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Old 06-19-2014, 02:48 PM   #1
Basque32
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Default 73 Master Cyliner Vacuum Booster

Hi all,
It's been a while since I've checked in. I found my 73's MC leaking so I ordered a replacement combo MC/PB from Zips but the MC did not fit the PB so I sent them back. So I ordered combo MC/PB from Ecklers and the 2 parts fit properly so I installed them. Interesting findings: there was quite a bit of surface rust on the braketry under dash so I cleaned as best I could and sprayed some neutralizer on them. Also had to drill out top 2 holes in firewall a little, bolts looked like 3/8" and 3/8 bit cleared out some, still didn't fit, checked bottom holes and found next drill bit size up cleared holes so I drilled top 2 and PB then fit

So, all is good, bled MC (what a pain), then all 4 wheels with wife on break pedal and me on bleeders. Did this about 3 times and filled about a large asparagus jar (quart+ ?), used 1.5 quarts of dot 5 so far.

here's the rub, the brake pedal seems hard with engine not running but almost goes to floor with engine running. Thus the multiple bleed attempts. Took the car out in the cul-de-sac for test and brakes stop car well, actually feels like it's got power now (not so much before). So where am I going wrong here?

BTW, the MC/PB came with a short push rod and some type of puck insert but also a longer push rod. As the original had a long rod I used the long rod.

Any advice from you all would be greatly appreciated. (missing another car show this weekend. dang!)
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Old 06-19-2014, 02:52 PM   #2
MelWff
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you are supposed to measure the distance between the end of the rod and the piston in the back of the master. Were the two rods the exact same length? Do you have the factory service manual? You bench bled the master? Read the section on pushrods

http://www.classicperform.com/TechBo...oubleshoot.htm

Last edited by MelWff; 06-19-2014 at 03:01 PM.
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Old 06-19-2014, 03:01 PM   #3
Basque32
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Originally Posted by MelWff View Post
you are supposed to measure the distance between the end of the rod and the piston in the back of the master. Were the two rods the exact same length? Do you have the factory service manual? You bench bled the master?
Thanks for your quick reply.

I bench bleed the MC, I tried to test fit the short rod and puck but the MC did not seem to fit flush on the PB, so thus the long rod decision.

I also forgot to mention that I purchased some speed bleeder so I can do this myself as the wife is not always available.

However, I did not measure the distance before assembly but would think that if came as a set it should work without modification. Just don't know if supposed to use the short rod w/puck thingy or the long. Eckler's tech advise was limited
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Old 06-19-2014, 03:13 PM   #4
MelWff
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so you dont know the clearance between the end of the long rod and the piston in the back of the master? Can you try to measure with some clay or similar substance or observe how far in or out the long rod is from the booster mounting surface and also the position of the master piston with regard to the booster mounting surface. Too much distance and you get excessive pedal movement.
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Old 06-19-2014, 03:22 PM   #5
Basque32
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Originally Posted by MelWff View Post
so you dont know the clearance between the end of the long rod and the piston in the back of the master? Can you try to measure with some clay or similar substance or observe how far in or out the long rod is from the booster mounting surface and also the position of the master piston with regard to the booster mounting surface. Too much distance and you get excessive pedal movement.
MelWff,
I tried to take the MC off w/o remove brake lines again but would only back off a little. However, I read where someone suggesed removing the bolt that holds the switch the line connect to from the chassis and then the lines would all move together. I might give that a try.
So I was wondering how one measure a confined space like that, using clay huh? Otherwise off the MC brake line come again!
Do you have any idea why the send out 2 different types of push rod assemblies, I'm guessing the short rod & puck would be a tighter fit as my test fit suggested?
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Old 06-19-2014, 03:52 PM   #6
davidchristopher
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Quote:
Originally Posted by Basque32 View Post
Hi all,
It's been a while since I've checked in. I found my 73's MC leaking so I ordered a replacement combo MC/PB from Zips but the MC did not fit the PB so I sent them back. So I ordered combo MC/PB from Ecklers and the 2 parts fit properly so I installed them. Interesting findings: there was quite a bit of surface rust on the braketry under dash so I cleaned as best I could and sprayed some neutralizer on them. Also had to drill out top 2 holes in firewall a little, bolts looked like 3/8" and 3/8 bit cleared out some, still didn't fit, checked bottom holes and found next drill bit size up cleared holes so I drilled top 2 and PB then fit

