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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?
 
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.
 
phatvw said:
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...
... 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.
This question got definitively answered on another thread, and I'm putting it here as this thread has a great concentration of knowledge. From Aaron in http://mr2oc.com/showpost.php?p=4370783&postcount=7:

Yeah, they're only different by about 1/4", early ones being longer, so you don't have to change cables just to use the bigger brakes.
 
Great Info Here! I have referenced this thread many times!

Plus, I have noticed that there have been quite a few questions about this in the various areas of the MK2 section. Sooooooo.....

MODS, CAN THIS BE A STICKY PLEASE!!!!

Daniel :thumbup
 
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
 
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?
 
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
 
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
 
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...
 
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.
 
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.
 
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 :)
 
phatvw said:
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 :)
Thanks for the help man. :)
 
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