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Factory Manual Brakes converted to Hydroboost???

 
Old 01-18-2019, 12:04 PM
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JohnRR
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Default Factory Manual Brakes converted to Hydroboost???

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?

As always, I appreciate all the help,
John
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Old 01-20-2019, 12:16 AM
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jyounane
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Hi, There will be others here with more experience, however I'll kick off the replies. The pedal box is the same for manual and power brakes but the clevis connection for the booster uses the lower hole on the brake pedal, and the upper hole (previously for manual brakes) is used for the striker for the brake light switch. The firewall has to be opened up for the booster which mounts lower than the original master cylinder. While I've never installed a hydroboost, perhaps it is designed to replace the booster in the power brake system, so you might have to make the changes needed to convert to power brakes which will lower the master cylinder. You will need the correct master cylinder for power brakes, correct striker for the brake light, and perhaps the correct clevis to install on the hydroboost.

I hope someone will chime in with any corrections.


Joe
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Old 01-20-2019, 08:13 AM
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Pedal boxes are different. Look at the pictures in the thread below. It will explain it all. You could use a power brake pedal box for manual brakes with the adapter I use and is pictured in the above thread. If the hydro boost uses holes the same as a stock booster, you will not be able to use your manual brake pedal box. Easy change to make though. As said above, just make the required hole in the firewall, get a power brake pedal switch striker, master cylinder, and change the hole in the pedal. And, of course, getting a power pedal box. I believe Gordonm, in that below thread, has a nice restored power pedal box for sale in parts. You could do the same to yours and sell it. Now I must also say, I love the feel of well done manual brakes. Much better than any power assist I have driven. If yours isn’t leaving you feeling this way, maybe something else is going on.

https://www.corvetteforum.com/forums...onversion.html

Last edited by 69ttop502; 01-20-2019 at 08:28 AM.
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Old 01-20-2019, 09:06 AM
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As said above the pedal boxes are different. Not only the location of where the Clovis is attached but the actual location of the holes. If you order a new kit you have to specify if you have a PB car or a manual brake car. They will send you different mounting kits depending on which pedal box you have. If you are putting it together yourself you wil have to figure out the mounting location. I had a manual brake car and bought one of the manual brake HB kits years ago. I have since switched over to vacuum assist brakes but I changed the pedal box over to a PB pedal box. SO to the above post I have used the restored PB pedal box but I have a manual one in my basement.

Last edited by Gordonm; 01-20-2019 at 09:07 AM.
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Old 01-20-2019, 07:02 PM
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Hi All, Thanks for the correction on the differences in pedal boxes. I believe the manual pedal box can be modified in-car by removing the studs and drilling out the lower weld nuts as well as possibly new holes for the upper booster studs. The hole in the fiberglass firewall can be opened up as shown in the threads above. Can you confirm this is true?

Joe
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Old 01-20-2019, 08:16 PM
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Yes you can certainly do it that way Joe.
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Old 01-20-2019, 08:50 PM
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John don't just do this the same as every one else has .
look at modifying the hydro boost mount to fit what you have.
you can used the four original bolts in the firewall to mount the booster .
The bottom studs and the two original master cylinder mounting holes.
You will have to drill a new hole on the pedal to do it this way.
Or use the bottom hole on the pedal , depending on how fare you move the unit down the firewall
Bfit
ps The pedal boxes are the same pressing, just punched differently and finished off for the different applications. also depending on what year you have there are a few variations

Last edited by bfit; 01-20-2019 at 08:54 PM.
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Old 01-20-2019, 09:26 PM
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Originally Posted by bfit View Post
John don't just do this the same as every one else has .
look at modifying the hydro boost mount to fit what you have.
you can used the four original bolts in the firewall to mount the booster .
The bottom studs and the two original master cylinder mounting holes.
You will have to drill a new hole on the pedal to do it this way.
Or use the bottom hole on the pedal , depending on how fare you move the unit down the firewall
Bfit
ps The pedal boxes are the same pressing, just punched differently and finished off for the different applications. also depending on what year you have there are a few variations
I think I'm beginning to understand all this, and please correct me if I'm wrong. It appears to me that I will need to do the following:
- Enlarge/lower the big hole in the firewall so that the HydroBoost pushrod will line up with the lower hole in the brake pedal.
- Install a new Brake Light Switch Striker in the upper hole on the brake pedal.
- Drill new holes in the HB Faceplate and bolt it on using the four factory bolts on the firewall.

Yay or Nay?

John
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Old 01-20-2019, 10:03 PM
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Default HydroBoost Pic

Here's a picture of the HydroBoost unit I have.

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Old 01-21-2019, 09:06 PM
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Hi,
I thought you had this unit pictured below and my comments relate to drilling etc. to accommodate this to fit where a booster would go.
Is your "backing plate" from Hydroboost or custom?

