Stop—brake Help - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Wobpb377 · 03-29-2023, 09:31 PM

Well I can’t stop since my brakes go to floor.

1986 suburban 7.4 with 13” rear so Jb7 brakes

Went for an easy job, replace rotor and pads. Did they and truck still pulled hard right when heavy braking. Replaced hard and soft line on driver side. Installed new master cylinder and bench bleed that with zero bubbles. Installed all that. Bleed/flushed entire system. Pedal is super fine. When to start it and pedal goes right to floor. Read could be brake booster—sourced and got one. Installed. Rebleed all lines and now bubbles. Pedal firm. Start truck boom pedal to the floor. Only brake components I didn’t replace was proportioning valve and rear wheel cylinders. And thoughts or tip to stop the pedal from going to floor when I start the motor?

kipps · 03-30-2023, 07:44 AM

Hydroboost or vacuum booster?

cadillac_al · 03-30-2023, 10:01 AM

Master cylinder still has problems. Does it ever pump up hard?

rick1956 · 03-30-2023, 10:15 AM

Braking systems don't provide pressure to the wheels until there is equal pressure in all the lines. In other words, if you have one wheel cylinder that is sticking, the system 'thinks' that wheel has achieved pressure that matches the other wheels. Truth is, that wheel cylinder may only be barely be pushing on the shoes because of the sticking cylinder.

ALWAYS replace wheel cylinders when doing brake jobs! Don't just check to see if they leak.

Note: This comment was addressing the original post about it pulling to one side... not the flat pedal. :-)

Wobpb377 · 03-30-2023, 11:55 AM

It’s a vacuum boost.

Perhaps the propvalve Needs reset? Any tips On that?

bigdaddy4x4 · 03-30-2023, 01:46 PM

you need to replace both calipers and front brake hoses that should fix your problems

Wobpb377 · 03-30-2023, 01:54 PM

I replaced the driver side. Went to replace passenger side and the hose a got seems thinner from driver side even though it’s supposedly for my truck with the Jb7 so I didn’t replace it. Didn’t want to put a thinner line on the passenger slider before verifying it was the right line.

Mathew21 · 03-30-2023, 02:57 PM

Not on my Square body but on my Tahoe I just installed a new master cylinder. The new one from oreillys auto parts was bad out of the box. Warrantied it out they gave me another one it was bad out of the box also. I retuned it and ordered an AC Delco one from Rock auto and it was good. Do you still have the old Master cylinder? If you do put it on and see if it fixes the brake pedal issue.

Wobpb377 · 03-30-2023, 03:17 PM

It’s my daily driver and I am limited to Napa autozone oreillys. I would
Like to get Acdelco but cost to get here is around 85-100 and that is essentially the price of parts. Plus it would not get here until next weekend. I tend to stick with Napa.

I’m gonna try and swap out the new caliper I got from Napa with another one and see if it helps.

03-29-2023, 09:31 PM	#1
Wobpb377 Registered User Join Date: Aug 2019 Location: Aiea,HI Posts: 187	Stop—brake Help Well I can’t stop since my brakes go to floor. 1986 suburban 7.4 with 13” rear so Jb7 brakes Went for an easy job, replace rotor and pads. Did they and truck still pulled hard right when heavy braking. Replaced hard and soft line on driver side. Installed new master cylinder and bench bleed that with zero bubbles. Installed all that. Bleed/flushed entire system. Pedal is super fine. When to start it and pedal goes right to floor. Read could be brake booster—sourced and got one. Installed. Rebleed all lines and now bubbles. Pedal firm. Start truck boom pedal to the floor. Only brake components I didn’t replace was proportioning valve and rear wheel cylinders. And thoughts or tip to stop the pedal from going to floor when I start the motor?

03-30-2023, 07:44 AM	#2
kipps Registered User Join Date: Jul 2014 Location: North-central Virginia Posts: 1,104	Re: Stop—brake Help Hydroboost or vacuum booster? __________________ 1987 C6P V20 truck, 2010 LMG 5.3, AFM delete, 2010 Camaro exhaust manifolds, 1997 nv4500, 1991 np241c, hydroboost, 2005 14bff axle & driveshaft, drop-n-lock gooseneck, 4.10 gears, stock suspension, rims, and tires. Still a work in progress. Any questions or suggestions are welcome!

03-30-2023, 10:01 AM	#3
cadillac_al Registered User Join Date: Oct 2013 Location: Maine Posts: 2,376	Re: Stop—brake Help Master cylinder still has problems. Does it ever pump up hard? __________________ 76 Chevy K20 76 GMC K15 77 Chevy C10 77 Chevy K10

03-30-2023, 10:15 AM	#4
rick1956 Registered User Join Date: Jan 2009 Location: Edgewood, WA Posts: 108	Re: Stop—brake Help Braking systems don't provide pressure to the wheels until there is equal pressure in all the lines. In other words, if you have one wheel cylinder that is sticking, the system 'thinks' that wheel has achieved pressure that matches the other wheels. Truth is, that wheel cylinder may only be barely be pushing on the shoes because of the sticking cylinder. ALWAYS replace wheel cylinders when doing brake jobs! Don't just check to see if they leak. Note: This comment was addressing the original post about it pulling to one side... not the flat pedal. :-) __________________ I may be old, but I still enjoy the feeling of the earth rotating beneath my wheels... Last edited by rick1956; 03-30-2023 at 04:28 PM. Reason: added clarification

03-30-2023, 11:55 AM	#5
Wobpb377 Registered User Join Date: Aug 2019 Location: Aiea,HI Posts: 187	Re: Stop—brake Help It’s a vacuum boost. Perhaps the propvalve Needs reset? Any tips On that?

03-30-2023, 01:46 PM	#6
bigdaddy4x4 Registered User Join Date: Aug 2012 Location: concord ga Posts: 188	Re: Stop—brake Help you need to replace both calipers and front brake hoses that should fix your problems

03-30-2023, 01:54 PM	#7
Wobpb377 Registered User Join Date: Aug 2019 Location: Aiea,HI Posts: 187	Re: Stop—brake Help I replaced the driver side. Went to replace passenger side and the hose a got seems thinner from driver side even though it’s supposedly for my truck with the Jb7 so I didn’t replace it. Didn’t want to put a thinner line on the passenger slider before verifying it was the right line.

03-30-2023, 02:57 PM	#8
Mathew21 Registered User Join Date: May 2010 Location: Clinton township, MI Posts: 1,192	Re: Stop—brake Help Not on my Square body but on my Tahoe I just installed a new master cylinder. The new one from oreillys auto parts was bad out of the box. Warrantied it out they gave me another one it was bad out of the box also. I retuned it and ordered an AC Delco one from Rock auto and it was good. Do you still have the old Master cylinder? If you do put it on and see if it fixes the brake pedal issue. __________________ It only has original paint once

03-30-2023, 03:17 PM	#9
Wobpb377 Registered User Join Date: Aug 2019 Location: Aiea,HI Posts: 187	Re: Stop—brake Help It’s my daily driver and I am limited to Napa autozone oreillys. I would Like to get Acdelco but cost to get here is around 85-100 and that is essentially the price of parts. Plus it would not get here until next weekend. I tend to stick with Napa. I’m gonna try and swap out the new caliper I got from Napa with another one and see if it helps.



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