Front brakes locking up - The 1947 - Present Chevrolet & GMC Truck Message Board Network

polevault1977 · 01-27-2004, 09:33 PM

My friend has a 71 lwb with discs on front, of course. He was asking me about his front brakes locking up. He has a new mastercylinder and booster and calipers. This does not happen very often. He has to manually bleed both of them off to release the calipers. Sounds weird to me. Couldn't be hoses breaking down cause it happens on both sides. Port. valve? Faulty mastercylinder? Any ideas? BTW it was doing this with the old calipers and the new ones. Thanks, Danny

jhow66 · 01-27-2004, 09:42 PM

Sound like your rubber brake hoses gone bad inside or your porp. valve.

Gordo · 01-27-2004, 11:25 PM

The next time it happens try this, using your hand or foot pull up on brake pedal and check to see if the brakes release. If it does you need to look for interference or adjustments on the linkage. The plunger in the master needs to return ALL the way back or you wiil have those symptoms.

Ed ke6bnl · 01-28-2004, 09:52 AM

My boys brakes did the same thing, we did not do the work on the truck front end it was all done b34 we got it. turned out from the help of this group that the master cyl. still had the check valve in the m/c that was holding the front brakes on. we removed it and it worked fine. Ed ke6bnl So calif BUT I would think it would do it always. We found it while working on something else and the truck was up in the air.

tom hand · 01-28-2004, 09:58 AM

Quote:

Originally posted by polevault1977
He has to manually bleed both of them off to release the calipers.

I had this happen before and it was a bad master cylinder. It was brand new...carried it back and got a replacement and the trouble went away

polevault1977 · 01-28-2004, 04:01 PM

Thanks folks, i'm sure one of these fixes will work. I'll let you know what it turns out to be. Danny

sactoC10 · 01-28-2004, 06:54 PM

I had the exact problem on my 71 LWB. I went (in this order) to the pads, fluid, calipers, lines then up to the master cyl and finally the booster...replacing everything with new parts. Ended up being the small rubber boot from the firewall into the booster...it was torn and would not let the MC release the brakes, yet there was always pressure at the pedal.

This drive me nuts. You'll find the problem and darn will you feel good after you resolve it!

polevault1977 · 01-28-2004, 08:14 PM

And the winner is...... Tom Hand. My friend took his "new" mc back and got another one. That fixed the problem. Thanks for all the leads. This is the place to come if you have pu problems! Danny

jhow66 · 01-28-2004, 09:35 PM

What they gave you the 1st time was more then likely for drum brakes as they have a check valve in each port to keep some pressue on the wheel cylinders. This keeps the shoes from retracting all the way.

01-27-2004, 09:33 PM	#1
polevault1977 Pick'n up the pieces! Join Date: Sep 2002 Location: Marietta, Oklahoma Posts: 198	Front brakes locking up My friend has a 71 lwb with discs on front, of course. He was asking me about his front brakes locking up. He has a new mastercylinder and booster and calipers. This does not happen very often. He has to manually bleed both of them off to release the calipers. Sounds weird to me. Couldn't be hoses breaking down cause it happens on both sides. Port. valve? Faulty mastercylinder? Any ideas? BTW it was doing this with the old calipers and the new ones. Thanks, Danny

01-27-2004, 09:42 PM	#2
jhow66 Registered User Join Date: Jun 2002 Location: Knoxville Tenn. Posts: 3,058	Sound like your rubber brake hoses gone bad inside or your porp. valve. __________________ 56 Chevy Bel-Air 2dr. HT (purchased new) 71 Chevy Cheyenne SWB PU (502HO) 65 GMC short bed step--work in progress and my gofer

01-27-2004, 11:25 PM	#3
Gordo Registered User Join Date: Jan 2001 Location: Killingworth, CT. USA Posts: 3,378	The next time it happens try this, using your hand or foot pull up on brake pedal and check to see if the brakes release. If it does you need to look for interference or adjustments on the linkage. The plunger in the master needs to return ALL the way back or you wiil have those symptoms. __________________ 1971 C10 swb stepside 350/700R4/3.73posi (retired as of 4/22/03) 1998 S10 short bed 2002 S10 Blazer 1942 Oldsmobile 1958 Massey Harris Pony 1951 Wife Killingworth, Connecticut May those who love us, love us, any of those who do not love us, may God turn their hearts. And if God is unable to turn their hearts, may he turn their ankles so we may know them by their limping. A man who works with his hands is a laborer; a man who works with his hands and his brain is a craftsman; but a man who works with his hands and his brain and his heart is an artist.

01-28-2004, 09:52 AM	#4
Ed ke6bnl Registered User Join Date: Mar 2002 Location: Agua Dulce, Ca. usa Posts: 179	My boys brakes did the same thing, we did not do the work on the truck front end it was all done b34 we got it. turned out from the help of this group that the master cyl. still had the check valve in the m/c that was holding the front brakes on. we removed it and it worked fine. Ed ke6bnl So calif BUT I would think it would do it always. We found it while working on something else and the truck was up in the air. __________________ Ed ke6bnl Agua Dulce 70 S.E. Los Angeles 70 Chevy short bed 1948 F3 ford pu 1949 F1 stock V8 flathead 3 on floor 1950 F1 pu street rod 1948 F6 Ford Dually/350sbc no bed stock trans&rear 1972 El Camino 4" chop 1953 Chevy 3100 2b daily driver 1970 SB 4X4 400ci 6in lift

01-28-2004, 06:54 PM	#7
sactoC10 71 DELUX Join Date: Sep 2003 Location: Northern CA / Sac Posts: 1,055	know your pain... I had the exact problem on my 71 LWB. I went (in this order) to the pads, fluid, calipers, lines then up to the master cyl and finally the booster...replacing everything with new parts. Ended up being the small rubber boot from the firewall into the booster...it was torn and would not let the MC release the brakes, yet there was always pressure at the pedal. This drive me nuts. You'll find the problem and darn will you feel good after you resolve it!

01-28-2004, 04:01 PM	#6
polevault1977 Pick'n up the pieces! Join Date: Sep 2002 Location: Marietta, Oklahoma Posts: 198	Thanks folks, i'm sure one of these fixes will work. I'll let you know what it turns out to be. Danny

01-28-2004, 08:14 PM	#8
polevault1977 Pick'n up the pieces! Join Date: Sep 2002 Location: Marietta, Oklahoma Posts: 198	And the winner is...... Tom Hand. My friend took his "new" mc back and got another one. That fixed the problem. Thanks for all the leads. This is the place to come if you have pu problems! Danny

01-28-2004, 09:35 PM	#9
jhow66 Registered User Join Date: Jun 2002 Location: Knoxville Tenn. Posts: 3,058	What they gave you the 1st time was more then likely for drum brakes as they have a check valve in each port to keep some pressue on the wheel cylinders. This keeps the shoes from retracting all the way. __________________ 56 Chevy Bel-Air 2dr. HT (purchased new) 71 Chevy Cheyenne SWB PU (502HO) 65 GMC short bed step--work in progress and my gofer



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