My 29 roadster has a stock gas tank, somewhat shortened swing pedals and a late 50s to early 60s chevy truck dual master cylinder this setup has been in this car for decades. It is a great young guy car as it takes two feet to press down the clutch and to brake it to a stop. I am in my mid seventies and find it quite uncomfortable to drive. I played with the clutch linkage some, got a little better but nowhere near what my other fords were effort wise. My only alternative was to play with the hydraulic rations to gain more mechanical advantage. The master cylinder was 1 1/8 in diameter I had it bushed down to 3/4, my clutch now feels like it is power ***ist, My brakes are my problem. Braking effort is minimal pushrod adjustment is my problem 1/16 of an inch adjustment takes the brakes from going to the floor on the first push down, to being right at the top where the more i drive the more the brakes drag I bled the system multiple times, no difference! this really has me stumped. Are both sides of these master cylinders functionally the same? Any other Ideas? Need help on this one, Thanks guys, Rich
Had a similar problem at one time when I was running a tri five type single master. I finally replaced the master cylinder and the problem went away.
Three fingered or diaphragm clutch? I have an HD 11" diaphragm clutch that is almost easy to push. It may be time for an add on hydraulic ***ist to both the clutch and the brakes.
Sounds like you addressed the clutch... You haven't shared if you have drum/drum or disc/drum or even disc/disc set up. That's important information. Your master cylinder may or may not match your set up and I'm going to residual valve issue/problem/lack-there-of in my thought process for a start...if the master cylinder is for a disc/drum, no, it is not internally the same front to back so the first step is to figure out what you exactly have for existing components...and there are other smart folks here too.
The master cylinder sounds like early 60's Chev pickup, which is meant for drum/drum. One side for hydraulic clutch, other side for front and rear brakes: https://www.cl***icindustries.com/product/mc34404.html @Deuce Man , what size wheel cylinders are installed on the front and rear?
When you say 'somewhat shortened' pedals, my question would be, what is the pedal ratio? Is there enough leverage for non power brakes? https://techtalk.mpbrakes.com/how-to-series/calculating-pedal-ratio
My roadster has lincoln bendix brakes in the front 39-40s in the rear. Again as I stated the master cylinder is a 59-60 chevy truck dual master cylinder one of those square ones. With the bores reduced to 3/4 inch from 1 1/8 inch pedal pressure is greatly reduced, I love it, just have this crazy situation I described above. The lack of leverage is exactly why I reduced the bore size in the master cylinder.
Phil how do you! calculate the pedal ratio? The present pedals have been in this car since the mid sixties whatever the ratio is, it has to stay. Pivot point is just about up against the bottom of the stock gas tank, the pads are uncomfortably close to the flat floor. The problem at the moment is the master cylinder. Again one more time!! My problem is with the brake side of the master cylinder clutch side is fine brake side goes from topped out pedal with brakes dragging to all the way to the floor, first push with just 1/16 of an inch of adjustment
Pedal ratio is important. For manual brakes you need 6:1 ratio. Here is a tech with illustrations: https://techtalk.mpbrakes.com/how-to-series/calculating-pedal-ratio I've found with mixing parts from different cars, similar size master cylinder and wheel cylinders solves a lot of pressure issues. I suspect your wheel cylinders are quite a bit larger bore than your 3/4" bore master cylinder? I think we are working on the same thing, you want a solution, and I'm trying to gather enough info that we may be able to identify the cause of your problem.
If you think master might be bad, pinch off all flex hoses or make plugs out off short length of brake line and fittings installed in outlet of master cylinder and step on pedal, should be no movement of pedal, like stepping on a rock, other than linkage play. If pedal still sinks, master is bad.
- Pedal ratio as said above - Decreasing the bore down to 3/4" makes the effort easier but the pedal stroke greater Is it really on the floor or I expect not but close to it? - If the brakes keep getting tighter and drums heating up, you don't have enough free play or the return orifice in the MS is covered up partially. Maybe the 3/4" sleeve is blocking it or hoses as said already. - With a 1-1/16" bore pedal stroke is less but effort more. What about using a softer brake shoe compound or a booster?
I had a similar issue when I first got my coupe on the road. It had good brakes, but took a lot of brake pedal pressure to stop the car, and pedal travel was not too much, but more than I wanted. So I measured the ratio and discovered my donor pedal ***embly was likely for a power brake system, as ratio was around 4.5:1 on it. No way to change the ratio at the pivot point, but the pedal hung high enough to easily change it on the arm length. So I removed the arm from the car and cut the pedal off. I lengthened the arm to get about 6.5:1 ratio, and then temporarily hung it loose to check the length in the car. It was great, so I welded a 1/2" lugnut to the end side of the extended arm, and bought an early Ford truck round pedal that had the 1/2" NF stud on it. Screwed it on, and re***embled the arm to the car. It stops fantastic now, and not like power ***ist, but very easy on my worn out 72 yr. old leg.
