There is always a lot of discussion on here about brakes . I'll throw this out there , something I found 20+ years ago when I was building my T. Speedway offered an inexpensive front disc brake kit using pinto/ mustang II calipers / shoes & rotors. I had an 8" rear out of a 79 mercury monarch The master cylinder was the same for both cars . The combo valve was the same for both cars. The calipers & wheel cylinders were the same for both cars . The manual brake pedal ratios were also the same . The pinto was 1000lbs+- lighter than the monarch. I found that the hydraulic components were used throughout fords small & intermediate car lines. The differences between the small & larger cars was rotor diameter , pad size , brake drum & shoe size , everything else was the same . I had can old Wagner full line brake catalog & IIRC , Ford was pretty much this way through all the 70's.... At least in this case , it wasn't rocket science...
That brings back up my skepticism about those combination (AKA 'proportioning') valves they sell us yet again. What this tells me is the OEMs paid better attention to swept braking area to achieve 'balance' than we do. And strikes me as the best way to do it in any case. I'd be very curious to know just how many different part numbers of those valves were actually used in OEM applications. If they were truly 'generic', it becomes obvious they aren't doing any 'proportioning'...
A 73 mustang II , '76 pinto , 75 t bird ,79granada are exactly the same valve , the old junkyard I went to , my buddy said they never sold any so he let me have few to investigate , disassembly showed they were the same ..
I think I've told this before but, a long long time ago in a galaxy far away, I had a 58 Ford 1/2t that got a hemi and auto instead of its original 3sp/y-block. So the front was a little heavier that stock and was almost always unloaded. A real handful on wet pavement, stopping and starting. Bias plies and all. Back end would lock way before the fronts were doing much work. Rather than weakening the rear brakes somehow, it got a set of 12x2 1/2 front brakes from the same Chrysler that donated the engine. Just a little spindle massage, spacer plates was all it needed. Fixed the front rear balance issue and stopped MUCH better.
On the cars that I have built, if the rears locked up before the fronts on hard stop, I changed the rear wheel cylinders to a 1/16" smaller size until I had a good balance. 15/16" most often was the right size for me. This was on Ford 8 & 9" rears, and the wheel cylinders are cheap, compared to the cost of adjustable proportioning valves, and you end up with full hydraulic pressure to each wheel.
Good thread on something that we don't think about but is pretty simple to figure out. There are a few rigs out there that depending on the whole package might have the same drums on the rear but different width shoes from the factory. The big V8 or the tow package gets the shoes that match the drum width but the small V8 no tow package rig gets narrower shoes.
I'm not sure if visually comparing dis-assembled proportioning valves will show any differences without careful inspection/measurement but I know first hand there were many combinations of split points and percentages made by Bendix/K/H for the OEs. Pressure split/crack/knee values of 200, 350, 400, 500, 600 psi along with percentages of .27, .39, .43 and .59 are some that come to mind. I spent hundreds of hours of skid pad and track testing sorting out valve specs for certain vehicles, and this became more important after the D.O.T. 105/75 brake performance requirements became law in the mid '70s. Using a salvage yard or aftermarket combination valve with unknown specs is a crap shoot on how well it will work on a custom non-stock brake system, and is why I strongly recommend using only an adjustable proportioning valve. As for combo valves, metering was not necessary or exclusively used on disc/drum systems, and pressure differential switches are useless unless you intend to have a dash warning light, so with a stand-alone prop valve a distribution block is really unnecessary, resulting in a cleaner lower cost brake system.
Here is my solution.. Developed over 50 + years of building and modifying a wide variety of cars. First , I have never had good success with any factory combination valve unless its on the unmodified car it was intended for. Once you start mixing and matching components , it gets ugly fast .. So.. No factory combo valve. I also prefer to use manual brakes. Less space, less issues with vacuum etc. Most of the aftermarket small diameter boosters are junk in my experience. So.. Here is the combination.. # 1... 6 to 1 pedal ratio 4 wheel disc...69 corvette manual master cyl. Disc / drum .... 74 chevy C10 manual master cyl. # 2. 3 1/6 " front brake lines. 1/ 4 " rear brake lines.. This give a slight delay to the rear as it takes a bit longer to build pressure in the larger line. If this needs further balance then I add an adjustable prop valve.. Hard won knowledge here.. Gained by lots of trial and error.. I'd be glad to help anyone with brake issues.. Ya'll feel free to debate - argue this among yourselves.. I won't join in .... SQUIRREL might call me out on this.. I always listen to what he says.. Dave Sent from my SM-G973U using The H.A.M.B. mobile app
So, not trying to argue with anyone here, but I'm having trouble understanding how changing the diameter/size of the wheel cylinders helps achieve balance, just from a theoretical perspective. If the rears lock up before the front, and you go to a smaller sized wheel cylinder, the rears will now engage the brake pads with the drums earlier, but with less available pressure. Does this achieve balance? It just doesn't seem to be that easy or straight forward to me.
