Toyota Truck Calipers, Ventilated Brake Rotors, MM rear Disc Brakes

[zgeezer]

My Z has the MM rear disc brake conversion using 240zx calipers and 300z non ventilated rotors.

 

I have all the elements to install ventilated front discs and Toyota truck calipers.  I do not have a functioning proportioning valve as I gutted the original.

 

After reading all the posts describing this swap to be inherently unbalanced in that the Toyo calipers are too large in comparison with the 240zx rears, I'm thinking seriously about returning the front to stock specifications: stock rotors and calipers,  and keeping the MM rear discs [hey, they look good and the drums have long since disappeared].

 

I think I should install another after market proportioning valve in my rear brake line.  But I don't know if it is "necessary" or not  from a safety standpoint.   This is not a track car; but, I do wish to have predictable behavior for  panic  stops from a straight line. 

 

Does anyone have any experience with stock brakes using only the MM rear brake set up?

 

I tend to ascribe to both "more is better" and "while I'm at it I might as well ........  ." views of life.

 

This time I really want to do it right.

 

Please comment.

 

G

 

 

[Miles]

Car: 72 240Z 350 SBC daily driver. Never race etc.

 

I have been experimenting with various brake combinations for the last six years and believe that well maintained stock brakes are just fine for a daily driver even with a SBC 350 swap.

 

After six years of experimenting to balance the front MM ventedToyota caliper and  the MM 240SX  rear caliper set up I have gone back to stock front brakes. My MM vented front/240SX rear set up included a 280Z eight inch booster, a one inch Wilwood MC and Wilwood proportioning valve (PV).  The proportioning valve was useless since I, like many others, found that the 240SX calipers will not keep up with the Toyota vented front brakes thereby requiring the PV to be opened all the way to the rear. The main reason I installed the proportioning valve was to experiment with rear brake pads to better balance the front and rear brakes.

 

So my current set up is now: stock front calipers, 1 inch Wilwood MC, 280Z 8 inch booster, Wilwood PV and MM 240SX rear calipers with Hawk HP pads all around. The brakes are now better balanced and perform well except the one inch Wilwood MC makes the pedal a bit stiff (280Z booster helps).

 

My plan is to swap the Wilwood proportioning valve back to the stock PV and to swap the Wilwood MC back to the stock 7/8 MC and keep the 280Z booster. The stock 7/8 MC should make the pedal less stiff.

 

At this time my brakes are balanced and I like the Hawk HP pads. The Hawk HP pads have better cold bite than the KVR or Porterfield pads I tried.

 

Opinion: Well maintained stock brakes work fine. In retrospect, the MM 240SX rear caliper swap works well with stock front calipers, stock MC, stock PV  and stock booster. If you don't like drum brakes do the 240SX rear swap leaving everything else stock.  Some people complain that the stock MC "feels mushy" with the 240SX rear swap.

 

I have also run into quality problems with remanufactured 240SX calipers having three of them with the  piston sticking right out of the box.  Sticking pistons seems to be a known problem among the Nissan/240SX people.  Check the Nissan/240SX web sites for more information before you decide to do the 240SX swap as they do come with their own set of problems.

 

So yes, you can go back to stock front calipers with your 240SX rear calipers.  As for the PV I plan on using my stock valve.

Edited June 16, 2013 by Miles

[RebekahsZ]

I am not aware of any ill effects to having excessive front bias. Excessive rear bias will spin your car. It would be nice to get as much rear brakes as possible up to the point of having too much. Hope that makes sense. Stock brakes are fine except for road racing where you tromp them every 5-10 seconds to slow the car from 100 to 30 over and over for hours on end. In that case you are trading pad area for pad pressure to stop the car and the brakes get super hot, which makes the rotor soft and wear prematurely and pads crack and break. For autocross, which lasts about one or two minutes max and drag racing where you slow the car once every 5 minutes if the track isn't busy or every hour and a half of it crowded stock is fine. Street driving you just plan around a single panic stop on the freeway, for which the stock brakes are fine. You can match your brake equipment to your actual needs. I have had my Z for 20 years and the brakes have been fine until my first road course track day. Fewer laps and longer rest breaks and I bet my stock brakes would have been fine, but we beat the old car like a red-headed stepchild and I had to replace the whole system. It cost me about $200 to replace everything (lots cheaper than an upgrade). If I were you, I would do the vented Toyota swap and keep whatcha got in back. Sorry so long-winded.

Edited June 16, 2013 by RebekahsZ

[Miles]

If he does the vented Toyota front swap he will have created a very well documented problem with overly biased front brakes. That the 240Sx calipers can't keep up with the vented Toyota front brakes has been discussed extensively here. Additionally, he will have to install a one inch Wilwood MC to provide the extra fluid volume required by the Toyota vented calipers etc. 

