I've got a dual chamber master cylinder from a 70's Jeep that another HAMBer turned me onto that I think is going to work in my '41 Buick (due to placement of the stock MC, the replacement has to have the ports on the right side if it's going to mount close to the stock location on the frame). So now I'm working on getting it all to work together, and I had some questions. Here is a picture of the plunger on the stock MC as well as the end of the push rod. The flange on the end of the rod seats nicely into the recessed part in the center of the plunger.
Here is a picture of the new MC. When you line up the push rod with the plunger, the flange is exactly the same diameter as the opening to the plunger - I think this is the rear dust seal. When I push the push rod in, the plunger depresses. However, I'm assuming that what I'm pushing against (the four tabs at the top of the plunger) is actually some sort of snap ring or retainer, correct? I'm also assuming that that push rod when properly fitted should slide down into the plunger so that the end is all the way in...correct? And if all that is correct, can I simply machine the flange off of the end of the push rod? The diameter of the rod (minus the flange) is the same as the diameter of the inside of the plunger.
Would a GM pushrod (longer one) work? If you simply machine yours you are gonna lose some pedal travel. The pushrod should go down inside (GM's do anyway). I would think if you tried to use it as-is you might shear that flange on the pushrod in a panic stop situation. 2 cents is up!
i would make a new pushrod starting with the right one for your new master, the right one should have a rounded end and have some side play to allow for the arc of your pedal travel.
I can machine off the flange and still keep the length of the push rod end, which actually looks like it does fit inside the plunger with a little bit of breathing room (should be sufficient for the arc of the pedal). I figured it was supposed to run all the way into the plunger, just wasn't 100% positive since it obviously seats different than the stock set up. As far as length, once I get the new MC situated in a spot that won't interfere with the shift linkage and the clutch (it's a tight squeeze), I'll have to modify that push rod anyway. So here's another potentially stupid question. If the MC has to mount higher than the original to avoid clearance issues mentioned above, is there any reason the push rod couldn't be modified to create a dog leg? I'm no geometry major, but it seems to me that this shouldn't affect the arc, and as long as you're getting the right amount of travel (ie to depress the plunger) it should work. Take a look at the crappy sketch attached to see what I mean.
bending the push rod would make it weaker, it could bend, you can mount the master on an angle, lots of newer cars have them mounted on an angle. just have to make sure you still have enough travel also i'm just going through changing a 30 chrysler to a larger dual master, theres no room for a large standard chevy master so i'm looking at one for a honda accord, it has a 1" bore.
I'd have to agree with Budd in that you want to keep the push rod as straight as possible. I'm afraid that one with those bends in it would flex too much with pressure on it. It would also put pressure to one side of the piston rather than a direct push on the piston. If you have to do it that way put gussets on the bends to keep them from flexing.
I generally agree with Mr48chev on this......however you could "stack" two rods (welded together), or their equivalent, to avoid actual bends in the push rod. As a side note, what is the Jeep model and year this M/C is from? Ray
I was actually thinking I'd cut and weld the push rod, not just bend it. That said, I didn't realize you could mount the MC on an angle...that could really solve my problem. What's the rule of thumb for that in terms of how far you can go? Obviously I wouldn't want to angle it too far, but is it just a matter of determining the max amount of angle at which your still keeping the proper fluid level (and then staying within that range)?
Some M/C are at an angle in stock applications and, yes, just determine what is not too extreme for adequate reservoir capacity and mount it accordingly. As for geometry, there will be a slight loss in travel of the rod unless the pedal end of the pushrod pivot were "rotated" a like angle. Worth checking the total travel remaining if you do that, but I'm inclined to think it will still be more than sufficient. Ray
I've been working on the brake system on my '37 Buick. I also have the brake linkage and pedals from '40 Buick and saw they were quite different. My MC is behind the pedals. When I installed my dual MC I had to move it to the left and back about a foot because my Buick has a "X" crossmember. I moved the pivot on the bottom of the brake pedal and made a longer push rod out of 1/2", the original was 3/8". I also used the MC for a '68-72 Buick Skylark. I made the longer rod by turning it on my drill press. I needed a 3/8" fine thread on on end and rounded end on the other. I also needed a flange so I turned the other end down to 3/8" and welded a washer on and machined it to the shape I needed.
The MC I'm using is NAPA part number 36237. I don't know exactly what it was for originally...only that it was for a 70's Jeep CJ. Thanks for the explanation on how you made your push rod. It looks like on the original MC, there was a retainer that was held in place by a clip that caught that flange...I'm assuming that the purpose of the flange is to keep the rod from falling out if the pedal goes past 0 and into the negative range, is that correct? And with the new MC, since the push rod extends 1-1/4" or so into the piston, is that a flange necessary? Also, when determining the length of the new push rod, is the goal to fully depress the piston in the MC when the brake is fully depressed (and obviously to keep the rod in the piston when it's released)? Thanks for all of the input and help.
Be sure you keep the proper pedal ratio! (for manual brakes I "think it's somewhere around 6:1) Check out a 63 impala power system for ways to move the rod up. (be aware that it affects pedal ratio)
So after a lot of time lying on the floor under my car scratching my head, here's what I figured out. No matter how I angled the M/C, I kept having clearance issues. The problem was that the outboard "wing" on the M/C pushed the body too far out and interfered with 1st and 3rd gear on the shift linkage (or with the brake pedal). It looked like cutting a small notch in the frame would give me enough clearance (if I was lucky). I made a few cardboard templates and came up with the bracket design.
Then I cut it all out of 1/4" steel and double checked that all the mounting holes lined up. I used the old M/C to check against the plate that runs parallel with the frame because I didn't want to egg these out...didn't want to open up the possibility of the bracket creeping forward. Here are some shots of the finished bracket and with the M/C bolted in place. Since this is a brake part, I trusted a pro with the welds...thanks to my buddy Brian at Kundratic Kustoms for welding this up for me.
Here's the little window I cut through the frame. It kind of looks like a shot from when they discovered the Titanic, no?
And here it is installed. When I finally got it bolted up, I threw a short piece of scrap brake line in the forward outlet to double check clearance. When it's in 1st or third, it clears by about 1/4", so I was stoked. It's over at my buddy's shop now where we can run brake lines with it on a lift. I'll post updates once it's done...with any luck, everything will work and I'll have it up at the Showdown next weekend.
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