Power to Manual conversion questions

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67ValSig_UK

67ValSig_UK

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Hello,

Am am looking at converting my brakes from power to manual. The car is a 67 Valiant with 170 slant 6 and factory power front disc brakes.

This is temporary measure to give me time to find a replacement booster or get mine re-manufactured. Therefore I don't want to modify my original hardware/lines/etc so that I can directly revert to power brakes when the time comes, although I may be running the manual set up for a couple of years before I am in a position to revert to power...

From what I gathered, I need:
  • a new "disc-drum" Master Cylinder with 15/16" bore (smaller bore to reduce pedal effort required)
  • a different MC push rod, probably an adjustable one
  • new brake lines from MC to front distribution block/tee
  • a new MC gasket (plastic type used on all 60-76 A/B/E Bodies)
Then it should simply be a case of removing the original MC/booster/bracket assembly and bolting the new MC directly onto the firewall. There seems to be differences at the firewall between manual and power brakes. The bracket and MC bolt patterns are different for a start so I assume I will need an adapter plate (I can get one manufactured locally). So first question: are they any other modifications that I need to plan for in that area?

These are the bits I am planning to get:
  • Right Stuff Detailing DBMC15 Master Cylinder, 15/16" Bore, Front port: 9/16 in.-18 threads. Rear port: 1/2 in.-20 threads.
  • Mopar Performance adjustable push rod P4510640
  • Classic Industries MC Gasket MD2092

Manual%20Brakes%20Hardware.png


Anyone used these? Are they correct and suitable for what I am trying to do?

Many Thanks in Advance.
 
I've done this several times on Dusters/Darts. The only mod I do is get a manual brake push rod. I use the same master cylinder. Granted, these weren't '67's.
 
I would go with the DrDiff master set up. I used the cast iron one and it ruined the new paint on my firewall.
 
Sedanman said:
I would go with the DrDiff master set up. I used the cast iron one and it ruined the new paint on my firewall.
Click to expand...

Thanks Sedanman. I quite like the other MC because it looks original. Does that mean the MC is bolted directly on the firewall without any gasket to protect the paint?

By the way: do you still have these red interior parts I was interested in?
 
Sedanman said:
It still has a gasket. I still have the parts
Click to expand...

Does the firewall need to be modified? I have never removed the booster so have no idea what things look like underneath. The only clue I have of the differences is this:

Firewall%20Plate.png


Regarding the interior parts I am still interested. If you PM me with a price etc
 
You can use a factory manual brake pushrod. It does not need to be adjustable.
I don't know the parts availability in the UK, but see if you can get a rebuilt or new power brake MC for a 73-75 disc brake A body but run it MANUALLY. 7/8" bore. It's all a direct bolt in.
You may have to buy new pre-bent brake lines, bend and flare new ones from scratch, or rebend the ones you have.
There is a white foam gasket that goes between the MC and firewall. They are reproduced or make your own.
I predict that after driving the car this way you won't go back to your power brake setup.
There really is no reason to run power brakes on an A body unless you are physically limited or are seeking a 100% correct restoration.
 
Last edited:
The firewall plate shown in post 6 is probably a B-body only thing. My 64 & 65 A-bodies mount the MC directly on the firewall, as does the power brake stand-off brackets. My 1965 C-body has such a plate. Perhaps they list for A-body for somebody repairing rust damage.

You can probably use the same MC. Check rockauto. For most years, the manual and power MC's had the same bore ID. When they differ, the power MC often has a SMALLER bore. Why? Consider the lever arm ratio in the stand-off brackets. You can probably bend your existing tubes to fit the MC directly on the firewall. You will need a manual rod to the pedal. Many manual MC's come w/ a brake rod, at least for my years (see rock).

But, if you don't mind resto-mod, you can buy a new booster w/ brackets and MC for ~$140 on ebay. Most look like a GM style booster that can probably be replaced easy in the future.
 
Many thanks to all for the very useful answers and info.

Parts availability in the UK is almost non-existent. I have to get everything shipped, that's why I need to make doubly sure I order all the bits and that they are right. I have quotes for remanufacturing of my booster, but even then temporary manual conversion is necessary as I don't have the option to be without brakes while waiting.

I did consider one of the many aftermarket booster+master cylinder kits sold for power brake conversions, but they claim to bolt on directly if you had factory manual brakes but that a firewall modification is required if you had factory power brakes. It seems that they are just not specific enough with regard to models and factory power brakes set-ups.

These illustrations are taken from a 1967 shop manual and show two very different factory power brake assemblies.

If the booster canister is bolted directly onto the firewall, then a plate is used and there are firewall differences between manual and power brakes.
Power%20Brake%20Assembly%202%20small.jpg


If the booster canister comes with a bracket assembly, then no plate is used and there is no firewall difference between power and manual.
Power%20Brake%20Assembly%201%20small.jpg


Finally, regarding the Master Cylinder bore size: a smaller bore mean less pedal effort but longer pedal travel, so it comes down to driver preference. My factory MC is 1" and can be used in a manual set up, but I can also try a smaller bore if I want.

Many thanks again for the replies!
 
The stand-off brackets of the 2nd drawing raises the booster/MC up so it clears the left valve cover of V-8 small-block engines. All slants I have seen in the U.S. use the same brackets, though not sure that height was required. The plate of the 1st drawing still has the lever assembly, so also moves the booster up. That looks like a simpler solution, so wonder why U.S. cars didn't use it. Probably had to do w/ interference in our left-drive cars. There were many clever adaptations in right-drive cars for the Commonwealth market. One Malaysian owner posted photos of his interesting 1964 slant engine bay. BTW, Chevy cars were even simpler. Instead of a lever setup, they just angled the brake rod upward to get to the booster, also at a higher centerline.

Most people prefer a 15/16" or 7/8" ID MC bore for manual brakes, especially with front disks. I used an MC from a 95-99 Plymouth Breeze w/ ABS (2 ports) on a 2-4 bolt adapter plate, but many choices. Many here use one for a late 80's Dodge truck.
 
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