Pedal Ratio

Has anyone ever connected the power booster with the power master (1-1/8") to the top hole (for a manual master) in the brake pedal?
And if so, what were the results?
Can speculate, but would like some real world info.
TIA

No but I would assume lighter pedal feel, excessive travel....

Twin_Turbo said:

No but I would assume lighter pedal feel, excessive travel....

Click to expand...

I played with that location a bit on the motor home, but forget what position it is in now...and yes TT is obviously correct.... I didn't even notice any other position for the vette......:drink:

The pedal ratio for a C3 is:

5.40:1 for manual and 3.38:1 for power brakes

So you would get an increase in travel and hydraulic pressure.

Well the way I see it
Less pedal travel
More foot pressure required all for the same line pressure.
(Trying to look at this for desired results; pedal feel)

The power brakes are very soft for all these era gm cars and I'm just surmizing that they are "overboosted" and short of finding a weaker booster, switching ratios should have almost the same effect or at least aim in the right direction.

Of course calcs and test results always don't match so, that is why I wanted some feedback under actual trial.

Any more thoughts?

010752 said:

Well the way I see it
Less pedal travel
More foot pressure required all for the same line pressure.
(Trying to look at this for desired results; pedal feel)

The power brakes are very soft for all these era gm cars and I'm just surmizing that they are "overboosted" and short of finding a weaker booster, switching ratios should have almost the same effect or at least aim in the right direction.

Of course calcs and test results always don't match so, that is why I wanted some feedback under actual trial.

Any more thoughts?

Click to expand...

I fought a long battle with my brakes on this '72, gave up and went hydroboost....stops on dime 9 cents change...and that's with a direct changeover not touching the brake hydraulics....A-B comparison...the feel is totally different...after 7? years as a DD I was used to vacuum sux, first trip my nose went through the wheel....almost impossible to do with stock booster.....

I tore the booster apart to see why/what, it held vacuum nicely as when popping the check valve out, there was a goodly inrush of air....as had been done before over the years....so I could not manage to twist it, and so destroyed it by prying the tabs apart...inside everything looked fine, no water, no fluids, dry as bone,...so I start looking for troubles, and can't find any...everything LOOKED fine....except I noted one thing....a spring about a inch long, inch diamater made from valve spring wire on steroids.....it went between the output pin that looks like a large nail, and the input shaft, similar going the other way.....I looked at the diagram I scanned from the overhaul manual I have from the era, and sure enough, it's there....why I dunno, but trick is, when that spring does give, surely the pedal will travel further....so honestly I write it off as a design flaw....but that HB unit on there for some 5? years now and been fine....very consistent....

:gurney::drink:

Gene, I have oem HB on a 1 ton Chevy for the last 25 years or so.
The empty vehicle weight is over twice that of the vette and even when new the 1 ton had and still does have a little spongy feel to the pedal. Even when you lock them all up you can go further with the pedal, not as mushy as a stock pb vette but similar to other modern vehicle pb.
On a Vette, the HB is just grossly overpowering, I assume due to the weight difference. Did a setup on a vette a few years ago, so am familiar. I'm not knocking the HB on a vette, but just want a simpler route with a wider range of modulation.

The best brakes I've found outside of Mercedes has been on my wife's Caravan, oem 4 wheel disc setup (not too common). Free pedal travel is about 1/2", then pretty firm, with a little bit of sponge, with lockup at less than 2". There is still some sponge left in the pedal, can force it down another 1-1/2" for no gain.
IMO, it is at least as good or better than HB in the 1 ton. Very easy to modulate.
Copying that is really my goal.

Also have a HD 3/4 ton van which has oem 1 ton booster brakes.
This has a very spongy pedal, but activates at approx 1" down and will throw you into the windshield, and also the pedal will go down much further than needed. Very similar to oem vette pedal with less travel.

The stock vette booster has approx 1/2" of free play at first, probably to open the control valve (atmosphere) and then you have the movement in the master to move the seal past the compensating ports of about another 1/2" at the pedal. This play, you can't get rid of.

Newer vehicles just seem to have the booster and hydraulic system more accurately matched than the old GM.

Have you considered the "quick takeup" master cylinder? looks like it might work to decrease pedal travel and open the booster lave quicker (I think).

http://www.pozziracing.com/quick_take_up_master_cyl.htm

I dunno guys, I LOVE my HB '72 vette, and it was a huge improvement in the motor home too.....

I always found pedal travel being WAY too far on all my GM vehicles over the decades....but when getting this vette I was shocked that everyone thought the pedal travel was 'normal'....they all felt the same, every shark I drove seemed the same....3" or more to get lockup pedal really at end of throw on the floor type stuff....that's a problem IMO.....

and all the kraziness of trying to fix it was cured with HB.....MY opinion is that I finally have a GM car I feel confident will actually stop.....when I say, not when it's lazy ass get around to it.....

:crap::gurney::banghead:

BBShark said:

Have you considered the "quick takeup" master cylinder? looks like it might work to decrease pedal travel and open the booster lave quicker (I think).

http://www.pozziracing.com/quick_take_up_master_cyl.htm

Click to expand...

Most of the later ones are are for use with the zero drag calipers and some even electric. Something to consider, if I find no satisfaction with the other.

mrvette said:

I dunno guys, I LOVE my HB '72 vette, and it was a huge improvement in the motor home too.....

I always found pedal travel being WAY too far on all my GM vehicles over the decades....but when getting this vette I was shocked that everyone thought the pedal travel was 'normal'....they all felt the same, every shark I drove seemed the same....3" or more to get lockup pedal really at end of throw on the floor type stuff....that's a problem IMO.....

and all the kraziness of trying to fix it was cured with HB.....MY opinion is that I finally have a GM car I feel confident will actually stop.....when I say, not when it's lazy ass get around to it.....

:crap::gurney::banghead:

Click to expand...

I get lockup about halfway to the floor, I just want it a little firmer.

010752 said:

BBShark said:

Have you considered the "quick takeup" master cylinder? looks like it might work to decrease pedal travel and open the booster lave quicker (I think).

http://www.pozziracing.com/quick_take_up_master_cyl.htm

Click to expand...

Most of the later ones are are for use with the zero drag calipers and some even electric. Something to consider, if I find no satisfaction with the other.

mrvette said:

I dunno guys, I LOVE my HB '72 vette, and it was a huge improvement in the motor home too.....

I always found pedal travel being WAY too far on all my GM vehicles over the decades....but when getting this vette I was shocked that everyone thought the pedal travel was 'normal'....they all felt the same, every shark I drove seemed the same....3" or more to get lockup pedal really at end of throw on the floor type stuff....that's a problem IMO.....

and all the kraziness of trying to fix it was cured with HB.....MY opinion is that I finally have a GM car I feel confident will actually stop.....when I say, not when it's lazy ass get around to it.....

:crap::gurney::banghead:

Click to expand...

I get lockup about halfway to the floor, I just want it a little firmer.

Click to expand...

Over the years, that's one of the things that bug me about these sharks, given that most of the guys are competent mechanics, given that so much of this 'brake/steering/handling/shifting' type stuff is so subjective, the one item that should be easily duplicated on these cars would BE pedal travel, yet from what I read, it's not the case....damn if I know why....

but one curious question, I have the rear m/cyl port going straight to the rear line, and the front section of the m/cyl directly to the front brakes....

by rear port, I mean closest to the booster, if one would be looking at rebuilding the m/cyl they may say the section furthest forward in the car would be the 'rear'....thought I would cover THAT little possible semantic problem now too.....