Short Brake Pedal After Swap

[Cactus Camper]

Okay getting some really great technical advice and information. This is obviously not my wheelhouse so I’m learning from those wiser than I.
I left off with having removed the MC from the booster - that yielded good pedal travel. Trying to be methodical in my approach adding back in the MC to the booster but this time in a bench bleed configuration. Meaning I ran two short brake lines back into the reservoir to eliminate the front and rear brake circuits.
I observed great pedal travel. Next I hooked up the front circuit and that also had positive results - good pedal travel.
I then introduced the rear circuit and that’s where I recreated the original issue - hard pedal, hardly any travel. I even tried adjusting the prop valve to both extremes and did not notice any difference.
So at this point the issue is somewhere in the rear circuit. Could be a kink from when I bent the lines for the new MC or as @pb4ugo pointed out the rears may require adjustment. Will sleep on it and continue tomorrow. Really appreciate the inputs. I appreciate the technical assistance folks!

 

[mdsims]

How’d it turn out? I still think the bore size can be part of the issue here. Disc calipers need more fluid to engage than drums. I could see this master overwhelming the rear drums and maxing their engagement with less pedal than a disc/drum master.

Of course, I hope you find an easier and more obvious solution!

 

[Cactus Camper]

How’d it turn out? I still think the bore size can be part of the issue here. Disc calipers need more fluid to engage than drums. I could see this master overwhelming the rear drums and maxing their engagement with less pedal than a disc/drum master.

Of course, I hope you find an easier and more obvious solution!

Thank you for checking in! This community in simply awesome.
No time yesterday but had 5 minutes before work this morning. Jacked up the rear end, released parking brake, checked for free wheel spin. 1 benefit of the SWB and 6 ft wing span is being able to press brake pedal with left hand and check for spring with right hand. When brake pedal pressed, the tire would not spin. I think we found the issue!
So I think you and @pb4ugo had intuition on it being the rear drums.

Before I claim victory, one caveat. In this scenario I still have yet to bleed the front and rears. I’m surprised how hard the pedal feels, but am hopeful once the rears are adjusted, I’ll get more pedal travel and will feel a spongy pedal which typically indicates air bleeding is required.

So next step is to adjust rear brakes; however this would be my first time through this style. More experience with discs so want to make sure I don’t screw it up too much. I had a screen shot of the FSM. I’ll find it and drop it here to make sure I have the right path forward.
Found this in the 7x FSM

Also I’m a visual learner so I found this nice YT video walking through the process.
In my case I believe backing off the adjuster is needed, I think that means adjusting the star upward. Also, based on the video, it seems we want slight drag as opposed to none. Let me know if I have that right.

 

[mdsims]

Slight drag is listed in the 40 FSM. I’d have to pull mine out, but in the late 40 FSM I think it says back off 5-6 clicks vs the 7-8 in the 70 manual. I could be wrong. I’ve found that slight drag should mean ‘ever so slight’ drag, at least to me. When adjusted the first time, my rear axles were getting warm to the touch after highway driving. I backed them off another two clicks and it solved the issue. Now after every drive I’m touching the front hubs and rear axle flanges checking for a hot corner. That’s a benefit of never installing my hub caps.

 

[Cactus Camper]

Slight drag is listed in the 40 FSM. I’d have to pull mine out, but in the late 40 FSM I think it says back off 5-6 clicks vs the 7-8 in the 70 manual. I could be wrong. I’ve found that slight drag should mean ‘ever so slight’ drag, at least to me. When adjusted the first time, my rear axles were getting warm to the touch after highway driving. I backed them off another two clicks and it solved the issue. Now after every drive I’m touching the front hubs and rear axle flanges checking for a hot corner. That’s a benefit of never installing my hub caps.

This is gold! Thank you for sharing lessons learned. I’ll watch this closely once she gets moving again.