2nd MC & Booster Issues
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2nd MC & Booster Issues
Ok, replaced the mc & booster rebuild after install & brake pedal not coming all the way up. Got new rebuilt (I know, I know, no such thing), bench bleed it, placed onto truck (74', F100) bleed all lines until all air out. At end of day brakes felt good & firm & brake pedal rising all the way up on its own. Took brake pedal off to weld the brake switch on that I got at junk yard & put it on. After reinstalling brake pedal I noticed that brake was lower than what it was yesterday after bleeding. Push it down & it came up about 85% & then had to pull the remaining 15% up by hand. Rebleed all lines & it had a couple of bubbles in them but looked pretty good. After bleeding everything again (except for mc) the brake pedal still does not come all the way up. I did notice that when I did put pressure on the brake pedal & put it down as far as it can go that fluid was coming out of the top of the mc.
What are you all's thoughts on this.
Thanks
Garry
What are you all's thoughts on this.
Thanks
Garry
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From: Southern NM
Have you checked or set the height on the booster pushrod?When you bleed this system,does it flow easily or does it seem slow?Is there any difference in the pedal when the engine is fired and you have a vacuum source?Are the drum brakes adjusted?What condition are the lines in?And more importantly,what are the condition of the rubber jumper lines and calipers/wheel cylinders in?
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Have you checked or set the height on the booster pushrod?
When you bleed this system,does it flow easily or does it seem slow?Is there any difference in the pedal when the engine is fired and you have a vacuum source?Are the drum brakes adjusted?What condition are the lines in?And more importantly,what are the condition of the rubber jumper lines and calipers/ wheel cylinders in?
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When you bleed this system,does it flow easily or does it seem slow?Is there any difference in the pedal when the engine is fired and you have a vacuum source?Are the drum brakes adjusted?What condition are the lines in?And more importantly,what are the condition of the rubber jumper lines and calipers/ wheel cylinders in?
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Have you checked or set the height on the booster pushrod?
When I first put everything on everyting worked just right.
When you bleed this system,does it flow easily or does it seem slow?
Everything did flow good & free
Is there any difference in the pedal when the engine is fired and you have a vacuum source?
Yesterday when it worked good, it did work better when the engine was on.
Are the drum brakes adjusted?
I have not checked the rear drums, but it would seem odd that yesterday it worked good & then today not, is that possible.
What condition are the lines in?And more importantly,what are the condition of the rubber jumper lines and calipers/ wheel cylinders in?
Truck has been sitting up for a couple of years inside a barn, it doesn't seem that the rubber lines are collasping but they maybe.
Why do you think fluid is now coming out of the master today, I am sure it is all interrealted but dont know how.
Thanks
Garry
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When I first put everything on everyting worked just right.
When you bleed this system,does it flow easily or does it seem slow?
Everything did flow good & free
Is there any difference in the pedal when the engine is fired and you have a vacuum source?
Yesterday when it worked good, it did work better when the engine was on.
Are the drum brakes adjusted?
I have not checked the rear drums, but it would seem odd that yesterday it worked good & then today not, is that possible.
What condition are the lines in?And more importantly,what are the condition of the rubber jumper lines and calipers/ wheel cylinders in?
Truck has been sitting up for a couple of years inside a barn, it doesn't seem that the rubber lines are collasping but they maybe.
Why do you think fluid is now coming out of the master today, I am sure it is all interrealted but dont know how.
Thanks
Garry
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From: Southern NM
Well,I see you got the questions in my post copied down.Let us know some of your findings and results.I know these things are a pain,but we will try to narrow down a cause.I had some problems with my '78 F250 of this nature.My problems turned out to be the rubber jumper lines and old fluid/debris in the front calipers.I could not get the pads to retract into the calipers as they were full of debris and would not let the pressure relieve behind the piston.I rebuilt the calipers,after flushing the entire system,and replaced all the jumper lines front and rear.
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there was debris in the front calipers & they seemed to be still a little dirty on the last bleeding. I guess it could be the claipers. What would be the signs if they need rebuilding & the rubber lines?
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From: Southern NM
The chances are pretty good that as old as your truck is,that the outer and inner rubber seals for the caliper pistons are gone.They are easy to remove and reseal,and the repair kits are cheap.The rubber lines are most apt to deteriorate from the inside.They are aged and the rubber breaks down from the brake fluid.These are not expensive either.I would look at these items.Also need to check the pushrod length on the booster.It is adjustable and there are published lengths to set it at.It is done by year and booster type.Let us know how things look&how we can be of help!
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You have to adjust the rear drums for the brake system to work properly.
The pedal pushrod has to be adjusted properly as well. For power brakes it is the pushrod coming out of the booster that pushes the master cylinder. There should be zero slack, but at the same time it can't be pushing against the m/c either.
Fluid can come out of the top if you have too much fluid. Which may be happening if you top off the resevoirs, pump the brakes, find the fluid low, top it off again and then the drum brake springs retract the shoes pushing the fluid back into the resevoir.
Again ADJUST THOSE DRUMS. That isn't a casual command, but you have to in order for everything to work together.
I would suggest, adjust the drums, check your push-rod, bleed the brakes, then re-bleed the brakes. IT can take a lot of time to get ALL of the air out of the system.
Josh
The pedal pushrod has to be adjusted properly as well. For power brakes it is the pushrod coming out of the booster that pushes the master cylinder. There should be zero slack, but at the same time it can't be pushing against the m/c either.
Fluid can come out of the top if you have too much fluid. Which may be happening if you top off the resevoirs, pump the brakes, find the fluid low, top it off again and then the drum brake springs retract the shoes pushing the fluid back into the resevoir.
Again ADJUST THOSE DRUMS. That isn't a casual command, but you have to in order for everything to work together.
I would suggest, adjust the drums, check your push-rod, bleed the brakes, then re-bleed the brakes. IT can take a lot of time to get ALL of the air out of the system.
Josh
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what would think:
since my truck didn't come with a booster & I went to the junk yeard to get one & after getting it home discovered it was too rusted to work but I did take off the bracket that was on the back & put it on the rebuild. I did notice that the bracket had a grease fitting it seemed to be working ok by hand but without having it on the truck & checking it out I dont know for sure. Could this be the issue & if maybe how could I check to be sure?
thanks
garry
since my truck didn't come with a booster & I went to the junk yeard to get one & after getting it home discovered it was too rusted to work but I did take off the bracket that was on the back & put it on the rebuild. I did notice that the bracket had a grease fitting it seemed to be working ok by hand but without having it on the truck & checking it out I dont know for sure. Could this be the issue & if maybe how could I check to be sure?
thanks
garry
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If you think about it, the master cylinder has a snap ring in the bore to "stop" the piston. That is as far as it will go. With the push-rod up against the piston, and the pushrod seated into the cup inside the booster there should be any issues with pedal clearance.
I have a spare booster and the pushrod is adjusted out with about 8 to 9 threads showing.
Josh
I have a spare booster and the pushrod is adjusted out with about 8 to 9 threads showing.
Josh
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From: Southern NM
Here is the real deal measurement for the pushrod.The tip of the adjusting screw needs to be set @ 0.931 to 0.946 from the base of the booster where the M/C is bolted.If the plunger is set too long it will prevent the M/C piston from completely releasing hydraulic pressure,causing the brakes to drag.If the plunger is set too short it will cause excessive brake pedal travel.This can be accomplished with a caliper,or with a notched piece of cardboard,or with a piece of thin metal notched to that value.