[RebekahsZ]

Educate me: what negative driveability effect will excessive front bias cause?

[RebekahsZ]

PS- I know a bunch of guys personally who left the MC stock with all variety of disc upgrades.

[Miles]

Educate me: what negative driveability effect will excessive front bias cause?

 

Mostly stopping performance.

 

Think about it. If the fronts are doing most of the  work then the rear brakes are not contributing to the over all braking performance. 

 

On factory cars the braking systems are engineered to optimize front and rear brake performance.  The popular brake "upgrades" we do are not engineered brake systems such that everything is balanced and works together.

 

The best advise I can give is for folks to read the many complaints in the brake forum about how unbalanced the Toyota vented front and 240SX rear brake combination  swaps are.  Also, for those who are analytically inclined,  do the math before choosing a brake upgrade.

 

Example: http://forums.hybridz.org/topic/103856-need-help-with-240z-brake-bias-with-4-piston-toyota-and-240sx-brakes/

 

 

Unfortunately, there is very little engineering/performance  data for the  various "brake upgrades" that come to us by word of mouth on these  car web sites.  Several people here  have proposed side by side tests for the various "brake upgrades" to provide comparitive data.

 

Wouldn't be great if we could go to Summit Racing and buy a complete engineered brake system like what is advertised for  Fords and Chevys?

Edited June 17, 2013 by Miles

[zgeezer]

Thanks for the information.

 

I took the JTR book to heart; I'm running the 10" 2+2 booster and larger 13/16 inch MC.  I'll return to stock front calipers and slotted rotors [just for the bling], aftermarket PV and hope for the best.

 

G

[Leon]

Educate me: what negative driveability effect will excessive front bias cause?

 

Longer braking distances (than stock).

[ktm]

I was called out as a liar on another forum talking about this brake upgrade, but I managed to get my 240 SX and Toyota front calipers to work well where I've got balanced proportioning.. I am using Porterfield r4s is in the front and pads are supplied with the 240 SX kid in the rear. Maybe i just got lucky.

Edited June 23, 2013 by ktm

[seattlejester]

I'm running toyota front calipers (non vented disc) and maxima calipers out out back and I had to dial my proportioning valve to partially closed for the rear to keep the car from twitching in the rain under braking. 

I've seen the response above where some people whole heartedly state it does not work, and others swear the toyota 4x4 & 240sx caliper swap works great, even demonstrating lockup in the rear. 

 

Curious is this just a fallacy that this is an "upgrade"? I know the rear disc is not really an upgrade, just a convenience mod, but is doing the fronts actually harmful?

[Nigel]

There's a huge difference between the non-vented 4x4 calipers and the vented V6 4-Runner calipers. The non-vented caliper piston surface area is not that much bigger than stock 240Z calipers. It's only about a 3% increase. The V6 4-Runner calipers have an almost 27% increase in piston surface area! That results in a huge difference in brake torque. So, saying your "Toyota" front brake and 240SX rear brake combo is balanced is meaningless without specifying exactly which Toyota front calipers you have.

 

Keep in mind that stock 240SX front brakes are actually LESS "powerful" than stock Z front brakes. So, don't expect 240SX rear brakes to be suited to anything more than stock Z front brakes.

 

An engineered solution is doable. It's just a matter of gathering the appropriate data and doing the math, which is all available on-line. It's not voodoo magic, or guess work. By crunching the numbers, I can tell you that a V6 4-Runner/240SX brake combo has approximately a 74/26 front/rear bias, assuming equal pad coefficient of friction and full line pressure to the rear brakes. Non-vented 4x4 caliper/240SX brake combo has approximately 70/30 front/rear bias.

 

To expand on Leon's answer about excessive front brake bias, you need an adequate combination of front AND rear brake torque to transfer load to the front wheels to increase their grip to take advantage of the additional brake torque that bigger front brakes can generate. Without the rear brakes contributing enough to that load transfer, the front brakes will easily overpower the friction between the tires and the road and the front wheels will lock prematurely. Consequently, longer braking distances! And don't be misled by those "Big" front brake kits you see advertised for newer cars into thinking that excessive front bias isn't an issue. Those big front brake kits don't actually generate any more brake torque than the stock front brakes. Even though the rotors are enormous, and the calipers may look huge, the calipers actually have tiny little pistons in them to keep the brake toque in-line with stock, so as not to throw off the factory brake bias.

 

Nigel

[seattlejester]

That makes quite a bit of sense, it would explain why there is some discrepancy between those that swear by either story.

