Brake problems

I am attempting to boost the drum brakes on my '49 F1. I bought an under dash kit from speedway but, don't seem to be moving enough fluid to get a good solid stop. I'm fairly inexperienced with brake systems, especially older ones (this is my first classic). I have replaced some of the hard lines with new, bigger lines and the kit came with a dual reservoir master. Everything is tight with no leaks and the system has been bled perfectly. I know dual res masters don't do well with drums but, I don't know enough to say whether they don't do well or they won't work with drums.

My question: Could this be a proportioning problem or do I just need to look at moving more fluid with a single res master? I can't afford to make the switch to a complete disc kit right now.


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Is the master cylinder under the dash or do you mean you've changed the pedal from thru the floor to a suspended pedal? Is this a manual or power brake system?

Dual master cylinders can work fine with 4 wheel drum brakes. At least they have in the past. But things like proportioning and residual valves can come into play. Mixing them between drums and discs can be an issue. So can things like brake pedal ratios. Check your M/C's documentation as some cylinders have some of these valve already built in.

What prompted the brake system upgrade anyway? Did you also change shoes, drums or wheel cylinders recently? How did the previous brake setup work compared to what you have now?

Hang onto your hat... There's some sharp guys on this forum and they will more than likely be able to get you on the right track.

 

An F-1 had a 1-1/16" bore master cylinder originally. Maybe your kit came with a smaller bore master, that would take more pedal travel. Excessive clearance between the pushrod and booster and between the booster and master can effect pedal travel. How tight the brakes are adjusted can effect pedal travel. The master cylinder probably does not have built in residual valves, did you install external valves? This won't effect travel; but will effect operation. You said you replaced some lines with larger ones, should be running 1/4" to the front hoses and also to the rear hose. Again this won't effect travel; but can effect operation.

 

X2. I chased a brake issue very similar to this. Master cylinder bore was too small and wasn't moving a large enough volume of fluid to the calipers...

 

The master cylinder bore is what I suspect is the issue. The brakes are adjusted out til just before drag. This is a boosted system and the lines I replaced with are 1/4 inch lines. I haven't placed any external valves, residual or proportioning. The original cylinder had a proportioning valve but was a single outlet cylinder. The new, boosted cylinder is a quad outlet cylinder but, I am only using three outlets due to the single line to the rear. It is also a 1 inch bore which, in my head, could easily explain the difference in pedal travel vs. stopping power. Again, though, this is based on limited knowledge. The old, manual system worked ok but, this will be my 17y/o daughter's first truck and I want her to be able to stop, right now. Thanks for the help, fellas. I look forward to more of your ideas/knowledge.

Patrick


Iron Chief
1949 Ford F1 Custom

 

Your DAUGHTER'S first truck!?!? OK, sorta cool, however, if you are not familiar with braking systems, may I STRONGLY suggest you take this to someone who IS familiar with brakes??

I'm already hearing things that make me wince, like a four outlet master (should be a two outlet), which sounds like a fast take-up unit NOT well-suited to older car systems.
Also, most aftermarket boosters are crap. I much prefer to adapt a complete pedal/booster/master unit from a single car, ideally the master is matched to the front brakes.

Good luck, but please consider taking this to a professional.

Cosmo

 

See? This is why I ask. When I say "unfamiliar" I mean I have never built a brake system from the ground. I have spent plenty of time fixing brakes, everything from changing the neighbors pads to complete rebuilds ( parts changing). I have spent most of my life elbows deep in some part of a car or truck.

I just want to make sure this is right since my little girl will be running the streets in it. I hate the thought of trusting my daughter to someone else's craftsmanship. That's why I am asking you guys. I will take it somewhere else, if I need to but, only as a last resort. I don't think this is out of my league in any way. I just lack experience. That's where y'all come in.

I think I'm going to sit on it until I can find a master cylinder that is more suitable and then give that a try. I have seen a couple of things that make me think the master off of a 55-57 Bel-air might do what I'm looking for. Thoughts/ideas?


Iron Chief
1949 Ford F1 Custom

 

The line SIZE DOES NOT make any difference period!!!! It can be 1/4 or 1" and once it is full of fluid what goes in will be the same anount coming OUT !! Some M/C replacements are muli fit and will have outlets on both sides. With a dual M/C you have 2 pistons moving fluid so maybe a 1/16 smaller bore cylinder will work fine but no smaller. The smaller bore cylinder will give more line pressure with a givin pedal force. Check excessive pushrod clearances both pedal and M.c to booster and pedal ratio. If this is a single diaphram 7" booster they do NOT work well !! Go back to orignal pedal without the booster and use the 1" M/C adding residiual valves both sides. Drum/drum systems do not need prop. valves.

 

Speaking of the booster, do you have it supplied with a good strong source of manifold vacuum? Are the hoses in good condition? Is there a vacuum check valve somewhere in the line to the booster? Is it installed correctly and working properly?

 

So, after listening to yall, it sounds like the first thing to try is.....

Cap two of the outlets and make it a two outlet master.

Then add a residual valve to each line. Adding the residual valves on the front lines after a split at a metering valve.

The residual valves effectively shortening the pedal travel and firming the brakes for more sincere stops.


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Good manifold vacuum to the booster with new line. No check valve.


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Install the residual checks at the M/C.

 

Did the master cylinder come with any instructions? They might specify that the front outlet supplies the rear wheels and the rear outlet supplies the front. Or they may specify the exact opposite.

