Front calipers locking up, bleeding solves it. What???
Thread Starter
|
Posting Guru
Joined: Jun 2005
Posts: 1,254
Likes: 0
From: Location, Location.
Front calipers locking up, bleeding solves it. What???
Gentlemen,
1979 F250 with 351M, 2wd, front disks, rear drums.
Just replaced the master cylinder with a rebuilt unit. Bench-bled m/c on the truck. Then bled the rear lines, but it was -20 outside and I couldn't feel my fingers anymore, os I said I'd do the fronts another day.
Before I could get back at it, had to drive to a work site. About 20 miles later, the truck is working hard to maintain speed. Brake pedal is rock hard, almost no travel. I check and the front rotors are burning hot. Jack up one axle, and I can't turn the wheel by hand.
So, I bleed the front calipers in the Home Depot parking lot - works like new. Kept checking carefully for the next 50 miles, no problem. Seems to be fixed.
BUT, I'm wondering what specifically could have done that? If there was air in the line that expanded when heated, I'd expect the pressure to escape through the m/c, just like the pressure does when you remove your foot from the brake pedal.
Any ideas?
Thanks.
1979 F250 with 351M, 2wd, front disks, rear drums.
Just replaced the master cylinder with a rebuilt unit. Bench-bled m/c on the truck. Then bled the rear lines, but it was -20 outside and I couldn't feel my fingers anymore, os I said I'd do the fronts another day.
Before I could get back at it, had to drive to a work site. About 20 miles later, the truck is working hard to maintain speed. Brake pedal is rock hard, almost no travel. I check and the front rotors are burning hot. Jack up one axle, and I can't turn the wheel by hand.
So, I bleed the front calipers in the Home Depot parking lot - works like new. Kept checking carefully for the next 50 miles, no problem. Seems to be fixed.
BUT, I'm wondering what specifically could have done that? If there was air in the line that expanded when heated, I'd expect the pressure to escape through the m/c, just like the pressure does when you remove your foot from the brake pedal.
Any ideas?
Thanks.
Cargo Master
Joined: Jun 2003
Posts: 2,982
Likes: 7
From: Somewhere Saskatchewan
Have a closer look at the flexible hoses.
They will collapse internally and act as a one way valve.
The bleeding process proves the point.
There is a rod from the booster to master cylinder that may need adjusting as well.
If it is too long there will be slight pressure delivered to the front brakes.
They will collapse internally and act as a one way valve.
The bleeding process proves the point.
There is a rod from the booster to master cylinder that may need adjusting as well.
If it is too long there will be slight pressure delivered to the front brakes.
Last edited by stuart1; Dec 17, 2005 at 03:27 PM.
Thread Starter
|
Posting Guru
Joined: Jun 2005
Posts: 1,254
Likes: 0
From: Location, Location.
Hoses were brand new 12 months ago.
But the booster push rod issue is a very interesting one. When I changed the m/c, I didn't touch that rod. But, who knows. Of course, I assume you mean it would apply slight static pressure to the front calipers. It;s not like that pressure would keep building up or anything. That is, it would always be like that, a constant slight pressure - whereas this was a buildup of pressure. But I'll check it.
But the booster push rod issue is a very interesting one. When I changed the m/c, I didn't touch that rod. But, who knows. Of course, I assume you mean it would apply slight static pressure to the front calipers. It;s not like that pressure would keep building up or anything. That is, it would always be like that, a constant slight pressure - whereas this was a buildup of pressure. But I'll check it.
"Mifflin Clay"
Joined: Jul 2005
Posts: 3,177
Likes: 4
From: Mifflin, PA
Originally Posted by fred_79f250
Hoses were brand new 12 months ago.
But the booster push rod issue is a very interesting one. When I changed the m/c, I didn't touch that rod. But, who knows. Of course, I assume you mean it would apply slight static pressure to the front calipers. It;s not like that pressure would keep building up or anything. That is, it would always be like that, a constant slight pressure - whereas this was a buildup of pressure. But I'll check it.
But the booster push rod issue is a very interesting one. When I changed the m/c, I didn't touch that rod. But, who knows. Of course, I assume you mean it would apply slight static pressure to the front calipers. It;s not like that pressure would keep building up or anything. That is, it would always be like that, a constant slight pressure - whereas this was a buildup of pressure. But I'll check it.
Last edited by alchymist; Dec 17, 2005 at 06:29 PM.
Thread Starter
|
Posting Guru
Joined: Jun 2005
Posts: 1,254
Likes: 0
From: Location, Location.
Can't wait to tell the wife the problem with the truck is probably that my push rod is too long.
But seriously -this does sound like my symptoms. But the rod is very flimsy when the engine is not running and there's no vacuum. So just fitting the m/c up to the booster and hoping to feel it contact the rod before the base plate probably won't work. Certainly if I had felt that during installation I would have stopped and wondered.
It's a pretty oddly shaped cup the rod fits into - difficult to get an accurate measurement from the m/c mounting face to the bottom of the cup to compare to the protruding length of the push rod.
How the heck does on check and adjust this?
Thanks again.
But seriously -this does sound like my symptoms. But the rod is very flimsy when the engine is not running and there's no vacuum. So just fitting the m/c up to the booster and hoping to feel it contact the rod before the base plate probably won't work. Certainly if I had felt that during installation I would have stopped and wondered.
It's a pretty oddly shaped cup the rod fits into - difficult to get an accurate measurement from the m/c mounting face to the bottom of the cup to compare to the protruding length of the push rod.
How the heck does on check and adjust this?
Thanks again.
