Help with brakes

[Mark L]

I just completed the following:

 

New flanged rear axles

Turner disc brake conversions, front and rear

All new brake tubes

All new flex hoses

New dual master cylinder

Eliminated the hydraulic stop light switch and installed a mechanical switch at the brake pedal. The port on the MC for the hydraulic switch is plugged and sealed.

 

Today I filled the system with fresh DOT 4 fluid and bled the brakes. I found two leaks in the rear circuit. I tightened the leaky fittings and bled the rear brakes again.

With the engine not running, the brakes feel firm as they are applied, and I can see the booster and master cylinder flexing upward slightly very soon after I start pressing the pedal and as resistance builds up in the pedal.

This is the problem. The car is completely off the ground on jack stands and the wheels off. When I start the engine and apply the brakes, the pedal goes almost to the floor before I feel any solid resistance in the pedal. The booster and master cylinder do not flex up slightly until the pedal is nearly to the floor. As the pedal is nearing the floor, I can hear a change in tone in the engine as if there is an additional load on the engine.

With the engine at idle and the transmission in drive, and no pressure on the brake pedal, the rear axle turns. If I apply the brakes, the rear axle does not stop turning until the pedal is nearly to the floor, which seems to indicate to me that the booster is not applying pressure to the MC until the pedal is near the floor.

I removed the check valve on the booster and confirmed it only allows air to move towards the engine. I removed the vacuum hose between the check valve and fitting on the intake manifold and verified it is clear. With the check valve installed and twisted into position, it is still a little loose on the booster. There is one gasket in place.

When I installed the MC, I had to shorten the length of the actuating pushrod. The contact point on the piston is at a more shallow depth than the original MC. I adjusted the rod so that the rod is not putting any pressure on the piston as the mounting flange seats on the face of the booster. Lengthing it by one or two flats of the nut changes how the MC seats on the booster, so I know it's adjusted right.

What am I missing? What should I check next? I'm not going to drive it until I figure this out.

It wasn't doing this before I did all this work. The front brake pads were worn out, but the car was stopping and the brake pedal resistance was better than this.

 

Edited September 10 by Mark L

[Mel]

There are several videos on YouTube on how to test boosters, both in place and on the workbench.  Also, there are videos on proper adjustment of the actuating rod using a particular tool made for the job.  The tool, as I recall was $12-$14 and removes the guesswork.

I'd check to see if the gasket around the check valve is leaking.   With the engine idling, use a small rubber hose and, with one end in your ear, probe around the gasket with the other end listening for leaks.  You can also pull the hose off the valve, plug the hose and see if there is any difference in braking with the engine running.

Good luck.

[Mark L]

Regarding the tool, the Avanti shop manual has a drawing that shows how to make a tool, but it would only work with the stock MC. I could make a custom tool that does the same thing but matches the dimensions of the new MC.

Removimg the hose and plugging it while the engine is running would be just like shutting the engine off, letting the vacuum bleed down, then pumping the brake pedal until all the vacuum onside the booster is used up. I've already done that. The brakes work better in manual mode with the engine not running.

I tried installing an O-ring instead of the gasket, but the O-ring I had was too thick. I couldn't get the valve to reinstall.

[aardvark]

The measurement is 1.248ish-1.25" on the push rod from the booster face.    Don't exceed tie 1.25" This is according to the Avanti Repair book and also holds true in the paperwork that came with my new dual master (not installed yet.)

I'm running into other problems. sounding similar with the pedal going to the floor. It's on my original thread..

[Mark L]

The 1.245 to 1.250 measurement is for the stock single MC. Before I installed the new MC, I measured the distance to the piston from the mounting face. The old stock MC matched the dimension in the shop manual, but the distance to the piston on the new Raybestos dual MC was much less.  I shortened the pushrod to match the new MC. Otherwise, keeping the stock MC dimension with the new MC would cause the pushrod to compress the piston during installation. It's only suppose to have a small gap when installed.

[mfg]

Sure sounds to me like the pushrod is still to short… I would try lengthening it more, regardless if it begins pushing m/c piston in  upon installation.

[aardvark]

The paperwork on my dual master (not installed yet) is the 1.25" and the repair manual on the stock single is the same. So the Booster in my car is correct either way.

