Hydroboost to Master Cylinder rod length help.

[BoulderMike22]

I’ve installed a Astro Hydroboost, 1/2” clocking bracket to rotate 90*, and a Corvette style disc/drum master cylinder.

My first problem seems to be the HB does not engage the MC fully now that I have added the 1/2” spacer. I am assuming I either need a plunger rod from the HB to be another 1/2” or the adapter on the Master Cylinder needs to be 1/2” longer to get that immediate and full engagement of the two? Anyone know of or suggest an off the shelf solution?

My second question is about the pedal rebound. It’s fairly slow. From what I can tell, I don’t see any leaks. I re-sealed the piston seal so that’s fairly tight now. Any suggestions on what could be causing this?


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[thegreatjustino]

If you're running the brakes with that 1/2" gap between the booster and MC, that'll certainly affect your pedal movement.

If the Corvette master cylinder a deep cup piston or shallow cup? If deep cup, get a dowel rod the same diameter as the hole in the piston for the push rod and cut a piece off to make a slug the correct length to put inside the piston. If it's a shallow cup piston, your only solution is going to be to get a longer push rod for the hydrobooster.

 

[BoulderMike22]

Not entirely sure what you mean about shallow cup vs deep cup. It did come with a dowel to put in for power brake applications that is about 1.5” long and is about 1/2” in diameter. The instructions recommended leaving it out for manual brake applications.

Should I assume that means it is a deep cup and I could get a 1/2” diameter rod and cut it to the length I need to take up the space that the clocking bracket created?


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[DirtDonk]

Yes, if your master came with the separate dowel/spacer/thingy, it's a deep cup piston for manual brakes, with an "adapter" to make the piston shallower to work with most boosters. The master does not care what it's used with, as long as whatever it is has the right length rod.
The deep well for manual brakes was for security and not having the pedal rod fall out if you pulled the pedal too far back. With the master bolted rigidly to the booster this was not a problem and the booster rods could be short.

So the clocking bracket you're talking about is between the hydroboost and the master? if so then yes you need to make up that space somehow. Is it a kit, but it does not come with a way to extend the rod or whatever?
A gap at the master is like 6-times that size at the pedal. So that 1/2" gap makes for 3 additional inches of pedal throw before anything meaningful happens at the master. Approximately anyway, since I don't know the pedal ratio of Broncos exactly.
No matter what the ratio is though, extra space is not good for that warm and fuzzy feeling with brakes!

Never seen a clocking bracket like you're talking about (I don't remember anyway). Got pics?
If the bore is large enough to fit the master in to, how you would support an additional rod length? Is there a big long one that could be threaded on to the booster rod's threads? I wonder if there are different length rods that are easy to find. Don't remember any discussions about it here before.

And a Corvette master cylinder for disc/drum? I wonder how that works? Corvette's before '67 had a single reservoir master, and all 'Vettes after '63 had 4-wheel discs. So no such thing (in theory) as a Corvette dual-reservoir master for disc/drum brakes.
Seems like that would not be a thing then.

Paul

 

[toddz69]

Here's a pic that shows the difference between the deep and shallow master cylinder and some booster rod lengths (scroll to the bottom):

http://www.hydratechbraking.com/mastercylinders.html

Dirtdonk: take a look at this pic and you'll see the clocking bracket between the booster and the master cylinder (shiny aluminum piece):

https://www.wildhorses4x4.com/product/MOAB-HydroBoost-Power-Brake-System-B/Bronco_Power_Brakes

There are some differences in the booster pushrod lengths - the Astro van has one of the shorter ones I've ever seen and the Ford Super Duty units have one of the longest. Let us know if it matches the one on the right in the first pic and we may be able to help you depending on how much additional length you have. I'm guessing your clocking bracket is about 0.5" thick.

Todd Z.

