Brakes

TxPhPrerunner

Well-Known Member
Posts
64
Reaction
0
As some of you may know by now I'm building a 77 F-150. I am trying to plan as much of the project as I can before I start. I'm getting close on my suspension, I know what glass I'm going to use, and I have my engine narrowed down to two choices (400hp 351 or 500+hp 460). I want to run 37" tires(my truck is a super cab I want the larger tires to help counteract the long wheel base over bumps). There a couple of different sets of F250 spindles and rears I can pick up cheap and even a F350(82, 76, and 79). I should have at my disposal every thing I need to handle the larger tires. Now to the important question. Brakes, I want all the stopping power I can get. I have read that the hydraulic booster from a Ford 2 1/2 ton truck will fit and boost braking pressure. That could help but I want the best brakes I can afford. I have always driven with the gas and brake pedals and I'm very hard on brakes. I also considered the Nitto 38". They mount on an 18" rim and would give more brake clearance. Does anyone know what options are out there? Thom maybe?

I don't live on the edge. I fell over long ago.
 

ntsqd

Well-Known Member
Posts
2,429
Reaction
27
Use the largest rotors that will fit in the rim size you plan to use. Rule of thumb is that the rotor will be 3" smaller OD than the rim OD. You can go over that, but how much is dependant on the rim's inner contour and the backspacing. Calipers for 13" rotors are about the current limit. There are calipers made for larger OD rotor out there, they are spendy.
(On the backspacing note, I would plot the Steering Axis at ride height and set up for zero Scrub Radius.)

With a power booster in the mix everything I know about choosing the right bore size combo is out to lunch. The problem with boosters is that they are tuned for a specific application. So a 12" vacuum booster for a Coupe de Ville may or may not have the same tuning in it as the 12" booster for a Sedan de Ville. Same is true of the hydro boosters. One intended for an F-250 with a V10 is not likely to have the same 'tune' as one for an F-450 with a PSD.

If you keep all of the stock parts except that you increase the rotor's OD, you will increase the braking torque. Increasing rotor radius is just like increasing the engine's stroke. More torque.
The problem with OE calipers is that they have huge piston areas. If you put aftermarket calipers on you rarely can match the OE piston area. So then your m/c bore is too big to work with the aftermarket calipers and you have a stiff pedal that doesn't stop very well. Most likely you will need a smaller bore m/c if you go to aftermarket calipers.

Merely increasing operating pressure rarely pays off. You'll find much more tunability in pad compound selection. In stock Ford Sliding caliper pads the best I'm aware of is the Raybestos "Brute Stop" pad. Typically the Performance Friction type pads never get up to operating temp in the dirt. In any caliper you can get them for, you'll want to try the wilwood D or E compound pads. The E's are slightly higher temp and dust less than the D pads. Their Q pads may be worth a shot, I don't know. Wouldn't use the T pad on anything but a light vehicle and the A, B, & C pads are higher temp than the E's. There is a J pad that was developed for Endurance road racing, might be worth trying a set. I'm not familiar with other maker's compounds well enough to make any suggestions.

Rotor width is important. The wider the rotor, the better it cools so a lower temp pad can do the job. The downside is that wider rotors weigh more and you can cool to below the pad's operating temp. Wilwood has a 1-5/8" rotor & caliper combo for Martinsville. Very spendy, but pad temps and pad lifespan came up considerably from the previous 1-3/8" wide rotors.

TS

I used swerve around my halucinations, now I drive right thru them.
 

TxPhPrerunner

Well-Known Member
Posts
64
Reaction
0
Thanks for the info. I can already see I'm going to have a hard time sorting and applying it to my app. though. You mentioned the effects of changing rotors but not calipers. Was that a hypothetical for explanation purpose or is that possible? Brakes are important to me so I'll go some distance to make them work well. I gather that the 17" rims would be all I need to clear current brake tech.

I don't live on the edge. I fell over long ago.<P ID="edit"><FONT SIZE=-1>Edited by TxPhPrerunner on 03/15/03 10:43 AM (server time).</FONT></P>
 

ntsqd

Well-Known Member
Posts
2,429
Reaction
27
Calipers really only present you with two variables in terms of braking performance. One you can easily control and change, and one you can't. Piston area you can change. Caliper body flex you can only control by going to a stiffer design.
What makes for a stiff body design could take a while to explain. The simplest thing is to loose the OE sliding calipers. They have a lot of flex in the anvil, the part behind the outer pad. Caliper body flex shows up as part of what makes the pedal 'spongy' feeling. It is fluid displacement that has little to no effect on actual braking.

Going to fixed body calipers or larger OD rotors means you will be building caliper brackets. Rarely are they hard to make. Radial mount calipers present the biggest challenge and wilwood, at least - maybe others too, tries to make the radial mounts bolt to existing lug mount type mounts.

So you're left with piston area as the most easily changed variable. If you can get the same piston area in several different calipers, what becomes the decider(s) ?
Pad volume is one. How long do you *need* the pads to last ?
Availability for the rotor width you want/need is another. .810 thick rotor ? 1.375 thick rotor ?
Range of pad compound options for that caliper ? Ford Sliders are very limited. Wilwood Superlites have available a pad in every compound wilwood offers and that pad is very common to other makers, so their pads also fit.
Body rigidity would be one if there were some way for you as the customer to quantify that. Internally the aftermarket brake manufacturer's have verious means to test this, but I'm sure they all aren't the same method (so comparison of the data would be pointless) and I doubt they would give out that info anyway.

My order of importance looks like this:
Fixed body caliper
Largest OD rotor that will fit
Narrowest rotor that will do the job with low temp pads.
Idealized overall leverage ratio (mech. ratio * hyd ratio) <-this assumes no booster.



TS

I used swerve around my halucinations, now I drive right thru them.
 

TxPhPrerunner

Well-Known Member
Posts
64
Reaction
0
I like to brake at the very last second no matter where I'm driving. My truck should weigh between 5&7000Lbs when finished. I will be street driven often but not daily. I want my pads to last. If it isn't to inconvenient what would you put on it using Willwood off the shelf parts?

I don't live on the edge. I fell over long ago.
 

ntsqd

Well-Known Member
Posts
2,429
Reaction
27
What is the mechanical leverage ratio of the brake pedal you intend to use ? Knowing that makes choosing a master cyl bore size far easier.

TS

I used to swerve around my halucinations, now I drive right thru them.
 

ntsqd

Well-Known Member
Posts
2,429
Reaction
27
Also, when I say how long do you want the pads to last, remember that some calipers are designed to work with pads that are each .800" thick. That is ~.600" worth of friction material. Which is double or even triple the thickness of OE pads.
Depending on pad compound and how they are used they could last nearly forever or only one race. Prior to the STR combo it wasn't uncommon for a race car at Martinsville to finish with no friction material left and they would start the race with a high temp 'hard' compound that was at least .600" thick.

I don't have much experience with vehicles that are as heavy as your truck. Were it lighter I could say that a booster would not be required. I believe this to be true in your case too, but you may end up with a long pedal travel for that to be the case.

Were it me I would start with the BNSL6 caliper and the 12.88 x 1.1 rotor on the front unless other factors require a caliper with more piston area and then I would look at using the GN III on a 12.19 x 1.25 or a 12.19 x 1.375 rotor.

TS

I used to swerve around my halucinations, now I drive right thru them.
 
Top