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Front disc brake conversion, which master cylinder?

patr1ck

Jr. Member
Joined
Mar 1, 2005
Messages
101
Loc.
Tempe, AZ
I have just done the front disc brake conversion on my '69 bronco with a dana 44. The master cylinder on it has disc brake style reservoirs (one large rear one and one smaller front one) and was replaced by me a couple of years ago when it still had 4 wheel drums for a brake concern. I got it from checker. When I got it from them I asked for a 69 bronco master cylinder and that is what came out of the box. Is this ok to use or do I need to get something else? Ive read things about some valves in the MC that hold a residual pressure of 10psi that need to be removed when the disc brake conversion is done. Ive looked on my master cylinder for these things and have found nothing that stands out. Is the fact that it has disc style reservoirs mean its ok to use with no mods?

Thanks,
Pat
 

needabronco

Bronco Guru
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Jul 2, 2004
Messages
6,411
Loc.
Prescott/Farmington
You should be fine, I've pulled several 'original' master cylinders apart and never found a residual valve. NONE of the aftermarket masters I've seen have ever had one either. That doesn't mean that it won't happen, just saying it's a rare chance.

As far as using the master you have, I'd say it's worth a try and 90% of disk brake conversions are fine. One thing to consider which will make more of an impact would be to ditch the problematic 'H' block and install an adjustable proportioning valve in the rear of the system. That will separate the front and rear systems, and allow infinite adjustability to the rear brakes. The most common issue is that the rear brakes will lock up with minimal brake effort as the fronts are working much more effieciently than with drums.

Good luck
 

broncnaz

Bronco Guru
Joined
May 22, 2003
Messages
24,341
Many people have used the stock MC with good results most also leave the stock H block in place you only need a proportioning valve if the rear brakes are locking up before the fronts doesnt seem to be much of a issue for most of us.

The dual reservoir MC doesnt mean its a disc brake style it was designed as a safety feature over the old single reservoir/piston MC's So if you lost brake pressure you wouldnt loose all your brakes. I believe they were made manditory in 1967.

Might be a good idea to at least check to ensure there is no residual valve before installing and bleeding everything. In the pic I posted the check valve is located under the brass seat in the brake line port usually there is a small rubber duckbill and a spring thats the parts you remove then replace the brass seat. Most people use a sheet metal screw to remove the brass seat.
 

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patr1ck

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Mar 1, 2005
Messages
101
Loc.
Tempe, AZ
So, can I tell by looking into the ports past the seats if I have residual check valves? Or does it have to be taken apart before I know if they're there?

Thanks,
Pat
 

toddz69

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10,440
So, can I tell by looking into the ports past the seats if I have residual check valves? Or does it have to be taken apart before I know if they're there?

Thanks,
Pat

You have to take them apart.

Todd Z.
 
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patr1ck

Jr. Member
Joined
Mar 1, 2005
Messages
101
Loc.
Tempe, AZ
Many people have used the stock MC with good results most also leave the stock H block in place you only need a proportioning valve if the rear brakes are locking up before the fronts doesnt seem to be much of a issue for most of us.

The dual reservoir MC doesnt mean its a disc brake style it was designed as a safety feature over the old single reservoir/piston MC's So if you lost brake pressure you wouldnt loose all your brakes. I believe they were made manditory in 1967.

Might be a good idea to at least check to ensure there is no residual valve before installing and bleeding everything. In the pic I posted the check valve is located under the brass seat in the brake line port usually there is a small rubber duckbill and a spring thats the parts you remove then replace the brass seat. Most people use a sheet metal screw to remove the brass seat.

Do I reuse the removed brass seat? I have been having a bit of a MC fiasco. I ended up getting my money back from checker due to 5 failed rebuilt mc's and went to napa and bough a new one. It has the rubber deal under the brass seat that you mentioned. I saw your posts on the power brake booster thread I started. I havent decided what Im going to do yet. If the brass seats can be reused Ill go that route.

Thanks,
Pat
 

toddz69

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10,440
Do I reuse the removed brass seat? I have been having a bit of a MC fiasco. I ended up getting my money back from checker due to 5 failed rebuilt mc's and went to napa and bough a new one. It has the rubber deal under the brass seat that you mentioned. I saw your posts on the power brake booster thread I started. I havent decided what Im going to do yet. If the brass seats can be reused Ill go that route.

Thanks,
Pat

Yes, you re-use the removed brass seat. Carefully tap it back into the port after you remove the residual pressure valve.