So, all is good, bled MC (what a pain), then all 4 wheels with wife on break pedal and me on bleeders. Did this about 3 times and filled about a large asparagus jar (quart+ ?), used 1.5 quarts of dot 5 so far.

here's the rub, the brake pedal seems hard with engine not running but almost goes to floor with engine running. Thus the multiple bleed attempts. Took the car out in the cul-de-sac for test and brakes stop car well, actually feels like it's got power now (not so much before). So where am I going wrong here?

BTW, the MC/PB came with a short push rod and some type of puck insert but also a longer push rod. As the original had a long rod I used the long rod.

Any advice from you all would be greatly appreciated. (missing another car show this weekend. dang!)
1) You buy asparagus in jars?

2) Are both boosters the same?

3) Given that it's a kind of important part of the car- the ability to stop - I would suggest pulling the m/c off. Brake fluid is a lot cheaper than death.
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Old 06-19-2014, 04:01 PM   #7
Basque32
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Originally Posted by davidchristopher View Post
1) You buy asparagus in jars?

2) Are both boosters the same?

3) Given that it's a kind of important part of the car- the ability to stop - I would suggest pulling the m/c off. Brake fluid is a lot cheaper than death.
Yes to #1 when it's pickeled

Well good question #2, they look similar in size but the MC bale does hit the check valve, so ?

#3 can't disagree with common sense

Thanks for the reply
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Old 06-19-2014, 04:11 PM   #8
J.Abbott
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Originally Posted by Basque32 View Post
Yes to #1 when it's pickeled

Well good question #2, they look similar in size but the MC bale does hit the check valve, so ?

#3 can't disagree with common sense

Thanks for the reply
What brand booster did you buy from Ecklers? The only booster that is made that is new is by MBM which is what we sell plus everyone else. Unfortunately they decided to use a 10mm stud in it instead of a 3/8. They are a little difficult to get the retaining nuts on but using wrench they will go on. Curious as to what issue you had.
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Old 06-19-2014, 04:53 PM   #9
Basque32
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What brand booster did you buy from Ecklers? The only booster that is made that is new is by MBM which is what we sell plus everyone else. Unfortunately they decided to use a 10mm stud in it instead of a 3/8. They are a little difficult to get the retaining nuts on but using wrench they will go on. Curious as to what issue you had.
That's a good question, don't know for sure as all I did was put the tape on the end and 3/8" is what it read on both the old and new PB.
In hind sight I would have actually preferred the Zips combo product as the MC had bleeders and supposedly the original manufaturer numbers.

However, when the Zip person I spoke to said that I would have to drill out (MC I assume) to make it fit, is when I said no. The Ecklers MC had no numbers/bleeders but fit, however the bale closest to PB hits the PB check valve, so much for after-market.

NBD, as I'm keeping the old parts and will most likely get them rebuilt by hopefully someone reputable at some point. Just want to get the car back on the road!

Yes, I believe both the MC and PB boxes showd MBM now that you mention it.
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Old 06-19-2014, 05:07 PM   #10
dtianen
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Just changed my Master cylinder on my 75. Bought a new one from Advance Auto parts "Cardone Select Master". It was a perfect fit. Bench bled the MC before putting it in the car. All fittings were identical. Bled all the brakes and exchanged all the old fluid in the process and now good to go.
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Old 06-19-2014, 05:28 PM   #11
briankeery
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Originally Posted by dtianen View Post
Just changed my Master cylinder on my 75. Bought a new one from Advance Auto parts "Cardone Select Master". It was a perfect fit. Bench bled the MC before putting it in the car. All fittings were identical. Bled all the brakes and exchanged all the old fluid in the process and now good to go.


This is probably all the OP needed to do, don't know why the Booster was replaced when the Master Cylinder was leaking.
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Old 06-19-2014, 05:44 PM   #12
Basque32
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This is probably all the OP needed to do, don't know why the Booster was replaced when the Master Cylinder was leaking.
the booster was all crapped up inside, probably wasn't working well if at all. With the new one it actually feels like what I expect a car with power brakes to feel like.

