[NeighborsComplaint]

Finally pulled my '71 GTO out of storage yesterday. It was relatively uneventful, car fired right up and settled into an idles ready to go. I was parked nose-in tight in the corner of the barn (metal building) so I had to "inch the car over" out of the corner with small 3 point turns for lack of a better term. Once I was far enough away from the corner to clear the passenger side front corner, I was able to back down the central aisle and out of the barn.

The entire time, the car was fighting me like I was trying to park a 4wd with the front hubs locked. The brake pedal was not normal (high and hard) and the brakes were dragging excessively. Coasting in neutral felt like a downshift.

This persisted for the 10 minute 30-35 mph ride home. Once home the rear wheels were hot and the fronts hotter. Because they were evenly locked up at all 4 corners (wheel disc brakes). I can only assume the MC had somehow stuck when I initially applied the brakes. Pretty unlikely all 4 calipers would rust and lock up stored indoors.

The car was a little dusty and it just started to rain, so I figured the rinse would do the car good. It rained pretty good and washed the car spotless so I toweled it down with some quick detailer and pulled it in the garage ... I immediately noticed the pedal had returned to normal and the brakes were no longer dragging.

I checked the fluid in the MC and no signs of rust. I figured for sure I would be flushing the brake fluid and replacing it.

Any idea what happened?

[gtospieg]

Your car was showing its displeasure about not being driven for a long period. Now that it knows you still care it lost the attitude and is forgiving you.

[67drake]

I would guess the master cylinder if all 4 were sticking, but it reminded me of something I dealt with a few months ago-
http://forums.maxperformanceinc.com/...ghlight=Brakes

[NeighborsComplaint]

Originally Posted by 67drake

I would guess the master cylinder if all 4 were sticking, but it reminded me of something I dealt with a few months ago-
http://forums.maxperformanceinc.com/...ghlight=Brakes

Good thought but the connecting hoses are about 3 years old. It braked and tracked perfectly straight like all 4 brakes were applied with the pedal stuck at the top of it's travel. I could apply braking pressure but the pedal felt like it wouldn't yield. I've never experienced that before and it just self-corrected somehow.

I may throw a new master cylinder on just the same.

[NeighborsComplaint]

All was well until it wasn't. lol

I drove to the hardware store and parked it for about half an hour. As I was backing out of my parking spot, I could feel the brakes beginning to drag and the car fighting to get moving. I drove a few blocks and they were damn near locked up again. I was about 12 miles from home so I took the backway and drove about 30mph on the side streets until I could smell the brake pads. Pulled over as sat about 15 minutes to let the cool a bit and got back home. Backs are dragging but the fronts are nearly locked. Pedal is rock hard with no travel.

I'm thinking the prop valve is stuck with full pressure on the front circuit. I just ordered a new master and prop valve and hope to pre-bleed them and install as I can no longer work under the car with my paralysis. Getting on the ground is easy, it's the getting up part I can't do anymore!

[NeighborsComplaint]

Well here's a coupple of revelations I had ... while looking into this.

Looking back, I was never really happy with the 4 wheel disc brakes I installed. Bled them multiple times, couldn't get a decent pedal, swapped a dual diaphragm booster from '80-'81 Firebird T/A Turbo for better boost with my low engine vacuum (108 LSA cam). The master cylinder (Corvette 4 port) required the shorter pushrod so I retained that. Stopping was still not good.

I was never happy with brakes which required lifting my foot while swinging my knee clear of the steering wheel knee and then slipping my foot down sideways and rolling it to the flat of my foot to apply the brakes. Everyone who drove the car made the same comment that the seats were either too high or the steering wheel too low to apply the brakes. The brake pedal was too high to heel and toe and adjusting the brake pedal lower wouldn't allow enough travel in the pedal to stop the car.

I took it upon myself to lower the brake pedal to require less leg lift and more heel and toe movement and installed the longer Firebird style (recessed master cylinder) pushrod which seemed to solve the problem and improved the stopping. I was happy with the result until the two incidents of locked up brakes this year. Apparently, the longer pushrod caused overtravel in the master and the shuttle in the proportioning valve would become trapped, locking the front brakes. Fortunately, it only happened with the car at rest with my foot on the pedal when starting.

This was a revelation in a couple of ways. I determined the shorter pushrod was needed but caused the brakes to have excessive pedal travel before brake engagement and poor overall braking. It also occurred to me to move the master forward to restore the proper piston travel in the master using the longer pushrod but that would expose the back of the master cylinder bore to contaminants. As an alternative, I could move the entire booster/master forward as a unit, use the longer pushrod and limit the depth of the master cylinder stroke by the pedal adjustment and rod position.

I also came across an interesting little tool I never knew existed ... a proportioning valve stop that screws in the brake warning light port and traps the proportioning valve shuttle to allow complete bleeding of both the front and rear hydraulic circuits that would otherwise interact and share any trapped air back and forth between the circuits when attempting to bleed the brakes.

The proposed (moving the master and booster forward) would likely create a hood clearance issue because my master and booster are severely inclined and just barely clear the hood now. The depth of the dual diaphragm booster pushes the master cylinder further forward and up (see pic). Additionally, the fact that the master cylinder is inclined at such an extreme angle, the front reservoir hardly holds enough fluid to keep the master from siphoning air. On hard acceleration, I can easily imagine the already low fluid level climbing up the back of the reservoir exposing the port in the floor of the master. A guick stab of the brakes and more air is siphoned into the system making the pedal travel even longer to compress the air.

In an effort to level the master cylinder better, I plan to slip a pair of beveled washers on the top booster studs between the booster and the firewall bracket to tip the booster forward more towards level. If I'm not happy with the result, I'll have to disconnect everything, install straight firewall brackets (level master cylinder) and then bleed everything again.

I'm hoping I can get the desired result without disconnecting the brake lines and requiring a full system bleed. This may sound hard to believe, but not a single ship in town will touch a car with aftermarket brake components. The best shops in town (no performance shops in this area) have told me unless they replace every aftermarket component with OEM replacement parts to original function, they won't touch it.

Proportioning valve bleeding tool ... its real purpose is to prevent the
proportioning valve from self-compensating and equalizing braking
pressure through fluid diversion front to back while bleeding:


Spacer to angle master/booster forward and down towards level:


Current level of master cylinder: