A couple points, the master cyl is ported to send fluid to the front brakes first, then the rear brakes - if you bench bleed you'll see this; whenfiguring out what is wrong i read pressure at the bleeder (stainles steel brakes sells a tool to do this), you'd want something in the neighborhood of 1200# i expect and that'll tell you what to do next; in looking at the pics, the wear pattern looks odd, almost like the drum is too large for the shoe.
shoes are not arc to fit the drum, not the end of the world but that will reduce the effectivness of the brakes till they wear in. The wear pattern isnt that unussual either, as they energize the shoes rock fowward at the top so theres a bit more wear on the top of the front shoe and the bottom of the rear shoe.
OK 2 problems #1 the SHORT shoe goes to the front of the car on Bendix self engergizing brakes. #2 The shoes are not making near enough contact on the front ,need to be arced/ground to fit the turned drums. Also I believe you have adjustable upper anchor pins on those Buick front brakes,if there is a nut on the outside of the backing plate on the other end of the anchor pin you do. The recomended procedure to adjust is tighten star wheel to lightly lock wheel, loosen lock nut on anchor pin ,rap backing plate with a heavy hammer. This should allow the shoes to center and the drum will now rotate easier,finish adjustment with the star wheel. But again SHORT shoe to the front!!!!
JohnEvans, Thanks. I assumed just the opposite. I don't recall there being an adjustable pin at the top, but will definitely check. Is there a correct way to "arc" shoes. Other than some heavy grit sand paper and a mask.
OJ, So it does make a difference which port the front and rear lines are connected to, right? I assume that the way to test while bench bleeding would be to uncap the the ports and compress the piston slowly. I would imagine that the port that is meant for the front brakes would begin to discharge fluid first. Is that anywhere close to correct? I'm going to swing by the parts store and have them look up my purchase log to find out a part number/application on my MC. Maybe I want to switch to another mc, and that wouldn't be tough as long as it has the 2 bolt mounting flange. If I can keep this one that would be best, though, 'cause it only cost $13 (or maybe that's why I'm not having any "luck" with this whole thing).
Arcing brake shoes. Back in the 60's I worked for a garage and the old man that ran the shop shoed me how to "fit the shoes" to the drum. He would take the drum which had just been turned and set the shoe inside and hold it in the middle and see if it would rock top and bottom, if it did he would take a ball pien hammer to the web and lay it on the vise, anvel and "spread" it a bit re check it until it did not rock and then tell me to but it all back together. Our barke lath did not have a arching tool so that is how he did it. I was just the grunt and thought that was how everybody did it. I never saw tha car or truck again until it needed a spoon job on the brakes.
Gee I thought everybody had a drum lathe and shoe arcing equip !! I do and anyone in the Phoenix area I'm available. As to which port for front or rear hydralicly it don't matter as pressure will not build untill you have resistance in both circuts, the rear piston moves the front untill it meets resistance then both sides build pressure. This front/rear no diff ONLY applies to a drum/drum system . The disk/drum combo the larger resivor is used for the disks as the pistons continualy move out towards the rotor as the pads wear,so need the extra capacity of fliud.
1st I say move the pivot point up, to increase the leverage,,, see what happens... As far as arcing the shoes, it is a good thing, but not essential.... with a little care in a safe spot away from traffic, they will arc themself in a little bit..
I'll stick with JohnEvans and the short shoe in the front. I would change the shoes and adjust the pivots adjust the brakes and see how they work. But I'm a cheap bastard.. I must have missed the day they past out the drum lathes. Good luck- Rich
the shoes in photo 2 look glazed. take some 80 grit sandpaper and cut through the glaze, hit the inside of drum also. cutting the shoes to fit the arch of the drum only increases stopping power. which seams rather important to me. good luck Cadillac Dave
After work I began working on the points that were brought up. I moved the pivot point for the mc pushrod to the next hole towards the axis, and that has given me a pedal throw of about 6" (8" at rest and 2.75" at compressed). I checked to make sure the pushrod isn't getting hung up in the cup on the mc piston as well. By the way, I DO have the master cylinder for a 1972 Maverick with drum/drum brakes. I switched the shoes on the drum I posted the pictures of. I scuffed the shoes before I reassembled and then I adjusted them so the wheel will spin 1 rotation with a good turn. When I took the driver's side drum apart I found that the shoes were correct, but I scuffed them anyway and it was out of adjustment so I adjusted it to the same drag as the other drum. Its 11pm here and my neighbors don't enjoy the sound of a open-exhaust 401 nailhead in the evening so I'm forced to wait until morning to test the brakes. I'll post again when I try them out. Thanks again for all the help. I checked with 2 brake shops and a parts store today and I guess its basic knowledge that the "shorter" pad goes on the leading side. Just another thing I've learned during this adventure. If the brakes still don't work well I'll dig into the line pressures and also check to see if the master cylinder has residual valves built in.
I drove it and the brakes are definitely better than before. The backs will lock up if I press firmly on the pedal, but I didn't stand on it to see if I could make the fronts actually lock up. Does that sound reasonable.....that the backs should lock up before the fronts? Or could that be back to the issue of having the reservoirs backwards on the MC? At any rate, it definitely with out a doubt stops a LOT better. The pedal is nice and soft until the very last little bit and has a decent amount more travel. Thank you everyone for you help. I was hoping it would be something simple, but didn't think it would be something as easy as the shoes on backwards.
