First - progress update. Rear brakes are installed. The drivetrain is assembled, and we were able to take it through all the gears with the rear end on jackstands. Going looks good. Also added straight pipes for an exhaust. Stopping is a challenge, and I think we solved it. With that solution, I need to decide if power brakes are worth the hassle of setting them up. First - background. The car came with the TCI master cylinder/clutch assembly installed: https://www.speedwaymotors.com/TCI-...er-Brake-Hydraulic-Clutch-Assembly,46286.html I currently have no pressure in the system. After several calls to Speedway and TCI I 'think' we found the issue. Since it has the power booster, the master cylinder needs a 'plug' so the booster pin can contact the piston. That wasn't installed, so there's too much throw before the pin contacts the piston. Hence, not enough travel to provide useful pressure. And yes, the master cylinder and lines are bled, no air. So, the main question now. The master cylinder can be used with or without the booster. There's a bit of work involved to make the power brakes work and serviceable. Those are: Run a vacuum line from the manifold to the booster. Easy, but I don't know if the engine will provide enough vacuum on its own (49 flathead v8). If not, I need to find a place for a vacuum canister (challenging). With the booster, the master cylinder sits right under the cross body support under the front seats. To access the master cylinder lid, I'll need to modify that support and frame it around the lid. Challenging. The master cylinder (Corvette style) can operate either manually or boosted. If I remove the booster, I can move the master cylinder forward and in front of the cross body support. And I don't need to worry about vacuum. My inclination is to convert it to manual braking. The fronts are 46 Ford and the rear is 76 Bronco. The Model A tudor is relatively light. I think it's be enough with manual brakes. For reference, my 69 Chevy pickup had manual drums for years. Stopping was work, but manageable. Since the A is MUCH lighter than a long bed c10, I think I'd be OK. Feedback?
Ran a 66 GTO with factory rear drums, 69-72 grand prix front disc brake set up using all stock parts and never had a problem bringing the 389 to a stop. Now coming to a panic stop required some pedal/foot force but never extreme. And daily stop and go driving was never a problem. Point is your Tudor is lighter and with the proper sized wheel cylinders and master cylinder it shouldn't be a problem... ...
My old '56 F-100 had 4 wheel manual disc brakes (stock Camaro clip & 10-bolt), daily driven with no concerns. Stopped as it should, even highway panic braking from 80mph as well as typical Austin bumper-to-bumper traffic.
On a model A with properly assembled / adjusted manual brakes no need for power brakes. Just get the front to rear bias correct with an adjustable proportioning valve. You want the brakes effective, but without locking up the wheels which can be a challenge with a lite weight car. Power brakes won't help.
My avatar has a Granada master cylinder, GM A body disk calipers, 9" drum rear and a proportioning valve. It stops great. I would abandon the power booster.
The 46 Ford brakes are Lockheed type, Ford truck isBendix. The Bendix is self actuating. For best results you might consider Boling Brothers Bendix style front brakes. This would give you a matched setup with no booster or proportioning valve. also the correct master cylinder is important. Be sure and get one for drum brakes front and rear. John
Power assist came out for big heavy cars with drums and then was pretty mandatory for discs, although there were some manual disc setups. A light car with drums can be set up to work fine with manual. Rule of thumb is 5 to 1 pedal ratio for power, 7 to 1 for manual. Check yours. https://mpbrakes.com/how-to-series-correctly-calculating-brake-pedal-ratio/ Also, you say it's bled and you need one more part to get it working right with the booster, but have poor access. After checking pedal ratio, I'd be temped to try it on the ground with the current setup installed, then try it without the booster vacuum connected. That should guide you on which way to go. For the engine developing enough vacuum, this will depend on cam selection mainly. There are reservoirs and pumps if this is an issue. Cross that bridge if that is the direction you decide on.
Thanks everyone for the info. I'll check the pedal ratio and some of the other items. Since the body is currently off, it's a bit tricky to take it out and see if I need a proportioning valve. Does anyone know if TCI offers different ratio pedals? Otherwise, I can modify the existing one.
Thanks, the poor access is only to the master cylinder lid when the body is on the car. Right now, it's a rolling chassis, so access is good. It is a 5-1 pedal ratio. Unfortunately, it looks like I need to remove the transmission to pull the pedal for modification or replacement. The pedal pivot bolt is too long to extract otherwise. Maybe I can make a bolt-in ratio 'changer'...
Sounds like a situation that needed fixing anyway. I hate stuff where servicing requires major disassembly. Be careful measuring changes in pedal. If you want more ratio, longer up and/or shorter down. The shorter down means less displacement from the master. You do not want to decrease displacement to unsafe amounts. A taller pedal and a heel block would be better.