 

[BoulderMike22]

Here's a pic that shows the difference between the deep and shallow master cylinder and some booster rod lengths (scroll to the bottom):

http://www.hydratechbraking.com/mastercylinders.html

Dirtdonk: take a look at this pic and you'll see the clocking bracket between the booster and the master cylinder (shiny aluminum piece):

https://www.wildhorses4x4.com/product/MOAB-HydroBoost-Power-Brake-System-B/Bronco_Power_Brakes

There are some differences in the booster pushrod lengths - the Astro van has one of the shorter ones I've ever seen and the Ford Super Duty units have one of the longest. Let us know if it matches the one on the right in the first pic and we may be able to help you depending on how much additional length you have. I'm guessing your clocking bracket is about 0.5" thick.

Todd Z.

My Master Cylinder looks like the one on the left (unless you put the dowel pin in to flush it up) and my Hydroboost looks like the one on the right (with the rod sitting tucked back inside the opening a bit.

Yes- my clocking bracket is made from 1/2” aluminum. I made it myself so I didn’t buy it from a kit.

I guess I should also clarify that the MC I bought is advertised as Corvette style but I’m using a disc/drum proportioning valve and the MC was also advertised for either manual or power brakes depending on whether I used the adapter pin.


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[toddz69]

My Master Cylinder looks like the one on the left (unless you put the dowel pin in to flush it up) and my Hydroboost looks like the one on the right (with the rod sitting tucked back inside the opening a bit.

Yes- my clocking bracket is made from 1/2” aluminum. I made it myself so I didn’t buy it from a kit.

I guess I should also clarify that the MC I bought is advertised as Corvette style but I’m using a disc/drum proportioning valve and the MC was also advertised for either manual or power brakes depending on whether I used the adapter pin.


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OK, so you're using the 4 wheel disc master with the the proportioning valve - sometimes the 4 wheel masters work ok without a residual pressure valve for the rear drums.

Usually the slow return on the pedal means there's some restriction in the low pressure return on the hydroboost.

With what you have for a pushrod and a master cylinder combo, I'm amazed that booster is activating your master cylinder at all!

Do you have a sense of how much longer a pushrod you need? I think I have an extra Super Duty one that I'd sell - I can tell you how far out beyond the master cylinder seating surface on the booster if that would help.

Todd Z.

 

[BoulderMike22]

OK, so you're using the 4 wheel disc master with the the proportioning valve - sometimes the 4 wheel masters work ok without a residual pressure valve for the rear drums.

Usually the slow return on the pedal means there's some restriction in the low pressure return on the hydroboost.

With what you have for a pushrod and a master cylinder combo, I'm amazed that booster is activating your master cylinder at all!

Do you have a sense of how much longer a pushrod you need? I think I have an extra Super Duty one that I'd sell - I can tell you how far out beyond the master cylinder seating surface on the booster if that would help.

Todd Z.

Thank you for the help Todd. I decided to try a longer rod length from the master cylinder to take up that slack. It seems to be working now. Am able to lock up the brakes with only about half a pedal travel.

I just cut some 1/2” steel rod down to about 1/2” longer than what was in the MC to accommodate for the 1/2” that was added with the bracket.


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[toddz69]

Thank you for the help Todd. I decided to try a longer rod length from the master cylinder to take up that slack. It seems to be working now. Am able to lock up the brakes with only about half a pedal travel.

I just cut some 1/2” steel rod down to about 1/2” longer than what was in the MC to accommodate for the 1/2” that was added with the bracket.


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OK - sounds good!

Todd Z.

 

[WILDHORSES]

I just added these to the line up. Might make things easier for the DYI.
https://www.wildhorses4x4.com/product/19419/Bronco_Power_Brakes

Jim

 

[BoulderMike22]

I just added these to the line up. Might make things easier for the DYI.
https://www.wildhorses4x4.com/product/19419/Bronco_Power_Brakes

Jim

Thanks Jim but the slack needed when you add the bracket between the HB and MC is internal and not the brake pedal bracket.

You can either do that by changing the length of the Hydroboost push rod or by changing the length of the dowel pin that goes inside some master cylinders. You can see in the picture below the HB push rod that engages the MC.

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[catfan]

If you don't want to use a bullet I make the rods any size.