Joe
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Old 01-22-2019, 05:57 AM
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Default Box

Pedal box


check the top two bolts they are the original non boosted master cylinder location
If any one is interested the pressure switch mounted at boosted flange, cuts power to the fan relay circuit when the engine stops

the makes on the pedal box show manual master cylinder mount position


centre hole is an extra I drilled , I did not use this position

I got the photos up upload finally
if you look at the booster mount above you will see that the top bolts are the original location for the manual masted cylinder .
there is no need to remove the original studs it only make fitting the hydro boost mode difficult
Bfit

Last edited by bfit; 01-22-2019 at 08:56 PM. Reason: ad photos
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Old 01-22-2019, 06:46 AM
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Back to the pedal box question. They are the same. the fiberglass hass to be modified and studs removed butbthe box is the same. I converted to PB and its pretty simple. Its not economically feasible for a car company to make 2 different boxes for brakes when they already did it for transmission types.

https://www.corvetteforum.com/forums...s-on-68-a.html
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Old 01-22-2019, 08:21 AM
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Pedal boxes are different. This pic is from another thread from Richard 454. Studs from manual box on left are lower than top holes on power box on right. No weld nuts on power box. Second pic is firewall differences.




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Old 01-22-2019, 08:56 AM
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Default More info from Oz.

Originally Posted by jyounane View Post
Hi, There will be others here with more experience, however I'll kick off the replies. The pedal box is the same for manual and power brakes but the clevis connection for the booster uses the lower hole on the brake pedal, and the upper hole (previously for manual brakes) is used for the striker for the brake light switch. The firewall has to be opened up for the booster which mounts lower than the original master cylinder. While I've never installed a hydroboost, perhaps it is designed to replace the booster in the power brake system, so you might have to make the changes needed to convert to power brakes which will lower the master cylinder. You will need the correct master cylinder for power brakes, correct striker for the brake light, and perhaps the correct clevis to install on the hydroboost.

I hope someone will chime in with any corrections.


Joe
Chiming in. My '74 coupe with PB now has a Hydroboost. I mounted it upside down so that the pressure reservoir is on top and the inlet and outlet ports are underneath. This gives a neater look. The hardest part was getting the nuts undone in order to remove the pedal box and modifiy it to suit the HB. I also used a Holden VZ Commodore master cylinder that has an inbuilt prop. valve. I then removed the factory brass distribution block and ran a quarter inch line down to the brake line with a female/female adapter.

Hope this helps.

Regards from Down Under.

aussiejohn
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Old 01-22-2019, 12:57 PM
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Originally Posted by 69ttop502 View Post
Pedal boxes are different. This pic is from another thread from Richard 454. Studs from manual box on left are lower than top holes on power box on right. No weld nuts on power box. Second pic is firewall differences.
They just added or removed studs, welded on a nut or not. easily converted to the box you need



yes same box, knock out the studs, drill holes in fiberglass. Even has the same pedal, with 2 holes. One is manual, one is power. Check the AIM

Last edited by Rescue Rogers; 01-22-2019 at 01:02 PM.
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Old 01-22-2019, 01:01 PM
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Those studs are not in the same place as the upper holes in the power box. Need to drill new holes and drill out weld nuts. Unless the 69 boxes are different. I had one of each side by side and the holes were definitely different as in the pics above. Manual pedal holes are 1/2 inch below top booster holes as seen in bottom pic. Unless I am seeing something totally wrong, boxes are different, or are at least configured differently, in 69 anyway.

Last edited by 69ttop502; 01-22-2019 at 01:05 PM.
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Old 01-22-2019, 01:07 PM
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Originally Posted by 69ttop502 View Post
Those studs are not in the same place as the upper holes in the power box. Need to drill new holes and drill out weld nuts. Unless the 69 boxes are different. I had one of each side by side and the holes were definitely different as in the pics above. Manual pedal holes are 1/2 inch below top booster holes as seen in bottom pic. Unless I am seeing something totally wrong, boxes are different, in 69 anyway.
no kidding. it's the same box. Read Willcoxs post I had in the previous post. GM just put posts in or weld nuts. Just change it it to the configuration you need.

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Old 01-22-2019, 04:42 PM
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Hydroboost mounted to firewall. Brake lever hole I’m middle I drilled
[img]blob:https://www.corvetteforum.com/a23cf6...1-9d7446a4d78a[img]blob:https://www.corvetteforum.com/529e31...a-28093f5775db

Last edited by bfit; 01-22-2019 at 04:43 PM. Reason: Photos not showing
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Old 01-22-2019, 04:54 PM
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Originally Posted by bfit View Post
Hydroboost mounted to firewall. Brake lever hole Iím middle I drilled
[img]blob:https://www.corvetteforum.com/a23cf6...1-9d7446a4d78a[img]blob:https://www.corvetteforum.com/529e31...a-28093f5775db
I couldn't get either link to work...
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Old 01-22-2019, 04:56 PM
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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.
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