Good point on the taller pedal. And it would much easier to access. Though it would add 3 inches to the height. Would be nice to just lose about 3/4 inch on the short end. We shall see.
3 inches taller pedals? to increase ratio 5:1 to 7:1? Something doesn't add up. how can a 7 inch booster fit in a 6 3/4 area plus pedals? How far down is it from the pivot to the master rod? Height from top of pedal assembly to bottom of booster is 6-3/4" Power brake kit has a 7” brake booster and matching master cylinder
As your photo shows, the pedal is the type on the right. I had no idea where you came up with the 6 3/4" measurement until I looked at the Speedway site. They have it wrong - it's 15 3/4". The actual measurements are: Top of pedal to top of booster = 8 3/4 inches Top of pedal to bottom of booster is 15 3/4 inches However, you DID make me re-measure wearing my reading glasses, and X was way off (10.125 inches vs. 9.0) Thanks for that As is: X=10.125 inches, Y= 1.75 inches, yielding 5.8:1 To get 7:1: Shorten Y - 10.25/7 yields 1.45 inches, shortening Y by .30 inches. (new result) Lengthen X - 1.75 * 7 = 12.25 inches. Lengthen X by 2.125 inches (new result). If I were to guess - TCI uses the same pedals and frame for manual and power brakes. The ratio is almost 6:1, which is a compromise between 5:1 and 7:1.
Update: I was able to convert it to manual braking pretty easily. I drilled mounting holes for the master cylinder in the mounting plate and fabricated a pushrod out of a grade 8 bolt. A little plumbing change for the new position, bled them and they came right up and seem to be working fine. Since the body isn't back on yet, it'll be a bit more challenging to see how effective they are. I'm working on a temp driving platform and hope to have it driveable(ish) this week. Maybe even today. Thanks everyone for the guidance and suggestions. You are the best.
FWIW, I had a Chevette with manual brakes and it handled pulling a light trailer up and down Lookout Mountain near Chattanooga several times just fine.
And yesterday, I took the Model A for it's first drive. No body, but I built a driving platform. The brakes worked. They're still a bit mushy, so I'm sure I need to bleed them more. I bleeding them by myself, using a vacuum bleeder, so I'm not too surprised.
Looks like you spent a bit of time on that platform, good job. Your face is one of concentration, observing and careful appraisal. Hope the grin came through at the end! A friend would deal with a fussy braked model by bleeding, letting it sit overnight, then go around and lightly tap each caliper/cylinder to get the air bubbles to rise to the top. Then a very gentle bleed at each corner to get the last little bit out.
The platform was pretty easy, and free. The floor is a section of pallet and the rest of the wood was laying around. Switches, etc were in my electrical pile. Someone was giving away the seat... Biggest expense was the seatbelt...only because I can't find the old ones that were in my other rod. Being autistic, grins don't come naturally to me. I'll bleed them some more as well. Great idea to tap the cylinders.
Good for you converting to manual, all of my cars (8) are manual front disc cars… no problem stopping any of them , power brakes do not belong on hot rods, maybe street rods!
My 40 Chevy has power brakes. I scavenged the whole master cylinder and booster off of a Caprice wagon. It stops almost too well.
My friend has a power disc conversion [from a vendor] for his early [not sure] 60's Cadillac from a later model Caddy, late 60's I think. He has bleed every which way and consulted forums [some good some bad advice wise] but can't get a pedal till one inch from floor. About half way down he starts to get some feel but then it goes to the one inch. He is getting brakes at the one inch, not sure if they will lock. Pedal ratio is a hair under 3:1 as best as he can check. I say air somewhere, some one says he needs a double booster. Thoughts?
@seb fontana He's gone thru asking and trying other's advice. You are asking at the end of another brake thread, on a forum where this is a monthly topic. Hate to say it, but document all of it, take pictures and start a new thread if you want good replies. You can look back at past Brake Problem threads and see what has been offered before, too.
I can tell you what I found with this system that had the same problem; no resistance until the bottom, and not enough pressure to activate the shoes. My master cylinder works with or without a booster. It was part of a kit with a booster. The booster's output pin was too short to reach the master cylinder's piston until the very end of travel. The master cylinder itself is supposed to come with a spacing 'slug' that goes into the piston so the booster reaches immediately. Mine was missing. I bought one, but decided to go with manual brakes. here's an example - https://www.summitracing.com/parts/...RomICqB2ZJeGBuodeCbEQSpCYrdLxr0RoCGiwQAvD_BwE
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