 

I hope this doesn't bother anybody if I ask this here, but would you mind if I bothered you for the numbers of the piston diameters for the fronts (of both types of Toyota calipers)? I know the rear piston has a negligible difference between the 240sx, maxima, 280zx pistons 38-43mm, I am curious about the fronts. So even though the Toyota S12 (solid rotor) calipers run a much wider pad compared to the stock S30 caliper, the effective piston area is what determines braking force?

Is there no difference in the distribution of the force into 4 calipers versus 2, or is this one of the cases where we just look at the end result of the moving part and the contact that it can apply?

 

Genuine curiosity here, I don't mean to berate at all, I know a string of questions can seem like that sometimes. 

[Leon]

That makes quite a bit of sense, it would explain why there is some discrepancy between those that swear by either story.

 

I hope this doesn't bother anybody if I ask this here, but would you mind if I bothered you for the numbers of the piston diameters for the fronts (of both types of Toyota calipers)? I know the rear piston has a negligible difference between the 240sx, maxima, 280zx pistons 38-43mm, I am curious about the fronts. So even though the Toyota S12 (solid rotor) calipers run a much wider pad compared to the stock S30 caliper, the effective piston area is what determines braking force?

Is there no difference in the distribution of the force into 4 calipers versus 2, or is this one of the cases where we just look at the end result of the moving part and the contact that it can apply?

 

Genuine curiosity here, I don't mean to berate at all, I know a string of questions can seem like that sometimes. 

 

Correct, piston area affects braking force, not pad surface area.

 

This is physics 101: F=μN. Brake force depends on the coefficient of friction between the pad and rotor (μ), the amount of force the pad exerts on the rotor (normal force, N), and rotor diameter at which the force is exerted.

 

It's the force that matters. Two small pistons don't necessarily exert more force than one big one, it's the combined area that matters.

 

I don't know the piston areas off the top of my head.

Edited June 25, 2013 by Leon

[Nigel]

That makes quite a bit of sense, it would explain why there is some discrepancy between those that swear by either story.

I forgot to mention that there are two versions of the 240SX rear caliper as well, which adds to the confusion even more. There's an early 34mm piston version, and a later 38mm piston version. The bias ratios I gave are for the 34mm version. However, even the 38mm piston caliper is marginal with the V6 4-Runner front caliper, but would be well matched with the 4x4 caliper.

 

I hope this doesn't bother anybody if I ask this here, but would you mind if I bothered you for the numbers of the piston diameters for the fronts (of both types of Toyota calipers)?

V6 4-Runner: 43mm/43mm

I4 4-Runner (also vented rotor): 43mm/34mm

4x4: 43mm/34mm

 

I know the rear piston has a negligible difference between the 240sx, maxima, 280zx pistons 38-43mm,

While the difference may seem small, a 43mm piston provides substantially more clamping force than a 38mm piston.

 

I am curious about the fronts. So even though the Toyota S12 (solid rotor) calipers run a much wider pad compared to the stock S30 caliper, the effective piston area is what determines braking force?

Piston surface area is one of the factors. Hydraulic pressure, rotor diameter and brake pad co-efficient of friction are the others. Brake pad surface area has nothing to do with it.

 

Leon got the rest of it.

[seattlejester]

Fascinating! Thanks!

 

It has really been a while since I have taken physics, and sad to say I have lost some of the key elements working with biological systems the past few years. I really do miss clear equations and such. Thank you two for answering. 

 

Right, any clamping force (normal to the pad) would be multiplied by 1/2 of any diameter increase in the piston (squared) x pi. So when people upgrade the to the toyota 4-runner caliper with a significantly larger piston area they are drastically increasing the bias ratio. So looking at pad bite only (leaving tire compound, pad material, brake line pressure, etc in another category)...

 

Just compiled for future reference:

 

Stats:

Fronts:

Datsun 240z Front Caliper (~54mm) rotor 271mm

Toyota 4x4 non-vented (~43mm, ~34mm) rotor 271mm

Toyota 4-runner vented (~43mm, ~43mm) 

 

Rear:

Nissan 280zx Rear Caliper (~43mm) rotor 285.115mm <- apparently my rears are bigger than my fronts!

Nissan 240sx Rear Caliper (~38mm)

Nissan Maxima Rear Caliper (~38mm)

 

Setups:

Toyota vented 4-runner and Nissan 240sx rear caliper setup

Toyota 4-runner Front (43mm/43mm) = ((0.5*43)^2)*pi*2 =  2904mm^2 = 72%

Nissan 240sx rear (38mm) = ((0.5*38*pi)^2) = 1134mm^2 = 28%

 

Toyota vented 4-runner and Nissan 280zx rear caliper setup

Toyota 4-runner Front (43mm/43mm) = ((0.5*43)^2)*pi*2 =  2904mm^2 = 66.7%

Nissan 280zx rear (43mm) = ((0.5*43)^2)*pi = 1452mm^2 = 33.3%

 

