Not so far, Moedog07. I'm beginning to believe that what I have may be as good as it gets! I would expect that Cadillac ElDorado calipers coupled up with a Corvette disc/disc master cylinder would at least lock up the rear wheels on loose gravel. I'm only using one reservoir with the other blocked off. Wonder what would happen if i connected both reservoirs with a T fitting and sent that to the rear calipers? I'm considering setting up a power brake configuration. I hesitate only because I would expect better performance from the existing manual brake system. I've tried everything that all of you have suggested but so far not any improvement. I.ve bled the brakes so many times the parts house knows me by my first name. Still open for any suggestions, tho.
Lynn, I have tried the adjustment both ways with pretty much the same result. I currently have the push rod out so that it is not making contact with the master cylinder. I have a soft pedal. I also thought of going to a T connection for using both reservoirs but there is very little room under there to do this. I may still try it. It could be done if I pulled the master cylinder(again)and installed the T fitting. I'm considering changing the bore size either larger or smaller. Unfortunately, I have no access to a pressure gauge. Buying a pressure gauge kit is expensive for a one time use. I have a gauge that if I could find the proper fittings, I think would work. So far no luck in that department. The current MC is a Corvette style, Disc/Disc setup with a one inch bore If I knew I needed more PSI, I would know which way to go with the bore. I'm not a great mechanic but I do know which end of the screwdriver to use. LOL!
2old2fast, That is a good question. I have observed both reservoirs and the blocked has a little fountain of brake fluid when I push the pedal. I am assuming( ass out of U and me) that the pressure is just backing up into the unused reservoir. Any thought s would be appreciated.
You say ElDorado rear calipers. Are those the ones with the built-in parking brake? Those things are a disaster. A real pain in the ass to get adjusted.
I'll put this up again @Jim Hewitt. You may have missed it. Check the proportioning. Rears are not supposed to work as well as fronts.
Yes, they are the ones with the parking brake and I totally agree they are a pain in the ass to adjust. I believe a previous owner converted from drum to disc using a conversion kit. I have been able to find a Kit using these same calipers. I would consider changing calipers, but I don't know if new calipers would fit the brackets on the differential.
Are you suggesting that I switch the brake line to the other reservoir? Isn't the PSI the same coming out of each reservoir on a disc/disc MC? Remember I have no front brakes installed, just rear brakes. I have learned a lot about brakes on this thread and I'm sure I have more to learn. I am reading the "Brakes 101" tutoring article and it is very helpful. I received the link from a member.
I had a set of those built-in parking brake calipers on my hotrod. Never could get the rear brakes to work right. I shit canned them. Replaced them with regular GM metric calipers. I don't have a parking brake now, but I have good rear brakes. If you don't care about the parking brake, just replace with a GM metric caliper. Available just about anywhere. And will fit the bracket on your rear end. Those ElDorado calipers have a 2" piston. The GM metric front calipers have 2.5" pistons and will have more gripping power. Probably a lot better for your rear brakes only hotrod. Again, they will fit your brackets.
Four wheel disc brakes certainly are proportioned. If your disc/disc master cylinder has an attached/inbuilt proportioning valve, or there is one in the system somewhere, the rear brakes will be getting fed a lot less pressure. It isn't the PSI that is the reason a disc/disc master cylinder has two larger reservoirs. It is for the extra fluid volume required by the disc brake system. By the way, good front brakes and a suitable tire contact patch are a real good idea. The rear brakes are really only to keep the car straight and stable when the brakes are applied. It is the front brakes and tires that are supposed to do the hard work. Not having them, or having a sub-standard front brake/tire combination for the sake of looks, is not up to scratch. Just sayin'..........
Jim.....watch this carefully and over and over if needed to understand what is going on with a dual master cylinder. The good part starts at about the 1:10 point. The little "fountain" of fluid you see is the fluid pushing back into the reservoir until the piston cup passes the compensating port on that circuit. I could be completely wrong, but with one circuit blocked at the master cylinder port where the line(s) connect, and you still have a soft pedal, I think there's still air trapped in the active brake system. One thing to check is that the bleeders on the calipers are at the "top" of the caliper. Sometime calipers have been installed upside-down not thinking about air trapped at the top of the caliper with no way to bleed it out. Taking them off to bleed "right side up" could be done but it might be a challenge to do, and correcting the problem would be a better choice. The second thing is to check that the pistons and brake pads aren't retracting real far away from the brake rotor when the brakes are released. If that's happening much of the travel of the master cylinder would be used up just taking up the slack before pressure really starts to build to apply the brakes. Not being familiar with the emergency brake type calipers, there might be a relationship with the adjustment of the emergency brake workings to excessive pad retraction, but that's just me guessing. Lynn
That is exactly the problem with the parking brake caliper. You have to turn the piston to adjust it out. A real pain!
Jaw22, I have the piston so close to the rotor now. There is maybe .2 mm spacing. If I move the emergency brake lever forward on the caliper maybe 1/3 of an inch I get good contact with the rotor. Of course this is just a static test. Tthe T Bucket is off the ground so there is no inertia of the car to deal with. I will try adjusting once more to see if anything has improved. I have also backed out the brake push rod so that at rest there is no contact with the MC piston. I get contact with minute pedal movement. Of course, I will bleed the brakes again. The last couple of times I have positioned the caliper so that the bleeder valve is on top. My pedal is soft now and goes down quite a bit. I have checked the push rod to make sure it has plenty of clearance and is not rubbing or hanging up on anything. I will likely change these calipers to the GM Metric calipers if only because they are a pain in the ass to adjust!! Do you know what models and years they were used on? that could make my search much easier. Thanks for the videos. I have watched it several times just to make sure I know what is happening with the MC.