A smaller wheel cylinder will not engage the shoes any earlier than a larger cylinder, but will provide less braking force that may help front/rear balance. The question is whether this change will work well at LLVW and GVW, along with low coefficient road surfaces.
Same pressure but smaller area = less force on the shoes. 600 psi on 1 sq in cylinder = 600 pounds of force on the shoes. 600 psi on .5 sq in cylinder = 300 pounds of force on the shoes. Sent from my iPhone using The H.A.M.B. mobile app
It has to, it's basic physics. Pedal effort may increase, but travel will be reduced, meaning the shoes will contact the drums earlier, but with less force.
IMO, the time to contact is more dependent on return spring pressure than anything else. Yes, in your example the cylinder will move faster, but will not move the shoes until the spring pressure is overcome. With disk fronts, they move outward with very little pressure, no spring to deal with. And braking doesn't really start until the pressure starts to rise, after contact with the drum or disk. So even though the start and move faster, they won't brake any sooner due to the lack of pressure then they brake less due to less area. At least that's the way I see it.
This is an excellent thread... Finally, some clarity on proper parts choice. I was going to reply last night but was feeling a bit 'under' and self-medicated a bit too much so decided the coherence of any reply was questionable... LOL. I'm going to summarize what I think I've learned... Achieving 'balance'. Basically there's two scenarios; one, if the rear brakes lock first under heavy application you have either 'too much' rear brake or not enough front brake. Two, if the front brakes lock first, it's opposite; you need less front brake or more rear brake. Now before anybody leaps on this, this is vastly simplified but I did this to show the 'general rule'. If 'perfect' balance is achieved, all four wheels would lock at once. In practice, having the front wheels lock just a bit before the rears is preferred to maintain vehicle stability. If the front brakes lock first, you lose steering control but the car will tend to go straight. Lock the rears first, the car will want to swap ends. So if you have a disc/drum system that locks the rear wheels first, the fix is fairly straightforward; reduce the effectiveness of the rear brakes. Smaller wheel cylinders or narrower rear shoes can accomplish this, the OEMs used these changes themselves. I would think that narrower shoes should be chosen last as retaining as much swept area as possible helps with heat dissipation (as well as wear). You could also 'proportion' yourself out of this with an adjustable valve but I don't think this is the right way to go about it depending on the mis-match. The fly in the ointment these days is walking into a parts house and saying 'I need one of these only different' is likely to get you a 'deer in the headlights' look as their look-up is based on applications. Find someone who can do this, cultivate them; you've got a good one. If the front brakes are locking first, it gets more difficult. It's never recommended to reduce front brake effectiveness, so increasing rear brake performance may entail whole new brakes. Larger cylinders is a possibility, larger drums/shoes maybe not. And maybe look to see if your front brake selection is actually suitable for your application. Disc/disc systems present the same problems but the solutions are harder. With any given disc assembly, you're stuck with severely limited choices. You generally can't do anything about rotor or caliper piston size, and probably only minor differences in pad size/composition. If the rear brakes lock first, you may be able to correct it with an adjustable proportioning valve. Fronts lock first, you probably need to change your brake choice at one end or the other. Now I'll admit that I'm ignoring two solutions that could address all of these issues on any system. One would be a 'stepped' master cylinder with different bores for each end, but whether or not you could find one for your application I can't say; I don't know how common these are. The other is a fully-split race-type setup with dual masters (one for each end) and a balance bar between them. I don't see this as a viable solution for most of us for various reasons, space considerations being one of them. I'll bring up one more issue that I think is critical if using a disc/disc system. Full disc systems were pretty much non-existent on US cars in the '70s (usually a high-cost option if even available), more common in the '80s, and by the mid-'90s almost standard equipment. You'll be hard-pressed to find something that doesn't have 4-wheel discs these days. And the technology has evolved considerably. I've owned multiple cars (not trucks) with 4 wheel discs and nearly all of them have two features in common; one, there's a marked F/R size difference in rotor diameters, with the rears almost always smaller. This is something we don't think about from growing up with drums, being used to seeing same-diameter brakes at both ends; if there's any difference, it's almost always in drum width. The other issue is the OEMs have abandoned single-piston front calipers in all but the smallest cars, favoring 2 or even 4 piston versions. I think this is important because as the supply of older rear axles available for swapping decreases, we'll be getting more modern rear brakes whether we want them or not that are designed as complements to these. As the aftermarket is primarily selling mid-'70s tech for front conversions ('generic' GM single piston), it seems that gross mis-matches are almost inevitable. There's myriad other issues not yet discussed but should be. Tire sizes; big 'n littles, wider on one or both ends will affect braking performance. Static weight distribution, and more importantly, dynamic weight distribution; a taller car will transfer more weight forward during braking than a lower one, all else being equal. Am I asking for too much? LOL... And I fully believe this; those aftermarket combination valves are all but useless...
