Brake bleeding questions...

[Earl Filter]

I put new brakes on my '77, including new master cylinder, hoses, calipers, rear wheel cylinders, etc. The only things not touched were the proportioning valve, hard lines, and booster. I bench bled the master cylinder well (or so I thought), and have bled the lines a bunch. The brake pedal goes almost to the floor still. The brakes work, but not until they get towards the bottom. I'm pretty sure that this is an air-in-the-line issue, but I'm open to suggestions. Now that it's all together and this is the problem, what should I do? Any tips on bleeding the master cylinder again? I seem to get a push of fluid at the calipers with no air bubbles or sputtering of fluid. Anything else I should look at as well?

[r0lf-]

Are they power brakes? Mine do that too ever since I touched them once to rebleed the lines, I dont think theres any air in the lines still, I bled them very thuroughly. Is there something I need to do to the booster?

[Earl Filter]

Yeah, power disc up front, 13" drums in the rear.

[Earl Filter]

Anyone....?

[boxrodz]

Do you have a metering pin on your combination value? I had to depress mine to hold open the combination value to correctly bleed the system.

[Overcamber]

make sure your rear brakes are adjusted up as well..makes a big differencel

[Earl Filter]

I have no idea on the metering pin on the combo valve. I don't even know what to look for. Any help here would be good!

As far as the rear brakes, I adjusted them to just slight drag, which has always been good on other cars.

[boxrodz]

I don't know if your '77 has the same combination valve as the 83. The combination valve is mounted on the front cross backet between the frame rails under the shroud on the driver side opposite of the steering gear box. All lines coming from the master cylinder lead to the combination valve and the lines leaving the valve head towards the brake calipers and cylinders. Should look something like the pic below.

[Earl Filter]

I do believe that it's the same combo valve, or similar. So I push in on the pin while bleeding? I haven't seen this part of the procedure. Thanks for the diagram!

[86 GMG]

Please Explain The Metering Pin In More Detail Its Veg To Me Just Press It In Before,after, During, Bleeding Brake? I Dont Know What It Does

[N2TRUX]

Originally Posted by Earl Filter

... I seem to get a push of fluid at the calipers with no air bubbles or sputtering of fluid. Anything else I should look at as well?

Brandon are you getting a good stream of fluid at the bleeders? A trick I use is to add a section of vacum line on my bleeders and run the other end into a hal full bottle of fluid. Open the valve and push the peddle completely down, close the valve etc. The vacum line allows you to cycle a good stream of fluid/air out of the system, and keep air from flowing back in before the valve is closed.

It sounds like you may have air trapped up stream though....

[boxrodz]

As I understand it, the metering valve affects the front circuit of the brakes. It's function is to allow some pressure build up on rear wheel cylinders before the front disc calipers are applied somewhere between 70 to 120 psi.

I was able to wedge a block of wood between the frame and the metering pin to keep it depressed. Then, the manual process of bleeding the system can begin. You probably followed the procedure below, but I'll list it again just in case you missed something (or I ).

It's important to maintain at least 1/2 full of fluid in the master cylinder at all times otherwise air may be re-introduced back into the system.

1. Release the vacuum reserve by applying the brakes several times. (Engine off.)

2.To bleed the master cylinder:

2a. Disconnect the forward brake tube connector at the master cylinder.
2b. Allow the fluid to fill the master cylinder bore until it flows from forward brake tube port. (Contain the excess fluid.)
2c. Connect and tighten the forward brake tube connector to the master cylinder.
2d. Depress the brake pedal slowly and hold. Loosen the forward brake tube connector at the master cylinder to purge the air from the bore. Then tighten the connector and slowly release the brake pedal.
2e. Wait 15 seconds.
2f. Repeat steps 2d and 2e, until all air has been removed from the bore. (Be careful not to get the fluid on painted surfaces.)
2g. Repeat steps 2a thru 2f for the rear brake tube connection.

3. Bleed the calipers/cylinders in the following sequence:
- Right rear wheel cylinder.
- Left rear wheel cylinder.
- Right front wheel caliper.
- Left front wheel caliper.
For each cylinder/caliper:

3a. Attach clear tubing over the bleeder valve (screw) and submerged the other end in a glass/clear plastic bottle partially filled with fluid.
3b. Depress the brake pedal slowly and hold. Loosen the bleeder valve to purge the air from the caliper/cylinder. (Observe the air bubbles thru the tube and bottle.) Then tighten the bleeder screw and slowly release the brake pedal.
3c. Wait 15 seconds.
3d. Repeat steps 3b and 3c, until all air has been removed.

I had to repeat the sequence quite a few times (about 1/2 dozen times) to completely remove all air from the lines. Repeating the sequence a dozen or so times is not uncommon.

BTW, don't forget to remove the block of wood after completing the process.

The full shop manual write-up is on Jeff's site at Bleeding Brake Hydraulic System.

Good luck. Let us know how it goes.

[MylilBowTie]

I used a wide thick zip tie on mine to depress the valve.

[Earl Filter]

I believe that this will take care of the problem. Thanks for the details. I'll do it this weekend, and see how it goes.