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critter · 11-30-2003, 03:54 PM

This weekend's junkyard run was much more productive. I pulled the calipers, shields, backing plates and proportioning valve from an 83 Seville. I know, everyone says 79 but this all measures out like it will work. Even the line hookup to prop valve from the MC is the same as my car. Wish me luck.

Jeffzilla · 12-05-2003, 06:32 AM

Maybe the proportioning valve for the brakes would be different?

PMDRACER · 12-05-2003, 12:00 PM

Should be fine. The car you got it from is similar in size and weight to the A-body.

TIGER EFI - Electronic Fuel Injection for the Traditional Pontiac Engine. bill@tigerefi.com

The point to life isn't necessarilly the decimal.

Scarebird · 12-05-2003, 06:34 PM

OK, got a few in and they fit great. E-mail me if interested...

My ebay auction ( I do sell them off ebay of course...)

http://cgi.ebay.com/ebaymotors/ws/eB...ADME:B:LC:MT:1

jays68yak · 12-24-2003, 12:02 PM

Hey Scarebird
Whats the size of the hole in that the bearing goes through? I have the setup from a 79 Transam with the backing plates and what not. Im using a custom rearend, a fab9 with the 10 bolt axle flanges and a bigger bearing. I had to cut the hole bigger in the backing plates that I have. Still dotn have them on the car cuz I need to find someone to turn down the axle flanges to fit into the rotor. Yours look more bling then mine so I might consider them down the road.

-----------------------------
68 Lemans 350/th350/fab9(3.89s, locker, SS axles)/NOS Cheater kit

I need to get off my lazy butt and get my car back to the track......

Scarebird · 12-28-2003, 12:23 PM

2.625"

critter · 01-12-2004, 07:36 PM

OK, fellows, I need help. As you know, I'm swapping the rear drums for the Caddy calipers/TA rotors on my 1974 Trans Am. Everything is bolted up and I've bled brakes until I'm blue but I can't get a firm pedal. Here's the skinny:

Drum/disk master cylinder
Caddy proportioning valve
Caddy calipers, rebuilt

I can pump the pedal but it never gets firm. This makes me wonder is my/our theory of the drum/disk MC working is wrong. What do you think? Should I swap out the MC for a disk/disk setup?

PMDRACER · 01-12-2004, 08:30 PM

First off, a disc/drum master cylinder from what car? If it's the older style A/F-body master, you won't push enough fluid through that rear port to get the rear calipers taken up, and a low pedal will result.

Secondly, the rear pads need to be within 1/32 to 1/16 of the disc rotor. If you are much farther than that, you won't get a good pedal for reasons as explained above.

For the front calipers - I'd suggest opening the bleeder, and compress the piston with a c-clamp until you get solid fluid.

Since you cannot do this with the rear calipers because of the adjusting mechanism - remove the master cylinder lid, open the bleeder on the caliper, and use a mity-vac to draw on the caliper until solid fluid comes out.

Now fill the master again, put on the lid and pump the brakes until the front calipers push out again. You should have plenty of pedal as long as that master cylinder is correct for the application and your problem was just air in the lines.

TIGER EFI - Electronic Fuel Injection for the Traditional Pontiac Engine. bill@tigerefi.com

The point to life isn't necessarilly the decimal.

[This message was edited by PMDRACER on January 12, 2004 at 10:43 PM.]

critter · 01-12-2004, 08:47 PM

The MC is from a 1974 TA with a disk/drum setup.

Now I'm going to really mess things up. I don't have standard, single piston calipers on the front disks. I'm running the Howe dual pistons that I adapted to the front spindles. You can see them here:

http://www.arkansaspontiacs.org/BudgetBrakestory.htm

The brakes worked swell and had a good pedal prior to starting on the rear disk.

I did adjust the rears to the point of having slight contact with the rotors. I've re-bled the fronts and backs due to having the entire system open to install the new proportioning valve from the 83 Cadillac Seville.

It would seem that a hydraulic system is a hydraulic system. If the air is out, the pedal should firm up, right? The only thing I'm questioning is that perhaps the valving in the MC is different and not allowing enough fluid to move to the rear to give a firm pedal.

My main reason for this line of thinking is that, with air, I've always been able to keep pumping the pedal until firmed up. I can't do that right now.

critter · 01-13-2004, 07:42 AM

One other thing, I'm running DOT5 silicon fluid. I know that it tends to be softer than other types of brake fluid. Could that be part of it?

PMDRACER · 01-13-2004, 10:37 AM

From what you say, everything is spot-on, except for the master cylinder.
I have to believe that if you swapped to a 4 wheel disc T/A master, your problems would be solved.

But now you mention besides the addition of rear discs that take more fluid to apply, now you have the dual piston front calipers. Without measuring total bore area of the 4 pistons versus the old 2 pistons, I'm gonna have to assume that now the front calipers are needing more fluid to apply too.
If the master cylinder you are using does not push into the lines the appropriate volume of fluid needed to apply the brakes, you will never get a high pedal and effective brakes. Sounds like you may need a master cylinder with larger bores that pushes more fluid like the GM aluminum unit from a pre-'91 Chevy Caprice or wagon.

Make sense?

TIGER EFI - Electronic Fuel Injection for the Traditional Pontiac Engine. bill@tigerefi.com

The point to life isn't necessarilly the decimal.

PLAY400 · 01-13-2004, 10:50 AM

DOT5 is just fine. I put a Ford disc brake 9" in my 68bird last year and the brakes worked fine. Been using DOT5 for the last 3 years in all the toys. But there are big differences in Master Cylinders. When I buggered up my first 1 from a Caddie I started looking for a replacement.
While all the porpotioning valves from the 4 wheel disc cars looked the same I noticed different bore masters and then I got curious and started opening them up. Looks like they have a 'pill' in them restricting the fluid flow. Same bore, same brake setup, different pill? And to make things worse both my part suppier and junkyard x-over books indicate they are all the same. I found what I was looking for eventually. Good luck with you problem. Side note, just pulled the 9" and replacing it with a 12 bolt from a 70 Nova, drum brakes. fun again

critter · 01-13-2004, 11:19 AM

PMD and Play400, thanks for the responses. Sometimes a little advice helps keep me sane.

PMD, it makes perfect sense. The MC I ordered is supposed to be a 1 1/8 inch bore which is the largest I've seen so far. I'm thinking that's the issue. The front brakes were working fine with the rear drums so I think having the added volume to the rear disks is all that's needed.

critter · 01-13-2004, 07:42 PM

The new disk/disk MC is making a difference. I put it on tonight and began bleeding. I could immediately feel the difference. After several bleed sessions with the MightVac I was making progress. I'm still not there but I'm using DOT5 silicon fluid so I need to stop and let the bubbles settle overnight. I'm also going to buy a couple of bottles of new fluid so I'm not recycling areated fluid.

Thanks everyone for all you your help.

PMDRACER · 01-14-2004, 05:16 PM

Cool beans!

TIGER EFI - Electronic Fuel Injection for the Traditional Pontiac Engine. bill@tigerefi.com

The point to life isn't necessarilly the decimal.

critter · 02-07-2004, 12:56 PM

The disk brakes conversion on the rear of the 1974 TA is finished. I officially had the shake down run today. All I can say is that I wish I'd done this a long time ago. I'll get some hard numbers from braking tests as soon as I can and I'll post them here. I think it might be time for a baffled oil pan now.

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