Most any vehicle without a anti-lock system the rears will lock first. The fronts lock = no more steering control, not a good thing. As the linings wear into fit the drums better [more contact] your brakes will inprove. As far as old lining goes it can look good but does not have the friction qualities of new, it does age. Learned this little factiod with old motorcycles ,replaced old orignal factory lining with new factory lining and brakes were much better. Back when I sold autoparts 60s-80s the better relined shoes would have different friction ratings leading shoe/trailing shoe. You could see the difference in the materials in most cases.
It DOES make a difference which way the m/cyl. is connected, That is why it has different size fittings, so the guy on the assembly line, and the guy who replaces it, connect it correctly. In other words if it didn't matter there wouldn't be two different size fittings.
Could you please elaborate? As far as a street rod application goes, with drums front and rear and nothing other than maybe RPV's between the master and the wheel cylinders, is it that critical? Did all manufacturers connect their masters the same (drum/drum) or was it just the preference of each that dictated it.
One thing I'd like to mention is that as a rule of thumb I'd usually plumb the bigger reservoir to the front brakes (I've seen Fords have the bigger one in the rear and GM's on the other end although they were disc/drum) but what if they are the same size?
I will beg to disagree with you here in referance to a drum/drum system. A drum/drum system will need residial valves for both ends. A disk/drum system for sure needs the clocked/handed/sized ports for correct install. But remember the first rule of hydralics "equal pressure at all points". In a dual MC system WITHOUT any sort of delay/pressure reducing/restricting device in either side will efectively have the same pressure at all points at the same time. I spent many years in the HD truck/autoparts biz and attended more that a few classes on brakes AND hydralics. All most all dual MC's use a floating front piston that is engerized by fluid displaced by the rear [primary] piston. And untill the front piston starts to build more than a few PSI needed to over ride the internal springs the rear piston will not produce any higher PSI either. This floating action provides a bit of varaible displacement BUT if very much you will have a lower than normal pedal. This can be very noticable on a disk brake vehicle with badley warped rotors kicking the pads back.
The '72 Maverick MC I'm using (for a drum/drum maverick) has 2 identical reservoirs. The only difference is that the reservoir farthest from the mounting flange has a larger fitting for the brake line. I have done quite a bit of reading due to my brake issue, and have found that the reason the front axle needs the larger reservoir on a disc/drum setup is because a disc brake will need more fluid over time as the pads wear and the pistons need to extend farther to make the pad contact the disc. I'm not a hydraulic guy, so I just wonder why they put a larger fitting on the one reservoir on a mc that's designed for a drum/drum car?
Simple Adavis: less parts to stock, same front line could be used on either drum or disk braked cars.
I know this is an OLD thread but I thought I'd give one final update for those that care. I ended up selling the car this spring and decided I would try to fix the brakes before it left my garage. The car stopped fine, but it never really STOPPED like I thought those big 12" drums on a little car should. I put in a proportioning valve on the back brakes and I could eliminate the rear axle lockup but it really deminished the braking power of the car. My final solution was to swap the front and rear lines on the master cylinder. I WISH I WOULD HAVE DONE THAT 4 YEARS AGO! Don't let anyone tell you that it doesn't matter which port goes to the front or rear axle. It makes all the difference in the world!!! As soon as I got the lines swapped on the MC and bled the brakes I pulled out on my street. With the car stopped I pressed on the brake pedal and then gave it gas. I'd never really been able to do a solid burnout because the car would just move. This time I got the same result so I was disappointed until I saw smoke coming from the FRONT tires. The front tires were locked up and the back was just pushing me down the street! That's what I always expected from that nailhead but never got to see it because I'd plumbed the front and rear brake lines wrong on the master cylinder. So, in closing, make sure that you connect the brake lines to the correct port on the master cylinder for proper brake function. Don't let anyone tell you that it doesn't matter, because it makes all the difference in the world.
So in reading all of this; which port did you finally use for which? The big fitting for the front brakes? Or in re reading your first post; which reservoir did you finally use?
Sorry, I should have explained. I connected the front axle to the small port which was closest to the mounting flange. With all the research I did and looking at diagrams of how a master cylinder works it appears to me that as the piston is compressed, it actually applies fluid to the first port (closest to the flange or rod) just slightly before it does the second port. Therefore throughout the entire stroke of the piston it is applying more fluid to the first port than the second, causing the first port to apply stronger braking force than the second. At least that's the way I interpret the diagram. And I definitely know it works that way in real life.....whatever is going on inside that thing.
First rule of hydrailcs equal pressure at all points. Now if you had a MC with a stepped bore it would be possiable to have different pressures in each 1/2 of the system. Normal MCs all have straight bores ,one exception off hand is for GM low drag metric disk calipers they are setup to move extra fluid to the calipers to take up the extra clearence those have. In a straight bore MC a 100lbs force on the rear piston you will transfer the same to the front piston. Not sure what you did would cause the improvement but sometimes cars is cars and things happen for no logical reason.
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