Rear disc brake problem - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Ackattack · 02-08-2010, 12:34 PM

I have LT1 camaro calipers installed on my truck with new everything (rotors, brake lines, disc-disc proportioning valve, MC, and line lock for the front). The brake booster is not new.

I currently have the rearend up on jackstands, when I put the truck in gear, I can barely get the rear tires from turning at idle if I push on the brake pedal with all of my might.

I bench bled the MC, bled the brake lines, fixed leaks, replaced a kinked SS flex line, bled the brakes lines, bled the brake lines some more.

I would think disc brakes should have no problems stopping the rear tires when up on jack stands, I mean if I drove it, they would essentially be doing nothing.

I can't really think of anything else to do except start replacing new parts. [BTW the proportioning valve is from CPP and the MC is a remanufactured one from Autozone for a 72 if it matters, and I rebuilt the calipers]

Anyone else have similar problems, or suggestions

**Hart_Rod** · 02-08-2010, 01:44 PM

Can you put a pressure gauge anywhere to get a reading on the line pressure? Also, try setting and releasing the ebrake multiple times. It helps keep the calipers adjusted somewhat like backing up does with drum brakes. That's all I got.

Ackattack · 02-08-2010, 03:34 PM

Thanks for the suggestions. I don't have the ebrake hooked up yet (just haven't gotten there) but the way that is set up (kinda goofy setup) that might just do it.

I could put a pressure gauge in there if I need to (T block with a couple adapters). Think I'll try the ebrake first.

thanks

cdowns · 02-08-2010, 03:52 PM

if you proportioning valve is the normal type there's a way to lock it in center for proper brake bleeding// a very common mistake people make on brake bleeding

Ackattack · 02-08-2010, 04:16 PM

Quote:

Originally Posted by cdowns

if you proportioning valve is the normal type there's a way to lock it in center for proper brake bleeding// a very common mistake people make on brake bleeding

I assume its a "normal type"

http://www.classicperform.com/Store/...Trucks/PV4.htm

how do you lock it in center?

junkyardjohn · 02-08-2010, 04:40 PM

I HAD A 71 BLAZER THAT I REPLACED THE M.C. & ALL THE LINES ON. I BLED & BLED & BLED THOSE BRAKES TO NO AVAIL. I JUST NEW SOMETHING WAS BROKE CAUSE I'VE NEVER HAD TROUBLE LIKE THAT B-4. FINALLY AFTER ALMOST A GALLON OF BRAKE FLUID THRU IT THE PEDDLE FIRMED UP & EVERTHING WORKED GREAT. I'M STILL A LITTLE PUZZELED ABOUT IT.

JOHN

Ackattack · 02-08-2010, 05:12 PM

my pedal is firm, just not enough clamping force on the rear

jay6891 · 02-08-2010, 05:25 PM

You stated that the M/C is from a 72. Just thinking out loud. Doesn't that mean that you need a M/C from a vehicle that has disc on the rear instead of one with drums. I believe the metering/flow rate/ pressure is different.

OhOneWS6 · 02-08-2010, 07:00 PM

Quote:

Originally Posted by jay6891

You stated that the M/C is from a 72. Just thinking out loud. Doesn't that mean that you need a M/C from a vehicle that has disc on the rear instead of one with drums. I believe the metering/flow rate/ pressure is different.

Exactly what I was thinking. You need a disc/disc master. I'm subscribing to this one. I have the parts laying on the bench for this conversion.

**Hart_Rod** · 02-08-2010, 07:58 PM

Quote:

Originally Posted by OhOneWS6

Exactly what I was thinking. You need a disc/disc master. I'm subscribing to this one. I have the parts laying on the bench for this conversion.

Later style master cylinders have a separate proportioning valve instead of having them built in like earlier ones. Since the proportioning valve is seperate, a disc/disc proportioning vavle (which is what he has) is all that is required. At least that is my understanding...

OhOneWS6 · 02-08-2010, 08:19 PM

Quote:

Originally Posted by Hart_Rod

Later style master cylinders have a separate proportioning valve instead of having them built in like earlier ones. Since the proportioning valve is seperate, a disc/disc proportioning vavle (which is what he has) is all that is required. At least that is my understanding...