Here's another thought... in my research on all of this there was one thread that mentioned a "reaction disc" that could be missing, typically falls out into the booster (http://www.autoshop101.com/forms/brake05.pdf). I did not find one on my old one and none came with the new one, so not sure but if there's supposed to be on in there (goes between end of push rod on PB end) then that would take up some of the missing length?

BTW, my old (original) push rod has a disc that's on the rod that has what looks like an integrated seal that move freely on the rod the end that goes into the MC looks like it has a nut behind the rounded end but no threads (looks like adjustable on others I've seen).
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Old 06-22-2014, 09:40 PM   #13
Basque32
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Well I install speed bleeders over the weekend and bled the brakes manually once again, pretty sure there's no air in the lines. I made my own brake fluid recovery jar out a mason jar with a hold in the lid got a 5/16" clear tube from the parts store and could see that all the fluid had a purple hue to it (synthetic) so pretty sure all the old fluid is out.

However, the brake pedal still goes pretty much to the floor but the car stops fine. In fact it has better stopping power than before, kinda throws you forward in the seat. So I'm thinking my old original vacuum booster was shot and not doing anything, just mostly had manual brakes I'm guessing.

I know synthetic brake fluid is finicky about allowing air in the system, tried to be careful with the bleeding process. Does anyone know if this is normal pedal operation for power brakes or should the pedal stay fairly high when applying the brakes power or otherwise (had a higher pedal before).

Thanks for any advise/feedback, I appreciate the wisdom of those who have gone before...
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Old 06-22-2014, 10:15 PM   #14
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Originally Posted by Basque32 View Post
However, the brake pedal still goes pretty much to the floor but the car stops fine. In fact it has better stopping power than before, kinda throws you forward in the seat. So I'm thinking my old original vacuum booster was shot and not doing anything, just mostly had manual brakes I'm guessing.

Thanks for any advise/feedback, I appreciate the wisdom of those who have gone before...
For peace of mind and the safety of you and those who ride with you, it would be wise to take it to a Corvette shop or reputable brake shop that specializes in these older cars and have them look at it. You've done the best you could, and with the help of all who have chimed in here. You're still not convinced everything is right with the brake system. And it's a damn critical system.
I couldn't get the air out of my system after replacing all pads, shoes, and the MC. I flat bedded it to a vette specialty shop, and my trouble (and worries) were over. They knew the car and what to do, and now the brakes operate like when it left the factory. Done.


Steve
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Old 06-23-2014, 12:15 PM   #15
Basque32
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For peace of mind and the safety of you and those who ride with you, it would be wise to take it to a Corvette shop or reputable brake shop that specializes in these older cars and have them look at it. You've done the best you could, and with the help of all who have chimed in here. You're still not convinced everything is right with the brake system. And it's a damn critical system.
I couldn't get the air out of my system after replacing all pads, shoes, and the MC. I flat bedded it to a vette specialty shop, and my trouble (and worries) were over. They knew the car and what to do, and now the brakes operate like when it left the factory. Done.


Steve
Thanks Steve. Yeah, that's pretty much where I'm in my thinking, need to take it to a shop that can get the brakes working properly. Got to have a safe car!
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Old 06-23-2014, 04:44 PM   #16
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I have a 72' vette that I am changing from manual to power brakes. I purchased my kit from Corvette Central and it too came with an extra push rod in the kit. I was told that the rod can be pulled out of the holder and changed over to the other one. Before knowing this information I tried tugging on that rod and it was not coming out, it turns out that there is an o-ring at the end of the rod that you need to overcome. CC did tell me that the rod installed in the unit as delivered should be fine.
I already have things assembled and I tried bleeding but the brakes are not where they should be. Will bleed again and check how they feel.
My bigger problem is that I got my holes mixed up (don't try this at home men) , and installed the booster clevis to the top hole of the brake pedal. So I put the shorter brake switch bracket back on. It took me so long to get the pin in and the cotter pin bent that I just left it.
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Old 06-23-2014, 04:44 PM
 
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