I’m starting to learn more about brake systems here. No opinions to offer, yet. I have a disc/drum system that locks the fronts while the backs don’t seem to be doing much. Need to improve on that. Sent from my iPad using The H.A.M.B. mobile app
Well, if you have one of those 'proportioning' valves that has the brake warning switch installed, my first order of business would be to remove that then go from there.
On my coupe I have disc-drum with two small willwood masters and a balance bar pedal set up as Steve mentioned . Works well. On the track I also can deploy the parachute.
Wondering how tire size affects brake bias......I've got bigs and littles on my coupe, it seems to have way more brake at the front than the back. 4 wheel drums... Makes sense that a taller tire/wheel has more leverage than a smaller one?
Here is a picture , you can see the masters on the fire wall. Front master is 7/8 bore, the rear master is 1'' bore.
Yep, got one of those. That’s probably one of several small problems, adding up to a system that could be improved. Too cold for wrenching right now, and can’t go test it anyway, so researching now and collecting information on what I have. Sent from my iPad using The H.A.M.B. mobile app
Ray, this sort of 'real world' knowledge is what I'm hoping for in this thread. It seems there's a lot of 'everybody says' pseudo-knowledge out there that leads some down the wrong path or at best into a detour. I'm assuming this was a under-floor master with the residual valves. Your system is of interest to me as my avatar also has the same rear brakes but smaller front discs with a power booster. It's on the firewall and I would like to get rid of the booster (I don't mind the master being there). Otherwise the brakes work 'ok' but nothing to write home about.
I admit that up to now, I attribute my success at getting mismatched brake components to work out to just lucky guesses and blind luck. My next project waiting in the wings may require help from you guys. The car is a 1934 Austin Ruby which is so small that it makes an Anglia look like a stretch limo. Since it is such a light car, small brakes should suffice. For front brakes I will probably go with go kart disc brakes with a very small diameter rotor. The problem is the rear brakes since I have sourced a narrowed Ford 9" rear end, chosen because it was the right width; having previously been in a pro-street Mustang. What can I say? The price was right. Since this came without rear brakes, what is the smallest drum brake that I can use?
If the 9" rear housing has big-bearing ends, I doubt if you'll be able to find a 'small' rear drum, or at least small enough.
What I'm really hoping for is someone who knows of a calculation (even if a bit crude) for front/rear brake size that would put you in the ballpark if you have the basic info for your car. There must be something of the sort, I doubt if the pros just take shots into the dark...
The only early 70's cars that I recall that would fall in the 2000# category are mustII/ pinto/ bobcat , chev. Vega , chevette .Did Chrysler have a small car offering ? These would be candidates for disc/ drum systems without a lot of frills . It shouldn't be terribly difficult to identify caliper , disc , wheel cylinder , drum , shoe/ pad & MC sizes . Other than pedal ratio. that should provide approximate sizes .Same goes for 2500# , 3000# etc. I've never investigated GM ,but as I attempted to point out in the opening , the difference between a 2000# & a 3000# ford was larger rotors & pads in front & larger drums & shoes in the rear .As someone stated about the combo valves , it appears many of the early ford units were distribution blocks with safety valves in them .....I don't know about GM. In my foggy mind , if your pedal ratio is 6:1 & you put 100# pressure on the pedal , that should equal 600# exiting the MC ...
I don’t think there’s a simple rule of thumb that’s going to work for all builds. Between this and the DeSoto thread, I’m hoping to learn enough to know where to start looking for what I need to know. Maybe we can develop some good information here. Sent from my iPad using The H.A.M.B. mobile app
I'm not seeing how this works. For example, say instead of just 1/4" line you have a installed a huge tank with a 1/4" fitting on one end and the same on the other into the middle of your system and it is filled completely with brake fluid. If your hypothesis is correct, the amount of fluid in this tank will prevent the rear brakes from coming on til next Tuesday. But I don't think hydraulics work like that. You push a certain amount of fluid with the master (let's just guess two fluid ounces for argument's sake). It doesn't matter if it's flowing through a 3/16" line, a 1/4" line, a large tank, or your intestine. The other side is going to pump out two fluid ounces. The only way it can take extra time getting there is if the route expands for a moment (your intestine). Brake fluid is not compressible.
Yes, this bothered me too, but I didn't want to look like I was just arguing with everyone, so I let it go. I think this idea fails Pasquals Law.
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