Ya gotta watch extending it too far since it will damage the Master.

Edited September 10 by aardvark

[Mark L]

I'll call Jim Turner tonight since I bought the MC from him. His instructions say to make sure it's adjusted properly, but doesn't give a value.

I bench bled the MC, but thinking back, I may not have had enough arm strength to fully push the MC pistons against the internal springs and get a full stroke. Since the MC is now installed, I think I'll re-bleed the MC on the car, since the brake pedal and my leg will provide more leverage.

Also, I was thinking about the plug I installed in the brass junction block where the line to the rear axle use to connect. The junction block is now oriented so that the plug is somewhat above the center of the block. There may be an air bubble trapped at the end of the plug that can't be flushed out. After I re-bleed the MC and the lines, I'll have an assistant push on the brake pedal while I loosen the plug to see if there is any air trapped in the junction block, then I'll re-bleed the front lines.

[mfg]

Good idea to re bleed the system, but to tell you the truth I highly doubt there is any air trapped inside that junction block.

[Mark L]

I confirmed in the instructions provided with the MC by Jim that the rod is to be adjusted so there is only a small gap (0.005 or less) between the end of the rod and the cup on the piston when the mounting flange of the MC is against the face of the booster. Since the piston cup on the new MC was as not as deep in the piston as on the original MC, the rod had to be shortened vs. the measurement of 1.245 to 1.250 listed in the shop manual in order to get the MC to seat on the booster.

It's very possible there is air trapped in the drilled passage between the plug and the center of the junction block. The block started out as a solid piece of brass. The areas drilled/tapped/machined for the flare nuts are at most only 5/8" deep into the sides of the block, but the block is about 2" across. That means there's about 3/8" length of a drilled passage that's only 1/8" to 3/16" in  diameter before all the drilled passages come to a common point in the middle. If the passage is oriented with a vertical angle, there's space for an air bubble to be trying to rise up against the plug I installed.

You have to remember, I replaced all the brake tubes, and I removed the junction block from the frame to clean it. There was absolutely no brake fluid anywhere in the system before I refilled it, only air. Any part that touched brake fluid was replaced, except for the junction block, and that was thoroughly purged.

[aardvark]

I would think that brake pedal pressure and fluid rushing thru when bleeding things out would push any air out of that small part.

[mfg]

4 hours ago, Mark L said:

I confirmed in the instructions provided with the MC by Jim that the rod is to be adjusted so there is only a small gap (0.005 or less) between the end of the rod and the cup on the piston when the mounting flange of the MC is against the face of the booster. Since the piston cup on the new MC was as not as deep in the piston as on the original MC, the rod had to be shortened vs. the measurement of 1.245 to 1.250 listed in the shop manual in order to get the MC to seat on the booster.

It's very possible there is air trapped in the drilled passage between the plug and the center of the junction block. The block started out as a solid piece of brass. The areas drilled/tapped/machined for the flare nuts are at most only 5/8" deep into the sides of the block, but the block is about 2" across. That means there's about 3/8" length of a drilled passage that's only 1/8" to 3/16" in  diameter before all the drilled passages come to a common point in the middle. If the passage is oriented with a vertical angle, there's space for an air bubble to be trying to rise up against the plug I installed.

You have to remember, I replaced all the brake tubes, and I removed the junction block from the frame to clean it. There was absolutely no brake fluid anywhere in the system before I refilled it, only air. Any part that touched brake fluid was replaced, except for the junction block, and that was thoroughly purged.

Good point…. Impressive job!

[Mark L]

After work today I bled the master cylinder again, on the car using the brake pedal to provide a full stroke and additional leverage over the internal springs. I think some additional air was bled out. Since I disturbed both brake lines coming off the MC, I re-bled the entire system. It appears there was additional air in the rear circuit. I then had my daughter hold pressure on the pedal while I slowly loosened the plug I installed on the junction block. I heard a tiny pffft, immediately followed by a dribble of brake fluid and my daughter saying the pedal was now slowly moving toward the floor. I then quickly tightened the plug while she kept pressure on the pedal.

The brakes felt better afterward, but I wasn't able to start the car to really test it. I determined all my activity at the MC had disturbed the lead wires at the start solenoid. By the time I figured this out, it was getting dark and time for dinner. I'll test the brakes using the booster tomorrow after work.

