MR2 Owners Club Forum banner

Brake FAQ - Rotor, caliper, MC sizes

63K views 72 replies 29 participants last post by  Ignatius_Reilly 
#1 · (Edited)
Brake FAQ - rotors, calipers, master cylinder sizes, proportioning valves, etc.

This post summarizes the specs and operation of brake components for the MkII MR2. The focus is on North American cars but the info should apply to other cars as well.


Rotors:
Rotor diameter and thickness is given. To calculate effective radius for brake torque calculations, use Re=((OD?+ID?)/2)^0.5 where OD is outer-diameter and ID is inner diameter where the brake pad ends. For best all-around track/race performance, choose plain OEM-style rotors and steer clear from "cross-drilled" or "slotted" rotors.

  • Front
  • 1993+ Turbo vented [275mm*30mm] [replace@28mm]
  • 1991-1992 Turbo & 1991+ NA vented [258mm*25mm] [replace@24mm]
  • Rear
  • 1993+ Turbo vented [280mm*22mm] [replace@21mm]
  • 1991-1992 Turbo & 1991+ NA vented [262mm*16mm] [replace@15mm]



OEM Pads:
  • Front
  • 1993+ Turbo MKD582 (50cm?)
  • 1991-1992 Turbo MKD489 (49cm?)
  • 1991+ NA MKD242 [15mm thick] [105mmx47mm overall size]
  • Rear
  • 1991+ NA/Turbo MKD657 - all cars use the same pad



After-market Pads:
  • Front NA
  • Hawk HB191.590 [HPS/HP+/HT-10/Blue-9012]
  • Porterfield AP242 [R4/R4E/R4S/R4-1]
  • Ferodo SD242 [DS2500/DS3000, etc]
  • Axxis Ultimate 109.02420
  • Carbotech CT242 [Bobcat,AX6, XP8, XP10, XP12]
  • Front Turbo 1991-1992
  • Porterfield AP489 [R4/R4E/R4S]
  • Ferodo D489 [DS2500/DS3000/etc]
  • Axxis Ultimate 109.04890
  • Carbotech CT489 [Bobcat, AX6, XP8, XP10, XP12]
  • Front Turbo 1993+
  • Porterfield AP582 [R4/R4E/R4S]
  • Ferodo D582 [DS2500/DS3000/etc]
  • Axxis Ultimate 109.05820
  • Carbotech CT582 [Bobcat, AX6, XP8, XP10, XP12]
  • Rear (all)
  • Porterfield AP309 [R4/R4E/R4S]
  • Axxis Ultimate 109.06570
  • Ferodo D528/D657 (not available any more)
  • Wagner PD309/PD657
  • Carbotech CT528/657 [Bobcat, AX6, XP8, XP10, XP12]



Aftermarket high-performance brake pad compound data
Included in this list are approximate friction coefficients (determines max brake torque) and temperature ranges (fade resistance and cold bite) Note that pad compounds rarely have a constant cF over the whole temperature range. for example EBC pads:

  • Street/Track
  • Axxis Ultimate [cF=0.40] [0?F-900?F]
  • EBC Yellow [cF=0.55] [0?F-900?F]
  • Porterfield R4-S [cF=0.40] [0?F-900?F]
  • Hawk HPS [cF=0.40] [0?F-750?F]
  • Hawk HP+ [cF=0.45-0.50] [0?F-900?F]
  • Ferodo DS2500 [cF=0.50] [100?F-1000?F]
  • Carbotech Bobcat [cF=0.45] [0?F-900?F]
  • Carbotech Panther Plus/AX6 [cF=0.54] [150?F-1250?F]
  • Track/Race
  • Porterfield R4 [cF=0.485]
  • Porterfield R4-E [cF=0.485??]
  • Ferodo DS3000 [cF=0.62] [300?F-1500?F]
  • Hawk Blue 9012 [cF=0.52] [250?F-1000?F]
  • Hawk HT-10 [cF=0.55] [300?F-1600?F]
  • Carbotech Panther XP8 [cF=0.58] [200?F-1350?F]
  • Carbotech Panther XP10 [cF=0.6] [300?F-1600?F]
Note that Hawk and Ferodo pads are only available for front brakes. Rears are not produced any more.

