1969 Manual Brakes to Power Brake Conversion - Clarification
 

I see several posts on the Manual to Power Brake conversion - but I am unclear on a few issues.

Please do not insert/suggest topics of Hydroboost. :)

IF I understand correctly, here are the differences:

PARTS Required:
1. PB has Power Booster (obviously)
2. PB has different Master Cylinder (1 1/8" Bore rather than 1" Bore)
3. PB has different stop light switch bracket (it is simply a longer bracket).
4. PB has shorter brakes lines (beacause the master cylinder will be more 'forward' in the engine compartment)
5. PB has vacuum hose/connections (obviously needs vacuum supply now)
6. PB has different gasket at firewall (it is larger and rectangular rather than diamond shape w/round edges)
7. PB has 1 gasket and 1 seal (both round) between the Master Cylinder and the PBooster (rather than a 'boot' on manual brakes). This seal goes around the circumference of the bore and evidently almost never included in replacement M/C's and is suggested by a forum member to not be necessary, although he had his.

ALTERATIONS Required:
A. PB requires an eggshaped hole in firewall (as Pbooster sits lower than manual master cylinder))
B. PB requires the 2 lower weld nuts on the pedal bracket to be drilled out or removed (so they can receive the PBooster studs)
C. PB requires the 2 upper holes to be relocated higher (drill both firewall and pedal brace)
D. PB uses same pedal arm and pedal arm bracket
E. PB requires Clevis (U-shaped bracket) to be relocated from top hole in pedal to lower (old stop light bracket) hole.
F. PB requires stop light bracket to be relocated (& replaced w/longer bracket) from lower hole in pedal to upper hole.
G. PB requires the shoulder on the PBooster rod to be directly connected/torqued against the clevis (preventing any adjustment at this point as in manual brake rod)

Here are my questions/confusion: Answers in Blue
There is discrepancies on what holes to use, to drill higher/lower, cut off welded nuts, etc. See B and C above

Obviously the brake pedal housing HAS to stay in the same position. Yes I believe the pedal housings are identical on each model (aside from welded nuts being removed). Yes If this is the case, the lower welded nuts (on the brake pedal bracket) need cut off. I understand you can do either - but I ground mine off smooth. There is an OEM rectangular cut-out in the reinforcement behind the firewall that looks like it would allow for the upper booster studs to enter about 1/2" HIGHER. Correct

If you use the upper OEM holes from the Manual system as a basis (which is suggested in one of the articles), the lower holes you drill to accommodate the lower Pwr Booster studs will not go through the inner brake pedal bracket. Do not use the upper holes as a basis This means the lower booster studs are only supported by fiberglass. Which is incorrect and locates the PBooster too low If you use the lower OEM holes from the Manual system, you would need to cut off the weld nuts... Or grind them off and now the upper Pwr Booster studs will need NEW holes drilled 1/2" ish higher and THEY would go through that rectangular OEM cut-out in the upper area of the Brake Pedal bracket. Correct The removal of the lower welded nuts on the brake pedal would make sense to allow the Pwr Booster studs to come through. That's the correct way and what I did. But I ground teh nuts off - it makes a much cleaner mounting method.

So (if I understand correctly)... if one were to pursue this conversion, the items REQUIRING major INITIAL work are to the brake pedal bracket itself and the firewall. Yes On the brake pedal bracket simply cut off the lower OEM welded nuts then drill 2 new upper holes in the brake pedal bracket about 1/2"ish higher. Yes Then on the firewall, drill the center hole larger into an eggshape, using the interior reinfoircement as a guide. Yes Then drill out 2 new holes in the firewall to match the new upper holes that were drilled in the brake pedal bracket. The method of drilling holes in the pedal bracket works better than drilling holes in the fiberglass first....that is, if the bracket is not in the car. Once the holes are drilled in the bracket, and you re-install it.. drilling the holes is easy with a pilot hole and wallowing with adremel to perfect size/location. This method works for the creating the larger PBooster hole in teh firewall.

On the eggshaped hole - is there a need to re-glass the hole - or what did the factory do? Need input - as I did not glass it in...nor the 2 manual master cylinder holes I would assume that the manual brake master cylinder hole was precast and when a power brake option was selected the factory wallowed the hole out? Need input Oh - I guess the Manual brake bolt holes that held the master cylinder would need glassed in??? I did not

On they rod adjustment and mounting to the pedal itself, I need to re-read on those items.

I will update above as this thread moves forward.