From what I understand, Disc calipers require a larger volume of fluid than drum wheel cylinders. Therefore a master for disc/disc is required to provide that volume along with the proportioning valve for disc/disc.

lovnthe70 · 02-08-2010, 08:28 PM

to me is dosent sound like you have any air in the system (you said no squishness) and you have the correct proportioning valve, and if your power brake booster wasnt working you would still have brakes you just wouldnt have the power assist. Did you bleed it with the rear wheels up in the air? i would give it another bleed and service and after that i would suspect the proportioning valve cause it is designed to adjust the pressure between the front and rear brakes depending on how hard you are stopping and sounds like it might not be working right. only thing i can think of.

jay6891 · 02-08-2010, 08:28 PM

x 2 ^^^ Anybody else know about the M/C.

lovnthe70 · 02-08-2010, 08:31 PM

oh looks like OhOneWS6 is on to something, i just found this

A drum master will differ from a disc brake master in two ways: The amount of fluid that a drum brake master moves is less than that moved by a disc master and drum masters have 10 lb. residual valves to the drums. If you use a drum amster for disc brakes you would move an insufficient volume of fluid and the disc brakes would drag because of the residual valves.

jay6891 · 02-08-2010, 08:39 PM

I was wondering because if what Hart Rod said is true. Then why would CPP list master cylinders as Drum/Drum, Disc/Drum, Disc/Disc in thier parts.

cdowns · 02-08-2010, 08:46 PM

i think alot of the 4wheel disc guys run corvette masters that are 4wheel disc setuos

mbgmike · 02-08-2010, 08:57 PM

We sell the MC's for Dual disc. Corvette style booster $40.00 new. 1.1/8in bore. Their could be other problems as well however.

http://estore.websitepros.com/126980...-MC/Detail.bok sale price is not in affect but has not gone up much

ERASER5 · 02-08-2010, 08:59 PM

You can use a disc/disc with residual valve for disc/drum, but not the other way. No 72 MC will work correctly with a disc/disc system.

For more info check this. http://www.mpbrakes.com/

mbgmike · 02-08-2010, 09:03 PM

Quote:

Originally Posted by ERASER5

You can use a disc/disc with residual valve for disc/drum, but not the other way. No 72 MC will work correctly with a disc/disc system.

For more info check this. http://www.mpbrakes.com/

correct. We are dealers for MP Brakes also

**Hart_Rod** · 02-08-2010, 09:13 PM

Quote:

Originally Posted by ERASER5

You can use a disc/disc with residual valve for disc/drum, but not the other way. No 72 MC will work correctly with a disc/disc system.

For more info check this. http://www.mpbrakes.com/

Good information. I forgot about the bore size. I still think the problem may be with your parking brake. Even with a smaller bore size, you should be able to stop the rear end from turning in drive at idle without much pedal pressure....

Ackattack · 02-08-2010, 09:37 PM

What are others using for a MC and proportioning valve with thier camaro calipers? I know I'm not the first one to use these.

Also, my front calipers are dual piston where the rears are single piston, so I would imagine that the fronts still need more fluid than the rear.

I thought the residual valve was only if the MC was mounted in the floor.

suville · 02-08-2010, 10:50 PM

looks interesting, think I'll pay attention to this issue as I am setting up rear discs also. I am of the understanding you need the vette MC tho or at least disc-disc regardless what its off of I've got Cad rear disc,porp valve and MC

Bullseye54 · 02-08-2010, 11:27 PM

I put the eldorado rear disc on my 68 a few mos ago & had the same problem. I used POL m/c (which is a vette type) & prop valve,they look exactly like CPP FWIW.My problem was the prop valve not being centered.Check the switch (white plastic piece on prop valve)with a test light,hook alligator clip to pos battery term & probe the terminal on switch(switch is ground) if it lights the piston isn't centered.I just took the switch out & used a probe to move the piston to center.The piston is hour glass shaped so move the V under switch,this should be forward.I kept having to reset the valve,so I put speedy bleeders on all 4 corners & bled both left then both rt at same time now have great breaks.......Bob

danman987123 · 02-09-2010, 01:20 AM

i dropped in a complete 96 camaro rear end so i could have 4wheel disc so now i have 5x4.75 pattern and disc on all 4 corners...i have not encountered this problem yet but i will be using a new booster with mc from cpp most likely

Frizzle Fry · 02-09-2010, 02:09 AM

Ok guys, you ready for some outside-the-box-thinking?

This is a pieced together conversion. The MC compatibility is not the problem. I know since I have driven the same setup. Though mine did seem to drag a bit, they certainly provided plenty of braking force. Sounds like the system is well-bled and kink-free.

Here's my question: What is the thickness of your rotors and pads? Did you install pads...? (just kidding

) Assuming impala/caprice rotors, right?

