Gave my mechanical brakes a quick adjust this morning and have spent all day out in my coupe....mostly in the rain. Bostin'! Great fun... I'll echo what Weemark said...our MOT is very strict on brakes. Mine have surpassed the recommendations every time.
"Give me a long enough lever and I will move the world" That said it really has little to do with mechanical advantage. A well designed mechanical brake system could very easily duplicate or surpass the PSI at the shoe - I'm not saying they do - I'm just saying EVEN if they did you still cannot duplicate the stopping power of more modern systems. WHY? Simply because as brakes evolved they discovered that the bias front to rear was an ever changing relationship - hence the birth of the proportioning valve. The proportioning valve is a DYNAMIC device - altering the brake bias (in an effort to maximize it) as various load conditions. Something mechanical brakes are unable to do. So unless you guys are really challenging the laws of physics it seems to me that this is a dead horse.
not the answer i was looking for, i`m sure someone must has stuck a scale on just to see what the number came up as at some point in history, do 4 wheel drum brake systems have proportioning valves?, i know my truck doesnt and i dont recall any drum systems i have had that did, some may have them.
I thought this was a discussion about the merits of mechanical vs. hydraulic brakes. Now we're comparing mechanical brakes to state of the art hydraulic brakes with dynamic proportion? How about throwing in anti skid and stability control while we're at it. I doubt if one out of ten cars on the road have a dynamic proportional valve, and I don't personally know of any car that started life with mechanical brakes that has one. Lots of hotrods have an adjustable valve, but it's certainly not dynamic. I'm not even sure when this design started showing up in mass-production cars, but it wasn't that long ago. I'm sure someone, somewhere, has an old car with a dynamic instead of a fixed differential proportional valve, but this would be a rare machine. Heck, lots of retrofitted disk brake systems on cars with big and littles don't need a proportional valve at all. I've even heard of a reversed proportional valve installation to cure front wheel lockup.
....well ya see,...my Subaru has killer brakes, and,..... I wholeheartedly agree with Max on this, I was going to post something very similar but hesitated. Lets get back to facts and not fiction,...we're talking traditional rods here,....I cant see to many traditional rods being equipped with all sorts of proportioning valves, etc. when all is said and done,...I can't think of one guy running them, not to say they arent a good idea,...hell i think I may be looking into running one on my '53 Buick and my '27 T coupe since she'll be light and fast,...(wow its easy to get sidetracked!!) BUT,...this is not the path I thought we were on either,.... I myself am very interested in the facts of mechanical vs. juice,...this has been very enlightening via those who have actually rode/drove in cars featuring them both. I too would like the question answered about the psi difference in brake shoes in both realms. I too have heard the horror stories of mechanical brakes,..but have recently heard just as horrible stories of guys having juice brakes go out on them,....fact is, when God calls you're deli number,...you've got to pick up that Pastrami on Rye you ordered!!
