Master cylinder "bullet"

[zerostar2410]

So i decided to finally try to run brake lines and bleed brakes for my astro van hydroboost and Corvette Master cylinder from CPP.

I removed the master cylinder to bench bleed and realized that the "bullet" wasn't sitting flush with the black piston on the rear of the master cylinder. the bullet is pushed in about 1.5". Is this correct or is it supposed to sit flush like on the wild horses bench bleed video?

 

[Apogee]

I thought that the CPP C3 Corvette type master cylinders came with a pushrod spacer, which converts the deep pushrod hole to a shallow one (GM specification of course), as this makes them the most flexible. Otherwise, you can purchase the spacer separately if you like, or make one.

You didn't specify the bore size of the MC, however all of the factory C3 units were deep pushrod holes through '77, whether it was the 1" or 1.125" bore units for manual and power brakes respectively. In '78 manual brakes were no longer an option, so the 1.125" bore unit became a shallow pushrod hole and the deep ones went away. Since you're looking at aftermarket components, it is what it is. You should set it up such that you have a small amount of free-play or clearance between the output rod of the hydroboost and MC piston.

 

[zerostar2410]

I thought that the CPP C3 Corvette type master cylinders came with a pushrod spacer, which converts the deep pushrod hole to a shallow one (GM specification of course), as this makes them the most flexible. Otherwise, you can purchase the spacer separately if you like, or make one.

You didn't specify the bore size of the MC, however all of the factory C3 units were deep pushrod holes through '77, whether it was the 1" or 1.125" bore units for manual and power brakes respectively. In '78 manual brakes were no longer an option, so the 1.125" bore unit became a shallow pushrod hole and the deep ones went away. Since you're looking at aftermarket components, it is what it is. You should set it up such that you have a small amount of free-play or clearance between the output rod of the hydroboost and MC piston.

It may have come with a spacer and i just don't have it or remember where its at. This has been a 5 year project now in between school, new home, new kid, and a career change.

I dont really feel like messing with adapting lengths. Is there a master cylinder that I can just bolt up and go? I have disc/drum but would be looking to go rear disc in the future when i get this thing road worthy.

 

[toddz69]

Your 'bullet' or pushrod spacer isn't there. What you're seeing as 'pushed in' is just the master cylinder piston.

Todd Z.

 

[DirtDonk]

I'm not seeing what you guys are seeing then. I see what looks like a bullet in the back of the piston in pic #3 and with it removed in pic #1 & 2. Is that not correct?

Regarding the extra depth over any other pictures you see though zerostart, every master and it's piston can be different if it was made that way, and I'm pretty sure there are only a few, or maybe only one size bullet spacer thingy.
And I don't think it matters as long as your pedal rod (for manual brakes) or booster rod (assisted brakes) is the correct length to put the booster rod spacing at just the perfect length, or the pedal where it needs to be when it's seated in the bore to put the pedal where it's supposed to be for your foot.

Every master cylinder is allowed to be different. There are almost as many piston designs as there are master cylinders. The insert thingy may be the same aftermarket piece that's simply been inserted into a different master cylinder than it was originally designed for. The WH master you're using as a reference is a universal unit made specifically to be versatile and the insert is made for that specific piston.
I've never seen one from the factory (though they may exist), so it was always my "assumption" that the bullets are strictly an aftermarket method for letting master cylinders work in multiple applications without having to change the whole piston.

I'm not sure it even matters that you have one or not (nothing wrong with a deep well piston that I can think of) as long as the rod length matches.
Since you have a brake booster setup you're going to adjust the rod to fit the piston no matter what. Likely you won't have enough rod adjustment to work in a deep-well piston originally made for manual brakes, or a booster with an extremely long rod.
If that Corvette master was for a manual brake setup(?) then that would explain the deep piston well and you'll likely need the spacer as-is as long as you can adjust the booster's rod to the proper length. If it's not long enough after adjusting it out, then yes you will need to add some type of space filler under the bullet to push it closer to the booster.
Should be easy enough to tell if the booster rod can be adjusted that far.

If this is a master that came with a booster though, then apparently the factories started using spacers too. Likely so they didn't have to have completely different masters for each iteration of the brakes.

Bottom line is to try to adjust the rod. If it works, you're good to go.

Paul

 

[zerostar2410]

Apogee was right. I just finished tearing the garage apart looking for a spacer. Found the spacer that was made for this disc brake master cylinder.

I placed the spacer in the back of the master cylinder, attempted to reinstall but now realize that there is a gap between the master cylinder and H-booster. I cant tight down the nuts and eliminate the gap but is this correct or should i apply some washers between the MC and Booster?

 

[DirtDonk]

What does the spacer look like? And what is creating the gap? Is the rod touching the piston even with the spacer, or is something else holding it away from the booster?

