Brake pedal too low after manual drum to power disc conversion

[G_Money]

Hi guys. I’m wondering if anyone has any thoughts on this. Just did a Pirate Jack 4-wheel power disc conversion on my ‘66 Belvedere. Installed the booster and brake pedal linkage and the brake pedal is too low and doesn’t engage with brake light switch. My buddy thinks we need to cut and extend the brake pedal connecting rod, but it doesn’t make sense to me that the parts in the kit wouldn’t be the correct length. Here’s a picture…

Thanks for any ideas!
Greg

 

[carterafb]

Is the rod that goes into the Booster adjustable for length.

 

[Kern Dog]

The brake light switch is adjustable but Maybe you're just outside of the range?
I'm not sure why that is possible but I've dealt with this before. My idea was to cut the pushrod, spread the two halves apart and weld in a section in between. My plan was to get the pedal sitting where I wanted it and take a measurement.
Instead, a FBBO member had a better idea:

The man took this in his lathe and put male threads on one side and female on the other.

This meant taking two to make one.

I ended up extending the rod about 5/16" so I bridged the difference with washers. I used Red Locktite too.

The same could still be done by cutting and welding. I have a manual transmission and I wanted the pedals to be at the same height. If I had an automatic, I may have just left the whole thing alone since even with the shorter rod, there was still adequate travel from the pedal.

 

[steve340]

I believe the power disc cars had a physically lower pedal height than a manual drum brake car would have needed.
I extended the rod as Kern Dog has shown on my cars by cutting and welding in a piece of metal.
I like the pedal being that bit higher and I think the brakes actually worked a little better.

 

[gtx6970]

Odd, I just did a power drum to power disc conversion on a 66 Coronet and had no problems with the switch hitting the linkage

 

[YY1]

The rod that actually goes into the cup in the MC bore should be adjustable.

 

[G_Money]

Thanks for the replies everyone. I would have thought that it should be a plug ‘n’ play part if it’s a replica of OEM. But maybe there are differences in either the booster rod or the manual brake pedal set up. Or maybe some cars are just different? It’s also hard to believe there’s not an adjustable part available. Looks like it’s gonna be a cut and weld project! Will post some pics when I’m done.

Thanks again!
Greg

 

[steve340]

My cars are both factory power disc brake cars and I always felt the pedal was physically too low.
The brakes always worked OK but I felt it went too close to the floor.
I extended the rod by 8 mm and raised the pedal on both cars. Feels good now and not hard to operate.
Make sure you clamp the pushrod to a steel plate to keep it in alignment and straight while welding.
PM me your email and I can send you a diagram of the modification if you want.

 

[68 Sport Satellite]

My cars are both factory power disc brake cars and I always felt the pedal was physically too low.
The brakes always worked OK but I felt it went too close to the floor.
I extended the rod by 8 mm and raised the pedal on both cars. Feels good now and not hard to operate.
Make sure you clamp the pushrod to a steel plate to keep it in alignment and straight while welding.
PM me your email and I can send you a diagram of the modification if you want.

before you extended the rod for your car, was it already touching the brake switch? Mine already contacts the switch, but I would prefer the pedal a bit higher.

 

[steve340]

Yes the brake switch was working fine before and after the mod.

 

[G_Money]

@steve340. Thanks I’ll PM you my email.

Oh, Another question regarding my picture I posted above? Do I have the notch in the Z bracket facing the correct direction? The manual for the booster I bought shows it facing the direction I have it… but the FSM and TheRamManInc says it goes towards the booster. Could this make a difference?

 

[Geoff 2]

Make sure there is no air in the system. This may not be apparent with manual brakes, but manifests as more pedal travel with boosted brakes because the booster is providing more 'push'.

 

[steve340]

I am not sure if that bracket would make a difference.
IMO if you go with the factory manual you are unlikely to be wrong.
I will email you my diagram.

 

[MWbirdLOVER70]

I believe the power disc cars had a physically lower pedal height than a manual drum brake car would have needed.
I extended the rod as Kern Dog has shown on my cars by cutting and welding in a piece of metal.
I like the pedal being that bit higher and I think the brakes actually worked a little better.

I would think possibly with the manual brakes the factory did this for more pedal leverage?

 

[MWbirdLOVER70]

Thanks for the replies everyone. I would have thought that it should be a plug ‘n’ play part if it’s a replica of OEM. But maybe there are differences in either the booster rod or the manual brake pedal set up. Or maybe some cars are just different? It’s also hard to believe there’s not an adjustable part available. Looks like it’s gonna be a cut and weld project! Will post some pics when I’m done.

Thanks again!
Greg

I’ve heard there are longer push rods available out there in A/M available for purchase

 

[Archie Duiker]

Hi guys. I’m wondering if anyone has any thoughts on this. Just did a Pirate Jack 4-wheel power disc conversion on my ‘66 Belvedere. Installed the booster and brake pedal linkage and the brake pedal is too low and doesn’t engage with brake light switch. My buddy thinks we need to cut and extend the brake pedal connecting rod, but it doesn’t make sense to me that the parts in the kit wouldn’t be the correct length. Here’s a picture…

Thanks for any ideas!
GregView attachment 1744707

The brake pedal is purposely lower with power brakes so you can apply the brakes with your heel still on the floor. That gives you better control for smoother stops. Wouldn't it be easier to rejig the brake light switch so it contacts properly?

 

[MWbirdLOVER70]

The brake pedal is purposely lower with power brakes so you can apply the brakes with your heel still on the floor. That gives you better control for smoother stops. Wouldn't it be easier to rejig the brake light switch so it contacts properly?

I thought those had bracket adjustment because when we swapped mine over my buddy adjusted while I was working outside

 

[GiantRobo]

The brake pedal is purposely lower with power brakes so you can apply the brakes with your heel still on the floor. That gives you better control for smoother stops. Wouldn't it be easier to rejig the brake light switch so it contacts properly?

On my 65 Coronet had the same issue using a 68 disc booster.) I couldn't move the switch bracket close enough. No welder, etc. so added a short L-bracket to the pedal bolt (double-lock washers on the threaded side of the bolt to avoid binding the pedal.) Worked great for the 15 years I daily drove it. Yeah the disc power booster pedal sits much lower.

When I was restoring it, had the local brake shop rebuild the booster with the proper 65 rod welded to the 68 rod. Loved the height much better, and it stopped like no business. Laid 25ft of rubber from the tires if I stomped it. (The wife was not happy with that... )

 

[Kern Dog]

The brake pedal is purposely lower with power brakes so you can apply the brakes with your heel still on the floor. That gives you better control for smoother stops. Wouldn't it be easier to rejig the brake light switch so it contacts properly?

No, there is no legitimate reason to think that the position of the power brake pedal had anything to do with where a driver places their heel. My wife has tiny feet so her heel doesn't touch the floor when pressing any brake pedal. The cars had to be designed for a range of drivers sizes and shapes.
The reason for the lower position in power brake cars is because the pedal travel is much shorter with those systems. Manual brake cars need longer stroke for leverage, power cars have a booster to substitute for leverage.

 

[Ron H]

There’s a brake pedal ratio factor for manual and power brakes, in case you may not have checked this. On my ride, there are two holes in the pedal arm, upper and lower holes for manual or power brake linkage connection. Upper is for manual, lower for power brakes. There is a lot of info on the web about this. With my ‘kit’ it came with a crappy eye-bolt so a friend machined a new one with more adjustment and surface area to contact the brake light switch, similar to what a member posted. I should have re-thunk before getting the kit I bought creating extra hassles, as it ended up, I made the manual brake ratio work with the power brakes getting the pedal height where I wanted it.