Swapped out my manual drums on my 71 Elky with a power disc setup from a donor Chevelle. Seemed kind of crazy to even use the brake setup cause I replaced all most all of it with new or rebuilt stuff but thats another story. I was pleased how well it came out but now that I've driven it I'm not sure it was worth it. Is it normal not to able to lock up the brakes? I mean, it stops ok but its almost like what ABS feels like. I can slam on the brakes hard and it doesn't pull one way or the other and like I say it stops ok, but in no way does it feel like its even close to locking the wheels. Its like what I imagine it would feel like if the car was severly over loaded, it stops but not overly quick. They don't feel mushy like air in the line. I'm assuming that the pads that came loaded in the calipers when I got them are probably on the cheap side but I wouldn't think that would affect the stopping power that much, just the wear.

Any thoughts or is this typical of an Elky with stock disc's?

I can lock mine up - but it takes an awfully hard stop. I'm not sure what might be the problem or if you even have one at all, but someone smarter than me will chime in. Did you use new brake lines? Either way, are you sure there's no dirt or anything clogging in them?

Good luck!
Ryan

after a couple of days and many stops, the pads will become seated(for lack of a better word) and the brakes will probably work better, give them a chance.

Jeffry- My 70 has the front disks off of a 71 montecarlo.... I can lock them up no problem.

Braking on mine is about the same as my old 69 with manual drum brakes- only this one takes a much lighter pressure to slow down/stop. Much better of course in wet weather. My current pads are parts store cheapies like yours- My next set of pads (this spring) will be the "praise dyno" ones that are supposed to be considerably better than stock...

I think the main advantages of stock disk brakes on our cars over the drum ones are, no pulling to the side (because of misadjusted drums)- less brake fade than drums- and better wet driving condition.

I could be wrong, but I don't think they really help stop the car that much quicker- but they will stop it better after a bunch of quick stops(less fade).

Anyway, you might take a look at these guys:
http://www.praisedynobrake.com/
maybe their pads/shoes will help stop a little better.

Talk to ya later!
Ben

You went from a manual to power setup?

If so, you'll need to make sure you hooked the brake pedal push rod into the brake pedal power hole and not the manual hole.

Did you swap out the proportioning valve too?

And like was said, did you bed the brake pads?

Joe

I put new brake lines on and had the system power bled. I actually didn't see the donor car but I have seen and compared every componet with other cars and the assembly manual and everything appears to be correct. I did replace the proportioning valve but I don't know how to tell if it works or not. As far as the booster rod goes, I didn't even know there was two holes there until installing it and it wouldn't fit in the top hole so I did some research and found out it goes in the bottom for power, top for manual.

How do you seat the pads or does it just happen with time and stops? I've probably only put 40 or 50 miles at the most on it since the swap and a lot of that was mashing on the brakes. I don't know if it is my imagination or if I'm just getting used to it, but I think it might be getting a little better.

Thanks for the help guys!

What kind of master cylinder are you running? Might not be getting enough pressure.

Later
Steve

I second what Steve said. Did you use the master cylinder from the power disk car? If you reused your manual one, I think they are different.

What pads are you using and did you break them in before using the brakes hard? You might have glazed the rotors over if you didn't "bed" the pads as Joe said. Also, if you are using cheapo pads, that could be it also!

Please answer some of the other questions and we'll try to help more.

Bill C.

The car doesn't sound right to me. I can lock them up no problem. You need to check the booster and master cylinder to make sure they are correct and getting enough vacuum.

It's always seemed to me that drum brakes lock up easier than discs, but that disc brakes stop the car better.

FWIW, when I first did my disc brake conversion, it took a few trips around the block to bed the pads. It seemed a little scary until then.

The master cylinder is new and looks just like the original that I turned in for the core charge, I told them the application so I wasn't concerned. The calipers came with pads already loaded in them and I'm pretty sure they don't use the highest quality. I've had quite a few people tell me that would the effect the longevity more than the stopping capability. This post is the first time I've ever heard of of "bedding" the pads. How do you do that? The first couple of test drives I didn't push them to hard but I did warm them up. Since then I've only attempted to lock them up a half a dozen times with no luck.
I'll be driving it today for 35-40 miles to pick up some parts for my 4-door so I'll just drive it normally and see what its like when I get back.
Thanks for the help guys, with you on the team I'm sure we'll get it worked out!

Digging back into the brain archives from my college days, I remember doing analysis on disc and drum brake systems. The general rule is that a drum system will lock up sooner than a disc system using the same pressure (and all other factors being equal). This is because the friction between the drum and shoe increases exponentially as pressure is applied to the pedal, but the friction between the rotor and disc increases linearly. If I remember correctly, you actually get more stopping power from a drum than a similarly sized disc system, but only if you can keep the parts cool. Superior performance is possible by going to discs because of the larger sizes available and the improved cooling. Also, the wheels will lock up when the friction between the brake surfaces exceeds the friction between the tire and the road. Therefore there are a lot of factors affecting brake lockup, ie just going to wider tires will reduce lockup.

Jeff,
The master cylinder is different and larger for the disk setup. I'm willing to bet thats the problem.

spoken like a true genious wilbur. :D i believe the wodr you are looking for chev64 is burnished.

Yes a disc brake master cylinder has a larger reservoir but has smaller bore to generate higher pressure. You should check the master cylinder to make sure it is for a disc brake application.

I checked and I do have the correct master cylinder. After driving it for another 30 or 40 miles it seems to be stopping with a little more authority. I didn't try locking them up but I'm gaining confidence they will stop me fairly quickly.
Thanks for all the input guys!

Yeah, I guess I should have mentioned that I don't always speak literally.

When I say "a few times around the block", that usually means 50 miles or more. Short drives just aren't any fun for me. :cool:

Glad to hear that things are improving.

Where does your booster get its vacuum supply? If it is tee'd into the pcv system it may not be getting full vacuum. It should be hooked to the fitting on the rear of the carb or directly into the manifold.