Edited September 12 by Mark L

[aardvark]

Good luck, Bro.

Not going well on my end (other thread_)

[64studeavanti]

FWIW, change the front pads. The Dunlop system has stops when pads are worn so they do not contact rotors.

[John D]

Hmm, The change in engine tone would indicate the booster is using vacuum, I wonder why this wouldn't occur sooner in the stroke... did you leave the existing booster in place? btw brake booster exchange is in Lynnwood, in case you decide to go down that rabbit hole. They turned my 79 booster around in a couple days. Also it's probably different but I have a working booster from a 63 Cruiser on the shelf. 

[silverstude]

Have you readjusted the brake pedal height with the eccentric bolt?

 

[Mark L]

Yes, I initially adjusted the eccentric to get the 7/8" measurement in the shop manual. Since the pedal is going to the floor, I've temporarily adjusted the eccentric to get the pedal as close to the seat as possible so I can get more pedal travel.

I've spoken with Jim Turner for additional advice, and when the weather improves in a few days I will work with the pushrod adjustment some more, experimenting with various changes to see what happens.

Other than adjusting the pushrod, I have not disturbed the booster.

I still have my Lark manuals. I'll compare the part numbers and let you know if I can use it. Even if it's remporary, it looks like it would be an easy swap. Thanks.

Edited September 14 by Mark L

[Mark L]

John, I checked my Lark chassis parts manual. If the '63 Cruiser the booster came from had disc brakes, it's the same part number as on the '63 Avanti.

[Mark L]

Short story:  After consulting with Jim Turner, we believe the new master cylinder is bad, out of the box.

Today I had more time to work with the pushrod between the booster and the master cylinder.  I initially shortened it, and the brakes were much worse when the engine was not running and running.  With the engine not running, there was a lot of pedal travel before there was any resistance.  With the engine running, the pedal went straight to the floor.

I then returned the pushrod length back to its starting point, then began incrementally lengthening it one or two full turns each time.  After each adjustment, with the engine not running, the brake pressure built up earlier and earlier ("higher" brake pedal) and was firm.  With the engine running, the pedal still moved about 3 inches without any resistance before finally building up pressure towards the end of the stroke, getting firm about 1/2 to 1 inch above the carpet.  Then, the pedal slowly sank to the floor as I held pressure on the pedal.  The single MC on my Lark Daytona was like that before I replaced it.  The pedal would initially be firm, then pressure slowly bled off due to an internal leak.

Also, each time I lengthened the pushrod, I checked to see if I could turn the rotors at each wheel by hand when the brake was completely released.  The longer the pushrod was, the harder it was to turn the rotors by hand.  This meant the pushrod was too long (wasn't allowing the fluid pressure to release from the calipers).

I spoke with Jim Turner.  He had one last new MC on the shelf, so he's shipping it to me tomorrow.  I should have it later this week.

Edited September 16 by Mark L

[Mark L]

After consulting with Jim Turner, we decided the new master cylinder might have been bad out of the box. The new one arrived on Friday Sept. 20. After bench bleeding it, I installed it, along with a good used booster I got from John D. I installed them Sept. 21 and re-bled the entire system. Same results, pedal goes to the floor with almost no resistance.

Thinking I may have not adjusted those finicky Cadillac rear calipers the right way, today I did a complete simulated rear pad replacement and readjusted the parking brake levers so they have no more than 1/8th inch travel off the stops before the pads clamp on the rotors, and re-bled the rear lines. No good. The brake pedal still goes to the floor with the engine running.

I've been through almost 4 quarts of brake fluid bleeding the system. All the connections are dry.

Other than capping the front line, then capping the rear line to isolate the side where the problem is, I'm not sure what else to do.

[aardvark]

I feel Your pain.

I went thru everything in the Stock Configuration and am still not getting anywhere near the braking power needed,,, Then the power Steering drained itself,, so I couldn't road test right away... Then.. the Ignition Key broke off in the Ignition.

(Sheesh,,, What next??)

So I haven't been able to even Road test.

[Mark L]

I'm finally getting back to working on the car this weekend. I had a death in my side of the family, and my wife I flew to Indiana for the services.