The very nature of the proportioning valve is that it IS dynamic - this is nothing NEW. What would be NEW is to show me a proportioning valve that ISN'T dynamic. There is this SPRING - springs have RATES.... ahh hell I give up. Find out what "Changeover Pressure" is - in a nut shell it allows the bias to change at a predetermined pressure. That is what separates it from a "balance bar" type brake set up. Guys it is all an evolution of IMPROVEMENTS. All this " I have this REALLY OLD car with mechanical brakes - I can lock up the brakes so it must be good." Is a statement that seems to imply (maybe I am just interpreting all this wrong) that they compare to "better designs. Makes me wonder how Bendix ever stayed in business all these years when these "killer" early systems were so damned good all of the sudden. Seems to me you guys you are only FOOLING YOURSELVES. Fellas - you wanna run mechanical brakes then by all means go ahead knock yourself out - All I ask is please don't drive behind ME. Here's my point in a nut shell - run what you like - it's your car - but do yourself a favor and fairly evaluate it so that you TRUELY KNOW what your limitations truely are. The guys suggesting that since their car passed some "safety check" with flying colors and that translates into having better brakes than their "new" car that squeaked by - well then I'd say that's pretty good evidence your new car needs a brake job. Take that baby for some REAL world testing and then we'll talk - until then you're gonna have to chalk me down as an unreasonable non-believer. BTW - do any of these "tests" check the system in WET CONDITIONS or are you guaranteed perfect driving conditions where you live?? Let's review some of my favorite past HAMB statements: Near the very top was the guy who once posted that "you can achieve brake bias by INDUCING AIR into your rear brake lines". And to think I've beeen spending all my life trying to get the air OUT! WHo knew?? Then there was the fella that stated his car "stopped on a dime" with rear brakes only. Put me down as unreasonable non believer again. And no I never rode in his car - sorry you just won't convince me - no way no how, because if it was remotely true we all know it'd stop WAY BETTER with all 4 brakes working- ain't rocket science. And ISN'T that what we are really talking about??? Making stuff better -isn't THAT the root of Hot Rodding??? This wraping yourself in blind traditionalism is all fine and dandy - but a bit boring (that whole restoration arguement thing) bottom line IF you are gonna decide to draw the line in the sand at any particular place - then fine - just honestly know where you are and adjust your driving habits accordingly - trying to suggest that some ancient system can compete with improved versions is silly. and NO I'm not talkign about anything newer than the 60's here. Derailing the point with comparisons to anti lock brakes and traction control is just hiding behind unrelevant facts. There is NOTHING magical in hydraulic brakes in of themselves. If it was able to simply be boiled down to PSI at the shoe then by all means Mechanical brakes would fare very well in this discussion. And if THAT is the point being made then - I fully agree. My point is that once you go "juice" brakes then a whole world of improvements is at your feet. The best part is that most of it is so easily hidden preserving the traditional look. If you are so hard core that you can't use a part newer than 1950 (insert year of your choice here) then I would suggest that you also forego setting up your ride with the proper steering geometry too - because let's face it most "old hot rods" had that screwed up too. Of course you may want to avoid driving any canyons or mountains especially in the rain. My old Hot Rod - what ever you want to call it - I added disc brakes (and a balance bar) to the spindle mount wheels back in the late 80's. Do I now think I have the best brakes out there?? Sure don't - but it stops 100 times better than when I first got it. You wanna call it non traditional?? Go ahead - won't hurt my feelings a bit. I wish I could put those wheels on all my cars.
Should be fine for a country car. My brother has an 30 A open car with a banger & mechanicals, he lives in Nor Cal, I drive that car all over the backroads, Main Sts, & his neighborhood. All ok for now as long as they are adjusted, I have totally orig 34 woody V8 as well Pat's & my 32 V8 roadster, Yes-It gets scary @ times driving around,but as Elmo Rodge stated above, he's still here to talk about it. Just keep em adjusted & be careful .
My Model A stoped ok at best when I kept on the brake adjustments. Although Im sure it could be ALOT better dew to the fact that my brakes were a bit "tired" and worn. Most rods were bent to take up slack and were in pretty sad shape but still worked and were reliable once you got use to them. Id say go for it....just use all good peices, no bent/worn anything and you should be fine.
I thought I would hot rod my 4 banger model A coupe and just for fun while doing the 35 wheel swap, I decided to fit a complete 35 front axle with good brakes to get that rake and what I hoped would be better front brakes with cast drums for less fade out etc. It was rather an easy swap, but I got to say the 35 brakes may not fade out but boy that dont feel as effective as the model A tin pan items, just for the record I screwed the steering up by lowering the front and lost all my castor, it is much heavier to steer now also. Guess the rear end will now need to go down to claw back some castor.
