Brake pedal pressure - The 1947 - Present Chevrolet & GMC Truck Message Board Network

1968CHEVYC10 · 05-09-2010, 07:16 PM

I recently replaced all of the brake lines in my truck along with new wheel cylinders and spring kits all the way around, anyway I finally got around to bleeding them. they all bled fine in one sense but the pedal pressure seems really low. the front brakes work ok from what I could tell but the rear brakes I couldn't get to lock up, does anybody know why they aren't locking up? I did re-bleed everything and found no air bubbles so I really have no idea why it's not working. I've checked for leaks everywhere and found nothing. also it's on jack stands so to check them I had someone push the pedal while I tried to turn the drums. Thanks in advance!

68gmsee · 05-09-2010, 07:39 PM

Manual or power?

Hydraulic fluid does not compress. So if it feels mushy or you feel it's not solid, then there's either air in you system or fluid is being bypassed inside the M.C.
Even a new M.C. can be defective.

cdowns · 05-09-2010, 07:57 PM

r the brake shoes adjusted properly?they should only b a couple of thousandths from the drums

68gmsee · 05-09-2010, 09:35 PM

I adjust new brake shoes so they barely rub the drum as I rotate it. I find that I get a better adjustment if I tighten them until the drum won't turn anymore and then back off until the shoes barely drag.

**LockDoc** · 05-09-2010, 10:39 PM

-
Are you sure that the proportioning valve isn't off center?

LockDoc

1968CHEVYC10 · 05-09-2010, 10:43 PM

they are manual, and yes I did adjust them, but not real exact, I should probably do it again. and also it's a '68 so no proportioning valve. the truck belonged to my grandpa before and I know he replaced to MC not too long ago. is there anyway to check this to make sure its workin good?

Murphy IRE · 05-09-2010, 10:52 PM

Check all vacuum lines and valves. I replaced everything on mine and they were better, but not great. Once I found the vacuum leak (s), the brakes worked great!

1968CHEVYC10 · 05-10-2010, 12:52 AM

call me a newb... but whats a vacuum line? and where would I find it?

OhOneWS6 · 05-10-2010, 09:38 AM

Quote:

Originally Posted by Murphy IRE

Check all vacuum lines and valves. I replaced everything on mine and they were better, but not great. Once I found the vacuum leak (s), the brakes worked great!

Quote:

Originally Posted by 1968CHEVYC10

call me a newb... but whats a vacuum line? and where would I find it?

Manual brakes not power. Vacuum will have noting to do with it.

68gmsee · 05-10-2010, 10:59 AM

Mine is a 68 GMC and I also have manual brakes. Thoroughly bleed the brakes again and then carefully recheck the adjustments on the brakes as mentioned above.

Be sure and start with the passenger side rear, then driver side rear, passenger side front and driver side front. I've always done it this way and have had good luck with getting all the air out.

One more thing. I've found out that new master cylinders are not always defect free.

Murphy IRE · 05-10-2010, 04:25 PM

Sorry didn't see your post with "manual"

05-09-2010, 07:16 PM	#1
1968CHEVYC10 Registered User Join Date: Aug 2009 Location: Tomball, TX Posts: 578	Brake pedal pressure I recently replaced all of the brake lines in my truck along with new wheel cylinders and spring kits all the way around, anyway I finally got around to bleeding them. they all bled fine in one sense but the pedal pressure seems really low. the front brakes work ok from what I could tell but the rear brakes I couldn't get to lock up, does anybody know why they aren't locking up? I did re-bleed everything and found no air bubbles so I really have no idea why it's not working. I've checked for leaks everywhere and found nothing. also it's on jack stands so to check them I had someone push the pedal while I tried to turn the drums. Thanks in advance! __________________ '68 C10 LWB 6.2NA/NP833 3.73's

05-09-2010, 07:39 PM	#2
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	Re: Brake pedal pressure Manual or power? Hydraulic fluid does not compress. So if it feels mushy or you feel it's not solid, then there's either air in you system or fluid is being bypassed inside the M.C. Even a new M.C. can be defective. Last edited by 68gmsee; 05-09-2010 at 07:40 PM. Reason: Just can't spell today.. :(

05-09-2010, 07:57 PM	#3
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: Brake pedal pressure r the brake shoes adjusted properly?they should only b a couple of thousandths from the drums __________________ 71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY

05-09-2010, 09:35 PM	#4
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	Re: Brake pedal pressure I adjust new brake shoes so they barely rub the drum as I rotate it. I find that I get a better adjustment if I tighten them until the drum won't turn anymore and then back off until the shoes barely drag.

05-09-2010, 10:39 PM	#5
LockDoc The Older Generation Join Date: Aug 2006 Location: Montezuma, Iowa Posts: 25,773	Re: Brake pedal pressure - Are you sure that the proportioning valve isn't off center? LockDoc __________________ Leon Locksmith, Specializing In Antique Trucks, Automobiles, & Motorcycles (My Dually Pickup Project Thread) http://67-72chevytrucks.com/vboard/s...d.php?t=829820 -

05-09-2010, 10:43 PM	#6
1968CHEVYC10 Registered User Join Date: Aug 2009 Location: Tomball, TX Posts: 578	Re: Brake pedal pressure they are manual, and yes I did adjust them, but not real exact, I should probably do it again. and also it's a '68 so no proportioning valve. the truck belonged to my grandpa before and I know he replaced to MC not too long ago. is there anyway to check this to make sure its workin good? __________________ '68 C10 LWB 6.2NA/NP833 3.73's

05-09-2010, 10:52 PM	#7
Murphy IRE Registered User Join Date: Oct 2009 Location: South Denver Metro, CO Posts: 385	Re: Brake pedal pressure Check all vacuum lines and valves. I replaced everything on mine and they were better, but not great. Once I found the vacuum leak (s), the brakes worked great!

05-10-2010, 12:52 AM	#8
1968CHEVYC10 Registered User Join Date: Aug 2009 Location: Tomball, TX Posts: 578	Re: Brake pedal pressure call me a newb... but whats a vacuum line? and where would I find it? __________________ '68 C10 LWB 6.2NA/NP833 3.73's

05-10-2010, 10:59 AM	#10
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	Re: Brake pedal pressure Mine is a 68 GMC and I also have manual brakes. Thoroughly bleed the brakes again and then carefully recheck the adjustments on the brakes as mentioned above. Be sure and start with the passenger side rear, then driver side rear, passenger side front and driver side front. I've always done it this way and have had good luck with getting all the air out. One more thing. I've found out that new master cylinders are not always defect free. Last edited by 68gmsee; 05-10-2010 at 11:00 AM.

05-10-2010, 04:25 PM	#11
Murphy IRE Registered User Join Date: Oct 2009 Location: South Denver Metro, CO Posts: 385	Re: Brake pedal pressure Sorry didn't see your post with "manual"

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