Excessive brake pedal travel

[Mheiron]

Hey y’all,

So I have a newly installed brake system on a 69 Charger and the car will stop but the pedal can be pushed to the floor. The brakes start to work when the pedal is about ~1/2 way depressed. The car will stop sharply but the pedal is almost to the floor. I haven’t been able to lock the wheels up so far

I’ve installed a new booster and master, new lines, proportioning valve, etc. I think the system is bled with no air. The master cylinder was for a disc/drum setup which seemed correct

I had a shop rebuild the front suspension and the stock disc brakes. I thought everything was like-for-like but the shop pointed out that the old calipers were 2 cylinder and the new were a single.

Is it possible something in the system is mis-matched? Do I need a master that provides greater volumes than the one I have?

I also installed longer wheel studs so I could run aluminum wheels with modern tires. I also replaced the steering box with a firm feel unit and installed longer pitman arm. The car is much less of a white knuckle affair at highway speed and seems to corner pretty flat. As ‘I mentioned before, it’s wonderful having the stock AC working.

Do the wheels look OK or are they to much?

 

[Don Frelier]

Are the rear drums adjusted so the drum drags slightly on the shoes?

Does the pedal come up if you pres it several times, " pump it"?

 

[Mheiron]

The rear drums are adjusted and drag slightly. I don’t think pumping the brakes really change anything at least not noticeably.

 

[Don Frelier]

The rear drums are adjusted and drag slightly. I don’t think pumping the brakes really change anything at least not noticeably.

Maybe a brake pushrod length issue?
Too short.

 

[Unkle Krusty]

I have quite a bit of pedal travel, but the Tukvan stops. All new bits. I will watch this thread for ideas. Originally I thought bleeding was the issue. I also heard the master cylinder can fail. That is also new.

 

[Black_Sheep]

Do you know the bore size of the master cylinder? The smaller the bore, the more travel it requires to displace the same amount of fluid. I think B-Body power disc brake master cylinder bores are around 1" - 1.125". How far is the pedal from the floor to start with? Is the brake booster pushrod to master cylinder clearance adjusted correctly? Is the pedal ratio correct for a power brake car? It could be a lot of things, or a combination of things...

FWIW, I like the wheels!

 

[Kern Dog]

That is a good looking car. I like the overall appearance of it.
The brakes should engage well before the pedal reaches the floor. When you press the pedal for the first inch or so, is it spongy or soft? Does the pedal feel get progressively harder the further that you press? If so, that is often due to air still remaining in the system.
Sometimes, the wheel bearings are not snugged up right so the disc rotor moves around a bit when the calipers try to clamp down.
If the first half of pedal travel feels like nothing is there, the pushrod in the booster itself probably needs to be adjusted.
See the threaded nub in between the 4 mounting studs here?

That is adjustable. In new booster assemblies, it is often fully seated into the pushrod and may need to be unscrewed and extended a bit. There is a proper service method and correct tool to do it but I have always just backed it out, tested it and adjusted it again if needed....no special tools, just trial and error.
Also, as stated, the size of the master cylinder has an effect on pedal travel, pedal feel and the effort needed to stop the car. The smallest bore that is commonly used is a 15/16" bore. This takes the least effort to press but has a longer amount of travel to work. A bore size of say 1 1/8" would be harder to press but the amount of travel will be less since it moves more fluid for every inch of travel.
PLEASE return to update this thread once you fix the car. These topics come up occasionally and it helps others to read and see what worked for these problems. Good luck!

 

[Geoff 2]

Another possibility: the rear piston in the m/c has to close off the inlet port [ it feeds into the reservoir ] before any pressure is developed. Some m/cs have an internal adjustment for this in the rear piston. If the piston has to travel a long way before the seal blocks this port, then there will a LOT of pedal travel.