Need help bleeding brakes - The 1947 - Present Chevrolet & GMC Truck Message Board Network

bluec10 · 01-22-2022, 08:36 PM

I installed a new brake booster and master cylinder and need to bleed the brakes.I bench bled the master cylinder - it wasn’t a new one but it was only used for a few hundred miles.

I put my vacuum pump on the right-rear brake and pumped up to 20psi pressure. No fluid came out after a lot of pumping. The mc is full of fluid.

The bleeder screw was well open.

Any ideas?

**Steeveedee** · 01-22-2022, 08:41 PM

It has a dual master, right? Perhaps you triggered the shuttle valve? I'm guessing that you're working on the '69 in your signature?

**Accelo** · 01-23-2022, 12:07 AM

Did you bench bleed the brake master cylinder? I always do this to confirm everything is working correctly.
I also leave the lines loose at the MC and pump the brakes till I get some seepage at the joint then I fully tighten the fittings.

Pump the brakes, see it that works. If not, it is easy to get the rod between the pedal and the MC out of adjustment when retrofitting brakes. As in it could be too long. Confirm you have some slack there.

**Getter-Done** · 01-23-2022, 12:16 AM

Did you try (pushing or pulling) the button on to proportioning valve?

**Jason Banks** · 01-23-2022, 02:04 PM

Just throwing this out there. I had the same problem, turned out to be the original rear brake hose from frame to diff was blocked.

jimijam00 · 01-23-2022, 02:29 PM

If you remove the vacuum pump, open the bleeder, and push on the brake pedal, does any fluid come out?

Quote:

Originally Posted by Accelo

Did you bench bleed the brake master cylinder? I always do this to confirm everything is working correctly.

The second sentence of his post stated he did.

**Accelo** · 01-23-2022, 03:06 PM

Oops, thanks for the correction

**Steeveedee** · 01-23-2022, 04:07 PM

Quote:

Originally Posted by Jason Banks

Just throwing this out there. I had the same problem, turned out to be the original rear brake hose from frame to diff was blocked.

That's a good point. An easy way to verify would be to close the open bleeder and hook the vacuum pump to the other side. Of course, if it has the shuttle valve and it has moved, switching bleeders won't help. When the right front wheel cylinder on my truck started leaking, I just went to disc brakes (and rebuilt the front end, which it probably needed at 210k miles). No idea how old the rear hose was, so it was a no-brainer to change it out.

kaycee · 01-23-2022, 07:16 PM

Pull your bleeder screw all the way out and see if the hole is not plugged, you wont loose any fluid if you put the cover back on the MC .

**Chevy Fan Always** · 01-24-2022, 09:20 PM

Make sure the button is pushed in on the proportion valve, you can use a c clamp. There is a tool made for it. In forbleeding.

01-22-2022, 08:36 PM	#1
bluec10 Registered User Join Date: Apr 2002 Location: Manitoba, Canada Posts: 663	Need help bleeding brakes I installed a new brake booster and master cylinder and need to bleed the brakes.I bench bled the master cylinder - it wasn’t a new one but it was only used for a few hundred miles. I put my vacuum pump on the right-rear brake and pumped up to 20psi pressure. No fluid came out after a lot of pumping. The mc is full of fluid. The bleeder screw was well open. Any ideas? __________________ Present: 2015 Tacoma. Yeah, not a GM, but I love it. 1969 GMC 32,000 - fix, drive, relax, fix... 2019 BMW R1250 GSA - Yahoooooooo 1979 Honda GL 1000 - retro touring at its best. Past: '05 Sierra 4x4 - Had 270,000 KM and running well when it was written-off by a stop sign runner. '94 F-150 from the "F word" company. I'll admit it...good truck. Sold what was left of it for $800 to a guy who came to pick it up at 11:00 PM with cash in hand. Hmm. '79 Sierra Grande (Black) organ donor - perfect rebuildable 4-bolt 350 and a good TH350. '76 Sierra Grande (Orange) - hate isn't too strong a word. Kid who bought it turned it into a hot rod. '68 C-10 R.I.P. - Dad's old truck...too far gone to resurrect. '59 C-50 - with hoist. Truck is gone, wife isn't. Nuff said.

01-22-2022, 08:41 PM	#2
Steeveedee Who Changed This? Join Date: Jan 2013 Location: Simi Valley, CA Posts: 10,614	Re: Need help bleeding brakes It has a dual master, right? Perhaps you triggered the shuttle valve? I'm guessing that you're working on the '69 in your signature? __________________ ~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA

01-23-2022, 12:07 AM	#3
Accelo Senior Member Join Date: Mar 2015 Location: washington Posts: 2,282	Re: Need help bleeding brakes Did you bench bleed the brake master cylinder? I always do this to confirm everything is working correctly. I also leave the lines loose at the MC and pump the brakes till I get some seepage at the joint then I fully tighten the fittings. Pump the brakes, see it that works. If not, it is easy to get the rod between the pedal and the MC out of adjustment when retrofitting brakes. As in it could be too long. Confirm you have some slack there. Last edited by Accelo; 01-23-2022 at 12:21 AM.

01-23-2022, 12:16 AM	#4
Getter-Done Senior Member Join Date: Dec 2009 Location: TN. Posts: 8,330	Re: Need help bleeding brakes Did you try (pushing or pulling) the button on to proportioning valve? __________________ ________________________________________________________________________________________ ____________________________________________ 84 Chevy K-20 63 Impala (my high school car) http://67-72chevytrucks.com/vboard/s...Crew Cab Build

01-23-2022, 02:04 PM	#5
Jason Banks Senior Member Join Date: Dec 1999 Location: TX Posts: 1,612	Re: Need help bleeding brakes Just throwing this out there. I had the same problem, turned out to be the original rear brake hose from frame to diff was blocked.

01-23-2022, 03:06 PM	#7
Accelo Senior Member Join Date: Mar 2015 Location: washington Posts: 2,282	Re: Need help bleeding brakes Oops, thanks for the correction

01-23-2022, 07:16 PM	#9
kaycee Registered User Join Date: Jan 2000 Location: Wyoming USA Posts: 2,446	Re: Need help bleeding brakes Pull your bleeder screw all the way out and see if the hole is not plugged, you wont loose any fluid if you put the cover back on the MC . __________________ 2001 Silverado K-1500 2005 FXDWG stage3 69 CHEVY Short/Step 327/4L60 373 posi 63 IMPALA 327

01-24-2022, 09:20 PM	#10
Chevy Fan Always Registered User Join Date: May 2015 Location: Ashland, Ohio Posts: 579	Re: Need help bleeding brakes Make sure the button is pushed in on the proportion valve, you can use a c clamp. There is a tool made for it. In forbleeding. __________________ 1972 Highlander Custom 10



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