 

[BoulderBronco22]

I am a little perplexed. I am trying to dial in the Hydroboost to Master Cylinder engagement and I made a bullet to go into the Master Cylinder to take up the 1/2" of the spacer I installed. I had the truck propped up in the front and was able to spin the front tires freely so I took it for a test drive. After a short time, it seemed as though the brakes were engaging without depressing the brake pedal- making me think that maybe the hydraulic system is pressurizing and causing the rod from the hydroboost to engage the master cylinder. When I got back from the test drive, the front driver brake was smoking.

I propped the front end back up and turned the Bronco on and depressed the brake pedal about 20 times to try to pressurize the system again but the front tires still move freely. I am not sure how to determine how much to shorten the MC bullet since I can't seem to replicate the issue on jack stands.

Any advice?

-Mike

 

[DirtDonk]

In your case, are you certain it's pressurizing the main system, and not just one of the calipers sticking? This is almost as common as the rod adjustment being slightly off, but can happen any time.

Is yours a disc brake conversion using the GM setup? Got daylight showing between the caliper and knuckle?
Possible bad caliper? I had that happen on mine just last year. Got a couple of miles down the road and the driver's side started smoking. This on a rig that had been driven for about three years and several thousand miles with no trouble. Crappy caliper just froze apparently. Could not find, and can't think of any other culprits in my case.

As far as the rod adjustment goes though, did you have to push the master cylinder on to the booster with any pressure? Or did it seat fully mounting surface to mounting surface with zero touching of the rod to piston?
If it seated fully without touching the rod, but it turns out to be system pressurization, I'd suspect a faulty booster or proportioning valve.
Not sure what goes wrong with hydro-boost, but vacuum boosters seem to have this issue a lot with the poppet valve on the back.

Are you running a standard proportioning valve?

Paul

 

[toddz69]

As far as the rod adjustment goes though, did you have to push the master cylinder on to the booster with any pressure? Or did it seat fully mounting surface to mounting surface with zero touching of the rod to piston?

I'm curious about this issue as well. Can you tell us about how it fits onto the booster?

Todd Z.

 

[BoulderBronco22]

Yes on GM conversion kit and standard proportioning valve for drum/disc.

It is not a stuck caliper. I drove it around the block and came back and immediately propped the front end up again and both sides are locked up. I unbolted the MC and there is about 1/4" of gap now if I do not force the two together. I decided to cut 1/4" off the bullet in the MC and it appears to be working better. (I now have a coolant leak that I need to fix that perpetuated on my test drive before I can test the brakes further). If it is not one thing its another!

When I originally mated the MC and HB, there was not resistance. It seems like the short driving of the Bronco is changing the distance between the HB and MC and I am not sure if that is indicating an issue with the HB or not. It is an ASTRO VAN JY unit that I resealed. I do not have any leaks and it seems to be working but I don't have any more experience than this with these HB conversions.

 

[toddz69]

I unbolted the MC and there is about 1/4" of gap now if I do not force the two together. I decided to cut 1/4" off the bullet in the MC and it appears to be working better.

When I originally mated the MC and HB, there was not resistance. It seems like the short driving of the Bronco is changing the distance between the HB and MC and I am not sure if that is indicating an issue with the HB or not. It is an ASTRO VAN JY unit that I resealed. I do not have any leaks and it seems to be working but I don't have any more experience than this with these HB conversions.

Wait - you initially had no issue mating them together (no resistance) and when you got back, you took it apart and had 1/4" of distance to 'force them together'???? Never heard of that happening.

I'm trying to picture in my mind what is happening. Something is happening to force that power piston to move out on its own or not retract properly when you get off the brakes. Perhaps an internal leak of some sort or some stiction somewhere in the unit? Someone with better knowledge of the internals will have to chime in.

Todd Z.

 

[BoulderBronco22]

Wait - you initially had no issue mating them together (no resistance) and when you got back, you took it apart and had 1/4" of distance to 'force them together'???? Never heard of that happening.

Todd Z.

That is correct-- Like I said-- I am a bit perplexed myself, but I am a YouTube mechanic so have limited knowledge on diagnosing symptoms like this.