I bought a power brake kit with a 7" booster and dual master cylinder for my 59 buick. The 59 orig had a tredle vac unit under the floor. I opted to put the booster on the firewall and hang the pedal. All went in well but the car isn't stopping the way I want. I have orig buick drums on front and back. I have a high enough pedal but doesn't seem to stop the car like it should. I have new brake cylinders,hoses, hard lines and shoes. I turned all the drums. I bought the kit for the car. Since I am retaining the drums front and back do I need a perportioning valve. The people I bought it from told me no. I may not have the shoes adjusted out enough. I remember from when I was a kid that you adjusted until the wheel locked up then back off 9 clicks. Is that right? I haven't done this yet. I adjusted until there was some drag on the wheel. Do I need more drag and seat the shoes to the drum or do I need to install a perportioning valve. I'd like to hear some ideas on what to do. What am I over looking? Seems like the big ole buick drums with power should stop it on a dime. Am I expecting too much?
You're saying it's not stopping the way it should. You'll sure need to provide a lot more detail than that if you want help. First thing i'd do is a few reasonably aggressive stops, and get out and see if all the drums are hot/warm. See if one end is hot and the other not, or one end hot and the other barely warm. A proportioning valve's only needed when the rear tires skid with very little pressure on the brake pedal. Sounds like this ain't the case. For adjusting, i like to go real tight to center the shoes, then back off until you barely hear scuffing. If you just initially adjust to a light scuff, you might hit the brakes (this also centers the shoes) and then discover they're too loose afterwards.
Double check that you've got the right cylinder on the M/C going to the front. If the ports on the M/C are different diameters, the larger one should go to the front. Of course you bench-bled the M/C... I always adjust drums until there's just the slightest scuffing. Pedal ratio sounds like a good candidate too.
ok guys I went back out to make sure all is right. The large port is to the front wheels, I did bench bleed and I ran all new rubber and steel lines. I have bled the complete system a couple of times. Since I don't readily know the brake/pedal ratio how do I figure it?How do I change the ratio? Don't really know the piston size either. I ordered this specifically for the car. I'll try and find my receipt. I think that I will do as grouncho said and run them down tight to center then back off to light scuff. I have plenty of pedal,just doesn't seem to stop right. It has gotten better as I work on it. I had to lengthen the rod into the master cylinder at first.Tell me why it would need a residual valve now and didn't have one in the beginning. Is it because I changed systems? I building this for my son and it will be right before he gets loose in it. Thanks for your opinions.
Still a bit of a guessing game, but from experience with aftermarket power boosters and large bore master cylinders I am willingto bet your pedal is a bit firmer than you expected and you really don't slow the car down. Do yourself a favor. If you still have the original master cylinder around, pull it off the old servo and measure the bore size. Compare that against your new master cylinder's bore. They should be the same size. It is real common for aftermarket guys to force feed everyone 1 1/8" bore cylinders lately even when you may only need a 7/8 or 1". If your master is larger than stock, replace it for one that matches. The aftermarket boosters are pretty unsophisitated. Rarely do they have enough volume internally to stop a large car like your Buick. The valving internally is also not so progressive. This can give you an initial feeling of good power assist that rapidly dissapears the harder or longer you push the pedal down. The only proper solution is to match an appropriate booster to the application.
TP, I have the same problems with the '58 and have done all kinds of things to try to improve the braking but I'm still not happy with the way it performs. EL polako has a good point about the master cylinder and I need to check mine too.
The aftermarket boosters are pretty unsophisitated. Rarely do they have enough volume internally to stop a large car like your Buick. The valving internally is also not so progressive. This can give you an initial feeling of good power assist that rapidly dissapears the harder or longer you push the pedal down. The only proper solution is to match an appropriate booster to the application. __________________ I think ELpolacko is right on the money with this. I had the same experience when I tried the 8" dual diaphragm booster from MPB, most useless piece of garbage I ever bought. After a year of tearing my hair out over this problem I replaced their $250 booster with a $10 junkyard booster and the problem was solved. Before someone says I got a bad one this was the second one it was sent to replace the first because of this problem. Their claim is that in order for their booster to work properly the motor has to put out 18" of vacumn. He's also right about some companies promoting the 1 1/8 masters when smaller would be better
Well I have worked on it all day. Went to mp brakes website and looked at all the options. as of now it'll stop on a dime. Like in life my rod was a little too short to begin with. I adjusted a couple of times. Also my shoes were not "seated or centered " i guess against the drums. I drove it around for about an hour and did a few power stops. seems to be fine . It does not pull at all. Maybe I just got lucky. I now want to wait until it rains and drive again.The original was a single not a double master cylinder.. Thats one thing I wanted to get away from. It was also a tredle vac., under the floor. Someone explain why a 7/8 or 1" would be better than a 1-1/8".TP
A 7/8 or 1" bore M/C isn't necessarily BETTER (depends on how you define better) in your case IF your pedal effort was Too High AND you have room for additional pedal travel - then by going to a smaller M/C bore you reduce pedal effort at the expense of increased pedal travel. The reverse is true at the opposite end - increasing your Wheel Cylinder diameter also reduces pedal effort while increasing travel (it's all a trade-off). I think what Elpolacko was hinting at is that some of the aftermarket guys push a standard size - regardless of what you may origionally have had - which as he suggests is goofy - keeping your "new" sytem close to what the origional manufacturer had will start you off CLOSER (rather than farther) from where you will want to end up. I babble.
The Jalopy Journal
