Booster to master cylinder push rod adjustment - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**NC67Chev** · 01-20-2015, 08:33 PM

My booster to master cylinder push rod was too long by approx 1/8 - 3/16". After adjusting it I know it's close to where it needs to be now, but what's the correct tolerance? Obviously its bad to have forward pressure on the m/c piston, but I'm assuming you don't want too much play either. Any tricks to get it just right? Thx!

Longhorn 70 · 01-20-2015, 10:05 PM

watching....I had issues with mine too........

I did finally get it adjusted to where it works but want to see what the pros say.

farmallboy15 · 01-21-2015, 10:44 AM

I had the same problem. Put it on the grinder. Gave myself 1/16 or 1/8" clearance, forget which. No problems and my brakes work great.

Longhorn 70 · 01-21-2015, 02:28 PM

I have a disk master cyl on a drum booster. I know tha'ts where my problem is.

What I had to do was...

Find out how short to make the push rod by removing the adjust tip.

Then placed a blob of my daughter's modeling clay in the bore of the MC.

Measured how much space there was when all was bolted together. I unbolted the MC and measured the thickness of the clay.

Then I had to grind off the front end of the MC push rod a bit shorter than the push rod with the tip installed.

Drill and tap the end of the push rod until the correct assembled length was about 1/32" too short.

Then adjust the front end of the push rod until all worked happily.

I guess I could have gone to AutoZone and bought the correct unit for $149 and put it all back quickly.

**NC67Chev** · 01-21-2015, 02:45 PM

This booster was originally mated to a drum m/c also. Fortunately, it's adjustable, so shortening isn't difficult. I'm just trying to figure out what the correct clearance is supposed to be. I guess I'll just get it to where it barely touches or as little clearance as possible. Clay is a good idea. Thx!

**jeffahart** · 01-22-2015, 11:35 AM

1/4" based on this. I was just reading it a couple days ago because I put in a Disc Drum MC with a prop valve. Now I'm having rear lock up problems. Anyhow scroll down in this doc it's a good doc from cpp.

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

01-20-2015, 08:33 PM	#1
NC67Chev Senior Member Join Date: Oct 2009 Location: Greensboro, NC Posts: 698	Booster to master cylinder push rod adjustment My booster to master cylinder push rod was too long by approx 1/8 - 3/16". After adjusting it I know it's close to where it needs to be now, but what's the correct tolerance? Obviously its bad to have forward pressure on the m/c piston, but I'm assuming you don't want too much play either. Any tricks to get it just right? Thx! __________________ 1967 Chevy C-10, 250 L6, Powerglide, 3.73, SWB, Fleetside Upgrades: Power steering, Offset air cleaner, Rear Sport bumper, 3 point safety belts, HEI, -1/-2 springs, 16x5 wheels, McGaughy's disc brake conversion, Sway bar

01-20-2015, 10:05 PM	#2
Longhorn 70 Registered User Join Date: Dec 2012 Location: Chandler AZ Posts: 1,149	Re: Booster to master cylinder push rod adjustment watching....I had issues with mine too........ I did finally get it adjusted to where it works but want to see what the pros say. __________________ 1970 Longhorn, Front Disc, 350/4 bolt, 882 heads, HEI, Edelbrock, 700R4, HO-52/4.11. 1996 Corvette, Collector Roadster, LT4, 396, 450RWHP, 6sp, 4.11/Dana44/posi 5 point roll bar And let us not grow weary of doing good, for in due season we will reap, if we do not give up. Gal 6:9

01-21-2015, 10:44 AM	#3
farmallboy15 Registered User Join Date: May 2014 Location: Lancaster, OH Posts: 81	Re: Booster to master cylinder push rod adjustment I had the same problem. Put it on the grinder. Gave myself 1/16 or 1/8" clearance, forget which. No problems and my brakes work great. __________________ 70 GMC K2500 82 GMC K3500 09 GMC 2500HD 4x4

01-21-2015, 02:28 PM	#4
Longhorn 70 Registered User Join Date: Dec 2012 Location: Chandler AZ Posts: 1,149	Re: Booster to master cylinder push rod adjustment I have a disk master cyl on a drum booster. I know tha'ts where my problem is. What I had to do was... Find out how short to make the push rod by removing the adjust tip. Then placed a blob of my daughter's modeling clay in the bore of the MC. Measured how much space there was when all was bolted together. I unbolted the MC and measured the thickness of the clay. Then I had to grind off the front end of the MC push rod a bit shorter than the push rod with the tip installed. Drill and tap the end of the push rod until the correct assembled length was about 1/32" too short. Then adjust the front end of the push rod until all worked happily. I guess I could have gone to AutoZone and bought the correct unit for $149 and put it all back quickly. Attached Images __________________ 1970 Longhorn, Front Disc, 350/4 bolt, 882 heads, HEI, Edelbrock, 700R4, HO-52/4.11. 1996 Corvette, Collector Roadster, LT4, 396, 450RWHP, 6sp, 4.11/Dana44/posi 5 point roll bar And let us not grow weary of doing good, for in due season we will reap, if we do not give up. Gal 6:9 Last edited by Longhorn 70; 01-21-2015 at 02:34 PM.

01-21-2015, 02:45 PM	#5
NC67Chev Senior Member Join Date: Oct 2009 Location: Greensboro, NC Posts: 698	Re: Booster to master cylinder push rod adjustment This booster was originally mated to a drum m/c also. Fortunately, it's adjustable, so shortening isn't difficult. I'm just trying to figure out what the correct clearance is supposed to be. I guess I'll just get it to where it barely touches or as little clearance as possible. Clay is a good idea. Thx! __________________ 1967 Chevy C-10, 250 L6, Powerglide, 3.73, SWB, Fleetside Upgrades: Power steering, Offset air cleaner, Rear Sport bumper, 3 point safety belts, HEI, -1/-2 springs, 16x5 wheels, McGaughy's disc brake conversion, Sway bar

01-22-2015, 11:35 AM	#6
jeffahart Senior Member Join Date: May 2012 Location: Scottsdale, AZ Posts: 1,907	Re: Booster to master cylinder push rod adjustment 1/4" based on this. I was just reading it a couple days ago because I put in a Disc Drum MC with a prop valve. Now I'm having rear lock up problems. Anyhow scroll down in this doc it's a good doc from cpp. http://www.classicperform.com/TechBo...oubleshoot.htm __________________ White K20



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