The only way a proportional valve can be dynamic is for it to be able to sense loading and/or road conditions. The only way I know of this happening is to have a mechanical connection that senses load or an electronic connection through a computer that has control over the valve. Some pickups have a lever attached to the valve that measures the load in the pickup bed by the position of the chassis and allows lesser or greater rear wheel brake pressure accordingly. A garden variety proportioning valve does nothing more than set a predetermined pressure differential between the front and rear brakes. Typically, this will always be 70/30 or 60/40 regardless of load or anything else. Combination valves, that include proportioning, do a couple of other things such as sending pressure to the rears first and holding residual back pressure, but the relative front/rear pressure is preset. The "changeover pressure" has nothing to do with proportioning, it's the bias provided by a combination valve that sends pressure first to the rear drums for smoother braking. There's a spring loaded valve within the combination valve set at 150 psi or so that must be overcome before pressure goes to the front disks.
Max, I think you are confusing the "changeover Pressure" with the "hold off pressure". And while I will agree my use of the word "dynamic" conjures up a slightly different meaning than I intended it isn't entirely wrong either, But I admit I could have used a better word (other than I couldn't think of one better). BY "dynamic" I don't mean one that sense road conditions - but I mean one that IS NOT a simple pressure curve as you have suggested. 70/30 60/40 Example you state is exactly what proportioning valves are NOT. A Balance bar system would work as you describe but NOT a proportioning valve. A proportioning valve has basically TWO distinct pressure curves. The point at whihc you change from one to the other isd called the "Changeover Pressure" - this is done in an effort to try to emulate the optimal braking relationship front to rear - see attached pics for clarification.
I've got a long history of being confused, so this is a distinct possibility in this case. You're correct that I was referring to holdoff pressure. My reference material indicates that holdoff is a function designed into a combination valve and that the holdoff period is the only time the front to rear preset pressure ratio will deviate from the design. A standard proportion valve does not have this function but a separate holdoff valve can be installed. Since holdoff occurs only during initial brake application and during very light braking, I think we can agree that it contributes little to safety. As far as a pressure crossover point being engineered into a proportional valve, I'll have to take your word for it as nothing in my materials mention such a thing. But, I am curious as to how such a feature would work and what the benefits would be. Here's the description of a combination valve I recently ordered from Inland for a project: Proportioning Valve - Street Rod Street Rod - Brass 5 Port Valve Front Disc - Rear Drums Brass $85.00 Valve Notes: The 5 port valve works great on factory cars that have been converted to disc brakes. This valve is preset for disc brakes in the front and rear drums. The 5 ports are; 2 ports on top for the lines from the master cylinder to the valve, 1 right front port, 1 left front port and 1 port for the front to rear brake line. This valves serves as a replacement on all GM cars from 1971-86. This valve is also used on the 1964-72 GM disc brake conversions. There is no adjustment on the valve. It is set to be 70% front brake, 30% rear brake pressure.
I`m running mechanicals on my 31 coupe,can anybody give me the run down on the adjustment,or,send me in the right direction (books etc.) on how to adjust mine as after 1000 miles they dont work as well as before,and! the pedal will not come all the way back up so the brake lite stays on(I added the spring thats suposed to pull the pedal back up)but it doesnt work.Any help would be appreciated thanks Bill
Ok guys,...apples and oranges here,... Very interesting tech info thanks for BOTH of those views!! I'd still like others who actually drive both mechanical and juice to weigh in if there are any others reading this. HemiRambler had a good point, when he said something to the effect of "...but were their brakes worn, or in need of a tuning??...what about wet conditions?..." I'd like to know the same. I think I "might" run mech brakes,..at least untill I can get together ALL the parts to do a changeover properly!!!
is it a repro spring? where did you get it? You might want to take a look at it and see if something's hanging it up,...dirt, etc. and then take it off, look at the bushing inside, maybe there's something there that's not right. After all of that,....I'd say try to match the spring at an industrial hardware store or likewise somewhere (Granger's comes to mind),..get the same style but beefier,...that's just my thoughts on it,...but then I'm still just learning
HemiRambler got my curiosity up about "Changeover Pressure" so I called an old friend who used to design mechanical stuff for cars. I'm sure he simplified a lot for my feeble mind, but essentially he said the "Changeover Pressure Point" was nothing more than the point during brake application that the master cylinder builds up enough pressure to make the proportioning valve actually do something. Before the pressure reaches that point the proportioning valve does nothing (although the holdoff valve in a combination valve will be in play) and both front and back brakes get the same pressure. He wasn't familar with the term "dynamic curve", but he did say the rear brake pressure percentage would be a little less during heavy braking because of the non-linear force needed to compress the proportioning valve spring. I'm done!
