1973 brakes

[Joseph A.]

I have a 1973 with a real soft pedal and almost no stopping ability. I want to begin diagnosing the problem but need to first determine if dot 5 was used previously before I begin bleeding the system. Any ideas on how I can determine this? Any inputs on a publication or primer on 1973 brake system would certainly be appreciated. I've read some on ss sleeving and ss lines and the like and understand this may ultimately be the direction to resolve brake issues once and for all.
Thanks for your help with this.
Joe - 46306

[Gary Schisler]

Re: 1973 brakes

I believe from previous posts that DOT 5 is typically blue or purple (?) and is therefore quite different than the honey or tan color of DOT 3 or 4. Look in the archives for brake fluid.

Btw, I would start by looking for leaks at the calipers. Finding none, I would start at the master cylinder (which is my first hunch)]

Gary

[Jim T.]

Re: 1973 brakes

First thought in reading about your soft pedal on your 73 is air in the rear calipers. If your 73 rear discs are not attached to the spindle with the original rivets like it left the factory I would bet that you have to much runout and the rotation of the brake disc is moving the caliper pistons in their bore when you drive the car. If you properly bleed your rear calipers and get air out of them and subsequently get a strong full brake pedal you most likely have the runout problem. I have experienced this on my 70. Silicone DOT5 is a thicker liquid than regular brake fluid. Old silicone brake fluid will lose its original color and can look similiar to regular brake fluid. If you find that your rear brake calipers are still rivetted to the spindle and you have no air in the calipers (2 bleeders per caliper) you may need to rebuild your master cylinder. If your rear calipers have air and your discs are not rivetted in my opinion the best money you can spend for the safety reliability of your 73 is to send your complete rear control arm assemblys to Bairs in Pa and have them rebuild the whole assembly. New rear wheel bearings, rivetting the discs, etc. Check out their web page, they even supply the shipping containers.

[Joseph A.]

Re: 1973 brakes

Thanks Gary, I'll take a look at the dot color and start my investigation as you suggest. Thanks for the information.
Joe

[Joseph A.]

Re: 1973 brakes

Thanks for your detail reply Jim. From a review of the previous owners receipts, I see where 4 calipers were purchased from NAPA in 1996 so your suggestion of the rear calipers not being rivetted to the spindle may very well be the issue. The safety is the big issue as I have other items I want to work on but this is taking priority due to the lack of safety. Thanks for your sage advice Jim. Regards, Joe

[Joe L.]

Re: 1973 brakes

Joe-----

Replaced calipers do not necessarily mean that the rear discs were removed and/or replaced. You need to look at them with the wheel off to see if the rivets are still in place (they'll be 5 large, flat-head rivets in the depressions between the lug bolts).

The best way to positively ID the fluid is to remove an ounce, or so, from the master cylinder and place it in a small, clear glass jar or vial. Add an ounce, or so, of DOT 3 or 4 brake fluid (or just water, if you wish), cap the jar and shake it. Then, let the jar sit for 5 minutes, or so. If you see a phase separation (i.e. there looks like 2 "layers" of fluid in the jar), then the fluid in the master cylinder is DOT 5 silicone fluid. If the mixture is completely homogeneous, then the fluid is DOT 3 or 4 glycol-based fluid.

[Roger S.]

Re: 1973 brakes

I believe Jim T was talking about the rotors being riveted to the wheel flanges as from the factory. The calipers are bolted to the carrier.

I rebuilt my calipers for my '73 two years ago. Bleeding the two rear caipers took forever. But since you have not just built them and the 'pedal' has gone soft you may have the 'wobble' effect, too much runout of the rotors that 'pump the caliper pistons and allow air into the calipers behind the pistons. If this is the case you will need to rebuild the calipers and replace the piston seals.

Roger

[Joseph A.]

Re: 1973 brakes

Thanks Joe on the rivet info and the DOT experiment. I really appreciate it. REgards, Joe Asselmeier

[Joseph A.]

Re: 1973 brakes

Thanks Roger, I reread Jim T's post and agree he was talking about the rotor riveted to the wheel flanges. I'll bet you guys are absolutely correct on the runout problem as when I removed the master cylinder top today it was clear this had been done with some frequency as there was pronounced scratching over the risers that the top steel bracket rests on. Thanks for all your great inputs and I will start digging into the problem as spring is coming here in North Carolina and I want to be ready for the good weather. Regards, Joe Asselmeier