Pad life on the racetrack?
http://mr2oc.com/showthread.php?t=403191

Calipers:

1993+ turbo calipers have the same size pistons as 1991-1992 calipers, but the caliper and bracket are much larger to accommodate the larger rotors.

  • Front
  • 1993+ Turbo dual piston front caliper [2x36.5mm = 2092.6mm?] (identification stamp: AISIN 36T30)
  • 1991-1992 Turbo dual piston front caliper [2x36.5mm = 2092.6mm?] (identification stamp: AISIN 36T25)
  • 1991+ N/A single piston front caliper [1x51mm = 2026.8mm?]
  • Rear
  • 1993+ Turbo single piston rear caliper [1x42.9mm =1452.2mm?] (idetification stamp: left:22VL right:22VR)
  • 1991-1992 Turbo/1991+ NA single piston rear caliper [1x41.3mm = 1339.6mm?] (identification stamp: left:16VL right:16VR)



Brake proportioning valves:
  • Here is how it works. After the threshold line pressure is reached, the valve kicks in and begins to reduce pressure to the rear brake pistons. So for moderate pedal pressures, the front and rear brake pressures are the same, but once you start to squeeze the pedal harder, the front pressure continues to rise, but the rear pressure rises at a slower rate.
  • Because the weight of the car transfers forward to the front axle under braking, the front tires have more grip and the rears have less grip. Because the rears have less grip, you need to reduce the braking force on the rear with respect to the front to prevent the rear wheels from locking up. Without a proportioning valve, the car would skid out of control very easily under braking. So Toyota, like most other manufacturers, installs a proportioning valve at the factory.
  • For the turbo cars, not only is the threshold line pressure higher, but the bias is more rearward. There are several reasons for this:
    • additional rear weight of turbo engine & accessories
    • wider staggered rear tires.
    • more piston area in front dual-piston calipers
  • Many track junkies report that with non-ABS cars, the front axle tends to lockup well before the rear. It follows that with proper brake pad and tire choice, the brake bias can be moved slightly rearward to better optimize braking performance under extreme braking conditions. So an OEM turbo brake proportioning valve is a suitable upgrade for an N/A car using wider rear tires and the turbo front brake calipers. Some folks opt for an aftermarket adjustable proportioning valve which allows finely tuned braking performance depending on tire choice and changing track conditions.A plot of NA vs Turbo proportioning valve performance:
Factory prop valves:
  • 1991-1995 NA with ABS (very rare, very expensive)
  • 1991-1995 NA without ABS
  • 1991-1992 Turbo with ABS
  • 1991-1992 Turbo without ABS
  • 1993-1995 Turbo with ABS
  • 1993-1995 Turbo without ABS
Although there are several different part numbers available, there is no evidence that the various valves have different proportioning profiles than described above.


Master cylinders:
  • 1991-1995 NA & 1991-1992 Turbo 7/8" bore size (~22mm)
  • 1993-1995 Turbo 15/16" bore size (~24mm)
  • Other options: http://www.mr2oc.com/showthread.php?t=185454
  • There are physical differences between master cylinders with ABS and without, but the bore sizes are as shown above.


Brake boosters:
  • 1991-1992 NA (with or without ABS)
  • 1991-1992 Turbo (with or without ABS)
  • 1993-1995 NA (with or without ABS)
  • 1993-1995 Turbo with ABS
  • 1993-1995 Turbo without ABS


Continued at: http://mr2oc.com/showpost.php?p=3250142&postcount=6
 
See less See more
2
Discussion starter · #6 · (Edited)
FAQ Continued

FAQ CONTINUED


Brake Ducts:


Parking brake todo: (re-organize this section)
  • The MR2 uses an integrated parking brake mechanism which rotates the rear caliper piston in its housing when the parking brake lever is pulled.
  • A common issue with this design is a failure of the parking brake cables. There are two rear cables and an adjustment. Cables from different model years and Turbo vs NA are different part numbers and slightly different lengths, but they are all interchangeable given that there is a quite a bit of adjustability in the parking brake mechanism. Do refer to the shop manual for proper adjustment procedure. The cables do stretch and wear out over time, so this is a good maintenance items to check.
  • For best operation of the parking brake. Hold the brake pedal firmly with your foot while pulling up on the parking brake lever. This will pre-load the caliper piston and allow maximum clamping force on the rotors. Also, manual transmission cars shoudl always be left in-gear when parking as an additional protective measure.
  • When changing the rear brake pads, you need a special tool to rotate the caliper piston while pushing it into the housing at the same time. Harborfreight has an "import rear caliper piston tool" or "caliper piston reset tool" available which works great. Or you can rent the tool from any national autoparts store. You can also use a c-clamp and pliers or an "import cube piston tool". But in my experience, the Harborfreight tool is the easiest to use.

http://www.harborfreight.com/18-piece-disc-brake-pad-and-caliper-service-tool-kit-97143.html

 
Discussion starter · #11 ·
MKIITMR2 said:
Since this is true couldnt you use 91t calipers on 93t Brackets and 93t rotors since the brackets accomodate the larger rotors? I remember a while back that someone was saying that I could get 93t caliper brackets and the 91t rear caliper fits right on thus allowing the extra room now for the larger diameter of the 93t rotors. Can anyone verify this for sure? The only downside I can think of is that you might have to shave the brake pads a little to fit the thicker rotor, but we arent talking much here(5-6mm so 2-3mm per pad tops).
You could try. Why not get a full 93t set and full 91t set side by side and take some measurements for us? Perhaps its as simple as fabbing a small adapter out of billet aluminum or something?
 
Discussion starter · #24 ·
Alex W said:
Do not change... but you arn't eliminating it entirely.
Indeed. I clarified the post to indicate that our cars ship from the factory with a proportioning valve which works just fine. But it certainly isn't optimal for all racing conditions which is why some folks swap it for aftermarket valves.
 
Discussion starter · #29 ·
The_Kong said:
So you're saying that the rear rotors are larger in diameter then the front rotors? that's not normal is it? Or is it cause we have a mid engined cars? Just asking.
Its true that most cars have larger front rotors by mass, thickness, and diameter. MR2 front rotors are only larger by mass and thickness, not diameter. The mid-engine design with rear weight bias would be a compelling explanation, but you'd have to ask a Toyota engineer to get a real answer for choosing the size they did.
 
Discussion starter · #31 · (Edited)
Blurvision said:
Is there a difference in 91-92 Prop valve compared to 93+

Yes. According to the parts catalog at www.1sttoyotaparts.com, there are 6 different factory prop valves:

1991-1995 NA with ABS (very rare, very expensive)
1991-1995 NA without ABS
1991-1992 Turbo with ABS
1991-1992 Turbo without ABS
1993-1995 Turbo with ABS
1993-1995 Turbo without ABS


Now I'm not sure if the 1993+ turbo valve actually changes the proportioning or not - I suspect it has the same proportioning just with an updated design or different parts supplier. I've added this info to the main post.

:thumbup
 
Discussion starter · #35 · (Edited)
Indeed you are correct. Haha an engineer can't do grade 6 math lol!

However, I'm not sure about the "effective" area you're talking about. The brake fluid only presses against the area of the piston so when you do the full calculation from brake line pressure through to brake caliper torque, you don't multiply that value by two. The load is just spread over the inner and outer pad via the caliper housing thats all. You do the multiplication later when you add the number of friction surfaces in.

Here are some great resource with all sorts of brake forumlae and whatnot:
http://www.engineeringinspiration.co.uk/brakecalcs.html
http://www.stoptech.com/tech_info/wp_brakebiasandperformance.shtml



So for the purposes of piston area, I think it should be like this:

Front
1993+ Turbo dual piston front caliper [2x36.5mm = 2092.6mm?]
1991-1992 Turbo dual piston front caliper [2x36.5mm = 2092.6mm?]
1991+ N/A single piston front caliper [1x51mm = 2026.8mm?]

Rear
1993+ Turbo single piston rear caliper [1x42.9mm =1452.2mm?]
1991-1992 Turbo/91+ NA single piston rear caliper [1x41.3mm = 1339.6mm?]