Part # 91031045 1978-Up GM Metric Brake Calipers, IMCA Approved $55.99 (36) Regal, Monte Carlo, Nova, Cutlass, Grand Prix, Steel
The rear only brakes should be able to lock up, especially on gravel. So you are not getting enough clamping force on the calipers, i.e. not enough brake fluid pressure. I am certain you still have air int he system, probably stuck in the unused reservoir. Since you are using the dual master cyl, at best you should tee both front and rear reservoirs together so that the master cyl is working as it is designed to do. If your calipers are adjusted properly, as it seems you have with the parking brake, then if you can't get enough pressure you need a larger piston like the metric calipers. Remember that Pi(r)^2 [Pi time radius squared] form math that is the area of your piston. A 2-inch piston is 3.14 sq in, and a 2.5 is 4.91 sq in. Or to put it in easy terms, the 2.5 is 56% bigger. That means you get 56% more clamping force for the same input pressure produced by the master cyl. In your light T-bucket the 2-inch piston should be plenty to lock up the rear tires. You need to get more input psi going to them. With no air in the system. Air compresses and keeps you from reaching the high enough psi fluid pressure. As a crutch, tee your master cyl outputs together into the rerar brake line. Bench bleed the master. Bleeders on calipers are always at the top, air rises and you need to let it out. Once you do all that it should give you better brakes. While still keeping your parking brake functional if you leave the ElDorado calipers.
@Jim Hewitt Can you explain what you did with 2nd port when you switched over to a dual M/C ?? [and kept 2 wheel only brakes] For them both to function correctly with only 1 circuit you need to "T" both ports into one circuit [effectively converting it back to a single M/C] You can also pull out the floating piston and slip a piece of tube inside the spring [again this converts it back to a single M/C] You have achieved Nothing by removing the old M/C and changing to a Dual M/C [you still only have 1 brake circuit to the rears only] ----------------------------------------------------------------------------------------------------------------------- Now you want to convert it to 4 wheel brakes which I highly recommend because it will be safer. You can certainly do this properly within the constraints of your present wheel choice. Assuming your front spoked wheels are motorcycle [eg: Harley], try and find discs that bolt on ,and hopefully matching calipers [mounting brackets need to be fabricated for them] To get the brake bias done correctly , you need to throw out ALL of your pressure residual valves, and existing M/C Then use a twin M/C pedal box with an adjustable balance bar [use a 1" single M/c for the rear if that worked OK before] You can buy Firewall mount, Floor mount, and Under floor mount cantilever design off the shelf from Wilwood. Here is a floor mount version [the balance bar is circled] Here is the innards of a balance bar. It is a spherical bearing pivot that is infinately adjustable across the pedal from L to R [Fr to Rr] This one component will help you fix all the dramas that come from mismatched components. With a pair of Motorcycle calipers I would suggest a 5/8" M/C for the front [as a start] Now to get around the residual valve issue [causing the fluid to syphon back] simply use the remote reservoir type M/c's [shown in the 1st photo] and mount the reservoir high on the firewall. [you could even mount them in the turtle deck/ pickup tray because gravity is gravity] This is how we plumb race cars and eliminate all the baggage that comes along for the ride [they are easy to bleed and don't syphon back] -------------------------------------------------------------------------------------------------------------------- One last thing.......If you dont want to "re-engineer" your existing pedal assembly! Wilwood make this neat little remote pedal box that operates off a pushrod from your existing pedal. [these are cheap] Here: you mount it in front of your existing pedal which pushes on the heim joint [blue arrow] This is mounted at a 60 degree angle so the M/C's are staggered The M/C pushrods are operated by a remote balance bar. They need flipping over in the photo [red arrows] This setup comes with a neat little bias adjustment dial , But it does alter the pedal ratio by 1.5 to 1 making it softer so larger M/C bores may be required Twin M/Cs and simple plumbing will fix most issues with brake systems [bias , bleeding etc]
Update to all of you who have been kind enough to give advice. I have been layed up for a while with a large kidney stone. Just got it busted up last week and have been able to do some on the T Bucket. I wasn't happy with the push rod linkage and the way it aligned with the master cylinder. I don't know what the original builder was thinking but the brakes had to be a problem from the beginning. After a new bracket and adjustment slots to better align the master cylinder, I also installed a T in the line to use both reservoirs. I haven't taken it out yet to test the brakes but hopefully they have improved. I have bled the system so many times both the old fashion way and with a vacuum system. I can't believe there is still air in the lines but I am not ruling it out. I am still planning on replacing the calipers with some that don't have the emergency brake hook up. I'll probably order those tonight. I am looking a calipers that have a 2 3/4 inch piston. I'll keep you all in the loop.
Looks like I have the brakes I was looking for. I ordered the GM metric calipers with the 2 3/4 inch piston. I also ran both reservoirs through a T fitting that feeds the rear brake calipers. I can now lock up the rear wheels on loose gravel with not much effort. Thank all of you for your input and suggestions. I will likely still install front brakes but now the car is much safer to drive and will stop quite well with just rear brakes.
Thanks for the update, seems lot of time we never hear the end results. I agree that adding front brakes is something you should do.
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