Brake upgrade on 89 LX 5.0 Mustang. Need help

[scottyz]

Guys, I need help here. This car is starting to drive me nuts. I am doing a brake upgrade on my friends 89 LX. This is the upgrades.
1. Rear disc brakes. He bought them used from another friend. WOrked good when removed. THey are the same kit as the rear disc brake swap from SSBC.
2. Larger Calipers. They are from a lincoln but also the same as the SSBC large caliper upgrade. Typical cast iron caliper with larger piston.
3. Master cylinder also had to be upgraded and this he bought from SSBC. It is actually the same as what is included in their rear disc brake upgrade.
4. He wants an adjustable proportioning valve for the rear brakes.

OK. I have installed everything and bled the brakes. Have not installed the rear brake proportioning valve yet. Bench bled master cylinder. It says in the instructions from SSBC on the rear disc brake upgrade the you have to take the front plug off the distribution block and remove the spring and u-cup seal. Reinstall the piston alone and leave the seal under the plug there. Well i have done this. Seem to have alot of pressure to the front wheels. No air in system but the rear wheels have next to no pressure at the calipers. With the car on the hoist and the engine running, I apply the brake and put the car in gear and let the clutch out. The rear brakes wont even apply enough to stall the engine https://static1.pt-content.com/images/pt/2007/01/ne_nau-1.gif . It should be able to stall the engine. INstead the rotors start to turn. This is with the brakes applied. Any ideas guys? There is no air in the system. And i have done what the instructions say as per SSBC. Any ideas?

[fast Ed]

Not sure if this matters or not here, but I'll ask. Are you gutting the original prop. valve, or a different one that's supplied with the rear brake kit? The reason I ask, I remember from doing a Ford Racing Parts rear disc kit on my old 87 Mustang (kit is similar to the SSBC one), that the kit supplied a new 1980 - 86 style prop. valve that got gutted, plugged, and installed in place of the original 87 - 93 style valve.

Is the new master cylinder a complete metal housing, or does it have a plastic reservoir like the original? I'm just trying to get a handle on what combination of parts you're using, to make sure that the fault doesn't exist there.


cheers
Ed N.

[scottyz]

Thanks Ed for the quick reply. The prop valve is in the distribution block. There is a plug on the front of the block that when removed has a spring and piston with a seal on it. you have to remove the spring and u cup seal from the piston and reinstall the piston itself without this spring and u-cup seal that is on the piston. I have done this. The plug on the front of the distribution block is aluminum and threaded and threads into the front of the distribution block. In the center of this aluminum plug is a rubber plug. If i remove the piston from the dist block and apply brake pedal then the rubber plug pops out. When you install the piston, the one end of the piston goes into a rubber seal on the back side of the aluminum plug which in turn stops the pressure from popping out the rubber plug. You with me? I hope so.
The master cylinder is the cast iron type.
Please respond back if you can or cant help.
Do you think i have to find a way to completely eliminate this piston and somehow block the pressure to the rubber plug in the threaded plug?

[scottyz]

Please bear with me Ed. I will further explain if needed

[fast Ed]

Hmm ... what is the stamping number on the prop. valve / dist. block you're working with? Does it start with E7 or E0? Anyway, the FRPP kit did include a threaded plug to cover the hole when you removed the guts of the prop. valve, piston and all. It's available as a separate part, FRPP # M-2450-A. But I'm not sure if it works with the 87 - 93 style valve, or just the 80 - 86 style.

I'm trying to recall why the FRPP rear disc kit included the new earlier style valve to be gutted, it was about 15 years ago when we did the conversion on my 87. I believe it was because the new master cylinder did not have a provision for a brake warning switch that went in to the original plastic / aluminium master, so they supplied the earlier style prop. valve that had a hole for the pressure warning switch. Does that jibe with the parts you have? Is there a switch in the original master that you don't have a spot for now?

