99+ PBR rear brakes on LSC axle?

[KAILUAZ]

So I've found my LSC rear brakes may be too big when I run PBR brakes up front. The brake bias will be too much in the rear, even with a proportioning valve cranked to the rear.
Does anyone know if I can swap the 99+ PBR calipers on the LSC rear end? I'm sure the brackets are different, how about the spacing for the rotor on the LSC axles?
Or should I just try to find a 99+ rear end? I don't care about them being wider like the LSC.
Thanks!

[Zephyr 351C]

I dont see how it would be an issue. LSCs and SVOs had 73mm front calipers, so the 38mm twin piston PBRs offer more clamping force than the front brakes originally on the cars that came with these discs out back.

I'm not trying to slap you in the face, sorry if it seems like I am, but are you sure you're turning the knob the right way on the prob valve?

I'm putting the same brakes on my car...

[KAILUAZ]

I dont have the brakes installed yet. Here are some posts I got from a MM rep:

Your rear brake calipers are way too large. With a 54mm piston, they have exactly double the surface area that the stock Varga 38mm caliper or the PBR 38mm rear caliper has. That means that the SVO rear brakes will have double the brake torque for a given hydraulic pressure than the stock Varga rear brakes will have. The rear brakes will lock up very early. You can't fix this with the proportioning valve, it is too large of a mismatch.

Unfortunately, there is no front brake option for the SVO rear disc, other than the SVO front brakes (73mm calipers with 11" rotor). Running all SVO brakes on the car will give you a proper brake balance, but they aren't really suited to track use since the front rotors are the same size as the 87-93 stock rotors. They have very little thermal capacity.

Also the brake pad selection for the front and rear SVO brakes is very limited.

To balance the SVO rear brakes with a 13" front brake, you are going to need a four piston front caliper with pistons sizes of about 52mm. This is huge. I've never seen anything this large.

I know you probably don't want to hear this, but it's the truth, if you are going to use the car in any situation where you will be using the brakes to their maximum capability (Track, AutoX or panic stops on the street), your cheapest solution is th get rid of the rear brakes. Find someone with Baer PBR calipers, 12" rotors or any 94 and up Cobra rear brakes (Varga caliper and 11.65" rotor). In either case, you will also need the mounting brackets for the calipers and the axles.

I assumed that PBR calipers on stock rotors, means dual piston aluminum floating PBR calipers (Corvette/Cobra type) on a stock 13" Cobra rotor.

Here are some numbers to explain what I'm talking about:

Caliper diameters in mm Area in sq in
SVO rear 54 3.55
SVO front 73 6.49
Varga/PBR rear 38 1.76
PBR/Cobra dual 38 x 2 3.51
PBR GT/V6 99+ dual 44.5 x 2 4.83
94-98 GT/V6 single 66 5.30

In a stock Mustang with an inline master cylinder setup, there are two master cylinders, but since they are inline and have the exact same piston area (they share the same bore) when you press on the brake pedal, you are going to get exactly the same pressure in both the front and rear hydraulic systems. Therefore the master cylinder can have no effect on the front to rear brake balance. It only effects the amount of pedal travel and effort required to stop the car. Once you have selected calipers, you select the master cylinder to get the correct effort and pedal travel that you want.

The primary thing that effects the front to rear brake balance in the car is the ratio of front to rear brake caliper piston areas. The ratio of front to rear brake rotor diameters affects it also, but since this ratio only varies about +/-4% in this case, I'm going to ignore it to simplify the discussion.

A stock SVO has a front to rear area ratio of 1.83 (6.49/3.55). For comparison a 99 Mustang has an area ratio of 2.74 (4.83/1.76). A 96 Cobra has an area ratio of 1.99 (3.51/1.76). The proposed brake system under question (99+ PBR dual front and SVO 54mm rear) has an area ratio of 1.36 (4.83/3.55). This is a huge change in the direction of increased rear brake bias. Compared to a 96 Cobra, it is 30% (1-(1.36/1.99))*100 increase in rear brake bias. This is huge.

You will have to use front pads with the highest coefficient of friction that you can find. Rear pads with the lowest coefficient of friction you can find. Install an adjustable proportioning valve and run it turned almost all the way down. Doing all of this, the car will probably still lock the rear brakes early and will have no tuning ability with the proportioning valve available. You'd be better off using the 94-98 front calipers. This will give you an area ratio of 1.49 (5.30/3.55). This will only be a 25% (1-(1.49/1.99))*100 increase in rear brake bias. Not a huge improvement, but some.

I'm not sure what is going on with shaqer74's friend running a Mustang in CP. My guess is that he is running a front race pad with a very high cf and a rear pad with a very low cf. In CP you are allowed to add a couple hundred pounds of balast to the car. People typically build the cars quite a bit under the weight limit and then add balast where they want it. Balast will always be added to the rear of the car to increase weight over the rear tires. Doing this will require an increase in rear brake bias over a stock Mustang to get maximum braking.
__________________
Jack Hidley
Maximum Motorsports Tech Support

[Zephyr 351C]

Well the MM guy can use his math, and I'll just try it. I do that a lot at work with the CNC press I run. They say it wont work and I do it anyway, most of the time it works.

