Anyone switch to conventional master cylinder and booster with PBR calipers?

sizemoremk

Registered User
Anyone switch to conventional master cylinder, booster, AND PBR calipers?

My SC has been sitting in the garage for several years, recently pulled it out and got to werkin on it.

Before I parked it, the brakes always had a low pedal and was weeping from the brakes ARC sensor, which I just recently plugged.

It leaked very slowly when I parked it, had the low pedal, but was drive-able but far from optimal.

I believe I have the rod adjusted about where it should be, IIRC using a piece of all-thread with an acorn nut. Seems like I recall adjusting several times to where I was pretty sure the rod engaged the MC piston right at the beginning of the pedal movement.

I assume there should be no pre-load on the MC piston???


I'm pretty convinced that all air has been removed.

I bled by conventional (wife pumping brakes while I bled each corner starting from far to close to MC)...

I gravity bled...

Then today I found some more air by reverse bleeding. I used a large syringe with a rubber tube zip-tied to the bleeders to force fluid from each corner back through the MC; then forced fluid through the bleed port directly on the MC. Then bled conventionally at each corner again while watching the tube connected to the bleeders to verify no more bubbles.


Before cranking the car, pedal was firm.

Then when the car was cranked the pedal went alot softer and about goes straight to the floor with little effort.

Don't know how it drives now, its still on jackstands, but will see how they work tomorrow.

There was a long thread here quite awhile back, spanning a few years on ABS to conventional. I scanned through several of the pages and never could see if anyone had done this swap, as well as the PBR swap???

I'm wondering if there is a compatibility issue here between the bore/sroke and fluid displaced vs these and the stock calipers???

Any ideas?

Thanks guys!
 
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I installed a booster T-bird I think and MC, splitter from a Crown Vic "I think" years ago. Last winter I installed PBR calipers ect and everything works great full pedal car stops great. Before the PBR's Brembo rotors and pads I had a bit of a hard time slowing the car down after a 1/4 mile pass at Beaver springs drag way, no trouble after the install.

No there should be no preload on the MC rod.

Sounds to me like you are sucking air past a seal in your MC piston, I would replace the MC and go from there.
 
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We changed my brothers 94 markVIII to a non abs system using all the parts from a non abs 95 car, don't overlook the rear limit valves make sure if the car you pull the parts from uses it that you use it, and if it doesn't you don't.
Alan
 
I put a conventional master cyl and booster on my last 89 SC. Because the original unit went out. It was the biggest pain in the ~~~ I have ever done, and the breaks weren't great after.
 
I had the same thought last night, but after more reading, it sounds like if the MC was bad I would still be able to pump the brakes up to be firm with several pumps.

In this case, no amount of pumping will firm up the pedal.

I just read a thread where some poor guy with a Honda setup for road racing replaced everything (multiple MCs, multiple calipers, booster, prop valve, and even some lines) over a few months and swore he had all the air out after he bled gallons of fluid through his brake system multiple times, etc. This guy sounded like he pretty much knew what he was doing by reading the thread, but finally broke down and took it to a shop who found the air. Said this shop cracked every fitting and the proportioning valve during the bleeding process and the pedal finally came back firm.

So now I am thinking I must still have some friggin air in there somewhere...

Any opinions of the MC being bad enough to where it won't pump up a pedal at all with the car on?


I installed a booster T-bird I think and MC, splitter from a Crown Vic "I think" years ago. Last winter I installed PBR calipers ect and everything works great full pedal car stops great. Before the PBR's Brembo rotors and pads I had a bit of a hard time slowing the car down after a 1/4 mile pass at Beaver springs drag way, no trouble after the install.

No there should be no preload on the MC rod.

Sounds to me like you are sucking air past a seal in your MC piston, I would replace the MC and go from there.
 
If I were going to put a vac booster brake system on a sc I would add a storage canister and put a one way check valve in it so that it can store some vacuum.
Alan
 
Yes, you should run a vacuum canister, just as the MN12's originally equipped with the vacuum assist booster did. However, you'll want to install the check valve between the vacuum supply (the inlet plenum preferably) and the rest of the vacuum system rather than on the canister.

From the symptoms you're experiencing, it could be a failing MC, a booster rod that is set too short, or air somewhere in the system. I run a '97 4.6L MN12 non-ABS MC/vacuum-assist setup in my XR7 with PBR calipers up front on stock diameter rotors, and it has a good, firm pedal and stops very well.
 
Looks familiar. ;)



Provided you're using the inlet plenum as the vacuum source, it will never see boost. It will also see an abundance of vacuum as soon as you close the throttle blade on decel (mine pegs my 30 in-Hg gauge). By isolating the entire vacuum system from the source with a check valve, you preserve as much vacuum in the system as possible rather than ramping up and down with throttle input. The canister provides buffer to the system. The larger the canister, the larger the buffer. Additionally, isolating the entire system from the source effectively increases the size of the buffer.

None of this will correct the OP's issue though.
 
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I agree it should never see boost,but without the check valve you are putting vacuum backwards in the system. Ya ya we know you like to show off your beautiful car, most of us are a little envious at least :D. I probably would too.
Alan
 
Only thing I ever run was the factory little ball inside the RH wheel well about the size of a soft ball, no check valve, hose from the REAR INLET OF the supercharger so it don't see boost. I usually see 8-10 inches vacuum at idle

Though it would not hurt to run a larger canister I don't think it's needed.
 
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