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

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.