Front Brakes are killing me!!!
10-31-2010, 03:32 PM
#1
Instructor
Thread Starter
Member Since: Apr 2008
Location: Batavia IL
Posts: 143
Likes: 0
Received 0 Likes
on
0 Posts
Front Brakes are killing me!!!
I'm at the end of my rope on trying to get my front brakes to lock up. They have been iffy since I got the car @ 2 1/2 years ago (74 vert, 350)
About a month & half ago I had to do a panic stop as an a**hole truck driver pulled out right in front of me & I decided I need to get this pig to stop as a vette should.
This is only the front circuit- the rear brakes work great.
The fronts feel as if they are at about 75%, there is some stopping power, but not enough to lock the fronts up.
The pedal goes to the floor.
1. replace leaky front calipers with SS oring from Lonestar, also went to wagner semimetallic pads on front from organic, no significant change in braking power, but car didn't pull anymore during a stop. That to care of the air in system.
2. shim front rotors & tighten wheel bearings, .005 & .003 on outer edge run out
3. replace master, no change
4. added Summit line lock to fronts to diagnose front stopping power. Front brakes will not hold firm during a burnout, rolls forward @ 5-7 mph when backs are spinning.
5. dissassembled combo valve, cleaned out some dirt & stuff inside, no change
6. master cylinder pushrod adjusted to the point of lockup, then backed off 1/2 turn, no slop there, no change
7. replaced hard lines in front circuit, no change
8. ran new hard lines direct from master to calipers, bypassing line lock & comb valve, again no change
9. turned rotors & reshimmed, .002 runout at outer edge
10. added 2lb residual valve to frt. better pedal but no more braking power.
11.replaced 4yr old rubber hoses with S/S russell hoses, no change
12. replaced master again with a NAPA unit, no change
13. removed residual valve due to a slow bleed flow
14. disassembled comb valve & line lock again looking for any restriction, cleaned & replaced, no change
Master cylinders have been bench bled while level, tilted forward, tilted backwards, & on a sideways angle.
The system has been bled @ 20 times so far with no change. Bleeding has been by pressure bleeding & the old push on the pedal method. Either way, I'm not getting any air after initial bleed when changing components. Flow out of all four calipers is about equal when bleeding.
I've probably done brakes well over a hundred times, replaced calipers, masters & ran lines countless times & have never hit a brick wall like this.
I just changed my 73 FJ-40 to disk brakes, replaced all lines, master & vac booster. That will lock up 35" tires by barely thinking about it. I'm pretty confident in my ability, but this vette has me lost.
Before I hear HydroBoost, some please help me find a way to get the front tires to stop to the point of locking up. Remember, the rears work perfectly.
thanks, Todd
About a month & half ago I had to do a panic stop as an a**hole truck driver pulled out right in front of me & I decided I need to get this pig to stop as a vette should.
This is only the front circuit- the rear brakes work great.
The fronts feel as if they are at about 75%, there is some stopping power, but not enough to lock the fronts up.
The pedal goes to the floor.
1. replace leaky front calipers with SS oring from Lonestar, also went to wagner semimetallic pads on front from organic, no significant change in braking power, but car didn't pull anymore during a stop. That to care of the air in system.
2. shim front rotors & tighten wheel bearings, .005 & .003 on outer edge run out
3. replace master, no change
4. added Summit line lock to fronts to diagnose front stopping power. Front brakes will not hold firm during a burnout, rolls forward @ 5-7 mph when backs are spinning.
5. dissassembled combo valve, cleaned out some dirt & stuff inside, no change
6. master cylinder pushrod adjusted to the point of lockup, then backed off 1/2 turn, no slop there, no change
7. replaced hard lines in front circuit, no change
8. ran new hard lines direct from master to calipers, bypassing line lock & comb valve, again no change
9. turned rotors & reshimmed, .002 runout at outer edge
10. added 2lb residual valve to frt. better pedal but no more braking power.
11.replaced 4yr old rubber hoses with S/S russell hoses, no change
12. replaced master again with a NAPA unit, no change
13. removed residual valve due to a slow bleed flow
14. disassembled comb valve & line lock again looking for any restriction, cleaned & replaced, no change
Master cylinders have been bench bled while level, tilted forward, tilted backwards, & on a sideways angle.
The system has been bled @ 20 times so far with no change. Bleeding has been by pressure bleeding & the old push on the pedal method. Either way, I'm not getting any air after initial bleed when changing components. Flow out of all four calipers is about equal when bleeding.
I've probably done brakes well over a hundred times, replaced calipers, masters & ran lines countless times & have never hit a brick wall like this.
I just changed my 73 FJ-40 to disk brakes, replaced all lines, master & vac booster. That will lock up 35" tires by barely thinking about it. I'm pretty confident in my ability, but this vette has me lost.
Before I hear HydroBoost, some please help me find a way to get the front tires to stop to the point of locking up. Remember, the rears work perfectly.
thanks, Todd
10-31-2010, 06:52 PM
#2
Le Mans Master
Check the hole in the bottom of the master cylinder. Make sure it uncovers when the brakes are released. If it does not, no fluid is getting to the front.
10-31-2010, 07:08 PM
#4
Race Director
Maybe I missed it but is this standard or power brakes ? If its standard , are you putting 1" bore masters on it ?
I had a guy in that had 3 cylinders on his , problem was the parts guys were matching what he brought in , an 1 1/8" power master had been put on his standard brake car. It wouldn't stop for crap but had a great pedal. I put a 1" master on and it "put you through the windshield" brakes after that.
edit-dang Mike beat me to it-i'm a slow typer !
I had a guy in that had 3 cylinders on his , problem was the parts guys were matching what he brought in , an 1 1/8" power master had been put on his standard brake car. It wouldn't stop for crap but had a great pedal. I put a 1" master on and it "put you through the windshield" brakes after that.
edit-dang Mike beat me to it-i'm a slow typer !
10-31-2010, 07:57 PM
#5
Burning Brakes
Member Since: Dec 2007
Posts: 889
Likes: 0
Received 0 Likes
on
0 Posts
Hmmmmm - I have a 74' 350 also and my non-P/B pedal feels soft and the brakes are very weak. I'm busy with the interior right now and some engine stuff and intend to pressure bleed it soon. Will be interested in your 'fix'. I did pressure bleed the drivers side front a month ago, but again , the car is in the garage and not driving it now.
I'm at the end of my rope on trying to get my front brakes to lock up. They have been iffy since I got the car @ 2 1/2 years ago (74 vert, 350)
About a month & half ago I had to do a panic stop as an a**hole truck driver pulled out right in front of me & I decided I need to get this pig to stop as a vette should.
This is only the front circuit- the rear brakes work great.
The fronts feel as if they are at about 75%, there is some stopping power, but not enough to lock the fronts up.
The pedal goes to the floor.
1. replace leaky front calipers with SS oring from Lonestar, also went to wagner semimetallic pads on front from organic, no significant change in braking power, but car didn't pull anymore during a stop. That to care of the air in system.
2. shim front rotors & tighten wheel bearings, .005 & .003 on outer edge run out
3. replace master, no change
4. added Summit line lock to fronts to diagnose front stopping power. Front brakes will not hold firm during a burnout, rolls forward @ 5-7 mph when backs are spinning.
5. dissassembled combo valve, cleaned out some dirt & stuff inside, no change
6. master cylinder pushrod adjusted to the point of lockup, then backed off 1/2 turn, no slop there, no change
7. replaced hard lines in front circuit, no change
8. ran new hard lines direct from master to calipers, bypassing line lock & comb valve, again no change
9. turned rotors & reshimmed, .002 runout at outer edge
10. added 2lb residual valve to frt. better pedal but no more braking power.
11.replaced 4yr old rubber hoses with S/S russell hoses, no change
12. replaced master again with a NAPA unit, no change
13. removed residual valve due to a slow bleed flow
14. disassembled comb valve & line lock again looking for any restriction, cleaned & replaced, no change
Master cylinders have been bench bled while level, tilted forward, tilted backwards, & on a sideways angle.
The system has been bled @ 20 times so far with no change. Bleeding has been by pressure bleeding & the old push on the pedal method. Either way, I'm not getting any air after initial bleed when changing components. Flow out of all four calipers is about equal when bleeding.
