BRAKE HELP NEEDED, with 4.9
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Lead Driver
Joined: Mar 2008
Posts: 7,182
Likes: 380
From: Near Los Angeles
BRAKE HELP NEEDED, with 4.9
I need a bit of brake know how and help. I just completed the rear disc conversion on my 75 F350. The discs in the front are dual piston, and about 6 years old, but with new pads. I replaced the master with oem rebuilt, deleted the 35 year old proportioning valve, and installed an adjustable proportioning v. for the rear system. I also ran new hard line to the rear, and new soft lines at 4 corners, and center rear.
I've read 100 times all the probs people have the Caddy calipers I have. So If you just want to tell me how bad they are, pls don't bother.
I have bleed every thing well, even took off the rears and tapped with rubber mallet as others recommended. Still, I don't have the stopping ability I should have. I have never been able to lock up the brakes, and still can't. Even though the prop. valve for the rears is set at full force, I can't lock them up. Shouldn't I be able to skid? Shouldn't the fronts, at least, lock up?
I noticed the front cals were full of rusty colored brake fluid, and the bleeders were clogged. But even when fronts were new with rebuilt cals., I have not been able to stop as quickly as possible in emergency situations. Any advise is appreciated.
I've read 100 times all the probs people have the Caddy calipers I have. So If you just want to tell me how bad they are, pls don't bother.
I have bleed every thing well, even took off the rears and tapped with rubber mallet as others recommended. Still, I don't have the stopping ability I should have. I have never been able to lock up the brakes, and still can't. Even though the prop. valve for the rears is set at full force, I can't lock them up. Shouldn't I be able to skid? Shouldn't the fronts, at least, lock up?
I noticed the front cals were full of rusty colored brake fluid, and the bleeders were clogged. But even when fronts were new with rebuilt cals., I have not been able to stop as quickly as possible in emergency situations. Any advise is appreciated.
Post Fiend
Joined: Dec 2007
Posts: 8,521
Likes: 16
From: Lost
First of all, flush out all of the old fluid from the front part of the system. Brake fluid is hydroscopic, meaning it absorbs water. That rusty colored fluid, was rust from the water that has started to seperate from the fluid inside the calipers. This can/will cause the front calipers to start sticking, so that extra force is needed to apply the brakes, then they don't want to release.
I'm not familar with the conversion system, nor the rear calipers you mentioned. However, most rear disc brake setups are designed in a manner that makes locking the wheels a bit harder to do, as to prevent the rear from suddenly taking the lead.
Rear disc brakes tend to need more pressure and volume of fluid to operate than most drum setups. Did you change the master cyl to a different model?
I'm not familar with the conversion system, nor the rear calipers you mentioned. However, most rear disc brake setups are designed in a manner that makes locking the wheels a bit harder to do, as to prevent the rear from suddenly taking the lead.
Rear disc brakes tend to need more pressure and volume of fluid to operate than most drum setups. Did you change the master cyl to a different model?
Elder User
Joined: Dec 2000
Posts: 570
Likes: 1
From: Austin Texas (area)
Agree about the fluid. That old crap must be flushed out. Until the system has fresh fluid you really don't know what you have. Brake fluid should be replaced at least every 5yrs....I know, no one does that but, it is cheap insurance.
Post Fiend
Joined: Dec 2007
Posts: 8,521
Likes: 16
From: Lost
I actually try to flush the brakes and hydraulic clutch systems in my vehicles at least every other year. The RX7 usually gets this done every year, but I use the brakes much harder on it than I do any other vehicle, since I drive rather conservative on the street.
Thread Starter
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Lead Driver
Joined: Mar 2008
Posts: 7,182
Likes: 380
From: Near Los Angeles
I got the system flushed in the front. The rears are a PIA, but are coming together. I just have to adjust them today. I'm also changing from the organic pads to semi metalic, hoping for better grabbing.
One issue: I'm hoping someone will jump in here and resolve this. When I bought the truck it had had some very interesting changes made. One is that there is a bracket, about 3-4" deep, which separates the booster from the firewall, like on the 78-79 model. I can see where the pivot shaft may have been. But my booster is the 'long shaft' type, which connects directly to b.pedal. I'm thinking my booster is supposed to mount directly to firewall? And that extra 3-4" is the source of all my braking woes, depriving me of the power I should have.
Ebrake is clamping good and strong!!
One issue: I'm hoping someone will jump in here and resolve this. When I bought the truck it had had some very interesting changes made. One is that there is a bracket, about 3-4" deep, which separates the booster from the firewall, like on the 78-79 model. I can see where the pivot shaft may have been. But my booster is the 'long shaft' type, which connects directly to b.pedal. I'm thinking my booster is supposed to mount directly to firewall? And that extra 3-4" is the source of all my braking woes, depriving me of the power I should have.
Ebrake is clamping good and strong!!
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