Do you concur?
 
Discussion starter · #40 ·
oneslug said:
Can anyone answer why there are different part numbers for the rear parking brake cables pre-92 and 92+? For example, pre-92 cites 46420-17050/46430-17050. Starting in 92, different part numbers show up: 46420-17070/46430-17070. No one ever seems to list this part when talking about switching over to 93+ turbo brakes...

The turbo rear rotors and caliper carriers are larger. Most likely the 1993+ cable is slightly shorter to account for this, however, the 1991/1992 cable will probably work fine on 1993+ brakes if you adjust it correctly.


Note that the 1993+ switchover for North American models happened in 1992 for Japan. So some new parts may be on North American 1992 models already depending on when they were built. In general, part switchovers can happen at any time during a model run if the new part is deemed to be more reliable or cheaper to produce.
 
Discussion starter · #42 · (Edited)
oneslug said:
Thanks phat for the parking brake answer. I've got another question for the brake mavens... 93+ brakes have a larger piston, but still push on the same size pad as the rest. Does the larger piston just distribute the force better, or is it actually pushing harder for a given amount of force being put on the pedal. All else being equal (say 93 front brakes with 91 rears, vs 93 front brakes with 93 rears), would 93/93 would have more rear bias than 93/91?

The 1993 brakes have larger diameter front rotors, rear rotors, master cylinder, AND a slightly larger diameter rear piston. All 4 changes affect the front/rear brake bias.

Given the formulae at: http://www.engineeringinspiration.co.uk/brakecalcs.html

And specific measurements of the effective radius of the brake pads, you should be able to calculate the difference.

Given that all the 1993+ suspension changes effectively decreased oversteer, I suspect all the brake changes together would preserve the same overal bias or shift the bias forward.

Why did they choose a slightly larger piston in the rear? Who knows. Its only one variable in the whole design.

1993 Front + 1991 rear would be more front biased than 1993 front + 1993 rear BTW.
 
Discussion starter · #47 ·
msumr282 said:
Is someone able to please confirm the pad area of:

OEM Pads:

Rear
1991+ NA/Turbo MKD657 - all cars use the same pad

Thanks in advance for the insight...

Joe
I probably have a spare set of rear pads hanging around in the garage that I could measure. Just curious how you'd use the information though?
 
Discussion starter · #49 · (Edited)
msumr282 said:
Awesome; thank you. I'm looking for a suitable, track-only Wilwood front/rear design based loosely on the Wolfkatz BBK. I'm looking at the piston area, but also want to be cognizant of the pad area as well.

Cheers,
Joe

The rear pad surface is approx 95mmx40mm with a contour similar to this:
http://www.pegasusautoracing.com/bigpicture.asp?RecID=2275
43mm at its widest and 33mm at its narrowest.


It may be counterintuitive, but pad area is not critical to the front/rear brake balance - a bigger pad will just resist brake fade better and last a little longer.

A pad surface with its centroid closer to the edge of the rotor will be more effective and produce more brake torque than a different pad with centroid closer to the middle of the rotor. In brake calculations this is the "effective radius"

A great primer on brake system design is here:
http://docs.google.com/viewer?a=v&q...qyGE00&sig=AHIEtbTps2tiz_p69X6awB2JRIPlsxhEqw
 
Discussion starter · #51 ·
msumr282 said:
Thanks for the information, phatvw. I pulled off one of the old rear pads (from a 93+ N/A, Porterfield RS4). Using vernier calipers, and assuming that an a=1/2(b1+b2)*h calculation is appropriate; the addition of both sides equate to an area of approximately 32.5cm^2.

If someone can verify that my measurement and calculation is correct, then we should be able to fill in that missing piece of information.

I'm still having a difficult time wrapping my head around how a larger area pad isn't critical to the balance as more area would equal increased friction...

If all you do is increase the pad size, then the same force from the caliper piston is exerted over a larger area, so you have a lower pressure at each point by definition. And for all intents and purposes, the friction force is proportional to the pressure.

