Brake options

[LimeyMk1]

As previous post:

Front Hi-Spec Ultralite 4 pots + 285mm disks
Rear stock with Pagid pads (have had a set stashed away for a while ), considering 22Vs on the rear later.

[tonigmr2]

While I am here can someone tell me if rev3 turbo rear calipers are actually an upgrade to the existing rear MK1 calipers (I know the pads are interchangable).

[LimeyMk1]

While I am here can someone tell me if rev3 turbo rear calipers are actually an upgrade to the existing rear MK1 calipers (I know the pads are interchangable).

Yep. IIRC you can use them in 2 ways.

1. With a Corrado disk, but the calliper carrier needs to be 'adjusted' (cut and re welded)

2. With Mk1 or Mk3 MR2 front disks and only a spacer will be required. I can't remember the details of this one but I think you need a 6mm spacer for the Mk1 fronts and a 3mm one for the Mk3s. Details on TB, will go and grab a link.
http://forums.twobrutal.com/showthread.php?t=16464

[tonigmr2]

Cheers Chris, got some for my TC you see...though the WMS ones look nicer.

[Keri-WMS]

Cheers Chris, got some for my TC you see...though the WMS ones look nicer.

Are you talking about the rear? The WMS plan for the Mk1/2/3 has two phases:

1. Being big-disc (and rotor+ball) plus custom-made caliper carriers.
2. Being 2 or 4 pot WMS calipers with some kind of handbrake setup.

The main reason for this is that a rear 4 pot + handbrake kit usually costs 1.5-2.0x as much as the front, so most people would go for the cheaper option - at least initially.

[tonigmr2]

Yeah the only reason I haven't got AP rears is they didn't do them! I wanted to upgrade the back hence went for the rev3 calipers.

[toxo]

IIRC there are very few (or no?) places that do road legal rear upgrades for any mark of MR2 are there? Due to the comedy handbrake design and hydraulic handbrakes not being MOTworthy...

Obviously I mean outside of sticking a different mark caliper on as suggested above, or spacing the existing caliper out like Ant's big brake kit.

[Jim-SR]

ive got WMS 4-pot fronts with bell-mounted 280mm thin vented discs. im just waiting on bells and then il fit them.

on the rear im going to run the same bell-mounted 280mm discs with 22V rear calipers to save the hassle (and weight) of a seperate handbrake caliper to get it through the MOT.

it will all end up about as lightweight as any AW11 brake setup on the market. reducing unsprung weight was my core concern in upgrading. ST205 fronts were just ridiculously heavy. i could feel the handling difference.

[System-G]

Keri, what are your recommendations for master cylinder & bias control for big brake conversions?

Changing the capacity of the standard hydraulic system messes with efficiency in my experience.

[Keri-WMS]

IIRC there are very few (or no?) places that do road legal rear upgrades for any mark of MR2 are there? Due to the comedy handbrake design and hydraulic handbrakes not being MOTworthy...

Correct as far as I know, they all re-use the OEM caliper.

ive got WMS 4-pot fronts with bell-mounted 280mm thin vented discs. im just waiting on bells and then il fit them.

on the rear im going to run the same bell-mounted 280mm discs with 22V rear calipers to save the hassle (and weight) of a seperate handbrake caliper to get it through the MOT.

it will all end up about as lightweight as any AW11 brake setup on the market. reducing unsprung weight was my core concern in upgrading. ST205 fronts were just ridiculously heavy. i could feel the handling difference.

This will be a really nice setup once it's done, I'm struggling with getting the first batch done for an acceptable price - but I have managed to get a "batch" re-defined to "AW11 front bells and AW11 rear bells mixed" which halves the cost, so we're nearly there - just the bobbins to agree now, then jump in at the deep end with batch 1.

[Keri-WMS]

Keri, what are your recommendations for master cylinder & bias control for big brake conversions?

Changing the capacity of the standard hydraulic system messes with efficiency in my experience.

