Questions on Power Brakes

Today I finished putting my brake system together. The piping to the master cylinder isn't pretty, but I will clean it up later. As most of you know, I put a dual reservoir, vacuum boosted system with hanging pedal in the jeep in place of the old system. I put all new lines and wheel cylinders in as everything was pretty muchly toast.

Tonight, I re-bled the master cylinder to make sure it was good and tight, and then I began the process of bleeding each of the lines like I always have. By the time I got to the last wheel (and shortest line) the pedal was solid. I could push on it, and right away it would get hard to push. This was with the engine off.

Once I started the engine, I had the jeep in low gear and when I pushed the brakes, I could kill the engine. The only issue is that with the vacuum booster active, the brakes don't get solid until the pedal is halfway to the floor, and pumping them makes no difference. Any ideas? Is there a mechanical linkage adjustment I need to make, or is there something I have overlooked? Thanks in advance...

 

They are the standard drum brakes that came with the jeep originally. I don't know what size those are. I installed a firewall unit, complete. I don't know what it came from originally, because the PO had it in the pile of stuff he gave to me. So I am kind of asking generic questions in a sense. The brake pedal/booster/master cylinder assembly was cut out of the firewall in the original donor automobile and I just welded the whole assembly in place in an opening made in the jeep firewall. Like I said, the pedal will pump up as hard as a rock with the engine not running, but there is no resistance when the engine is running and vacuum is present, until the brake pedal goes halfway to the floor. That is why I am wondering if there is a linkage problem/adjustment that needs to be taken care of to make the pedal react more towards the beginning of its travel when vacuum is present.

 

Bleed your system with engine running.

 

OK, I can give that a shot, but just so I know, why would that make a difference? Thanks...

 

Might not, but its worth a shot. maybe you still have air in your line, maybe you will catch something you have overlooked. Its possible your master needs a rebuild or your rear shoes are mal adjusted. I have struggled with brake issues and hope to remedy my own very soon.

 

I've read that bleeding the system, a vacuum assisted system, the old fashioned way like most of us do ( pushing the brake pedal) will bleed off the vacuum form the system and give false results. Using a power bleeder or some other device may, and should, not bleed down the vacuum.

As noted above, make sure all of the shoes are in proper adjustment as well. I always start with this before doing anything else.

 

It's a love-hate relationship, isn't it? Thanks for the comeback. I was tired after working all day on the system, and you're right. Maybe I did miss something. Thanks for the sanity check. Later....

 

All shoes are in adjustment, and what you say about vacuum makes sense. I will give it a fresh look. I may not have time today, but as soon as I can, I will. Have a good day...

 

Bled the brakes with the engine running. Made a difference in where the pedal got hard, but it is still not near the top of the brake pedal travel. However, it is solid when it does get hard. I have enough braking power to kill the engine in low and low with not much pedal pressure -- nothing like what I had to use when I drove my Dad's '53 Jeep station wagon. I think it will work fine. It's still got about 3 inches of travel before it could hit the floor, so I guess it's ok. All I have left to do is to get the gas tank lines hooked up to the fuel pump and that should be good to go. I have a filter (oversized) between the fuel pump and the carb, but I would assume it would be smart to put one between the tank and the pump, too, correct, or is this overkill?

Later...

 

If you are using the old 9" brakes, they are hard to get adjusted right with all the adjusters, if you have the bucks put in 11" brakes all around, or disc up front, then you will have braking, one thing I screwed up on when converting one, I did not use a large enough line or orvice for the vacuum?

 

I had the same issue. I adjusted the pushrod and that took care of the problem.

 

I will have to check the pushrod (I am assuming you are talking about the piece that connects directly to the hanging pedal and not the piece on the other side of the vacuum diaphragm that pushes directly on the piston of the master cylinder) and see if it is in fact adjustable. At first glance, it doesn't appear to be. The brake light switch is part of this linkage. I have repaired one of these before, but that was decades ago and I don't remember how the switch is activated. The brakes work very well, and all shoes are adjusted to be the same and it appears that they are judging by the way the wheels stop together when the brake pedal is pushed. From what I can tell, the problem is the pushrod somehow needs to be longer. I will hopefully have some time to work on it this weekend and once I get this solved and the new gas tank plumbed in, I should be good to go.

 

I am using the same size hose that the connector on the vacuum assembly requires, and it is coming directly from the manifold via a connection designed for this purpose, on the adapter for the Weber carb to the intake manifold. I use this line to measure my intake manifold vacuum. It is definitely correct. I have the intent to switch to other brakes after I get this thing on the road and see how it performs. If it is not quite up to what I think it should be, I will sell it and move up a notch -- another project, but newer.

Thanks...

 

Nope, talking about the piece on the other side of the vacuum diaphragm going into the M/C. At first I adjusted it too much and my brakes were slightly dragging all the time. I backed off a little and that made a huge difference.

 

The threads on the piece you are speaking of are not "tight" on my booster. I can turn that adjustment by hand. Is there supposed to be a jam nut on that piece? Seems to me it can loosen or tighten with vibration. I think I will adjust it out further, making sure I still have a number of threads still engaged and put a jam nut on the threaded piece that hits the M/C piston. Whaddya think?

 

I backed mine out until it became loose, tightened it 1 full turn and left it there for now. I lost another brake line on a recent trip and I am trying to find time to bleed the brakes again. If you back it out too far you may not be able to easily remount the M/C, that was what happened when mine was too tight.

 

OK and thanks. I have been out of town on business, but hopefully this weekend I will get the gas tank plumbed in and the brakes feeling better and put this thing on its wheels for the first time in almost a year.