I've probably done brakes well over a hundred times, replaced calipers, masters & ran lines countless times & have never hit a brick wall like this.
I just changed my 73 FJ-40 to disk brakes, replaced all lines, master & vac booster. That will lock up 35" tires by barely thinking about it. I'm pretty confident in my ability, but this vette has me lost.
Before I hear HydroBoost, some please help me find a way to get the front tires to stop to the point of locking up. Remember, the rears work perfectly.
thanks, Todd
About a month & half ago I had to do a panic stop as an a**hole truck driver pulled out right in front of me & I decided I need to get this pig to stop as a vette should.
This is only the front circuit- the rear brakes work great.
The fronts feel as if they are at about 75%, there is some stopping power, but not enough to lock the fronts up.
The pedal goes to the floor.
1. replace leaky front calipers with SS oring from Lonestar, also went to wagner semimetallic pads on front from organic, no significant change in braking power, but car didn't pull anymore during a stop. That to care of the air in system.
2. shim front rotors & tighten wheel bearings, .005 & .003 on outer edge run out
3. replace master, no change
4. added Summit line lock to fronts to diagnose front stopping power. Front brakes will not hold firm during a burnout, rolls forward @ 5-7 mph when backs are spinning.
5. dissassembled combo valve, cleaned out some dirt & stuff inside, no change
6. master cylinder pushrod adjusted to the point of lockup, then backed off 1/2 turn, no slop there, no change
7. replaced hard lines in front circuit, no change
8. ran new hard lines direct from master to calipers, bypassing line lock & comb valve, again no change
9. turned rotors & reshimmed, .002 runout at outer edge
10. added 2lb residual valve to frt. better pedal but no more braking power.
11.replaced 4yr old rubber hoses with S/S russell hoses, no change
12. replaced master again with a NAPA unit, no change
13. removed residual valve due to a slow bleed flow
14. disassembled comb valve & line lock again looking for any restriction, cleaned & replaced, no change
Master cylinders have been bench bled while level, tilted forward, tilted backwards, & on a sideways angle.
The system has been bled @ 20 times so far with no change. Bleeding has been by pressure bleeding & the old push on the pedal method. Either way, I'm not getting any air after initial bleed when changing components. Flow out of all four calipers is about equal when bleeding.
I've probably done brakes well over a hundred times, replaced calipers, masters & ran lines countless times & have never hit a brick wall like this.
I just changed my 73 FJ-40 to disk brakes, replaced all lines, master & vac booster. That will lock up 35" tires by barely thinking about it. I'm pretty confident in my ability, but this vette has me lost.
Before I hear HydroBoost, some please help me find a way to get the front tires to stop to the point of locking up. Remember, the rears work perfectly.
thanks, Todd
10-31-2010, 11:08 PM
#6
Race Director
Member Since: Sep 2002
Location: San Diego - Deep Within The State of CONFUSION!
Posts: 10,362
Likes: 0
Received 2 Likes
on
2 Posts
Try replacing the calipers. Warranty those 'new' ones you have and let us know if that helps. Are these NAPA master cylinders you're buying new or reman?
11-01-2010, 01:35 AM
#7
Instructor
Thread Starter
Member Since: Apr 2008
Location: Batavia IL
Posts: 143
Likes: 0
Received 0 Likes
on
0 Posts
There are power brakes on the car. The first master cyliner was from RockAuto & the second was from Napa. No matching of parts, but a lookup for a 74 vette with power brakes.
I haven't taken the master apart to check bore size by going on the assumtion that 2 diff masters by 2 diff suppliers would not be wrong.
The frt calipers were replaced 2 yrs ago with Advance Auto units right after I bought the car when the clip came off the RF caliper pin & the pads came out. That was an exciting stop in traffic! The pads came out, the pistons blew out & there was nothing for front brakes.
Both frt calipers were again replaced 3 weeks ago with SS o-ring calipers from Volunteer Vette (Lonestar). I see no isues with calipers as there is no pulling left or right, it stops in a straight line, it just will not lock up frt tires at all.
I haven't taken the master apart to check bore size by going on the assumtion that 2 diff masters by 2 diff suppliers would not be wrong.