I can't speak for other upgrades, just the WMS kits and a lot depends on the driver and the car setup, BUT there are two options we're suggesting as of 2010:

1. A normal AW11 with AW11b rear calipers should take the 1.25/1.25" piston size calipers which gives you a drop in piston area to 77.5% of OEM (don't forget the bigger disc adds a bit of that 22.5% torque back).

2. An AW11 with 22v rear calipers should take the 1.38/1.38" piston size which is 94.5% of OEM area (plus big discs). The is because the SW20-22v caliper is 137.2% of the area of the AW11-rear caliper, a fair old shift to the rear normally!

For both setups you can keep the original master cyl, but when people are running the setup 2 it might feel nicer to upgrade to the larger SW20 one to cover the 22v's extra 37.2%.....assuming the SW20 master doesn't change the bias in itself which I can't confirm.

[AdrianS]

Just a note on gutting bias valves - the aw11 bias valve does not provide a fixed front/rear bias.
The effective bias varies with line pressure, and thus braking effort. The net effect is more front bias under heavy braking. This means less font bias in light braking situations, eg wet roads. Not an issue for a track or sunday car, of course.

I'm using data collected from various places. Please correct any mistakes.

pistons :
51.1mm front, 41.3mm rear.
disks :
mk1a : 243mm front, 240mm rear
mk1a : 258mm front, 258mm rear
master cyl.
7/8"
bias valve
aw11 n/a : threshold 35 kg/cm2, gradient 0.37
aw11 s/c : threshold 45 kg/cm2, gradient 0.37

As a rough calculation, using an approximated pad friction coeff. of 0.3, we can relate line pressures to braking torque.
This gives us

Static Bias (f:r)
mk1a 1.52:1
mk1b 1.50:1
mk1sc 1.50:1

45 kg/cm2 line pressure
mk1a 1.76:1 (0.56 G)
mk1b 1.74:1 (0.59 G)
mk1sc 1.50:1 (0.57 G)

60 kg/cm2 line pressure
mk1a 2.05:1 (0.71 G)
mk1b 2.03:1 (0.75 G)
mk1sc 1.77:1 (0.71 G)

90 kg/cm2 line pressure
mk1a 2.46:1 (1 G)
mk1b 2.43:1 (1.06 G)
mk1sc 2.15:1 (0.99G)

These are approximations, as pad friction is a black art, and varies with temperature etc., but it shows the behavior of the stock bias valve.
If my information is correct, you can see the effect with the s/c, which makes sense with the extra rear weight : at high line pressure the brake bias is still over 2:1, but there's much more rear bias at medium braking than the n/a.

[Keri-WMS]

Hi Adrian, that is some top notch info!

The only part I can comment directly on is:

pistons :
51.1mm front, 41.3mm rear.

...for the AW11 (not sure if A or B) I have numbers of 51.0mm and 36.50mm based on popping the pistons out and getting on them with a digital vernier.

I wonder if there are two types of AW11 rear calipers? It's a total nightmare if so as they'll be mixed up all over people's cars!

Similarly I got 42.75mm SW20 (late, 22v caliper) rear and 44.25mm ZZW30 rear for general reference as people mix and match the rear calipers a lot.

[AdrianS]

Hi Adrian, that is some top notch info!

The only part I can comment directly on is:

pistons :
51.1mm front, 41.3mm rear.

...for the AW11 (not sure if A or B) I have numbers of 51.0mm and 36.50mm based on popping the pistons out and getting on them with a digital vernier.

I wonder if there are two types of AW11 rear calipers? It's a total nightmare if so as they'll be mixed up all over people's cars!

Similarly I got 42.75mm SW20 (late, 22v caliper) rear and 44.25mm ZZW30 rear for general reference as people mix and match the rear calipers a lot.

Thanks for that. There's so much information cut and pasted around the web, it's nice to get a first-hand figure.
I've amended my spreadsheet accordingly.
new bias figures :

Static Bias (f:r)
mk1a 1.94:1
mk1b 1.91:1
mk1sc 1.91:1

60 kg/cm2 line pressure
mk1a 2.63:1 (0.66 G)
mk1b 2.60:1 (0.69 G)
mk1sc 2.27:1 (0.65 G)

90 kg/cm2 line pressure
mk1a 3.15:1 (0.94 G)
mk1b 3.11:1 (0.99 G)
mk1sc 2.79:1 (0.93 G)

That's a frighteningly high bias, especially compared to my figures for sw20 and zzw30. I'll do check my calcs.

