biased too much to the front, but it was still passed.

Yep, biased too much going off his wallchart for the vehicle weight and what the brakes should be seeing from the factory, but that doesn't mean it makes them unbiased on the road, that just means you have more braking up front than factory, which is the whole point of an upgrade.

I agree with Mart, gut the bias valve to give you a 50/50 split or fit your own adjustable valve.

[Keri-WMS]

I was told at my last MOT the car's braking was biased too much to the front, but it was still passed. The only thing different from the previous MOT was the ST165 2-piston calipers.

Is there any simple way to adjust this? All those graphs are giving me nightmares.

In simple terms the options are:

- Gut the rear bias valve (it is there for a reason though, to put a "delay" on the rate the rear pressure goes up).
- Fit bigger psiton rear calipers or bigger rear discs
- Fit a proper adjustable-bias pedal box!

What exact combo of brake parts have you got fitted F+R?

[MartG]

If it's just the ST165 twin pots that are different, I worked out when I fitted mine that on the basis of piston area and effective radius that just gutting the bias valve returned the bias to pretty near standard ( assuming the same pads front & rear so same friction coefficient )

[kaiowas]

I've never fully understood exactly what goes on inside the bias valve as I've never looked inside one but given that both brake circuits pass through it, wouldn't gutting it essentially link the two circuits together again thus negating the whole point of having two circuits in the first place?

[jb007]

Would some kind soul give me a step by step guide as to how to gut the bias valve please?

edit:Done it now

[ulysess1966]

Would some kind soul give me a step by step guide as to how to gut the bias valve please?

edit:Done it now

I haven't and the word 'gut' concerns me greatly as I used to work in a fishmongers, so any help on how to do this would be welcome.

I live in NI and our MOT here is computerised now (no more wall charts) and carried out in government centres and not garages. It makes it hard to argue if something like brake bias comes up because all you get is 'computer says no' as a reply. I've been lucky because my local centre seem to enjoy getting interesting cars to test, but there's a limit to what they can pass.

[PW@Woodsport]

Ok this thread is lacking some substance, so here you go.

Toyota made the stock bias valve a little on the conservative side, for god knows what reason, but we find the fronts locking too easily as a result, hence the mod for some Mr2 owners to even the balance out.

Instead of gutting the valve you can do this...



Just replace the valve with a T and a connector eliminating the bias valve altogether. Now before some keyboard mechanic starts screaming about safety, the car still has its dual circuit brakes, this just evens the pressure to all four corners instead of having a bias. Anyway Mk1 superchargers come already like this...



The much easier way is just to remove the innards from your stock valve... take out the plunger,spring and O ring from the bottom of the valve and replace the nut.



I have this set up on both my Mk1 V8 and my stock Mk1 and it works much better than standard.

Hope that helps.

[ulysess1966]

Paul

Nice substance. The thing I like about this mod is you can easily change it back.

Another idea... could the spring be replaced to give different bias? I'm only wondering because I have a tin box full of salvaged springs so it would be interesting to try a slightly lighter spring that would open more easily.

Ta

Glenn

[jb007]

Great work, I could of done with you a few days ago Paul!! especially that last picture.

Does the first option offer any advantages over simply stripping the valve?

[PW@Woodsport]

Hi Glenn, you could fit a different spring but seeing as the bias is only 55/45 there isn't much scope for fine tuning, gutting the valve makes it 50/50 which seems pretty spot on.

Does the first option offer any advantages over simply stripping the valve?

None at all really, it is the way a Mk1 SC is so perhaps Toyota felt the need for a little more rearward bias with the heavier SC drivetrain?

Some people replace the valve with T's so they can just refit the valve later to return to stock, but they are exactly the same mod.

[ulysess1966]

Hi Glenn, you could fit a different spring but seeing as the bias is only 55/45 there isn't much scope for fine tuning.

Fair point

I'll do this next weekend.

[Keri-WMS]

Very interesting regarding the SC, ta Paul!

I would suspect the SC is closer to "ideal straight line braking" / race brakes, but the more common non-SC is more likely to be driven by less skilled drivers meaning an increase in bias to the front was prudent.

This is because a "perfect" brake bias is fine in a straight line, but you'll spin if you turn in while braking or try any trail braking so most mfrs shift road car bias to the front. The thinking is most people can correct understeer under braking, where most WON'T catch oversteer under braking!

