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hi John I finally go photo's to upload check earlier post re photo's ( post 11)
Drill your mount to suit the firewall, and use the original studs and bolt locations.
you just have to work out the position where you want the booster to line up with the pedal.
bfit
Thank you Gordonm and 69ttop502.
Your approach is exactly what I followed in converting from manual to power brakes. It retains the geometry and leverage that GM intended. The annotated picture below shows what I did.
However, the OP JohnRR, has shown a picture of the hydroboost he has which appears to have a mounting plate intended to fit where the original manual master cylinder was mounted. The fact that he has hood clearance issues make me wonder whether the unit he has is correct for his 73?
Joe
John the photo above in post 24 is a great pic to show what I have been putting to you.
the square holes are the original top stud holes
the bottom set of holes are the original hole that are used to hold the bottom of the pedal box in place .
Drill you mounting bracket to use those four holes all you need to do is drill or gring the opening for the booster to proud through into the vehicle cab.
the hardest part for you will be adjusting the lenth of the push rod and getting the clevis pin into the pedal shaft.
bfit
ps don’t forget to use a gasket of some sort when mounting the booster ,to prevent water etc leaking into the the foot well
2020 Corvette of the Year Finalist (performance mods)
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Originally Posted by Gordonm
The holes are not in the same location from manual to PB. I just did mine and removed a manual pedal box and replaced it with a PB pedal box. The holes are in different locations. Yes the manual has studs up top and nuts on the bottom and the PB box has just holes but. They are in different locations.
okay... like I said. Drill 2 holes. it's the same box. You DO NOT need to buy a different box unless you want a newer version. The 68 boxes are different from the 69s, etc. But that's a year by year change. No difference in the same year other than studs and holes unless you are going from auto to stick. Those are obviously different.
Last edited by Rescue Rogers; 01-23-2019 at 11:17 AM.
Thanks to everyone for all the good insight to this problem. I'm going to relocate the HydroBoost unit lower by an amount equal to the distance between the two clevis holes in the brake pedal.
I appreciate all the help I've gotten from this forum over the past 10 years; THANKS!
John
I will get you a dimension to the middle of the booster mount from the two bottom holes. which ever way you go about this , those two holes remain a constant.
Bfit
John
I will get you a dimension to the middle of the booster mount from the two bottom holes. which ever way you go about this , those two holes remain a constant.
Bfit
Thanks. That would be most helpful. It would also be a double check for my other method listed above.
John scrib a line 2 7/16’’ from the centre of each bottom hole where they intersect is your centre of booster .
Bfit
Bfit, I'm not sure where the 2-7/16" you referenced is being measured. On the other hand, I took some measurements and scribed some lines on my firewall (see pics).
The center to center distance between the two holes in the brake pedal is 1.43". I feel that this is how much I need to lower the new master cylinder.
The center to center distance between the upper studs and the lower bolts is 2.80".
Therefore, the vertical distance from the lower two bolt centerline and the new master cylinder centerline is 2.80" - 1.43" = 1.37".
I'm feeling pretty comfortable with these figures, but would like some feedback so I don't commit a blunder
Center to center distance of holes in brake pedal = 1.43 inches.
Center to center distance between the upper studs and the lower bolts is 2.80 inches.
2.80" - 1.43" = 1.37". This is the centerline of the new HydroBoost master cylinder.
Bfit, I don't understand the 2.44" dimension that you referenced in the previous post.
Thinking about this , you did well taking that photo of brake lever under the dash.
The photo of the lever with rule looks like 1 1/2’’ centre line between the two holes . Mine measure 1 3/4’’ , I haven’t seen the 1.5’’ lever in my vette’s .
Some thing you can check , there is a metal reinforcement inside side of firewall .
you should be able to fell it through the master cylinder hole.
Fell down the inside of the firewall, if you can feel it, that is the bottom of the hole for the power booster opening .
I have a 79 on the hoist at the moment , I’ll see if I can get a photo of the inside area behind the mount area.
bfit
I'm trying to convert my '73 with factory manual (non-power) brakes to a hydroboost system. The problem is hood clearance. I have since learned that power brake cars have a completely different pedal box and firewall configuration. My question is: has anyone actually converted their manual brake system to a hydroboost? What exactly did you have to do to make it all work?
01-22-2019, 08:06 PM