[Keri-WMS]

Thanks for that. There's so much information cut and pasted around the web, it's nice to get a first-hand figure.
I've amended my spreadsheet accordingly.
new bias figures :

Static Bias (f:r)
mk1a 1.94:1
mk1b 1.91:1
mk1sc 1.91:1

60 kg/cm2 line pressure
mk1a 2.63:1 (0.66 G)
mk1b 2.60:1 (0.69 G)
mk1sc 2.27:1 (0.65 G)

90 kg/cm2 line pressure
mk1a 3.15:1 (0.94 G)
mk1b 3.11:1 (0.99 G)
mk1sc 2.79:1 (0.93 G)

That's a frighteningly high bias, especially compared to my figures for sw20 and zzw30. I'll do check my calcs.

lol, I got struck down with paranoia and just re-checked my rear reference caliper - I got 36.30mm on the rear piston with it 50% pulled out of the caliper and the seal removed (new boxed caliper, miiiiight be re-con but I even if they change the piston to oversize it won't be more than a few 0.1mm's).

[AdrianS]

The bias valve figures I'm reasonably confident in (taken from Toyota service manuals), and yes, the sw20 m/cyl has different bias behavior :

With ABS, I believe the bias is built into the ABS controller

Bias Valve behavior - it reduces the rear pressure above a certain threshold :


Plotted as a ratio :



regarding piston sizes -
I'll check my mk1a rear pistons when I upgrade to mk1b in a month or so; in the meantime I'll try to verify my original figures.
edit I have 36.5mm as the dia. of an sw20 front (twin piston), and 41.2mm as an early sw20 rear. A 41.2 mm rear would bring the aw11 closer to sw20 & zzw30 bias figures. Keri's other piston sizes match my data.

[AdrianS]

Here's my current spec sheet :



I have to add the BZR superstrut front brakes to the list; the calipers are supposed to bolt up, and there are a couple of disk options. I actually have a set, but they (and the disks) are soooo heavy.

[toxo]

Not sure if it's relevent in your figures, but above swapping to an SW20 master cylinder has been mentioned. They are different on the earlier SW20 (the same time the caliper & disc sizes changed). Rev2 (92+ on your sheets) upwards has 15/16" m/cyl but I believe the earlier ones to be a smaller bore.

Am I also right in thinking that doing this swap on a MK1a requires a MK1b servo as the master cylinder bolt pattern is different on the early MK1 (3 bolts instead of 4)? Probably outside of the scope of this discussion though

[AdrianS]

Ok. you may well be right about the early sw20 master cyl.
The master cyl. bore has no effect on brake bias, only pedal pressure / travel.

I did some calcs on pedal travel vs pad travel for different combinations, but never tidied it up. The intent was to plot pedal travel, effort and bias for various common swaps.
I lost interest because (most) toyota calipers are so heavy, as are the big disks, and I want too keep unsprung weight down.

An option to research :
I was helping with the brakes on a historic fiat rally car; we run a fiat three-piston alloy caliper, which is very light. This has one large inner piston and two small pistons on the outside, which helps with wheel clearance. Being opposed piston with external lines, it can easily be spaced out to fit any width disk. I would love to see if these calipers can be fitted to an aw11, and will take a look when I do my brakes.

[Keri-WMS]

Here's my current spec sheet :



I have to add the BZR superstrut front brakes to the list; the calipers are supposed to bolt up, and there are a couple of disk options. I actually have a set, but they (and the disks) are soooo heavy.

I've got:

AW11 f = 51.0 x 1
AW11 r = 36.3 x 1
SW20 late f = 36.4 x 2
SW20 late r = 42.75 x 1
ZZW30 f = 51.0 x 1
ZZW30 r = 44.25 x 1

...all from direct measurements - hope that helps!