Davidmij - Disc Brake Conversion & Rim Problems

[simplyconnected]

Dave Jones, I pray that your family and property are spared from the terrible fire in Los Alamos, New Mexico. In Michigan, we hear that fire is the worst in NM's history and it is only 5% under control, it threatens 20,000 metal barrels of plutonium, Indian Reservation land, and has already charred 93,000 acres of thick pine woodlands, after firefighters have battled it since last Sunday. We see satellite images of dense smoke spreading over vast areas. Again, I pray that you and your family are safe, and they get the blaze under control quickly.

...it seems to me that the regular bleeding with a hose and a can would be good? My pedal is firm and has a short travel range...

Bench Bleeding saves a lot of brake fluid. Most new M/C's come with a plastic set of hoses and holders for this task.

I counted about 25 full pumps before ALL the air was out and the recycle hoses ran clear (no bubbles in the fluid) in my M/C. Most folks never get a completely dry (new) M/C, so they don't need to Bench Bleed.

The internet if FULL of cautions and instructions regarding Bench Bleeding. I would say, if your pedal is not mushy (feels hard right from the top), you probably have no air in the lines.

I am bothered by the fact that your brakes won't lock up in a 'panic stop'. They should, just like a modern car without ABS.

[davidmij]

Thx Dave, some of the media (as always) is exaggerating the possibility of what is in the 20,000 barrels. Plus they are in no way threatened by fire - they are in an area of low growth sage that has been bulldozed to the dirt.
Yeah, I don't know what else to do with these brakes. The pedal feels good, the fluids run clear, they don't pull to either side, and the neither the front or the rear will lock up. I may end up taking it to our local mechanic if I don't get any ideas here on-line.
thx again as always

[simplyconnected]

Let's see some pictures of your setup, Dave. If you have any problem posting them, send them to my email address:
simplyconnected@aol.com
I would like to see the booster combination, the proportioning valve, and your front wheel brakes.

Original brakes had only one 3/16" steel tube coming off the M/C, which split four ways (to each wheel).

Our modern system splits the flow into TWO brake lines coming off the M/C. If we could lock the brakes with the OEM plumbing, the new split system should lock brakes much easier. It does on my cars.

[davidmij]

Here's a link to my pictures on "Picasaweb".

https://picasaweb.google.com/101492851059660555641/TBirdDiscBrakes2011?authkey=Gv1sRgCK6Gg9yhpdfGWg

The proportioning valve is plumbed just like this picture below. I can only believe that the MC booster isn't (completely) working still. They fixed the diaphragm on it and shipped the same one back to me. If I hold the brake pedal and start the engine I can feel the pedal drop a little when the vacuum kicks in, just like on a modern car. I may end up taking it to my local mechanic to see what he thinks. This really sux cuz I spent a lot of time and money on this MC setup.
Thx again, Dave J

[simplyconnected]

Dave, I only have a couple suggestions after looking through your pictures.

I see two green brake light wires dangling... what did you do with those?

I can't see from the pictures, but do you have a return spring on your brake pedal pivot shaft?

I noticed, your calipers are missing the rubbers. It's important you use all the rubber parts in these calipers. Auto parts stores sell kits for these calipers which include all the rubber details.



The only other thing I can suggest is for someone to step on the brake pedal while you (or a mechanic) makes sure the booster isn't running out of stroke at full pedal. - Dave

[davidmij]

Wow, very observant Dave, thx. The green wires are the ones that went to the switch on the old M/C. I thought that it was just a sensor switch that goes to a light on the dash, or the rear brake lights??? I'll look in my manual. I plan to hook it up once I get the correct connector.

I do remember there being rubber guides on those calipers when I got them so I'm not sure what happened to them. I would think that could definitely cause some binding.

I don't have a return spring - never did so I'll have to look at the manual once again and see where it goes. The pedal rests at about a half inch from the full return position - a little high for my liking, but at least it has that half inch of slop at the rest point. It depresses about half way to the floor and is nice and firm - seems to be just right. I'm pretty sure it isn't running out of stroke - if anything the stroke is too short.
Oh, and I have reinstalled the air canister and check valve since the pictures too. It said in the manual that it is important because it catches gas vapor or fumes that can deteriorate the parts in the booster. That didn't make any difference.
I'll fix the items you pointed out and let you know what happens. Thanks again for your help Dave!

