What's new
By:
Filters
Old Chevelles

Welcome to OldChevelles.com, built by Auto Enthusiasts for Auto Enthusiasts. Cars are not our only interests so please feel free to post about any subject the community might enjoy or you just feel you need to air.

We respect free speech and constructive dialogue however we don't allow threatening talk against members, nudity, or pornography. Threads are monitored and trolls are not tolerated.

This site is completely free and there are no costs. Please enjoy and provide feedback.

  • We've enabled the website app for anyone who wants to use it on a mobile or desktop device.

  • We've changed the header logo to display our Member's Cars.

    If you'd like your car to show up there, go to the forum Site Bugs & Feature Requests and post your image in the "Member's Car Pictures for the Header Logo" and we'll add your car into the lineup.

1970 El Camino 4 Wheel Power Drum Brake Issue

SSuperDave

SSuperDave

Veteran Member
Senior Member
I am at my wits end over these fucking brakes!! EVERYTHING in the brake system is new except the main distribution block to over axle hard line. All the rubber lines, wheel cylinders, distribution block, master cylinder and booster and master cylinder tyo dist block lines. I bought the "H" shaped tool to set the booster to master pushrod length, and adjusted the booster to brake pedal clevis. If I crack the bleeders, fuid flows freely at all 4 wheels. With someone in the car pumping the brakes, I get fluid with no air at all 4 wheels. But the pedal goes almost to the floor and the brakes barely engage. I have enough brakes to move it from driveway to garage, but I don't dare drive it. I have the correct power drum master cyl, and even replaced it as I thought the state of current remans might have gotten me a bad one.

The only thing that is a bit off is when bleeding the brakes, when the helper holds the pedal, both front bleeders shoot fluid hard for a foot, both rears it comes out about an inch. Its more than a dribble, but not by much. But with fluid flowing there, I can't see the low pedal and no real brakes. Something tells me ther is an issue to the rear, but I juast can't see it. Another master cylinder? The red brake warning light is connected and working, but does not come on during brake apply.
Any and all ideas are welcome.
 
With drum brakes, I was always taught to adjust the star wheel until you could feel a slight drag when you spin the tire.
Is that how you have yours adjusted ?
 
If you step on the brakes while in gear do the brakes hold for as long as you press the pedal, or do they start to release and the car starts to move after a little time?

Something tells me the reman MC may be an issue.
 
All 4 drum brakes have new shoes and hardware and are adjusted with slight drag. If the pedal is applied, it bottoms out but holds the car and the starts to release as Kevin describes. I guess I could have gotten 2 bad master cylinders, reman studd is very suspect thee days.
 
The last El Camino that I had, there was touble getting fluid to the rear, but it was a master cylinder to booster pushrod issue. The special tool ruled that out in this case
O'Reillys shows a new, not reman unit, I'll stop there on my way home tomorrow.
 
SSuperDave said:
The last El Camino that I had, there was touble getting fluid to the rear, but it was a master cylinder to booster pushrod issue. The special tool ruled that out in this case
O'Reillys shows a new, not reman unit, I'll stop there on my way home tomorrow.
Click to expand...
I bought a new 68 Vette MC at Napa and I’m happy with it, I have 4 wheel disc though
 
I had trouble with my Gold car getting fluid to the rear, tried everything. IIRC I the key was a hand vacuum pump and pressing the pedal at the same time.
 
I have fluid at all 4 wheels, it runs out freely. I'm hoping that the 3rd master cylinder will be it.
I have one of those compressed air powered bleeder/flush tools and it works very well.
 
Well, the new master cylinder made exactly zero difference in my problem. I've come th think that maybe the shuttle valve in the distribution block is sticking partly towards the rear. I've tried reverse pressure bleeding and stomping on the pdeal to reset it with no change. It is a new piece as well. Its very difficult to workl on in situ, so the next step will be to remove it to isspect and manually center the piston thru the brake switch hole, then use a screw in tool in the brake switch hole to hold the shuttle on center as I reinstall it, and then see what I have. Its pouring rain today, so I cannot push the car backwards far enought to jack it up and have access to the underside.

Days like this are when I really resent my ex wife for costing me my beautiful oversize 3 car garage with a giant work bench. I'm working out of a small 2 car with center door divider and two small doors instead of a larger single one. I'm glad to be free of her, but I really miss that garage!!
 
SSuperDave said:
Well, the new master cylinder made exactly zero difference in my problem. I've come th think that maybe the shuttle valve in the distribution block is sticking partly towards the rear. I've tried reverse pressure bleeding and stomping on the pdeal to reset it with no change. It is a new piece as well. Its very difficult to workl on in situ, so the next step will be to remove it to isspect and manually center the piston thru the brake switch hole, then use a screw in tool in the brake switch hole to hold the shuttle on center as I reinstall it, and then see what I have. Its pouring rain today, so I cannot push the car backwards far enought to jack it up and have access to the underside.

Days like this are when I really resent my ex wife for costing me my beautiful oversize 3 car garage with a giant work bench. I'm working out of a small 2 car with center door divider and two small doors instead of a larger single one. I'm glad to be free of her, but I really miss that garage!!
Click to expand...
Even though it’s a new part is it possible to be defective? or are those normally ok?
 
I think it's in the proportioning valve. Get it centered and install the tool to lock it.
I need to do the same with mine. I had the same problem.
 
The distribution blocks are normally ok, at least I've never had a failed one. I bought a new one before I knew about the shuttle valve inside. I tri
Bered to pull the brake switch with it in the car, but can't even get a wrench on it, its goping to have to come out.
Beth, on these, it is not a prop valve, just a distribution block. Up thru '70, disc brakes had a hold off valve plumbed in near the master cylinder, '71 on upi had it all in one and I believe that is a prop valve. This is what I have...

1710726622894.png
 
I have never had luck with the after market proportioning valves, ended up finding used. I even had one of the OEM valves rebuilt.

I too thought my valve was bad and replaced it, no effect. It did turn out to be pesky air in the lines. Have you looked at a power bleeder, one that puts pressure on the master cylinder to force fluid into the system?
 
SSuperDave said:
The distribution blocks are normally ok, at least I've never had a failed one. I bought a new one before I knew about the shuttle valve inside. I tri
Bered to pull the brake switch with it in the car, but can't even get a wrench on it, its goping to have to come out.
Beth, on these, it is not a prop valve, just a distribution block. Up thru '70, disc brakes had a hold off valve plumbed in near the master cylinder, '71 on upi had it all in one and I believe that is a prop valve. This is what I have...
Click to expand...
They call it a PV2 (disc+drum) proportioning valve. Obviously it's not adjustable.
Some eliminate the distribution block down on the frame (under the master cylinder) and install an adjustable PV.
I hope you get results from installing that locking screw on the shuttle valve.
 
Nashville Cat said:
They call it a PV2 (disc+drum) proportioning valve. Obviously it's not adjustable.
Some eliminate the distribution block down on the frame (under the master cylinder) and install an adjustable PV.
I hope you get results from installing that locking screw on the shuttle valve.
Click to expand...
I removed the valve on the frame under the MC and used a Wilwood adj valve, much easier to dial in front to rear bias but doesn’t look anything like stock, I also have 4 whl disc, are these new lines or original? If orig maybe Gunk built up inside the line?
 
You must log in or register to reply here.
Top Bottom