1970 Blazer Brake Question

[Chad22873]

Well its been several years but I am back. I started my frame off in 2016 and got about 80% complete and then quit for a few years. Got back to it last fall and am now about 95% done. The only real problem I have now is brakes. I dont have any. Everything in the brake system is brand new. Here is what I have done so far...Bench bled the master, then vacuum bled the system at each wheel about 5 times. Pedal still goes to the floor. Power bled the system twice. Pedal still goes to the floor. Replaced the new master cylinder with another new one. Of course, bench bled it first. Then power bled the system, 4 times and pedal still goes to the floor. I get no air at any of the wheels. My rear brake pads are adjusted correctly. When I push the pedal, all 4 wheels do engage but not tight enough to have brakes and pedal still goes to the floor. I have done this my whole life and I just cant seem to figure it out. I thought maybe you guys might have some ideas. Its a simple system but I cant make it work.

[Sheepdip]

Originally Posted by Chad22873

Well its been several years but I am back. I started my frame off in 2016 and got about 80% complete and then quit for a few years. Got back to it last fall and am now about 95% done. The only real problem I have now is brakes. I dont have any. Everything in the brake system is brand new. Here is what I have done so far...Bench bled the master, then vacuum bled the system at each wheel about 5 times. Pedal still goes to the floor. Power bled the system twice. Pedal still goes to the floor. Replaced the new master cylinder with another new one. Of course, bench bled it first. Then power bled the system, 4 times and pedal still goes to the floor. I get no air at any of the wheels. My rear brake pads are adjusted correctly. When I push the pedal, all 4 wheels do engage but not tight enough to have brakes and pedal still goes to the floor. I have done this my whole life and I just cant seem to figure it out. I thought maybe you guys might have some ideas. Its a simple system but I cant make it work.

You state "Rear Brake Pads" so I'm assuming you have 4 wheel disc? It's a common mistake to get disc brake calipers on the wrong side which puts the bleeder too low to properly vent all the air out of the piston pocket. This would apply to both front and rear disc/calipers.

[Accelo]

Possible the rod between the pedal and the master cylinder is too long. It should have some play when no pressure is on the pedal. I don't have the specification right now. Just check if there is some axial play in the rod. No play and the master cylinder will not open the window enough to allow fluid into it.

[Chad22873]

I mis typed when I said rear pads. They are shoes, which is why I looked at their adjustment. If they were a mile from hitting the drums that could explain some of the pedal going to the floor. The calipers are on correctly. I had not thought about the length of the rod going into the master cylinder. Thats something to check. Honestly, if its not that, I guess I lean towards it being a bad master. Its hard to imagine that two new masters in a row would be faulty. But what else is there? If your pedal goes to the floor and you dont have any leaks, then either the master is bad or you are compressing air....

[70STOVEBOLT]

Do you have the correct master cylinder for disc/drum? There are two different piston diameters. I don’t know which one is for which application though. If you bought it for a 1970 model it may be the wrong one.

[cj847]

The center of the brake booster is the center of the system. From there you have to adjust the length to the master cyl. It is either a screw adjustment or there are optional rods. I think your push rod is too short and is not activating the master cyl. See this for visual:

https://www.cjponyparts.com/classic-...BB9/?year=1966

You likely need one of these to get it right.

https://www.bing.com/shop/productpag...EE40C10986BA0F

PS> The rod inside the truck sets pedal position but won't help anything if the pin in the front of the booster is not adjusted properly.

[Dashman]

My first thought is an incorrect master cylinder that affected the rod length.

[Chad22873]

Originally Posted by cj847

The center of the brake booster is the center of the system. From there you have to adjust the length to the master cyl. It is either a screw adjustment or there are optional rods. I think your push rod is too short and is not activating the master cyl. See this for visual:

https://www.cjponyparts.com/classic-...BB9/?year=1966

You likely need one of these to get it right.

https://www.bing.com/shop/productpag...EE40C10986BA0F

PS> The rod inside the truck sets pedal position but won't help anything if the pin in the front of the booster is not adjusted properly.

I took it apart yesterday and this was exactly the problem. Too short. Cant believe, I missed it. Thanks for the reply.

[70STOVEBOLT]

Thank you for posting the remedy.