My car wont see the street for a while, so if you dont try it I'll let you know how mine turns out, a few years from now, if I remember...

My main reason for choosing the flipped lincoln rears was because of the number of posts I read where guys had to use spacers to get draglites or other 15" wheels to fit over cobra rear discs.

[KAILUAZ]

On a drag car I don't think its an issue, but this will be a road racer so the bias must be closer.

[Zephyr 351C]

Yeah, that makes a lot of difference.

[8T3Hatch]

Sounds like a complete new rear is probably the best choice if you're not concerned with the additional diameter. Very interesting read as i'm pondering additional brake upgrades myself.

[KAILUAZ]

Well now some people are saying not to gut the stock proportioning valve and run a aftermarket one also. This will give the rear less pressure.
Who knows, I'll just throw it in there and see what happens like Zephyr said.

[stockhatch]

Damn, so the jist of the story is that Lincoln rear brakes are too large to use even with Cobra fronts? That was my plan until now...

[wacostang]

The brakes you have will work, you just need to gut the pv and get an ajustable one. There are several people on this site running similar brakes, I am in the process of going to cobra fronts and mark 7 rears

[svoman2300]

I had PBRs up front and the stock SVO/LSC calipers out back and the pedal felt hard and it took alot of force to stop. I went with Cobras all around and will never go back.

[Zephyr 351C]

Originally Posted by KAILUAZ

Well now some people are saying not to gut the stock proportioning valve and run a aftermarket one also. This will give the rear less pressure.

Grrr, I've alrady gutted my stock PV...

Originally Posted by svoman2300

I had PBRs up front and the stock SVO/LSC calipers out back and the pedal felt hard and it took alot of force to stop. I went with Cobras all around and will never go back.

What bootser/MC were you running?

[svoman2300]

Originally Posted by Zephyr 351C

Grrr, I've alrady gutted my stock PV...



What bootser/MC were you running?

I was running the SVO master and booster. When I went with the Cobras I used a Towncar MC and SN95 booster.

[frankiesaysrelax]

Sorry to come to the party late, but I've been thinking about this same problem myself. Why couldn't you just leave the stock proportioning valve alone? Wouldn't it then direct most of the fluid to the front and less to the rear as if it were still operating front discs and rear drums?

I have a whole LSC disc brake rear and '94 spindles and brakes sitting around that I was going to use to convert to 5 lug until I heard about this problem myself. My thought was just to keep the stock proportioning valve. Does anyone know if this will work?

[82mustang]

drum brakes NEED a small amount of constant pressure to keep the wheel cylinder pistons from falling in and getting jammed in the wheel cylinder...but on drum brakes this isn't enough to engage the brakes so it's never a problem, swap out the drums for discs and you have a small amount of constant pressure on the pistons which directly push on the pads..dragging the brakes.

[frankiesaysrelax]

I actually got all my parts from another car. It had a stock master and booster with the aforementioned SN95 stuff up front and the LSC rear out back. The brakes did NOT drag at all, however the pedal was practically to the floor, I'm guessing because the master cyl did not have sufficient volume. It was an '85 former 4cyl notchback.

[machm1969]

I'm just wondering because this was my plan as well. I just bought a lincoln rear and SN95 fronts.

Thanks,

Matt

[machm1969]

Not to be a dumd*&^, but what are PBR calipers? What mm are the pistons?

Thanks,

Matt

[FoxChassis]

PBR International is a brake system manufacturer based in Australia. (They also have manufacturing in SC and TN.) They specialise in OEM braking systems.

PBR calipers have been OEM on Mustangs since '99...single piston front calipers on V6 and GT models, and dual piston on Cobra, Bullitt, etc.

[Zephyr 351C]

V6/GT SN95s had single piston front calipers from 94-98, the 99+ front PBRs have dual 44.5 mm pistons.

[RichV]

So did anyone except Rick do this with results?

Reading all the MM stuff has me a bit concerned now. I'm looking at the 13" upgrade for 2009 on my race car.

My conclusion makes no sense. What I gather is that the stock SVO brakes, which I have currently (F+R), are not matched well with with the front 13" Cobra setup. The SVO rear brakes stop too hard for the Cobra 13" brakes, which then makes the front SVO brakes more effective?? So, my 73mm single piston caliper puts down more force than a twin piston 44.5mm (89mm total)???? I would think the Cobra fronts would grab harder than stock SVO fronts.

Stock SVO brakes are decent, but nothing to write home about. They really have no more stopping power than the late Fox V8 brakes, maybe a little more bite, but not much.