And I think I'd want a check valve in the vacuum line to the booster. Otherwise, if the engine stalls you'll lose your vacuum boost.

 

NO!!!! A pic of the master would help tremendously. Sure, there are some masters designed to use either left or right side outlets, but there are far more masters designed as fast take-up for DIAGONALLY SPLIT brake systems that are NOT appropriate for this application.

NO!!! Get a proper master, perchance one from a 4 drum system car, which will have the proper residual pressure valve in it.

NO!!! Residual valves simply hold the cups against the wall of the cylinder, keeping brake fluid from leaking past those cups. They do nothing for or against pedal travel, pedal firmness or stopping power.

Cosmo

 

Sorry to be kinda harsh, but brakes are your life, or your daughter's life. Simple brake rebuilding has almost nothing in common with DESIGNING brake systems. You need know nothing about fluid dynamics, pressure differentials, or even leverage principles to properly REPAIR brakes, but you need to have a smattering in each to properly DESIGN a brake system. Throwing this part and that part and praying while holding a rosary will NOT STOP YOUR CAR!!!!

Please, please consider taking this to a professional.

Cosmo

 

Cosmo, take it easy, Brother. I'm not about to let this thing out of the driveway, if I feel like it is unsafe. My daughter won't be the test subject for an untried or unproven experiment. I'm just trying to learn here, My Friend.


Iron Chief
1949 Ford F1 Custom

 

Guess I may have been too hard, yet I work the counter (front manager) of an Advance, and I see and hear too much misinformation and plain bad wrenchin' that this kinda thing just scares me.

Cosmo

 

I'm not big on aftermarket brake kits myself. I'd rather get something factory and adapt that in. In your case, possibly a matched master & PB from a '67ish drum-drum F150. If it will stop that truck, it will work on yours. Get a suitable distribution block and plumb it up.

 

take a look at mpbrakes.com - they offer booster conversion kits, and good tech advice

 

I'd first agree with the others in that we need to see a photo and hopefully a part number on the master cylinder you are using. I don't believe it is intended to have lines run of both sides at one time but may be wrong on that. That style is usually a "multiple application" unit that allows the builder more options as to how he wants to run the lines from the cylinder.

I see that while I was posting this Bobss396 is pretty much on the same wave link I am on this. I've run the Master cylinders for drum brake 68/69 Chevrolet pickups on several rigs that I converted to dual master cylinder with good results. Simple, easy to get and inexpensive.

 

The problem with aftermarket brake components, one size fits most. Of course your application will not be in the MOST set. Back in the day, most dual master conversions were done right out of the bone yard, you knew what you had.

 

According to Speedway, the master cylinder I have is a GM master. The part number from Speedway is 9106001. I think y'all are right about not using all the ports.


Patrick

 

These are pictures from online. I'll take some pictures of my mounted m/c when I get home.


Patrick

 

These are single jar type master cylinders, not what you're lookin for.

 

Agree, line size is no difference. Brakes work on pressure, small or large line will still transfer pressure assuming no air and only fluid in lines. While the 7 inch single diaphragm booster does not provide as much boost, if the master cyl is too small diam, it could bottom out the pedal. It may need a larger diam master cyl. A drum/drum style should have the residual pressure valves in the outlets of the master cyl and additional external RPVs not needed.

 

These are actually on my truck.


Patrick

 

You don't want to hear this, but I'd feel I need to at least try.
That booster is crap. It's too small for a Fiat, much less what you're trying to do with it.
As someone posted, get a system from a similar vehicle, and burn that Speedway catalogue for the heat value, used the way you're using it will likely get you killed.
Next, reinforce the firewall!! It will, I mean WILL flex, crack and break with the load you're putting through it with the brakes. And I am 100% sure you have not tied the pedal assembly to the dashboard, as in every car made with hanging pedals, ever. Guess why the factory engineers do this.
And dare you think this is me talking without benefit of experience, you now get a dunce cap to wear. Further, I always get a matched pedal/booster/master assy, and I always tie it to the dash and a reinforced firewall.
I'm not even going to start with the brake switch, adaptors, lack of proper line support AND routing. Sorry, sir, but you are in over your head.

Cosmo

P.S. Does that one line REALLY go into the air filter?!?!?! Holy Cow!!!

P.P.S. Did you really thread a pipe thread switch into a inverted flare fitting??

 

Well, Jackass, thanks for reminding me of why I hadn't joined a forum up to this point. No, dummy, the brake switch isn't threaded into the M/C. It is screwed into an adapter that it was already attached to from the original setup. I'm using it to plug an unused port right now. Next is the lack of proper routing and support for my lines that I must have been an idiot to do this way. Well, dipshit, it's pretty well pieced together at this point well enough for me to troubleshoot the issues. Once I get it working like it's supposed to, I'll make it all nice and pretty.

People come to forums like this to learn from folks who have more experience, not to be treated like they are stupid. Unlike you, who works at a parts counter and gets to hear everyone's successes and failures, I fight for living. Wish you could come talk to me about the subject I'm more experienced in. How about next time you want to talk to someone like they're an idiot you do it while they are standing in front of you and see how it works out.

Please, refrain from troubling yourself with my stupidity any further, Chump.


Iron Chief
1949 Ford F1 Custom

 

Thank you to everyone else who has been trying to help me and give advice regardless of how stupid I am.


Iron Chief
1949 Ford F1 Custom