Todd Z.
 

broncnaz

Bronco Guru
Joined
May 22, 2003
Messages
24,341
Heck if you bought a new MC you should have just gotten a disc brake version non power you wouldnt need to be pulling anything apart. Although most disc barke versions are for power brakes and also have the fitting ports on the opposite sides. So that would mean you would have to adapt the brake lines.
 
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patr1ck

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Joined
Mar 1, 2005
Messages
101
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Tempe, AZ
Heck if you bought a new MC you should have just gotten a disc brake version non power you wouldnt need to be pulling anything apart. Although most disc barke versions are for power brakes and also have the fitting ports on the opposite sides. So that would mean you would have to adapt the brake lines.

I tried that, but the throttle linkage lever gets in the way. That would have been ideal. oh well.
 
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patr1ck

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Mar 1, 2005
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101
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Tempe, AZ
Thanks guys. I pulled the brass seats and removed the residual pressure valves. All is well.

Thanks,again,
Pat
 

Broncboozled

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Mar 30, 2010
Messages
156
Loc.
Nor Cal
Thanks guys. I pulled the brass seats and removed the residual pressure valves. All is well.

Thanks,again,
Pat

How did you get the brass seat out? I tried with a # 8 screw, I'm thinking it was too big. Going to try a #6 "thinner screw" and see how thatt works.

On further thought I have more questions. When you put the screw in to the brass seat and yank it out, you pull out the check valve and re use the brass seat. Isn't it boogered up because of the screw?
 
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Scoop

Contributor
Have Bronco, Will Travel
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Feb 1, 2006
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10,766
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Cuchara, CO
Thanks guys. I pulled the brass seats and removed the residual pressure valves. All is well.

Thanks,again,
Pat

Did you do both? If so, you should have only done the front (big reservoir).

Broncboozled, the screw just puts a thread in the orifice which is not critical. As long as the tapered side of the brass seat is not scored the brake line flare will seat and seal OK.
 

Broncboozled

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Mar 30, 2010
Messages
156
Loc.
Nor Cal
Did you do both? If so, you should have only done the front (big reservoir).

Broncboozled, the screw just puts a thread in the orifice which is not critical. As long as the tapered side of the brass seat is not scored the brake line flare will seat and seal OK.

Thanks I finally got it out.
 
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patr1ck

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Mar 1, 2005
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101
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Tempe, AZ
Did you do both? If so, you should have only done the front (big reservoir).
.

Yep I took both of them out as the old master cylinder that got replaced didn't have them. Neither did the 3 rebuilt master cylinders that Checker ordered for me. I went through 3 before I gave up and just bought a new one from Napa. they all had defects from gouges in the sealing surface on the top to a leak around the brass seat that never sealed up. The Napa one worked well. I didnt want to change anything so I pulled them both. Perhaps leaving the front port valve in probably wouldnt have done anything different.

Pat
 

Scoop

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Have Bronco, Will Travel
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10,766
Loc.
Cuchara, CO
Yep I took both of them out as the old master cylinder that got replaced didn't have them. Neither did the 3 rebuilt master cylinders that Checker ordered for me. I went through 3 before I gave up and just bought a new one from Napa. they all had defects from gouges in the sealing surface on the top to a leak around the brass seat that never sealed up. The Napa one worked well. I didnt want to change anything so I pulled them both. Perhaps leaving the front port valve in probably wouldnt have done anything different.

Pat

Not having the check valve will allow the pressure to bleed off the rear drum system. You may need to pump the brakes to bring the pedal back up after the shoes have worn down a bit. Also means you may need to adjust them more often but you should be OK.
 

Kyle.malone

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Mar 9, 2006
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Norman, OK
So if the disc brake swap is done. One can just put in a proportioning valve for the rear and hook the front disc directly to the MC or does it still have to go through a H block?
 

Broncboozled

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Mar 30, 2010
Messages
156
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Nor Cal
So if the disc brake swap is done. One can just put in a proportioning valve for the rear and hook the front disc directly to the MC or does it still have to go through a H block?

The proportioning valve takes place of the H block all lines run from the MC to the new P valve. The Proportioning valve regulates the fluid to allow more to be applied to the front and less to the rears, so the rears won't lock up" or something like that"

One of the Gurus can chime in for a better explanation.
 
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patr1ck

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Joined
Mar 1, 2005
Messages
101
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Tempe, AZ
Not having the check valve will allow the pressure to bleed off the rear drum system. You may need to pump the brakes to bring the pedal back up after the shoes have worn down a bit. Also means you may need to adjust them more often but you should be OK.

If your shoes have worn down and the pedal drops with them the automatic adjusters arent working properly.

Pat
 
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