Toyota solid 4x4 and Nissan 240sx rear caliper setup

Toyota 4x4r Front (43mm/34mm) = ((0.5*43)^2)*pi +  ((0.5*34)^2)*pi =  2360mm^2 = 67.5%

Nissan 240sx rear (38mm) = ((0.5*38)^2)*pi = 1134mm^2 = 32.5%

 

Toyota solid 4x4 and Nissan 280zx rear caliper setup

Toyota 4x4r Front (43mm/34mm) = ((0.5*43)^2)*pi +  ((0.5*34)^2)*pi =  2360mm^2 = 62%

Nissan 280zx rear (43mm) = ((0.5*43)^2)*pi = 1452mm^2 = 38%

 

I am guessing from my numbers compared to yours that I need to factor in the leverage arm provided by the rotor diameter?

Edited June 26, 2013 by seattlejester

[Nigel]

You forgot to show Pi in your equations, but your results look right.

 

However, yes, you do need to take into account the leverage arm of the rotor. But, it's not as simple as using the OD of the rotor. You're not actually applying full force at the OD. You have to subtract the pad height from the OD, since the force is averaged to the middle of the pad height. Finding pad height is not easy though, so I typically assume it's the diameter of the largest piston.

 

Nigel

[seattlejester]

Whoops, it was in the calculations just not in the written equations. I guess in the end it doesn't matter in calculating ratio since they get canceled, but still bad book keeping.

 

I am really sorry if this is trivial, but if you would mind entertaining me, to get the leverage arm then, you are using (roughly) the radius of the rotor minus the radius of the largest piston? 

 

I.E. for a front solid rotor aka Z rotor, 271mm - 27mm (for s30 front caliper), and 271mm - 21.5mm (for toyota 4x4 caliper)?

 

Once again, I do thank you for taking the time. My curiosity does tend to be a nuisance to many.

[Nigel]

I am really sorry if this is trivial, but if you would mind entertaining me, to get the leverage arm then, you are using (roughly) the radius of the rotor minus the radius of the largest piston? 

 

I.E. for a front solid rotor aka Z rotor, 271mm - 27mm (for s30 front caliper), and 271mm - 21.5mm (for toyota 4x4 caliper)?

 

271mm - 27mm is the rotor diameter minus the piston radius. You want the difference of the radius of both (or diameter of both divided by two). So, 135.5mm - 27mm and 135.5mm - 21.5mm.

[seattlejester]

I really am embarrassed.

 

So with that corrected, we are then comparing moments? As in Moment = Force x Radial Distance from rotational axis, where Force equals the area multiplied by line pressure, and the radial distance is the corrected radius of rotor - radius of piston.

 

So to calculate ratio Moments...

 

Front Bias = (Moment of Front / (Moment of Front + Moment of Rear)) x 100.

Rear Bias = (Moment of Rear/ (Moment of Front + Moment of Rear)) x 100.

 

Moment Toyota 4x4 front caliper = 2360mm^2 x Line pressure x (135.5mm-21.5mm) = 269040mm^3 x line pressure (in kg/mm^2)

Moment Toyota 4-runner = 2904mm^2 x Line pressure x (135.5mm-21.5mm) = 331056mm^3 x line pressure

 

Moment Nissan 280zx = 1452mm^2 x Line pressure x (142.5mm - 21.5mm) = 175692mm^3 x line pressure

Moment Nissan 240sx = 1134mm^2 x Line pressure x (142.5mm - 19mm) = 140049mm^3 x line pressure

 

The ratio removes line pressure from the equation assuming same line pressure goes to front and back (for our very simple calculation)

 

So we end up with biases of:

Toyota vented 4-runner and Nissan 240sx rear caliper setup

70%:30%

Toyota vented 4-runner and Nissan 280zx rear caliper setup

65%:35%

Toyota solid 4x4 and Nissan 240sx rear caliper setup

66%:34%

Toyota solid 4x4 and Nissan 280zx rear caliper setup

60.5%/39.5%

 

This would be my calculations using the slightly strange fact my rear rotors are larger than my fronts and using the stock z rotor for the front (not sure if the 4-runner guys run a different diameter, or if there is another size that most people run for the rear).

 

To calculate the actual braking force applied we would have to then start accounting for the leg pressure, master cylinder bore, mu of the tire, the radial distance from the rotational axis to the contact patch of the tire, and on and on, and factor in the weight shift of the car as one is braking and cornering, so this very brutal calculation is a very simple way of looking at comparable pad bites?

 

Well regardless, thank you very much Nigel for helping me fumble through all this math, I definitely need to pull out my physics books and brush up on them again.

Edited June 26, 2013 by seattlejester