trying to bleed brakes on my 67 - The 1947 - Present Chevrolet & GMC Truck Message Board Network

wlf89 · 03-24-2017, 09:40 PM

put a new master cylinder on today because the old one was leaking fluid,it didnt come with the plugs and tubing to bench bleed it so i bolted it up and had my brother pump and hold the pedal while i cracked the lines at the master. i got the rears bleed, but the fronts just keep on pumping air. is the master bad or have i just not got the air out yet, i have done went thru about 3 reservoirs of fluid just on the right wheel. the instructions say to just push the pedal 1/4 stroke, what is the purpose of that i have always pushed a full stroke.

**HO455** · 03-24-2017, 09:57 PM

Try gravity bleeding them to start. One you get flow down through the nearest caliper close it and open the other one. I don't know why one would only push the pedal part way. Some master cylinders won't even start moving the front plunger until it has moved 1/4 of the way. My guess it is a typo or translation error. After gravity feeding you should quickly be able to flush any remaining air out. If not don't waste time just take it back. I went through 3 master cylinders on my Javelin before I got a good one. Two of them had pieces of anodizing come off the plunger and damage the cups.

B. W. · 03-25-2017, 11:05 AM

Do what HO455 said for bleeding, I gravity feed almost everything & I do this for a living. BUT FIRST YOU MUST BLEED THE MASTER CYLINDER. You can bleed it on the truck but the easiest way is to remove it & bench bleed it. Get short pieces of brake line that fit and bend them around & back into the reservoirs. Slowly push the MC piston in & repeat until no air bubbles are seen, not even little tiny ones. I tap the MC lightly with a screwdriver handle to dislodge any trapped air. It may take 50 pumps to get all the air out, I pump a few times & let it sit so the air bubbles work to the top & repeat.

Now, once it is bolted back up & the lines hooked up you are going to have to completely bleed the system because the air that was in the MC is now in your lines. Most of the time, when you replace a MC that has not run dry you can just bench bleed & install & not bleed the brakes at all.

03-24-2017, 09:40 PM	#1
wlf89 69 c/10 lwb fleetside Join Date: Jul 2004 Location: saint joseph TN Posts: 195	trying to bleed brakes on my 67 put a new master cylinder on today because the old one was leaking fluid,it didnt come with the plugs and tubing to bench bleed it so i bolted it up and had my brother pump and hold the pedal while i cracked the lines at the master. i got the rears bleed, but the fronts just keep on pumping air. is the master bad or have i just not got the air out yet, i have done went thru about 3 reservoirs of fluid just on the right wheel. the instructions say to just push the pedal 1/4 stroke, what is the purpose of that i have always pushed a full stroke. __________________ 69 lwb fleetside 67 swb fleetside (2) 72 lwb fleetside 50 swb no bed 65 impala ss 65 1 ton flatbed

03-24-2017, 09:57 PM	#2
HO455 Post Whore Join Date: Feb 2016 Location: Portland Oregon Posts: 10,813	Re: trying to bleed brakes on my 67 Try gravity bleeding them to start. One you get flow down through the nearest caliper close it and open the other one. I don't know why one would only push the pedal part way. Some master cylinders won't even start moving the front plunger until it has moved 1/4 of the way. My guess it is a typo or translation error. After gravity feeding you should quickly be able to flush any remaining air out. If not don't waste time just take it back. I went through 3 master cylinders on my Javelin before I got a good one. Two of them had pieces of anodizing come off the plunger and damage the cups. __________________ Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. RIP Bob Parks. 1967 Burban the WMB,1991 S(stink)-10 Blazer,1969 GTO, 1970 Javelin, 1952 F2 Ford 4X4, 29 Model A, 72 Firebird. 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377

03-25-2017, 11:05 AM	#3
B. W. Registered User Join Date: Nov 2014 Location: Bigfork, Montana Posts: 1,137	Re: trying to bleed brakes on my 67 Do what HO455 said for bleeding, I gravity feed almost everything & I do this for a living. BUT FIRST YOU MUST BLEED THE MASTER CYLINDER. You can bleed it on the truck but the easiest way is to remove it & bench bleed it. Get short pieces of brake line that fit and bend them around & back into the reservoirs. Slowly push the MC piston in & repeat until no air bubbles are seen, not even little tiny ones. I tap the MC lightly with a screwdriver handle to dislodge any trapped air. It may take 50 pumps to get all the air out, I pump a few times & let it sit so the air bubbles work to the top & repeat. Now, once it is bolted back up & the lines hooked up you are going to have to completely bleed the system because the air that was in the MC is now in your lines. Most of the time, when you replace a MC that has not run dry you can just bench bleed & install & not bleed the brakes at all.



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