The frt calipers were replaced 2 yrs ago with Advance Auto units right after I bought the car when the clip came off the RF caliper pin & the pads came out. That was an exciting stop in traffic! The pads came out, the pistons blew out & there was nothing for front brakes.
Both frt calipers were again replaced 3 weeks ago with SS o-ring calipers from Volunteer Vette (Lonestar). I see no isues with calipers as there is no pulling left or right, it stops in a straight line, it just will not lock up frt tires at all.
Last edited by offroadtoyota; 11-01-2010 at 01:42 AM. Reason: reman masters
11-01-2010, 05:46 AM
#10
Team Owner
I didn't see any mention of the proportioning valve. Have you checked that 'puppy' out? Oh, and don't assume that the part number book is correct. I've seen books with incorrect data before...and they never get corrected [re. master cylinder selection].
11-01-2010, 07:59 AM
#11
Race Director
I've never seen a standard master on a power brake car , I would guess it would create a low pedal.
Just curious , when the pad pin fell out was it in with the head towards the inside ? Did you have stock wheels or mags ?
c31980 has an idea ,although the lines should be different sizes.
11-01-2010, 08:21 AM
#12
Le Mans Master
Is there a way to tell the bore size of the master cylinder without taking it apart?
I guess I'm a little late
I guess I'm a little late
Last edited by bashcraft; 11-01-2010 at 08:22 AM. Reason: I was sleeping
11-01-2010, 09:20 AM
#14
Race Director
11-01-2010, 09:53 PM
#17
Instructor
Thread Starter
Member Since: Apr 2008
Location: Batavia IL
Posts: 143
Likes: 0
Received 0 Likes
on
0 Posts
I did takout the prop valve twice & sprayed it with brake cleaner inside & out, then blew it out with air. The spring mounted part inside moves freely & the brake light does not come on during driving. The light did come on when I ran separate lines to bypass it & only the rears were going through it.
I have thought seriously about changing the front & back lines out of the master, but I'm not quite there yet.
When I drove to work today, in "normal" traffic, the car stops nice with no issues. During some "spirited" driving around the industrial park, with hard stops, the pedal goes right to the floor. About the time the pedal hits the stop, the backs are locked up. I have to stand on the pedal pretty good to get to this point.
Vaccum is on the low side with the cam, but not overly so. Comp cams 274. I'll have to check vacuum tomorrow.
I keep hearing ringing of hydroboost in my ears, but I would have to hit myself repeatly with a hammer if I spent the money & beer to change over & I still had the same problem.
I'm taking the line lock off tomorrow. Maybe there is a big air bubble in there that isn't bleeding out?
I have thought seriously about changing the front & back lines out of the master, but I'm not quite there yet.
When I drove to work today, in "normal" traffic, the car stops nice with no issues. During some "spirited" driving around the industrial park, with hard stops, the pedal goes right to the floor. About the time the pedal hits the stop, the backs are locked up. I have to stand on the pedal pretty good to get to this point.
Vaccum is on the low side with the cam, but not overly so. Comp cams 274. I'll have to check vacuum tomorrow.
I keep hearing ringing of hydroboost in my ears, but I would have to hit myself repeatly with a hammer if I spent the money & beer to change over & I still had the same problem.
I'm taking the line lock off tomorrow. Maybe there is a big air bubble in there that isn't bleeding out?
11-01-2010, 10:30 PM
#19
Melting Slicks
Let me start by saying you sound like you know what you are doing and I doubt that this is the problem, but, when my neighbor did it, he knew better and still he couldn't find the problem. He had the calipers on the wrong sides which puts the bleeder on the bottom and makes it impossible to get the air out. That's the only thing I didn't see you mention in your post.
11-03-2010, 08:13 AM
#20
Burning Brakes
Member Since: Oct 2003
Location: New Carlisle IN
Posts: 1,080
Likes: 0
Received 68 Likes
on
56 Posts
I was talking with a guy about brakes on a 69 a while back. He changed about every thing, but figured out he had some problems with not getting enough vacuum to opperate the brakes properly. He installed an electric vacuum pump in the system and his brake problems went away.