In any case, you may want to get in touch with the tech. dept. at SSBC tomorrow, to see if they can shed any light on this. Then hopefully you can figure out if you have the correct combination of parts, or if maybe something is faulty, and proceed from there.


good luck with it ...



cheers
Ed N.

[scottyz]

Ed. You are correct. There is no provision for a brake warning switch. I am going to try to get a normal plug for the dist block and therefore i will be able to gut prop valve. Also, for some reason there was a bunch of air trapped at the banjo fitting on the rear calipers. This helped quite a bit but still not as much pressure to the rear as I would like. Gonna have to gut that block. Thanks for the help.

[GAS]

I don't remember leving the piston in,but it has been awhile. As far as the rubber plug thing goes you can buy the steal block cap from ford or tap the old aluminum cover from the inside(for a cleaner look) for a 1/8 allen head pipe plug.

Micha
87 LX coupe, C Prepared AutoX

[scottyz]

What are you guys using for a master cylinder?
Also, i am having a problem with pressure being held. I completely eliminated the distribution block. I installed the adustable prop valve for the rear brakes. Does not seem to be any air in the system. 3 pumps of the pedal and it is hard. Let off the pedal for a couple of seconds and the next application of the pedal and it drops again. Any ideas there?
Also, master cylinder is from an 85 LTD, it is new. Should i use a different master cause there is still insufficient pressure to the rear. Any ideas here?

[fast Ed]

When you say 85 LTD, do you mean Fox LTD, or Crown Victoria? The old FRPP M-2300-C rear disc kit included a master from a 79-87 Crown Victoria / Grand Marquis. It is a 1" bore cylinder.

If I'm not mistaken, the SSBC rear disc kit includes a Mark VII / SVO Mustang cylinder, which is 1-1/8". I originally had the Crown Vic master on my 87, then we swapped to the SVO unit when changing to the large piston front calipers.

The Ford parts catalogue doesn't show the size for the Fox LTD master, but the Wagner catalogue lists it as 21 mm ... about 13/16. So if it is a Fox LTD master on there, I think you need a different one.

cheers
Ed N.

[scottyz]

Holy **** ED. That could be part of the problem. It has a 21mm bore. The guy I spoke to from SSBC said it will have a 21mm bore. He must have not realized that I had said it had the larger piston calipers in the front.
One other problem that i have is pressure loss. THree pumps of the pedal and the pedal is nice and hard BUT if i let off the pedal and let the car sit for a couple seconds and then press the pedal again the pedal will drop. 2 to 3 pumps and the pedal is hard again. Any ideas for that one?
Ed, also, when you upgraded to the large piston front calipers were they the same calipers as the Mark VII? Was it necessary to change to the larger master?

[fast Ed]

Yes, the front calipers I used were the Mark VII / SVO 73 mm units. I'm not sure if it's 100% necessary to go from a 1" MC to a 1-1/8" MC just for the large calipers. But if you have to change the master again anyway, might as well go for the 1-1/8".

Not sure about the pedal drop problem. I'd wait until you had a properly sized MC installed, then give it another go. Did you completely gut the prop. valve yet?


cheers
Ed N.

[scottyz]

I removed the distribution block completely and ran straight lines from the master. I also installed a Wilwood adjustable prop valve for the rears and there is still hardly any pressure in the rear no matter how prop valve is adjusted. I think it is in the master. Once i get the new one on there we will see. I also may need a residual pressure valve. I guess they hold 2 psi of pressure for the brakes. Although from what i read it is usually for applications where the master is mounted lower than your brake calipers. Will have to see.

[6'9"Witha69]

Resid valves are good even if the master is higher than the brakes. The larger MC will definitely help with the bleedoff problem though.

[scottyz]

Should a residual valve be used for the front and rear?

[6'9"Witha69]

Actually, I only needed one for the rear. The front can be used if needed.

[scottyz]

Thanks. I will try the master first but i have a feeling i will end up needing one. Just by the way this job has gone so far:lmao: