Sooooo close to driving - rear brake issue (1 Viewer)

[tdskip]

I’m down to my final issue before I can actually drive this thing (in 2wd anyway) and could use some help on the final trouble shooting. Thanks for being with all of my questions, everyone here has been just super supportive.

The basics: ‘68 SBC with Th350 / Np203 and Toyota T/C rig now running dual line Lexus dual line M/C and mid 80’s power booster. FJ60 front brakes and JT Outfitters rear disc set up. Lines are all new 10mm inverted flare. Wilwood rear brake proportioner adjusted for no reduction in rear stopping power. System is leak free, have bleed it but not 100% sure I got all the air out.

My brake pedal is out of the car so I’m pushing on the brake clevis with my hand but I can fully depress it with the engine running. It is very hard to push on the clevis with the engine off.

Issue: with rear of the rig secured on multiple jack stands I can start the rig and shift through all the gears. Brakes will stop the rear wheels in reverse and from spinning when I shift into neutral. When in drive they will momentarily stop the tires from spinning but the wheels will start spinning again even with the brake pedal continually depressed.

Does that sound like air in the system still or more like a booster pushrod adjustment issue? Other ideas?

Thanks again - this build has been all new to me between the Toyota and SBC drive train.

 

[duncanrm]

Without the leverage that a pedal will give you I dont think you can make any real assessment of your brakes.

 

[tdskip]

Thanks @duncanrm , hopefully that is all that it is. I'll focus on getting that back in (after I finish bending and welding it into shape) and see where I am at.

Appreciate the response.

 

[tdskip]

Well - close but no cigar. Got the brake pedal mounted and the pedal can be pushed easily by hand (rig is still securely on jack stands).

Brakes will stop the rear wheels from spinning in drive not but they stop spinning gradually over the course of a couple seconds rather than right away which I would expect for unloaded axle with truck at low rpm just off idle.

How much pedal travel should I have from testing point up against the brake light switch to brake system fully engaged?

Edit - I found a reference for about 245mm spacing. If that is OK then maybe booster pushrod?

Thanks!

 

[too tall]

I think you are speculating about" what should happen when I do this" too much. Does the pedal get firm when you push on it with your foot? Does it hold firm or slowly creep closer to the floor as you hold pressure? Is the engine running when you do the test ( do you have vacuum assist ) if you do , what happens when you hold pressure and turn the engine off?
Sorry for so many questions but why did you use a lexus dual line master? I believe the best master cylinder for your application that will bolt to a toyota booster is a non abs master cylinder from a 93 fjz80.
From my experience , you should have a slight bit of play while the brake pedal is at rest. As soon as you hear the brake stoplight switch while depressing the pedal you should immediately encounter some resistance from the master cylinder.
Given that you are using a bunch of non stock parts mixed in with some factory pieces, I would say the FSM measurements are not necessarily going to be correct. I would put some tires on it and try actuating the brakes somewhere flat so you can actually see if the brakes are working or not. Hard too troubleshoot a new configuration without real tests. Trying to simulate brake issues without wheels on the ground is going to provide inaccurate results.

 

[whitey45]

Don’t forget, new pads and rotors need to burn in and seat. They do not have good grip when new, not til you break them in.

 

[tdskip]

Good morning, thanks for the follow up help. I am under some significant time pressure so I apologize that the slight smell of desperation in the air.

I believe my issue, or at least the first one to deal with, is that I’m not getting enough pedal travel because the geometry of my brake pedal is wrong. I’m only getting about half the pedal travel before I hit the floor board as shown. The good news is that the brakes are biting even with reduced pedal travel, so I’m cautiously optimistic that once I fix that I’ll be in better shape.

Everyone has been super supportive and very gracious with my occasionally less than insightful questions, thank you!

 

[tdskip]

Success - reworked the brake pedal so it has proper travel and I have brakes now. She just drove around the block which I believe is the first time she’s run in 15+ years and first time ever with this drivetrain.

Thanks MUD!

(Now on to the 100 little and not so little things to sort out)