I had a hot rod with master under the floor. To improve pedal ratio, I had to drill new holes in the master cylinder frame bracket, to move the cylinder and allow it's pushrod to be repositioned on the pedal arm for a good manual brake ratio.
Pedal arm from top pivot to center of redal pad is 11 inches, distance from pivot to pushrod is 2 inckes kind of in the ballpark.I talked to the guy who sleeved the unit he said the super sensitive adjustment issue might be that with the piston adjusted ever so little inward , it is blocking off the return. the fact that the pedal goes down to the floor when pushrod is adjusted out a tiny bit is that it is in the normal operating position and possibly fluid is leaking around the sleeve. He suggested that I remove the brake line, put a plug in the brake line hole and see if the pedal stays hard or goes down, makes sense to me I am leaving for Napa to pick up a plug!
You may have gone too small in the brake bore of the master cylinder. The original 1 1/8" bore had an area of .994 square inches, Your 3/4" bore has an area of .442, or less than half of the original bore. That reduction equates to less pedal force, but also less volume being pumped out to the wheel cylinders. It also equates to pedal adjustment having more influence on brake actuation (you're now moving less than half the amount of brake fluid). It's a pain in the ****, but I think you'll have better results if you enlarge the bore of the brake side of the master until you reach the sweet spot. Good luck!
This is a possibility however we would need to know the area of the original wheel cylinders and the new ones, If they are different.
You guys are missing the point where he says the car has been unchanged since the 60s, except when he had the master bushed from a 1 1/8" diameter to a 3/4" diameter. As I understand those old Chevy dual master cylinders, other then sharing the fluid reservoir, each "side" is independent of the other "side". We are ***uming that he had both sides bushed the same to improve both the pedal effort of the clutch and the pedal effort of the brake pedal. The clutch side worked out great, the brake side not so much. Obviously, he doesn't want to mess with the clutch side since it sounds like its working great. The simple solution would be to pull the 3/4" bushing out of the brake side (if that would even be possible), and replace it with a 1" bushing. The smaller brake side bushing then what was original, but larger diameter then what is there now, may help with the brake pedal effort and still have enough fluid capacity to activate the brakes fully. The only other thing that concerns me just a little is if he has the clutch depressed and then steps on the brake pedal, is he running out of fluid capacity in that master cylinder, because of the longer required stroke of both pedals.
Regarding, "The only other thing that concerns me just a little is if he has the clutch depressed and then steps on the brake pedal, is he running out of fluid capacity in that master cylinder, because of the longer required stroke of both pedals.". The volume of fluid to actuate the wheel cylinders is the same. With the smaller bore, more stroke is required to get that volume. For example if the stroke to get wheel cylinder actuation is 2" and the bore is 1.125" then the volume is: V = π r² x h = (3.1416)(1.125/2)² (2.00) = 1.99 Square inches for the sleeved ¾” bore and the same 2” of stroke: V = = (3.1416)(0.75/2)² (2.00) = 0.884 Square inches To get the same volume from the ¾” bore, calculate h? 1.99 = = (3.1416)(0.75/2)² (h?) h? = 1.99/(3.1416)(0.75/2)² = 4.50” So 2" with 1 1/8" is 4.5" with a 3/4" bore. Note that this will give you a rough idea of the increase in brake pedal travel. The stroke of the master cylinder is far less but its stroke change will be in the same proportions that I calculated.
I converted my Model A Tudor to hydraulics. I used MT Car (BOLING bros) fronts and early Ford rear, same as your car. I used a early Ford master cylinder 1 1/8". Sounds like your setup. Had terrible brakes with high effort. I switched to a 1 inch dual circuit MC and brakes were great. Need residual pressure valve also. In my case they were built in. If you have enough pedal travel this should work. John
finally got my internet back, lots of good info to think about above !!! I originally wanted 7/8 bore , my shop that did the work said that they couldn't get 7/8 pistons only 3/4 and that they did a lot of these this size for hot rodders. I disconnected my brake line from the master cylinder and put in an inverted flare plug . pedal was solid as a rock while doing this I noticed that the brake side was labeled clutch and the clutch side was labeled brake . Is there a difference in the mechanics of either side ??? the plug test tells me that the Mc is working properly, and as mentioned maybe just not enough volume. I am going to ask my guy if they can change the brake side to 1 inch great info and suggestions. Thanks Guys.
If I remember correctly, the two sides were identical except the brake side had a built in residual check valve. I installed swinging pedals in my car back in the early ’70s. The pedal ***embly instructions said which truck M/C to buy and how to remove the residual check valve so the brake side could be used for the clutch. That made both sides the same. There was no mention of replacing the valve in the brake side. These days, I would verify that the valve is removed from the clutch side (sounds like it is) and put an inline residual valve in the brake line. I agree with Gene the 3/4” sleeve might be exacerbating the problem, 1” would be a better choice.
I'm sure if this hinges on their labeling and you deciding they got it wrong, but you didn't, that could answer your question? 4 wheels vrs. one clutch. Not enough volume could be it.
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