i'm running mech. brakes on my 31 RPU. 34 brakes all rebuilt. they work better than i thought they would. the shoes need to be arched to the drums, to make full contact. i have driven stock As with good mech brakes. and felt totally safe. you have to work on them, and keep them adjusted up right. to make them work.
The spring was from Bratton`s comes with a bent steel rod that raps around the brake pedel and the spring attaches to the frame...
My bet is THE MAJORITY OF THEM. I stand behind my previous statement on the subject dispite the people who have 'driven a billion miles and never wrecked' and the 'drove into a ditch with the brake pedal to the floor' retards. If the mechanical brake system on the (stock) vehicle is not properly stopping the vehicle, THEN THAT BRAKE SYSTEM HAS NOT BEEN PROPERLY MAINTAINED OR IS NOT PROPERLY ADJUSTED.
Since tech week is coming up would one of you be willing to do a article on the proper rebuilding and adjustment of mechanical brakes?
I believe the UK MOT brake test is done on rollers. They spin each set of wheels (Front then rear) up to a pre-determined speed & the brakes are applied to stop the rollers. It does not take weight into account, nor does it imply any "optimal" conditions - merely the condition of the brake system. It is a good test for the integrity and efficiency of the system. My only concern with the philosophy of, "I can lock up my wheels with my mechanicals, so it must be good enough" is the fact that modulating the pressure to the wheels just prior to the lock-up point is more important than being able to lock them up. Once you lock them up, you've lost... FWIW, I still plan to run mechanicals on a future very light weight modified project (that's still just in mental masturbation mode), but run hydraulics on the others...
I did the complete rebuild on mine a few years ago and never took photos so can't help with this one, but there is an excellent book on Model A mechanics that include a section on the correct adjustment of mechanical brakes. In fact I think it also covers their rebuild as well. The book is written by Les Andrews and is called the Model A Mechanics Handbook Vol. 1. All the Model A parts houses hold them and it's well worth getting hold of a copy.
Flat Ernie, If you're right about the UK MOT brake test - then it makes perfect sense why one would "score better" with an outdated brake system. First off a "new" brake system (ie. proportioning valve) REDUCES rear brake capability (in an effort to prevent lock up). Also IF the weight really is ignorred then you are NOT truely measuring the ability for the wheel to STOP your car. AS the LOAD (read: weight) on a wheel increases so does it's ability to brake - and of course the opposite is true - reduce the wheel load - reduce the braking efficiency - make it easier to lock up. This is exactly why things like C.G are important in brake calculations. The C.G. will ultimately affect the weight transfer . As weight transfer increases (to the front) during braking the ability for the rears to brake is reduced (this results in rear wheel lockup) and is why the proportioning valve REDUCES the pressure to the rear brakes. If this test works as you indicate it truely is a rather poor measure of "real world" brake capability - wouldn't you agree?? About as effective as "geez - I can lock 'em up - they must be good" And so long as we mention Real World - we then MUST consider things like poor road conditions - Rain, Ice - whatever. These things have a huge influence on your brake performance. Indy cars have a fully adjustable bias to that various conditions aren't disasterous. On "production" cars that isn't necessaryily so easy to do so a somewhat "optimal" curve is established and attempted to duplicate in the system function. Hence the birth of the proportioning valve. it's cheap - it's effective - it actually works. I run one on every car I own except one - my old coupe has a balance bar. The balance bar would loosely compare to the mechanical brake arguement. My balance bar system works freakin' great - no doubt. Of course that's on DRY pavement. And there's a point to consider - the improvement in brakes over the years are sometimes only gonna be realized under some less than optimal road conditions. I personally have been caught in downpours in every vehicle I own - enough incentive to make each own have the best brakes I can reasonably afford. YMMV Where's a fork?? I'm done.
