1970 El Camino 4 Wheel Power Drum Brake Issue

[SSuperDave]

Lines are new. I'll be taking Beth's advice and pulling the dist block to center the shuttle valve and installing the screw in stop, which I alredy have, and then crossing my fingers.
I have pressure bled thru the master, and suction bled at the wheels.

 

[SSuperDave]

Update... the distribution block was centered when I pulled it to check, 3rd master cylinder made no difference. I started at the booster and checked the rod to master cylinder clearance with the "H" tool again, and had the small amount of recommended free play. I took the brake lines off the master cylinder and out the tubes on it used for bleeding that loop from the holes back up the reservoir, and had my son pump the pedal and there was no air. I took the rear one out and put it in a container of fluid, and looked at the strength of the stream when he pressed on the pedal, it was steady but not very strong if that makes sense. I then removed the front one and the force of the fluid almost knocked the bottle out of my hand! Remember I have strong flow to the front cylinders, it shoots out hard when bleeding. I used a couple washers to space out the master cylinder and the flow to the rear almost stopped. I took them out and the weak rear flow returned. So despite grinding the pushrod to the correct spec, it appears to be too short. I have a couple others in my storage and will go get them tomorrow and see if one is a bit longer. Maybe the master needs to be preloaded a bit? I did find this pic in the overhaul manual, and had one of these threaded pushrods on another car, but I've scoured the internet and cannot find one. Have any of you ever seen or heard of this, or have one in your stash (yeah, I'm looking at you Derek, you seem to have everything else!). If you do it by the bookand it doesn't work, then get rid of the book!

 

[kmakar]

Would have never occured to me since you used the tool to measure.

 

[SSuperDave]

Yes, it defies logic, past experience and the shop manual. But there it is. I may also have the "slug" or spacer to use a deep master with short pushrod. Hopefully I can find this stuff. Ideally, I'd like the adjustable one, but can't understand why there are none out there. I never even knew they existed til I found one when swapping the booster in a prior vehicle.

 

[cheveslakr]

You are using the lower hole on your brake pedal correct?

 

[Shovelrick]

I had to make the push rod that goes inside the MC, longer are available but I just made one out of 1/2” round stock and ground it down to around .480-.490ish to fit the PR bore and used a 1/2” drill bit to give it a cup on the end, also using an adj Wilwood valve

 

[SSuperDave]

I am using the lower hole, I verifed that and adjusted the clevis to the suggested free play in the shop manual, all that does is set pedal height though.

 

[Shovelrick]

I am using the lower hole, I verifed that and adjusted the clevis to the suggested free play in the shop manual, all that does is set pedal height though.

I’m meaning the internal push rod inside the MC, Ill post a pic of the one I removed, this is just some thing that Might work for you Id do some reading about it first but different sizes are sold

 

[SSuperDave]

That piece is in there, plus it did this with two different boosters

 

[Shovelrick]

That piece is in there, plus it did this with two different boosters

Maybe like mine that needed about .250 longer PR Edit Im using a Napa MC for a 68 Vette & 4 whl disc though

 

[SSuperDave]

Update agian... I removed the master and had my son apply the brakes and the first pic is what I saw. This hard plastic thing the pushrod is in comes out with the pushrod, and it presses against the piston to the extent of its travel, and the pushrod is floatong loose in the master cylinder hole. I took the pushrod completely out and still had the small amount of fluid to the back brakes! I spaced the pushrod, and it was too long and engaged the brakes when I tightened the master to the booster. This hard plastic this spins freely in either direction, but will not unthread and I can't pull it out with a reasonable amount of force. I was thinking a bad booster somehow, but I had the same problem with a prior known good booster, although I never looked at it with the master off. The second pic is with everythng at rest, and it looks normal.
I have a new booster coming this week for my Caprice, I will compare and maybe install it on the Elky just to see.
This is weirder and weirder...

 

[Shovelrick]

Update agian... I removed the master and had my son apply the brakes and the first pic is what I saw. This hard plastic thing the pushrod is in comes out with the pushrod, and it presses against the piston to the extent of its travel, and the pushrod is floatong loose in the master cylinder hole. I took the pushrod completely out and still had the small amount of fluid to the back brakes! I spaced the pushrod, and it was too long and engaged the brakes when I tightened the master to the booster. This hard plastic this spins freely in either direction, but will not unthread and I can't pull it out with a reasonable amount of force. I was thinking a bad booster somehow, but I had the same problem with a prior known good booster, although I never looked at it with the master off. The second pic is with everythng at rest, and it looks normal.
I have a new booster coming this week for my Caprice, I will compare and maybe install it on the Elky just to see.
This is weirder and weirder...

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View attachment 19741

I dont remember a spacer looking sleeve on mine but I did need to change the PR inside the MC to a longer one that I made, think I posted about that but I don’t understand why you’d need to do anything like that since you’re using pretty much stock replacement parts but they do sell different size internal PR’s, good idea checking the other MC and compare parts Edit Im sure I didn’t have the spacer looking thing but Im using a new Napa 68 Vette MC for 4 whl disc brakes

 

[SSuperDave]

I think this plastic sleeve thing takes the place of an internal pushrod, and it won't come out for me to look any further.