02-08-2010, 12:34 PM	#1
Ackattack Senior Member Join Date: Aug 2002 Location: Valley Center KS Posts: 3,524	Rear disc brake problem I have LT1 camaro calipers installed on my truck with new everything (rotors, brake lines, disc-disc proportioning valve, MC, and line lock for the front). The brake booster is not new. I currently have the rearend up on jackstands, when I put the truck in gear, I can barely get the rear tires from turning at idle if I push on the brake pedal with all of my might. I bench bled the MC, bled the brake lines, fixed leaks, replaced a kinked SS flex line, bled the brakes lines, bled the brake lines some more. I would think disc brakes should have no problems stopping the rear tires when up on jack stands, I mean if I drove it, they would essentially be doing nothing. I can't really think of anything else to do except start replacing new parts. [BTW the proportioning valve is from CPP and the MC is a remanufactured one from Autozone for a 72 if it matters, and I rebuilt the calipers] Anyone else have similar problems, or suggestions __________________ Project Bruiser: 68 Pro-Touring C-10 5.3L / 4L60E Project Ironhide: 97 GMC Crew Cab 4x4 Cummins SOLD: '69 GMC 1/2T SWB TBI'd: Project No Buck Assembly Manual Index Sign up Thread!!! Factory Service Manual Index

02-08-2010, 01:44 PM	#2
Hart_Rod ************* Join Date: Apr 2005 Location: Pensacola, FL Posts: 17,858	Re: Rear disc brake problem Can you put a pressure gauge anywhere to get a reading on the line pressure? Also, try setting and releasing the ebrake multiple times. It helps keep the calipers adjusted somewhat like backing up does with drum brakes. That's all I got. __________________ Rob - https://www.instagram.com/hart_rod_c10 As Iron Sharpens Iron, So One Man Sharpens Another. Proverbs 27:17 FOR SALE: DBW pedal bracket - http://67-72chevytrucks.com/vboard/s...d.php?t=651123 FOR SALE: Hood Brackets http://67-72chevytrucks.com/vboard/s...d.php?t=679945 1987 Silverado SWB - 34.5K original miles http://67-72chevytrucks.com/vboard/s...d.php?t=801834 1969 SuperBurb - http://67-72chevytrucks.com/vboard/s...d.php?t=200387 1968 Farm truck - http://67-72chevytrucks.com/vboard/s...d.php?t=358692 1968 SWB - http://67-72chevytrucks.com/vboard/s...d.php?t=551258 1948 Chevy - http://67-72chevytrucks.com/vboard/s...=122164&page=3 Last edited by Hart_Rod; 02-08-2010 at 06:19 PM.

02-08-2010, 03:34 PM	#3
Ackattack Senior Member Join Date: Aug 2002 Location: Valley Center KS Posts: 3,524	Re: Rear disc brake problem Thanks for the suggestions. I don't have the ebrake hooked up yet (just haven't gotten there) but the way that is set up (kinda goofy setup) that might just do it. I could put a pressure gauge in there if I need to (T block with a couple adapters). Think I'll try the ebrake first. thanks __________________ Project Bruiser: 68 Pro-Touring C-10 5.3L / 4L60E Project Ironhide: 97 GMC Crew Cab 4x4 Cummins SOLD: '69 GMC 1/2T SWB TBI'd: Project No Buck Assembly Manual Index Sign up Thread!!! Factory Service Manual Index

02-08-2010, 03:52 PM	#4
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: Rear disc brake problem if you proportioning valve is the normal type there's a way to lock it in center for proper brake bleeding// a very common mistake people make on brake bleeding __________________ 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 Last edited by cdowns; 02-08-2010 at 03:53 PM.

02-08-2010, 04:40 PM	#6
junkyardjohn Registered User Join Date: Aug 2001 Location: SOMERSET KY. Posts: 6,425	Re: Rear disc brake problem I HAD A 71 BLAZER THAT I REPLACED THE M.C. & ALL THE LINES ON. I BLED & BLED & BLED THOSE BRAKES TO NO AVAIL. I JUST NEW SOMETHING WAS BROKE CAUSE I'VE NEVER HAD TROUBLE LIKE THAT B-4. FINALLY AFTER ALMOST A GALLON OF BRAKE FLUID THRU IT THE PEDDLE FIRMED UP & EVERTHING WORKED GREAT. I'M STILL A LITTLE PUZZELED ABOUT IT. JOHN __________________ junkyardjohn 69 1 TON TOW TRUCK // 84 4WD CUCV BLAZER// 85 1 TON 4WD STAKE TRUCK// 86 M1031 5/4 TON 4WD CUCV// ALOT OF OLD TRUCKS FOR ONE OLD MAN TO DRIVE. THERES ROOM FOR ALL OF GODS CREATURES RIGHT NEXT TO MY MASHED POTATOES// LIFE MEMBER OF P.E.T.A (PEOPLE EATING TASTY ANIMALS) DON'T RENT U-HAUL ALWAYS TELL THE TRUTH IT WILL AMAZE PART OF THE PEOPLE & ASTONISH THE REST

