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After further research into the actual job of what the proportioning valve does as described in this article
The Combination Valve - How Master Cylinders and Combination Valves Work | HowStuffWorks ,I now understand that the Wilwood valve is useless in my situation. It's now obvious that by having no metering in the front ckt of this valve, there is no delay to the calipers so that the rear W/Cs can "catch up" before engaging the calipers. In light of this, I think that the best answer is to re-install the stock valve and try it again with the only difference being the new larger W/Cs and see what happens. If the system still does not perform as expected, my other alternative is to gut the rear portion of the stock valve and install a 2 port valve down stream. If I've missed the mark, please correct me.
Thanks for the reply's.
 

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I'm sorry but that's just not true. Actual measurements done before and after with my car, 3 times with the 60MM, 3 times with the 73MM, same brand/composition pads yielded an average of 18 feet less stopping distance with the 73 MM calipers.
Someone else here posted words to the effect that all the 73MM caliper did was increase pedal effort, while this is true to some extent the reason that it increases effort is that it has more area, has more fluid volume, and will exert more force on the pad (with a slight increase in pedal effort).
Just my $.02, but from research and experience.
There will always be different experiences I suppose.

I was also told that 96- spindles would create bump steer. Not once, never ever has my car exhibited that in any way, shape or form.

Shrug.
 

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I've got tons of tech e-mails to answer, but I'm going to take a little bit of time to address this as it is already starting to spiral out of control.

The link above to HowStuffWorks is incorrect in this case. The Mustang combination valve does not have a metering valve in it. Note that this is usually called a delay valve. This is a valve that has been absent from most cars braking systems for 30 or 40 years. Anyone can take apart a Mustang combination valve and see that there are only two valves inside. One is the proportioning valve, which is on the end with the rear brake lines. The other is the differential pressure valve (shuttle valve). This is located in the center of the body. There is nothing located at the end of the body with the front outlets. Just empty space.

See the sketch linked below to see what is inside.

http://i1093.photobucket.com/albums/i424/ultrastang68/GuttedProportioningValve.jpg

It is ironic that the HowStuffWorks link shows a Mustang proportioning valve, which is one in particular that does not have a delay valve in it.

To analyze the 1984 Cougar in question.

It came with 60mm front calipers and 0.75" rear wheel cylinders. Given that the owner hasn't changed the rotor diameter or drum diameter the only thing we need to consider when looking at the brake balance is the ratio of front to rear piston areas (I'm ignoring the front brake pad change for a second). In this case, it is 9.91:1.

With the 73mm front calipers and 15/16" wheel cylinders, the ratio is 9.40:1. So the car has gained a little bit of rear brake bias (9.40/9.91=0.948, 5%).

Changing from stock front pads to HPS is going to add a fair amount of front brake bias. The exact amount will depend on the ratio of HPS to stock brake pad coefficient of friction. This will vary with temperature and also with the stock front pads quite a bit.

We recently ran into a car with a similar problem in our shop. The brake system ratios all looked perfect, but the rear brakes wouldn't lock. The problem ended up being gunk in the combination valve. We disassembled it, cleaned all of the parts and reassembled it. Problem solved. The more I think about it, the more I suspect that this is the problem on a lot of Mustangs as these valves are normally never cleaned.

It isn't clear from the OP comments, but the stock proportioning valve must be defeated when the adjustable proportioning valve is added on. If this isn't done, the pressure to the rear brakes will be reduced as you are running it through two valves. This can be done with an MM-2450-A kit.

If the OP has physically removed the entire combination valve, replaced it with an adjustable proportioning valve and there is a problem locking up the rear brakes, then the problems lies elsewhere.

The rear brake shoes must be adjusted to be nearly tight to the drum.

Assuming that the proportioning valve situation is correct, the most likely problem is this. The m/c has two pistons in series. The pushrod pushes on the primary piston which pressurizes the system for the front brakes. The pressurized fluid in the front brake system is what pushes on the secondary piston in the m/c which is what pressurizes the rear brake system. Therefore if there is any air in the front brake system, there will be virtually no pressure ever developed in the rear brake system. See the cross section below.

http://repairguide.autozone.com/znetrgs/repair_guide_content/en_us/images/0900c152/80/0a/eb/87/large/0900c152800aeb87.gif

The most common cause of this with 60 and 73mm Mustang brake calipers is that the calipers are on the incorrect side of the car. When they are swapped, air will be trapped in the calipers. When correctly installed, the bleeder screws on the calipers point rearwards, NOT upwards.