Paul

 

[zerostar2410]

What does the spacer look like? And what is creating the gap? Is the rod touching the piston even with the spacer, or is something else holding it away from the booster?

Paul

The "spacer" just looks like the "bullet".



This is creating the gap without the nuts being tightened down. I can tighten the nuts and the gap goes away but im not sure if thats the right thing to do.

I can:

1. Just tighten it down and close the gap.
2. Add washers to close gap and then tighten down.
3. grind down the "bullet" in order to close gap.

Not sure which option is the correct one.

 

[DirtDonk]

Is your booster rod not adjustable on that unit?
And isn't the piston/spacer(?) in your third pic in the first post the right spacing then, with that further recess?
Or is that as was said, just a different piston with a deeper recess?
Even if a more recessed piston, won't that one work? Are we talking about one master cylinder in all these pics, or more than one?

You are correct that just tightening the nuts is NOT the correct thing to do. You never want preload on a piston or you will have nothing but braking problems with dragging brakes and even full brake stops when you're not wanting to stop.
The rod needs to either just touch the piston, or have a tiny gap before touching.

If the rod on your booster is not adjustable, then you need to modify the piston, or as you said use spacers to hold the master away from the booster. Washers on the studs however are not really the best way to go.

Paul

 

[toddz69]

The "spacer" just looks like the "bullet".



This is creating the gap without the nuts being tightened down. I can tighten the nuts and the gap goes away but im not sure if thats the right thing to do.

I can:

1. Just tighten it down and close the gap.
2. Add washers to close gap and then tighten down.
3. grind down the "bullet" in order to close gap.

Not sure which option is the correct one.

Option 3 is the best option, in my opinion. Since the end is rounded (at least it should be - can't be certain from your photo), you'll want to only remove a little material at a time and check/recheck the fitment and be very careful with the shaping of the end. 0.010"-0.020" gap between the end of the pushrod and the back of the bullet is ideal.

Todd Z.

 

[zerostar2410]

Is your booster rod not adjustable on that unit?
And isn't the piston/spacer(?) in your third pic in the first post the right spacing then, with that further recess?
Or is that as was said, just a different piston with a deeper recess?
Even if a more recessed piston, won't that one work? Are we talking about one master cylinder in all these pics, or more than one?

You are correct that just tightening the nuts is NOT the correct thing to do. You never want preload on a piston or you will have nothing but braking problems with dragging brakes and even full brake stops when you're not wanting to stop.
The rod needs to either just touch the piston, or have a tiny gap before touching.

If the rod on your booster is not adjustable, then you need to modify the piston, or as you said use spacers to hold the master away from the booster. Washers on the studs however are not really the best way to go.

Paul

I dont think my booster rod is adjustable. How would i be able to tell? My H-booster is directly mounted to the firewall. I modified the brake pedal rod in order to directly mount it. I cut the rod and added a threaded coupling i believe. I did all of this 5 years ago so i dont really recall what i did much.

The first 2 pictures above are of my master cylinder. The last few pictures are of wildhorses bench bleed video for reference on what the "bullet"/spacer is.

Option 3 is the best option, in my opinion. Since the end is rounded (at least it should be - can't be certain from your photo), you'll want to only remove a little material at a time and check/recheck the fitment and be very careful with the shaping of the end. 0.010"-0.020" gap between the end of the pushrod and the back of the bullet is ideal.

Todd Z.

I agree. One side is flat and the opposite end of the bullet is concaved. I think ill just grind down the flat side until the master cylinder and H-boost make contact.

 

[toddz69]

I dont think my booster rod is adjustable. How would i be able to tell?

Correct - hydroboost pushrods are not adjustable like most vacuum booster's are.

Todd Z.

 

[DirtDonk]

Ahh, that explains it. I thought some were. Makes sense though.

You would have been able to tell just by turning the rod. If it doesn't turn, and you don't see a locking nut or other mechanism to hold it, then it's not adjustable.
That's for a vacuum booster apparently though. But not being able to turn the rod on yours would confirm what Todd said.

Paul

 

[gr8scott]

I think this is the master he's using:
https://www.summitracing.com/parts/clp-mc-118-ap/

If so, I'm running the exact one also with a Astro van hydro booster. Mine went together perfectly. And nope,
that rod is not adjustable. Hey zerostar, have you tried it with that "bullet" shown in pic #3? It might get rid
of that gap.

 

[DirtDonk]

I asked the same question. Turns out that pic is from another online source
From our video about bench-bleeding. So not his.

Paul

 

[gr8scott]

I asked the same question. Turns out that pic is from another online source
From our video about bench-bleeding. So not his.

Paul

Ahh...okay I got it now.