Power brake woes
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Elder User
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From: North Idaho
Power brake woes
I thought this might be of interest to all of you out there in cyber truck land.
When we overhauled Jon's 1950 F1 we installed 4 wheel disks and bought a power brake booster, MC, and mount from TCI.
It was installed and bled on the rolling chassis without the cab etc and all seemed well, that is until we finally got it assembled and began road tests. That's when we found that it would not/could not lock up the brakes, no matter how hard we stood on the pedal.
So, I pulled the MC and booster back off and made sure that the MC was properly bled and adjusted to the booster ram. I reinstalled the system and had the same results, good brakes but not 100% brakes.
So, everything came back out yet again and I began measuring the throw of everything and found that the MC and booster required 1.5 " of travel to achieve maximum braking but the TCI mount and pedal only provided 1" of throw.
So, after spending another day fabbing up a new pedal that had enough throw to bottom out the new booster and MC, the 50 stops on a dime.
This would have been such an easy thing to fix if I had only measured things to begin with.
When we overhauled Jon's 1950 F1 we installed 4 wheel disks and bought a power brake booster, MC, and mount from TCI.
It was installed and bled on the rolling chassis without the cab etc and all seemed well, that is until we finally got it assembled and began road tests. That's when we found that it would not/could not lock up the brakes, no matter how hard we stood on the pedal.
So, I pulled the MC and booster back off and made sure that the MC was properly bled and adjusted to the booster ram. I reinstalled the system and had the same results, good brakes but not 100% brakes.
So, everything came back out yet again and I began measuring the throw of everything and found that the MC and booster required 1.5 " of travel to achieve maximum braking but the TCI mount and pedal only provided 1" of throw.
So, after spending another day fabbing up a new pedal that had enough throw to bottom out the new booster and MC, the 50 stops on a dime.
This would have been such an easy thing to fix if I had only measured things to begin with.
Knuckle Bandage Sales Rep
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P-55,
The timing of this thread is beautiful.
How do you determine the stroke length? I'm about to install an aftermarket booster/MC to my stock pedals tomorrow and would like to know how you know it is at full throw. Is there a spec on the booster?
Tom
The timing of this thread is beautiful.
How do you determine the stroke length? I'm about to install an aftermarket booster/MC to my stock pedals tomorrow and would like to know how you know it is at full throw. Is there a spec on the booster?
Tom
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Elder User
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From: North Idaho
You should be able to clamp your MC in a vise and stroke it with a #3 Phillips or punch and measure the total throw that way.
BTW: I pulled the original manual (drum brake) MC off the shelf today and guess what, it has a 1" stroke. TCI must have put the wrong brake pedal on our power brake kit or they have failed to engineer it correctly.
Tuned
Joined: Oct 2011
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Man oh man,where was this a lot of $$$$ ago? I'm having same issues,gone to 4 different shops,paid ***** load of $$. In my mind it's not stopping good enough,in theirs it's fine. I've put in a new master cylinder,re-plumbed the front brakes,relocated proportional valve,built a firewall to keep heat off of reservoir,moved headers over some more,next I was going to wrap headers and replace booster. In my mind (which is dangerous),the original kit was for a disk/drum setup,then I switched to disc/disc using same equipment.Would this make a difference? My pedal goes down a bit before it starts to grab,then I have to lift the pedal some to get it back to the right spot. Now I'm wondering if the problem all along is what your talking about. Didn't mean to hijack your thread,I'm just frustrated and tired of throwing away $$ that could go towards something else. Thanks for your replies and help,L8R ZFLASH
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From: North Idaho
Man oh man,where was this a lot of $$$$ ago? I'm having same issues,gone to 4 different shops,paid ***** load of $$. In my mind it's not stopping good enough,in theirs it's fine. I've put in a new master cylinder,re-plumbed the front brakes,relocated proportional valve,built a firewall to keep heat off of reservoir,moved headers over some more,next I was going to wrap headers and replace booster. In my mind (which is dangerous),the original kit was for a disk/drum setup,then I switched to disc/disc using same equipment.Would this make a difference? My pedal goes down a bit before it starts to grab,then I have to lift the pedal some to get it back to the right spot. Now I'm wondering if the problem all along is what your talking about. Didn't mean to hijack your thread,I'm just frustrated and tired of throwing away $$ that could go towards something else. Thanks for your replies and help,L8R ZFLASH
When you switched from drum/disk to disk/disk did you change the relief valve from a 10 psi to a 2 psi? disk systems require the 2 psi valves.
If you have to lift the pedal with your toe you need a stronger brake return spring.
If you have a lot of free play in your pedal make sure that the booster to MC rod is adjusted so that it just contacts the MC plunger as they meet metal to metal, there should be no free play between the rod and MC plunger.
Tuned
Joined: Oct 2011
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When you switched from drum/disk to disk/disk did you change the relief valve from a 10 psi to a 2 psi? disk systems require the 2 psi valves.
If you have to lift the pedal with your toe you need a stronger brake return spring.
If you have a lot of free play in your pedal make sure that the booster to booster rod is adjusted so that it just contacts the MC plunger as they meet metal to metal, there should be no free play between the rod and MC plunger.
If you have to lift the pedal with your toe you need a stronger brake return spring.
If you have a lot of free play in your pedal make sure that the booster to booster rod is adjusted so that it just contacts the MC plunger as they meet metal to metal, there should be no free play between the rod and MC plunger.
.
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Stating the obvious:
Checking the travel on an MC is the same for disk as for drum or for drum/disk. Ideally, the pedal can push the piston fully into the cylinder. It should also be able to push through a booster's mechanical override when vacuum (or hydraulic assist) isn't present. You've got to be able to stop or it's a NO GO situation.
Great post, thank you for sharing.
Checking the travel on an MC is the same for disk as for drum or for drum/disk. Ideally, the pedal can push the piston fully into the cylinder. It should also be able to push through a booster's mechanical override when vacuum (or hydraulic assist) isn't present. You've got to be able to stop or it's a NO GO situation.
Great post, thank you for sharing.
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From: North Idaho
the braking problem had me stumped for several days and I felt (and still do) pretty stupid when I finally figured out that it wasn't anything I had failed to do but was actually the "engineered" brake mount that we bought that was the entire problem. When we buy kits like these from known dealers we (at least I did) assume that they are engineered correctly so this was the last (and I mean last) thing that I checked. I will inspect any future kit much closer before installation.
Tuned
Joined: Oct 2011
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55, had it measured today and it 1 1/4. Not 1 or 1 1/2,I know it's only a 1/4,but I think this is the prob. My guy asked me how you fabbed the new pedal and I told him I didn't know. Any suggestions on this would be great,thanks in advance. L8R ZFLASH
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From: North Idaho
What I did was cut off the ear from it's location and I made one that was 3/4" longer. I then rotated it forward (moving the booster bolt hole forward) approximately 1/2 inch. With the booster and MC removed I checked to make sure I had more possible throw than the booster could handle then I welded it in solid.
The longer ear makes the shaft into the booster dip a bit at the apex of it's arc but there is enough play in the booster shaft to allow this to happen without binding.
Probably not the perfect engineering solution but I had spent three days under the truck and was more than a little frustrated and wanted to get the brakes working.
It was probably a Fred Flintstone method of repair but the truck stops like a dream now so all is well, at least until the new engine locked up a valve.
Some days it just doesn't pay to get up.....man oh man.
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