The quote above from awhitegt, clearly indicates that they don't understand basic physics. In any system, mechanical, electrical, hydraulic, when the ratio of displacements increases, the energizing effort goes down, not up. In a static hydraulic system, where the forcing cylinder is a constant, the pressure in the system is a constant also. If the output cylinder increases in area, the output force goes up, not down. The ouput force is a function of system pressure multiplied by output piston area.
 

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To add:

Adjust the rear brake shoes so that you can just barely install the drum. If you leave 10 clicks of play, that will cause a lot of free brake pedal play. The system will self adjust to create clearance if it needs to. It can only reduce clearance if you back up the car and step on the brakes a bunch.
 

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To add:

Adjust the rear brake shoes so that you can just barely install the drum. If you leave 10 clicks of play, that will cause a lot of free brake pedal play. The system will self adjust to create clearance if it needs to. It can only reduce clearance if you back up the car and step on the brakes a bunch.
I installed the drum and wheel then adjusted the brakes with 10 clicks as a start. Then I did the reverse / forward dance to allow the adjusters (which are new and lubed) to do their dance.
This just occurred to me, that if the rear can't build pressure, the self adjusters won't adjust.....duh.
 

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Assuming that the proportioning valve situation is correct, the most likely problem is this. The m/c has two pistons in series. The pushrod pushes on the primary piston which pressurizes the system for the front brakes. The pressurized fluid in the front brake system is what pushes on the secondary piston in the m/c which is what pressurizes the rear brake system. Therefore if there is any air in the front brake system, there will be virtually no pressure ever developed in the rear brake system. See the cross section below.

http://repairguide.autozone.com/znetrgs/repair_guide_content/en_us/images/0900c152/80/0a/eb/87/large/0900c152800aeb87.gif
This is the kind of info that I'm looking for! I'm sure the system is properly bled BUT I will check again to be sure. The calipers are on the correct sides with the bleeders pointing back.
 

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Discussion Starter #129
The rear drums will not even get warm!!!
I still have the stock brakes on my 89.

I noticed after replacing the rear brake shoes that the drivers side drum gets way hotter than the passenger side drum.Passenger side is barely warm,not hot.

Thought it might be a wheel cylinder issue as they are original.
Took it to a reputable local garage and he said nothing was wrong with the rear brakes.(he said I had them adjusted properly)

He couldn't give me an answer why one side gets hotter than the other.
 

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One side gets hotter than the other because the hot-side shoe is 'dragging' more than the other side. It's not complex.
 

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FWIW, I ran the 73mm SVO calipers, 1-1/8" SVO MC, stock 86 GT booster, defeated stock prop valve, SSBC adjustable prop valve and SSBC rear disc conversion (same as the M2300C kit Ford offered). Never could get the balance correct. Either locked the fronts with no rear lock, or locked the rears first (now that was fun). Ultimately, I settled for front lock and no rear lock as the best balance. Ran that setup from around 92 to 06 when I swapped to the Cobra front brakes and 5-lug (still used the SSBC rear kit).

The 73mm calipers are just too big for the front given the rear brakes typically used on these cars. Now if one swapped to the SVO rear calipers, then the brake torque balance would be closer to optimal. But those calipers are an old design and performance pads are not readily available. The best option is to scrap the 73mms and go back to the 60mm unless upgrading to aftermarket or sn95 brakes.
 

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The most common cause of this with 60 and 73mm Mustang brake calipers is that the calipers are on the incorrect side of the car. When they are swapped, air will be trapped in the calipers. When correctly installed, the bleeder screws on the calipers point rearwards, NOT upwards.
My bleeders were pointing backwards....just not back far enough. I'll push my point when I think I'm right but when I'm wrong I man up and admit it.

I WAS WRONG!

I swapped the calipers from side to side, bled the system and guess what? The brakes work flawlessly. With the 15/16" W/Cs and HPS front pads, the valve needs to be all the way in. The C of F on the front pads is higher than stock but with the valve all in, the system is right at it's limit of lock up. With stock pads, the valve will most likely have to be backed out some.

Thanks to Jack for his invaluable information on the caliper issue.
 

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Discussion Starter #133
One side gets hotter than the other because the hot-side shoe is 'dragging' more than the other side. It's not complex.
Can you explain dragging more thoroughly?(what would cause this one side drag)

Maybe not complex to you,but I thought both sides should be close to equal temp if everything is working ok.

Nothing is sticking like the e-brake,it holds and releases on both sides.
 