Here are some reference links:

Zip 69 Power Brake Conversion KIT
1971 Power Brake Conversion
Gator79's Manual to Power Brake Conversion
rg70Vette's Wanting to Add Power Brake Booster to 70 Vette
Kaiserbud's Power Brake Conversion
My Old Post I forgot about...quit laughing

Hi KB,
As usual I looked at the AIM for the PB option. There's nothing that indicates the firewall needs any modification.
The spot for the 2 lower bolts on the PB booster has (on a manual brake car) 2 bolts that go through the firewall to 2 nuts. It looks to me as though the 2 lower bolts on the booster go through those same two holes and get the same 2 nuts.
That's all I have !
Regards,
Alan

The tech drawings at ZIP, that your link leads to, make the change seem quite straight forward.

Thanks Alan

I agree the Zip pic is pretty straight forward as far as parts and assembly, but it does not show mod details. :thumbs:

Also, I think you are correct that the lower two studs from the PBooster should go through the same lower 2 holes on the Firewall, but........in the AIM on pg J187 for manual brakes, you can see that the upper holes have carriage bolts from the inside with a HHnut on the master cylinder/engine side (as mine did). The lower 2 holes are secured by bolts from the engine side that go into the OEM pre-welded nuts on the brake pedal bracket (as mine did). On pg J353, the power booster shows its own 4 studs penetrating the firewall and thus would have to have the lower 2 weld nuts removed... ????:bigears

Hi KB,
Ah...... there's the rub!!!
I was thinking the 2 lower nuts were loose and thus would work on the booster's 2 lower mounts.
As usual I really only know about one car (No PB).
Good luck!
Regards,
Alan

I’m not sure how your car is, but on my ’69 the two lower bolts were not hard to remove. I had to remove them going from manual to hydro boost it should be the same for you.:thumbs:

The lower two holes are in the same position. I wouldn't remove the weld nuts, just drill out the weldnuts as suggested in the Gator 79 post and drill to the other dimensions specified in the same post.

Adjusted numbers and added new items above.

Need info: The Pwr Booster has a rod of its own that protrudes from the backside of the booster to the pedal. I am assuming the old Manual Master Cylinder rod (from pedal to master cylinder) needs to be removed and not used anymore? .,.... and just keep the clevis only? Correct


If that is the case - the Pwr Booster rod only has about 1/4" of threads with a hexhead nut molded into the rod. I always thought the adjustment was required at that point - See G above but it looks as though the Pwr Booster rod will go into the clevis all the way. No adjustment. See G above

In fact - if that is correct - then I could actually install the clevis on the Pwr Booster, rather than the pedal - that way - all I have to do is rotate the clevis/rod to the pedal and 'clip' it in. That is correct

Oh - for you Original Power Brake guys - are the 2 unused Manual brake holes for tha Manual Master Cylinder glassed in? ...or do you have 6 holes in the firewall? Still need input

The AIM shows on page J354, (View E) that the clevis should be torqued against the shoulder of the PBooster push rod. :thumbs:

I was doing more research on this for details and noticed one of my old threads... :leaving: ... so now that we all know I am getting senile.....

Gator and crew gave me a good overview of some of the details here:
Gator and crew Input

I will continue this thread as I believe the lists above will be advantageous. :flag: and also post pics.

I am still looking for information on how to adjust the rod on the Master Cylinder side. Still need input

If memory serves, mine turns. The chassis service manual might mention the adjustment.

:)

My conversion is almost complete - will post pics later.

Although I felt the adjustment on the rod to the master cylinder was aceptable, I will still have it verified when I get roadworthy for alignments, etc. I hope someone with good experience will comment on the procedure.


So - I still need input onm these items:

1. how to adjust the rod on the Master Cylinder side.
2. Original Power Brake guys - are the 2 unused Manual brake holes for tha Manual Master Cylinder glassed in? ...or do you have 6 holes in the firewall?

Question, do the studs from the booster go through the firewall or is there a bracket in between? I see that there are Booster brackets for sale.....

My take on this is that the holes for power brake master cylinders do not line up with any holes for the manual brakes. I have heard people trying to use them but they are not in the same locations. THe manual master cylinder holes are lower than the top holes for the power brake master cylinder.

I want to do the opposite, switch from power brakes back to manual....so if you want to sell any of the stuff you are removing, please PM me.

Not really anything much to sell.....old MS, connecting rod and switch bracket. Not sure what to do now.....drill new holes? Lots of possible issues with that without a template.