[moohamppenRob]

Im helping replace their brake system on a 1985 4Runner and needed to make sure I wasn’t missing anything on the shopping list. I plan on replacing everything except front brake lines and although there is a rear disk conversion kit, its not in the plans.

-Master Cylinder
-Steel Braided Extended Brake Hoses Lifted 6 Inches
front
-Outer Wheel Bearings
-Inner Wheel Bearings
-Calipers
-Rotors
-Pads
rear
-Drums
-Shoes

Not sure if there are seals in the rear that can should be replaced or anything that should be looked at while were elbow deep in this for the day. Am I missing anything? Any recommendations on brand or any shops that carry good deals for any or all of it?

All input is welcome and appreciated.

[Clarky_X]

Wow, that is a lot of info on this thread and opinion does seem to be divided. I thought I was reasonably smart, but I would need to go through all the stats several times to get my head around it all.

Now I am preparing my car for track, all I have to go on from personal experience is that my last Mk1 had std brakes then I had braided hoses, AP Racing DOT 5.1 fluid and Mintex M1144 pads with std discs put in/on and the improvement was massive for road use, I really like those brakes. Yes I could lock them if I was being silly on the road. I never had any fade, but then I probably never worked them hard enough.

When I used to work just outside Milton Keynes and had to pop into MK at lunch time in my old Mk2 Golf GTI, MK roundabouts used to cause terrible fade with std GTI brakes, but I never tested the MR2 in MK.

My current set up on my SC converted Mk1 is std pads with drilled and grooved discs, but I've had the car for 2 years, the discs were on when I bought it, I've done 25k on them, the pads are cheap, the fluid is old, the hoses are rubber and the brakes are just mediocre. Again, no particular testing done, just general feel and not confidence inspiring so have never pushed them.

Now I am preparing the car for track following the failed MOT (Welding at the front needed and hand brake failed) I think I will stick with standard at the moment, i.e. std discs and callipers, but upgrade the pads to DS2500 front, as I want to try them, probably another Ferrodo pad at the back because I don't think they do DS2500 rears. And put braided hoses on and AP Racing DOT 5.1 fluid. At least that will give me confidence on track, and If I trash the pads in a day or two on track then I can try other pads, before then deciding if I'm still happy or not and deciding then what to do about callipers and disc size.

Incidentally, last MOT my hand brake was only 2% effective and failed and I had reconditioned rear callipers from TCB Parts and brand new hand brake cables put on and set up. Before the MOT I had to keep it in gear when parked. After it was A OK. This year on the MOT, it is 5% effective and failed again. I don't need to keep it in gear this time, but am disappointed if the recon rear callipers are failing already, especially as I had the MOT done early so they were only 11 months old. Maybe it's not the callipers, maybe it just needs new discs and pads and the centre cable adjusting, I know it should be 5-8 clicks and I can get 10.

[Clarky_X]

And here is the static bias and pedal feel.
Pedal travel is ratio of master cylinder to pad travel, eg m/c stroke reqd to move all pads 1mm. More is worse.
Pedal pressure is the ratio of force on the master cylinder piston to braking force (retardation). This ignores the effect of the brake booster (anyone got data on boosters ?).

Note that brake bias curves will be different with bigger brakes. As the brake piston area goes up, the line pressure required decreases for a given braking force (deceleration), so the bias valve will have less effect.

These figures show that
a) Fitting larger brakes to the front with standard rears increases the front bias considerably (duh!)
b) Fitting a 15/16" or 1" master cylinder will keep the pedal travel close to standard with bigger brakes (also duh!)

Sorry to be a dumbaas. So is what you are saying, that to keep the std Mk1b travel and pressure, the closest option is ST205/SW20.

If the travel and pressure are almost the same, how do the brakes differ, is it better performance, i.e. more stopping power, i.e. more grip, but the same feel? If that is the case, doesn't upgrading the pad material for something with more bite give the same effect?

Is the pressure the pressure exerted at the disc by the piston or the pressure required at the pedal by the driver? If it is pressure at the disc by the calliper, aren't we looking for more pressure there to increase the braking force with the same effort as std at the pedal by the driver?

Too many variables TBH.

[toxo]

If it's of any interest, there is a thread in the Premium Member Discounts forum WRT OEM brakes from Toyota MK.

[Clarky_X]

Ta, will have a look

[Keri-WMS]

If it's of any interest, there is a thread in the Premium Member Discounts forum WRT OEM brakes from Toyota MK.

I just realised I never got round to adding a thread there (doh!!!) even though we offer a Premium Member discount as well, so I just sorted one out.