02-08-2010, 05:12 PM	#7
Ackattack Senior Member Join Date: Aug 2002 Location: Valley Center KS Posts: 3,524	Re: Rear disc brake problem my pedal is firm, just not enough clamping force on the rear __________________ Project Bruiser: 68 Pro-Touring C-10 5.3L / 4L60E Project Ironhide: 97 GMC Crew Cab 4x4 Cummins SOLD: '69 GMC 1/2T SWB TBI'd: Project No Buck Assembly Manual Index Sign up Thread!!! Factory Service Manual Index

02-08-2010, 05:25 PM	#8
jay6891 Car Knocker Join Date: May 2001 Location: jefferson,arkansas Posts: 664	Re: Rear disc brake problem You stated that the M/C is from a 72. Just thinking out loud. Doesn't that mean that you need a M/C from a vehicle that has disc on the rear instead of one with drums. I believe the metering/flow rate/ pressure is different. __________________ 68 c-10,91 sportside bed,350 .030 over,4 bolt,10-1 comp,2.05 intake/1.94 exhaust,1.6 Harland Sharp roller rockers,edelbrock rpm cam and intake w/750 carb, 700r4, 3.73 gears,Jacabbs Electronic Igntion w/Accel HEI distributer and super coil. ZR-1 roll pan, filled tailights. Blazer tank. Hidden hitch. 2 1/2" Flowmaster 40's. Parts bought but not installed>> ford 9" posi with disc. CCP front and rear lowering kit 4/5. Cab corners,foor boards,rockers, cab braces, Phatom grill, Painless wiring kit. Last edited by jay6891; 02-08-2010 at 06:24 PM. Reason: spelling....spelling

02-08-2010, 08:28 PM	#12
lovnthe70 Registered User Join Date: Nov 2008 Location: Tempe, AZ Posts: 181	Re: Rear disc brake problem to me is dosent sound like you have any air in the system (you said no squishness) and you have the correct proportioning valve, and if your power brake booster wasnt working you would still have brakes you just wouldnt have the power assist. Did you bleed it with the rear wheels up in the air? i would give it another bleed and service and after that i would suspect the proportioning valve cause it is designed to adjust the pressure between the front and rear brakes depending on how hard you are stopping and sounds like it might not be working right. only thing i can think of. __________________ 1970 GMC- 454 DONT GIVE ME NO JIBBA JABBA!!!

02-08-2010, 08:28 PM	#13
jay6891 Car Knocker Join Date: May 2001 Location: jefferson,arkansas Posts: 664	Re: Rear disc brake problem x 2 ^^^ Anybody else know about the M/C. __________________ 68 c-10,91 sportside bed,350 .030 over,4 bolt,10-1 comp,2.05 intake/1.94 exhaust,1.6 Harland Sharp roller rockers,edelbrock rpm cam and intake w/750 carb, 700r4, 3.73 gears,Jacabbs Electronic Igntion w/Accel HEI distributer and super coil. ZR-1 roll pan, filled tailights. Blazer tank. Hidden hitch. 2 1/2" Flowmaster 40's. Parts bought but not installed>> ford 9" posi with disc. CCP front and rear lowering kit 4/5. Cab corners,foor boards,rockers, cab braces, Phatom grill, Painless wiring kit. Last edited by jay6891; 02-08-2010 at 08:30 PM.

02-08-2010, 08:31 PM	#14
lovnthe70 Registered User Join Date: Nov 2008 Location: Tempe, AZ Posts: 181	Re: Rear disc brake problem oh looks like OhOneWS6 is on to something, i just found this A drum master will differ from a disc brake master in two ways: The amount of fluid that a drum brake master moves is less than that moved by a disc master and drum masters have 10 lb. residual valves to the drums. If you use a drum amster for disc brakes you would move an insufficient volume of fluid and the disc brakes would drag because of the residual valves. __________________ 1970 GMC- 454 DONT GIVE ME NO JIBBA JABBA!!!

02-08-2010, 08:39 PM	#15
jay6891 Car Knocker Join Date: May 2001 Location: jefferson,arkansas Posts: 664	Re: Rear disc brake problem I was wondering because if what Hart Rod said is true. Then why would CPP list master cylinders as Drum/Drum, Disc/Drum, Disc/Disc in thier parts. __________________ 68 c-10,91 sportside bed,350 .030 over,4 bolt,10-1 comp,2.05 intake/1.94 exhaust,1.6 Harland Sharp roller rockers,edelbrock rpm cam and intake w/750 carb, 700r4, 3.73 gears,Jacabbs Electronic Igntion w/Accel HEI distributer and super coil. ZR-1 roll pan, filled tailights. Blazer tank. Hidden hitch. 2 1/2" Flowmaster 40's. Parts bought but not installed>> ford 9" posi with disc. CCP front and rear lowering kit 4/5. Cab corners,foor boards,rockers, cab braces, Phatom grill, Painless wiring kit. Last edited by jay6891; 02-09-2010 at 03:51 PM.

