brake pedal differences ?

[Boog]

I have seen several times when a braking problem thread pops up one or two will suggest 'you need to drill another pedal rod hole 1 1/2" or so lower to adjust the ratio for a power booster conversion'.
In this thread for instance : https://67-72chevytrucks.com/vboard/...standard+brake
So what's the deal? Of all my junk yarding I have never seen any difference of truck brake pedals, at least of 1/2 & 3/4 tons.
From factory are there two different pedals depending on standard brakes or power assist brakes? Or is the drill a hole suggestion only a manner to adjust a mismatch of brake components?
On my '69 I have OE '71 power brake pedal assembly with large diameter power brake booster, front disc and rear drums. Fresh pads and shoes and all adjusted and bled the pedal travels more than I'd like and is soft. According to the above suggestion I should lower the rod attachment point and that will shorten the pedal travel and firm up the brakes. Or will that just require more foot pressure effort on the pedal to stop the truck?
What's the REAL deal?

[Andy4639]

I to have read a bunch of these threads and I have never seen a brake pedal that had both holes in it.

I posted this the other day and not one response on it. The 71 manual I have makes no mention of these measurements.

GMC service manual for 15000/35000 series trucks no matter if standard are power disc.
3.5" off the toe board for standard & disc brakes. If power brakes truck should be running to take the measurement.
C models 2.42"
P models 1.25" all off the toe board


http://67-72chevytrucks.com/vboard/s...d.php?t=801580

[LockDoc]

On my '69 I have OE '71 power brake pedal assembly with large diameter power brake booster, front disc and rear drums. Fresh pads and shoes and all adjusted and bled the pedal travels more than I'd like and is soft. According to the above suggestion I should lower the rod attachment point and that will shorten the pedal travel and firm up the brakes. Or will that just require more foot pressure effort on the pedal to stop the truck?
What's the REAL deal?

Try this....

On the drum brakes, one thing I found on mine is when you put everything back together and adjust the brake shoes you can’t just adjust them out until they start rubbing and quit. You have to adjust them out as far as they will go and you cannot turn the wheel or drum at all. This centers the whole assembly in the drum. (I even tap around the drum as I tighten them to help them center themselves) Then you back them off until the wheel or drum just turns, and stop. A little rubbing is OK as long as you can turn it by hand. If you only adjust them out until they start rubbing and quit, the first time you press on the brake pedal the brake shoe assemblies will center themselves and you will have too much clearance between the shoes and the brake drum. I also put three lug nuts on backwards to hold the drum tight against the axle on the rear while adjusting them.

I know it is a pain in the butt to try and hold the self adjusters off of the adjuster wheel while you back them off, but this is the only way I could get my drum brake shoes adjusted correctly.

If you try it let us know if it works for you.

LockDoc

[Boog]

I missed that post Andy. Interesting. Is that in a service manual?
Leon I have adjusted them correctly. Done them many times over my many years.
It's been so long ago now I don't remember if I installed the master cylinder/booster together as a unit or if I separated them to check the rod distance. I'm sure I bought them together from O'Reillys. This truck isn't ready for the road yet so all I can do is run it around the yard for now. It has the standard booster for a '71, 11" I guess.
I should probably separate them and start from there.

[Andy4639]

Originally Posted by Boog

I missed that post Andy. Interesting. Is that in a service manual?
Leon I have adjusted them correctly. Done them many times over my many years.
It's been so long ago now I don't remember if I installed the master cylinder/booster together as a unit or if I separated them to check the rod distance. I'm sure I bought them together from O'Reillys. This truck isn't ready for the road yet so all I can do is run it around the yard for now. It has the standard booster for a '71, 11" I guess.
I should probably separate them and start from there.

Yes. 71 manual and GMC manual. The 69 is just like the Chevy manual on the brake pedal.

[Mike C]

Most vehicles with power and manual brake options offer two pivot points on the pedal. On a 67-72 they account for the differences in required leverage through the linkage that hooks to the brake booster which is offset from the hole.

The manual master is inline with the pushrod on the pedal. If you are attempting a conversion with square body parts or something else, STOP. Get the correct brackets and linkage for a 67-72.

[68Gold/white]

Originally Posted by LockDoc

Try this....

On the drum brakes, one thing I found on mine is when you put everything back together and adjust the brake shoes you can’t just adjust them out until they start rubbing and quit. You have to adjust them out as far as they will go and you cannot turn the wheel or drum at all. This centers the whole assembly in the drum. (I even tap around the drum as I tighten them to help them center themselves) Then you back them off until the wheel or drum just turns, and stop. A little rubbing is OK as long as you can turn it by hand. If you only adjust them out until they start rubbing and quit, the first time you press on the brake pedal the brake shoe assemblies will center themselves and you will have too much clearance between the shoes and the brake drum. I also put three lug nuts on backwards to hold the drum tight against the axle on the rear while adjusting them.

I know it is a pain in the butt to try and hold the self adjusters off of the adjuster wheel while you back them off, but this is the only way I could get my drum brake shoes adjusted correctly.

If you try it let us know if it works for you.

LockDoc

Folks that have drum brakes need to read this post carefully, especially IF you have minimal experience working on drum brakes!!! Print this off and keep it somewhere, where you won't forget where you put it!!!

[Willys_MB]

I'm looking to do this upgrade VERY soon. I'm rebuilding the front end from a 71 and will be swapping it in and installing the brake booster at that time as well. I'm a little confused. It sounds like I may have to adjust the brake pedal location (obviously, I will check it when running), but I may not have to? Or is it pretty much a rule that when you install power brakes you need to move the brake pedal?

[Willys_MB]

Originally Posted by Willys_MB

I'm looking to do this upgrade VERY soon. I'm rebuilding the front end from a 71 and will be swapping it in and installing the brake booster at that time as well. I'm a little confused. It sounds like I may have to adjust the brake pedal location (obviously, I will check it when running), but I may not have to? Or is it pretty much a rule that when you install power brakes you need to move the brake pedal?

Is there a new linkage I would need to purchase or is it just as simple as drilling/elongating some holes?

[Andy4639]

Originally Posted by Willys_MB

Is there a new linkage I would need to purchase or is it just as simple as drilling/elongating some holes?

From what I have read it's a matter of taking the rod loose and pushing it as far up as it will go on the pedal arm, mark the spot, then push it down as far as it will go on the arm, mark the spot and measure the difference and drill new hole in center of the 2 marks.

[Boog]

I did get a look at the pedal last night and it only has the one hole. Pushing the brake with engine off the pedal goes down to just under 3” from floor board. I’ll separate the master cyl/booster next weekend and check that rod.

[Boog]

As I suspected, the rod between the booster and master cylinder was way short leading to the long pedal travel. I extended it to leave 1/8” gap and its better.

[70STOVEBOLT]

When I added a power booster to my ‘70 with manual drum brakes, I used the pedal rod that came with the booster and just installed it and carefully bevy the brake lines. There was only slight adjustment needed on the pedal rod to take out any slop. Been running it that way for over ten years. 11” Bendix booster.

[davischevy]

After I put disc brakes on the rear of my 55 210 I had no pedal. I had to move the rod up 1" on the pedal and that fixed it.

[Boog]

That 55 doesn't have the same type of brake rod linkage as these trucks does it?