new brake master cyl, bleeding tips? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

sactoC10 · 09-15-2003, 10:34 AM

Bought a new master cylinder for my 1971 yesterday. I've never bled the entire system before and my gut feeling is telling me that I am doing something wrong. I have a vacuum pump and have bled individual lines before, but never the whole thing after removing the master cylinder.

I am CERTAIN that there is air in the lines, just need to know the 1-2-3 steps involved getting the air out (correctly).

Thanks
JT in Sacto

Hotrodhenryj · 09-15-2003, 11:30 AM

Before installing the cylinder on the truck you need to bench blead it first. I do this in my vice to hold it. You need fittings and some vacuum hose to do this. Most brake manufactures give you this when you get the cylinder. The hoses are placed in the resivours and you pump the cylinder to remove air. Once this is done then install. Get someone to help bleed the rest of the system or install the pump. Good luck

sactoC10 · 09-15-2003, 12:34 PM

Thanks...yeah the information included was not clear at all so I did not know what to do with those tubes and fittings and I did install it. So now I have this question.

Can't I still "bench" bleed it in the truck with someone's help? Seems as though I could. Simply removed the lines, replace with tubes and two pointed fittings, have someone pump it slowly with the foot pedal, etc...

No?

Hotrodhenryj · 09-15-2003, 01:03 PM

Yes, you can do it that way. Seems I cant ever find anyone to help me. You just want to make sure all of the air is removed or it will go into the system. Bleed the wheel cylinders starting at the right rear and do them in order of farthest from the cylinder. Make sure you keep an eye on the fluid lever as you dont want to get more are in. Hope this helps

Fred T · 09-15-2003, 01:10 PM

Sacto - I bench bleed in the truck, but do it a bit differently than most, it's how I learned from old mechanics in the 70's.

Install the m/c in the vehicle and connect the brake line(s), but don't tighten. Fill the m/c with fluid and hold a rag under the fitting. Have asst depress pedal, tighten fitting, and repeat until fluid comes out. Just like bleeding a wheel cylinder. On many vehicles you don't even need to pump the pedal, just let fluid flow through.

tom hand · 09-15-2003, 01:20 PM

Well this advice is probably too late, but may help you next time. There is no reason to bleed the whole system when changing the mastercylinder. Just bench bleed the M/C and install it. Now here's the trick. DO NOT push the pedal all the way down...this will just force air into the system. Leave the top off the M/C and get to a position where you can see it...may need a helper or mirror if you have power brakes. Now barely push on the padal till you see bubbles rise up through the fluid. Release and repeat until no more bubbles rise. Then pump up the pedal and it will be rock hard...your done, go for a ride.

sactoC10 · 09-15-2003, 03:42 PM

Good to know I can keep it there to bleed it. Yup, the kids or the wife are willing to assist.

And now, more than ever, I am certain that I sucked all sorts of air into the master cylinder yesterday afternoon.

Oh well, it will get resolved soon.

Thanks! This info is what I needed.

09-15-2003, 10:34 AM	#1
sactoC10 71 DELUX Join Date: Sep 2003 Location: Northern CA / Sac Posts: 1,056	new brake master cyl, bleeding tips? Bought a new master cylinder for my 1971 yesterday. I've never bled the entire system before and my gut feeling is telling me that I am doing something wrong. I have a vacuum pump and have bled individual lines before, but never the whole thing after removing the master cylinder. I am CERTAIN that there is air in the lines, just need to know the 1-2-3 steps involved getting the air out (correctly). Thanks JT in Sacto

09-15-2003, 11:30 AM	#2
Hotrodhenryj Truck Farmer Join Date: Nov 2001 Location: Lake Havasu City, Arizona Posts: 1,192	Before installing the cylinder on the truck you need to bench blead it first. I do this in my vice to hold it. You need fittings and some vacuum hose to do this. Most brake manufactures give you this when you get the cylinder. The hoses are placed in the resivours and you pump the cylinder to remove air. Once this is done then install. Get someone to help bleed the rest of the system or install the pump. Good luck __________________ Arizona rust free sheetmetal

09-15-2003, 01:03 PM	#4
Hotrodhenryj Truck Farmer Join Date: Nov 2001 Location: Lake Havasu City, Arizona Posts: 1,192	Yes, you can do it that way. Seems I cant ever find anyone to help me. You just want to make sure all of the air is removed or it will go into the system. Bleed the wheel cylinders starting at the right rear and do them in order of farthest from the cylinder. Make sure you keep an eye on the fluid lever as you dont want to get more are in. Hope this helps __________________ Arizona rust free sheetmetal

09-15-2003, 01:10 PM	#5
Fred T Cantankerous Geezer Join Date: Aug 2002 Location: Bel Aire, KS Posts: 6,264	Sacto - I bench bleed in the truck, but do it a bit differently than most, it's how I learned from old mechanics in the 70's. Install the m/c in the vehicle and connect the brake line(s), but don't tighten. Fill the m/c with fluid and hold a rag under the fitting. Have asst depress pedal, tighten fitting, and repeat until fluid comes out. Just like bleeding a wheel cylinder. On many vehicles you don't even need to pump the pedal, just let fluid flow through. __________________ Fred There is no such thing as too much cam...just not enough engine.

09-15-2003, 01:20 PM	#6
tom hand CCRider Join Date: Feb 2000 Location: Olive Branch,MS,USA Posts: 2,232	Well this advice is probably too late, but may help you next time. There is no reason to bleed the whole system when changing the mastercylinder. Just bench bleed the M/C and install it. Now here's the trick. DO NOT push the pedal all the way down...this will just force air into the system. Leave the top off the M/C and get to a position where you can see it...may need a helper or mirror if you have power brakes. Now barely push on the padal till you see bubbles rise up through the fluid. Release and repeat until no more bubbles rise. Then pump up the pedal and it will be rock hard...your done, go for a ride. __________________ 72 GMC Sierra SWB almost finished---- 84 Softail Olive Branch MS

09-15-2003, 12:34 PM	#3
sactoC10 71 DELUX Join Date: Sep 2003 Location: Northern CA / Sac Posts: 1,056	Thanks...yeah the information included was not clear at all so I did not know what to do with those tubes and fittings and I did install it. So now I have this question. Can't I still "bench" bleed it in the truck with someone's help? Seems as though I could. Simply removed the lines, replace with tubes and two pointed fittings, have someone pump it slowly with the foot pedal, etc... No?

09-15-2003, 03:42 PM	#7
sactoC10 71 DELUX Join Date: Sep 2003 Location: Northern CA / Sac Posts: 1,056	Good to know I can keep it there to bleed it. Yup, the kids or the wife are willing to assist. And now, more than ever, I am certain that I sucked all sorts of air into the master cylinder yesterday afternoon. Oh well, it will get resolved soon. Thanks! This info is what I needed.



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