02-08-2010, 08:46 PM	#16
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: Rear disc brake problem i think alot of the 4wheel disc guys run corvette masters that are 4wheel disc setuos __________________ 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

02-08-2010, 08:57 PM	#17
mbgmike Registered User Join Date: Aug 2005 Location: Pasadena,Tx /Pto Pta DR Posts: 5,415	Re: Rear disc brake problem We sell the MC's for Dual disc. Corvette style booster $40.00 new. 1.1/8in bore. Their could be other problems as well however. http://estore.websitepros.com/126980...-MC/Detail.bok sale price is not in affect but has not gone up much Attached Images

02-08-2010, 08:59 PM	#18
ERASER5 Registered User Join Date: Jun 2006 Location: Indiana Posts: 4,859	Re: Rear disc brake problem You can use a disc/disc with residual valve for disc/drum, but not the other way. No 72 MC will work correctly with a disc/disc system. For more info check this. http://www.mpbrakes.com/ __________________ '70 GMC C1500 LWB Power disc brakes. WooHoo! Posi 6 Lug Dana 60 Last edited by ERASER5; 02-08-2010 at 09:01 PM.

02-08-2010, 09:37 PM	#21
Ackattack Senior Member Join Date: Aug 2002 Location: Valley Center KS Posts: 3,524	Re: Rear disc brake problem What are others using for a MC and proportioning valve with thier camaro calipers? I know I'm not the first one to use these. Also, my front calipers are dual piston where the rears are single piston, so I would imagine that the fronts still need more fluid than the rear. I thought the residual valve was only if the MC was mounted in the floor. __________________ Project Bruiser: 68 Pro-Touring C-10 5.3L / 4L60E Project Ironhide: 97 GMC Crew Cab 4x4 Cummins SOLD: '69 GMC 1/2T SWB TBI'd: Project No Buck Assembly Manual Index Sign up Thread!!! Factory Service Manual Index



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02-08-2010, 10:50 PM	#22
suville Registered User Join Date: Jun 2003 Location: Mtn. Home, Idaho Posts: 906	Re: Rear disc brake problem looks interesting, think I'll pay attention to this issue as I am setting up rear discs also. I am of the understanding you need the vette MC tho or at least disc-disc regardless what its off of I've got Cad rear disc,porp valve and MC

02-08-2010, 11:27 PM	#23
Bullseye54 Registered User Join Date: Jan 2007 Location: Ormond Beach Fla Posts: 43	Re: Rear disc brake problem I put the eldorado rear disc on my 68 a few mos ago & had the same problem. I used POL m/c (which is a vette type) & prop valve,they look exactly like CPP FWIW.My problem was the prop valve not being centered.Check the switch (white plastic piece on prop valve)with a test light,hook alligator clip to pos battery term & probe the terminal on switch(switch is ground) if it lights the piston isn't centered.I just took the switch out & used a probe to move the piston to center.The piston is hour glass shaped so move the V under switch,this should be forward.I kept having to reset the valve,so I put speedy bleeders on all 4 corners & bled both left then both rt at same time now have great breaks.......Bob __________________ 1967 C20 Custom - 396/TH400 1968 GMC short step-350/M21

02-09-2010, 01:20 AM	#24
danman987123 Registered User Join Date: Apr 2008 Location: texas Posts: 127	Re: Rear disc brake problem i dropped in a complete 96 camaro rear end so i could have 4wheel disc so now i have 5x4.75 pattern and disc on all 4 corners...i have not encountered this problem yet but i will be using a new booster with mc from cpp most likely

02-09-2010, 02:09 AM	#25
Frizzle Fry Registered User Join Date: Aug 2005 Location: Hillsboro Oregon Posts: 6,449	Re: Rear disc brake problem Ok guys, you ready for some outside-the-box-thinking? This is a pieced together conversion. The MC compatibility is not the problem. I know since I have driven the same setup. Though mine did seem to drag a bit, they certainly provided plenty of braking force. Sounds like the system is well-bled and kink-free. Here's my question: What is the thickness of your rotors and pads? Did you install pads...? (just kidding ) Assuming impala/caprice rotors, right?

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