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88 LX with stock brakes works fine, can lockup fronts and stops good. With PFC pads on fronts and good shoes on rears adjusted up I have run five track days with five 20 minute sessions each time and brakes always performed well with no fade.https://youtu.be/ldrDFD59NQU
 

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Back from the dead AGAIN. Will increasing the rear brake line diameter have any effect on front to rear bias with the 15/16" wheel Cylinder? I'm running full flow to the rear now and almost dead on except for the fact that the 225s on the front don't have the same contact area as the 255s on the rear do. With all tires being equal, I'm sure I'd have no issues. During full lock up testing, I flat spotted the fronts. Before I replace all the tires with new Sport Comps, I want to cover all my bases. I don't want to go discs until I've exhausted all my options. The curse of my engineering back ground won't leave any unanswered issue alone....LOL.
 

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Brake line diameter has no affect on brake bias. There is only fluid flow in the line before the pads are in contact with the rotors. Once contact is made, fluid flow drops to essentially zero, so the line diameter can't create any pressure drop and affect the brake bias.

If you go to higher grip tires, you will need to reduce the amount of rear brake bias. This is because more tire grip allows the car to stop harder, which allows more longitudinal weight transfer. A higher percentage of longitudinal weight transfer means that less rear brake bias is needed. With enough tire grip, you would need 0 rear brake bias as the rear tires would have zero weight on them.
 

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Thank you Jack. This makes sense. I tend to over think things. Whether its jetting, timing or brakes, I shoot for100% perfection.
 

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FINALLY DONE! With all the valuable info provided in this thread, I've finally achieved the results I set out for. My plan was to achieve optimal performance from a rear drum system that worked with my front system and rivaled a rear disc swap. As you can see from the posts, I started this in the fall of last yr. I've compiled a list of the parts below. First a brief description of the car used. My 84 Cougar is still a fox body but a little heavier than the traditional Mustang of that time. The car had the stock 302 CFI, AOD, 7.5 rear and stock suspension. I purchased an 88 Mustang LX with the H.O. T-5 and 8.8 /3.73 combo that had a rusted body but excellent drive train. After a drive line and front brake swap from the LX to the Cougar, I did multiple upgrades to the induction, exhaust etc. of which I won't bore you with as they don't pertain to this thread.

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Front spindles and 11" stock rotors from 88 LX
73mm calipers with steel pistons 84 Town car(OEM E4LY2B121A)
HPS pads (HB125F.650)
SS pin bushings from MM
Braided SS flex lines
1 1/16" MC from an 84 Lincoln TC
Wilwood prop valve (https://www.summitracing.com/int/parts/wil-260-11179/overview/)
15/16" wheel cyls (WAGNER WC 34876)
Porterfield R4-S #569 shoes

Before I did the rear shoe upgrade, I had the proportioning valve turned all the way in and the rears would only lock up on sketchy ground but never on good pavement. After the shoe upgrade, the rears locked up with ease. I had to back the adj knob out 5 full turns to get it to the proper bias. All I can say is WOW! The car never stopped that good. This may not be for everyone , but for me it was a challenge to see if I could duplicate a disk set up without a major swap.

Again, thanks to all involved in this thread.
Mark
 

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But you didn't duplicate a rear disc set-up. The rear drums will still overheat and become less effective and are still subject to water collecting in the drum. Moreover, brake "bias" is not controlled by a prop valve. Bias is determined by the size of the rotors and calipers (piston size and #), drum size, etc. With a 9" drum rear and 11" rotor with 74mm front caliper you are probably way over front biased. All the prop valve does is adjust the rear "knee-point" on the brake pressure slope. It moves that point up or down the slope to reduce/increase pressure to avoid rear lock before front lock. But this does not provide an optimal front/rear bias brake system. As Jack noted, during brake dive the weight shifts off the rear to the front placing more grip on the front tires and nearly eliminating rear grip (the rear jacking effect). This occurs with discs on all four too. Your better braking is more likely due to the new brake parts, pads/shoes and fluid rather than a swap to a 74mm caliper. But better is better no matter how it was achieved.
 

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The bias of the basic brake system is a function of the caliper/wheel cylinder piston areas, rotor/drum diameters and the coefficient of friction of the friction material.

The 73mm front calipers created a front bias shift of 32%. Changing the wheel cylinders created a rear bias shift of 36%. If the coefficient of friction of the R4S shoes is only 5% higher than the stock shoes, the brakes are balanced again. Granted when they get really hot, the rear brake torque will suffer, but even for excited street driving this shouldn't be a problem. The biggest difference between rear disc and drums will be in the modulation capability.
 
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