Something that always intrigues me is how much you guys say you have to keep adjusting your mechanical brakes. I am going to say this (and will get a ton of flack I'm sure!!) but for those of you that keep having to adjust, you have done something wrong. I do brake jobs on Model A's that require adjustments every 10K-15K. Are you guys actualy putting that kind of miles on your cars (10K a month)?? So ....I guess what I would like to know is the "why" you are having to re-adjust. Is it because the shoe linings were not "arc-ed" to the drum and so they are continually wearing in? Were the shoes centered properly during the rebuild? Could the adjusters be backing off some while you are driving? Do understand I am not being critical but I truly would like to know why you guys are having to adjust them and my customers are not. - - - - - - - - - - - - - - - - - - - - - - - - - - As far as the debate on Mechanicals vs. Hydraulics, ...isn't it funny how us as Humans here only believe what seems believable to us, --no matter what the facts are??
Well, perhaps weight was the wrong term. The weight of the car is on each axle, but since it is static, there is no weight transfer to increase/decrease braking effectiveness. What I should have said was mass as it relates to inertia. The test is static, so Model A brakes on an 18-wheeler would perform pretty much identically as they would on a Model-A. Yet in the real world, they would be woefully inadequate. The test does take leverage of the wheel height into account as the rollers dictate the speed, not necessarily the wheel. Of course, I only ever had my cars tested - I wasn't the one doing the testing & never really asked many questions other than, "did it pass?" ;D So I could have the test all wrong....
I can only speak for myself Brent, but the reason I check my brakes every month or so is simply through good ol' fashioned paranoia! I guess I'm guilty of subconciously believing what others say about them being poor so I feel happier if I'm checking them regularly. They don't always need any adjustment, but I'm more relaxed when driving if I know I've checked them out. It's good for the blood pressure! I'll definitely say that my brakes need adjusting at far less than 10K miles though. Far less. Maybe I am doing something wrong. What linings do you use on your brake shoes?
When I use of the term "I can lock 'em up" I'm not saying that that's the way I always stop...all I'm saying is that I can apply the pedal hard enough to stop the rotation of all four wheels - just like hydraulic brakes do when the pedal is pressed hard. I think all of us know that "locking up the brakes" isn't a good thing but I'll also be willing to bet that's what most of us will do in an emergency if we didn't have ABS - hydraulically operated or mechanically operated..
Having driven both, I don't believe you can modulate the mechanicals as well as the hydraulics - you know, the feathering right at the verge of lockup. Mass & inertia definitely have a lot to do with it too - in my '34 Tudor (hardly a heavy car) it was "exciting" to say the least, while my Model-Y stopped just fine & hydraulics seemed to be stupdendous overkill had I undertaken the conversion (which I didn't).
http://www.flatheadted.com/index.php This link will take you to a vendor who sells an excellent floater kit for mechanical Ford car brakes. If you follow the sequence: Store > Dead Stop Brake Energizer you get a good series of pictures on how the system works. There is information on the measured increase in braking following installation. At the bottom of this page is a link to a Video that shows the installation process and also the brakes in action. Elsewhere on the site are a number of statements from users who have installed the kit. Include me in the list of those with the brakes installed, mine are on a 28 Coupe. The increase in braking power is dramatic, pulling is eliminated and adjustment is simplified. Installation is simple. A prerequisite for good mechanical brakes is that all parts are not worn and adjustments are made correctly. This kit will not fix a worn, incorrectly adjusted setup but will enhance a good setup. I have driven this car across the country several times, on highways, through cities, in the rain, without problems. I feel the brakes are as good as the hydraulics on my 40 Coupe. Of course they will never be as good a modern discs, they require you to think a bit about how you drive, but yes, they do work well. And no, I don't have any connection with the vendor, except as a satisfied customer.
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