So the overall frictional force doesn't change (assuming a linear model)


Think about using sandpaper to rub off paint. If you use a small square of sandpaper, you can rub off the paint really fast without much force exerted by your hand, but if you use a larger piece of sandpaper, then you have to press harder to account for the larger area. Same analogy works for pad longevity - a small sandpaper piece wears out quickly.
 
Discussion starter · #54 ·
scarecrowX said:
FWIW, I'm still amazed at how little of the swept area of the supra rotor the Wilwood calipers use. If you want big, meaty pads on there, find some Brembo or Sumitomo OE calipers. It seems a waste to install that much larger rotors if you're only going to use 50% of the extra area with the Wilwoods.

Big rotors are not a waste as long as the whole rotor is heating up. If small pads cause local hotsports on the swept area and the rest of the rotor is cold, thats really bad and won't perform well. But typically, it only takes a lap or two for the whole rotor to heat up fairly evenly. As long as the pad is acting on the outermost portion of the rotor instead of the inner, its ok to have a large unswept portion.
 
Discussion starter · #57 ·
Sangha333 said:
Hey guys, just a quick question. Is the jdm 92 mr2 turbo brake setup the same as the usdm one? I need to change rotors and pads and have been getting mixed answers.
JDM 1992 turbo is probably the same as USDM 1993 turbo.

Measure the diameter and thickness of the rotors to be sure. Only takes a couple minutes to pull off the wheels and double-check.
 
Discussion starter · #59 · (Edited)
Sangha333 said:
Okay, so are all the specs that are posted here for the USDM brakes?
Yes.

JDM uses the same parts, its just that the model years don't match up. Typically when there is an update to a component to improve performance or reduce cost, the JDM model gets the new part the year before the USDM. There is also a chance that in the switchover between years, a car may have parts from the other year. To make 100% sure about part applicablity, you need to use the original VIN and ask a Toyota dealer or inspect the parts yourself. Any info on these boards is a guideline at best, especially when dealing with 20 year old cars :)
 
Discussion starter · #63 · (Edited)
Oteck, are you concerned about street or track braking? What modifications have you made? (wider tires, lost weight) OEM braking is really quite good on these cars, so unless you have done major mods, I would look into into maintenance issues like the slide pins on the calipers, condition of the pads/rotors before changing anything.

With heavy use, the front pads typically wear out twice as fast as the rears. If you're getting 3 sets of front pads to one set of rear pads then that might indicate there is a problem. Are there any other symptoms that would indicate that the rears aren't working right? Have you tried using a cheap laser thermometer to see what the temperatures are on all 4 corners? Its a really easy diagnostic. Harborfrieght has them for about $35 on sale.


My car also has a little too much front brake compared to the rear and always locks the front left first. I plan to change to a higher friction rear pad next season to correct that for racetrack use.

I disagree with ScareCrowX somewhat - I bet you can solve your issue without paying big bucks for bigger calipers/rotors in the rear :thumbup
 
Discussion starter · #67 ·
thinmyster said:
Can I ask why the 91-95na with abs is so rare/expensive?
My understanding is that there were very few North American non-turbo cars with the ABS option. So it follows that there would be very few replacement parts available for those cars.

You can see the prices if you goto https://www.1sttoyotaparts.com/oempartscat.html


For example look up "Pressure metering valve"



1991/1992 MY
Hydraulic system, Pressure metering valve


w/o Turbo, w/Anti-Lock
List Price : $403.95
Your Price : $291.42

w/o Turbo, w/o Anti-Lock
List Price : $214.52
Your Price : $154.76

w/Turbo, w/o Anti-Lock, Up To 1/92
List Price : $178.02
Your Price : $128.44

w/Turbo, w/Anti-Lock, Up To 1/92
List Price : $178.02
Your Price : $128.44




1993+ MY
Hydraulic system, Pressure metering valve

w/o Turbo, w/Anti-Lock
List Price : $403.95
Your Price : $291.42

w/o Turbo, w/o Anti-Lock
List Price : $214.52
Your Price : $154.76

w/Turbo, w/Anti-Lock, From 1/92
List Price : $189.43
Your Price : $136.67

w/Turbo, w/o Anti-Lock, From 1/92
List Price : $189.43
Your Price : $136.67
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top