[davidmij]

Well it turns out everything on the calipers is OK. The metal bushing is in place on the inside of the caliper and the photo you enlarged doesn't show the rubber washer because it is an "O" ring seated inside the caliper casing. In other words it's not visible while the caliper bolt is in place. Double checked everything while I had it apart and it all looks and works correctly. No kinked lines, no leaks, no binding parts, the pads slide smoothly while applying the pedal, etc. The only thing I can come up with is that the booster is still bad. It does help some, but no where near where it should be. Either that, or the vacuum isn't enough. I'm going to take it to my mechanic and have him spend an hour checking it out. At least that way I don't have to pull the darn thing again and send it back w/o an experts opinion.
regards, Dave J

[Astrowing]

David, since you do only have 13 inches of Hg at idle, your boost won't be as good as it would be with more vacuum. It is working since you feel the pedal move downward when you start the car. It just may not be working as well as you'd like it to.

Also, the key point for the brake pedal return is not the pedal itself, but the master cylinder pushrod. Does the pushrod return all the way back? if not you won't get full hydraulic fluid transfer and pressure down to the wheel cylinders. It can't bottom out prematurely.

Does the pedal not have a return spring? I thought they all did.

[simplyconnected]

David, since you do only have 13 inches of Hg at idle,...

That's not enough to make 700 pounds of boost.

Does the pedal not have a return spring? I thought they all did.

Here's a picture of your brake pedal with the spring:

[davidmij]

Thx Dave, my car didn't have one to begin with, and the clutch and brake pedal assembly I bought from Greg (purple bird) didn't have one either. Kinda weird. Anyway, I'm taking the car around the corner to a mechanic on Friday and he'll check my vacuum and look at the brakes. He should be able to tell me pretty quick if it's the MC or not.
thanks for your help and pointers.

[davidmij]

Hey Jim, the brake pedal does return fully to the resting point. The resting point has about a half inch of slop. In other words, if I reach down and pull on the pedal it takes about a half inch for it to be all the way up. If I let go it swings back down that half inch to the resting point. A spring would return it an extra half inch. I watched the pushrod as my daughter pressed and released the pedal - it looks good. I also had her reach down and pull it up from the resting point and it didn't move the push rod any more.
The 13 pounds at 6500 feet is really about 19. I check my 1992 F-250 460 ci at it's booster and it read the same, yet the brakes on big old truck are WAY better than the T-bird.
Can anyone tell me how to get more vacuum? The only current source on my car is the manifold. The other line off the manifold fitting has been plugged so there is no where else it goes except the brakes. See my pictures again at: https://picasaweb.google.com/1014928...CK6Gg9yhpdfGWg
I guess I can rig up a little spring to return the pedal all the way - it wouldn't take much because the pedal is just dangling there under it's own weight.
thx, Dave J

[jopizz]

You may be able to get more vacuum by adjusting the timing and/or the mixture screws on the carburetor.

[Astrowing]

There is a reduction of vacuum of about 1 per 1000 feet of elevation, so at 6500 feet 13-14 vacuum is about all you get. David lives up in the mountains in New Mexico. David, you might check and see which jets you have in the carb. High altitude ones would be in order.

[davidmij]

Thx Jim, I'll ask my mechanic tomorrow - he grew up here in northern NM so he'll know. He's the one that told me 13 was about all I'll see here.
I used a carb rebuild kit back when I bought the car but I didn't change any adjustments on the carb. Just took it all apart and cleaned it, and replaced the parts that it included - it was over flowing from a stuck float (sat for 15 years without running). It starts nicely but the engine smokes real bad, pretty sure i have some bad rings. Anyway, I'll know by Friday night what I need to do.
cheers to all!

[tbird430]

You could probably install an electric vacuum pump somewhere to assist your power brake system....