Hi!

I just purchased a 70 XLT on Monday and am trying to get it road worthy.
The brakes on the drive home were my particular concern. There was only a very small amount of brake at the bottom of the pedal. Unfortunately, I was unfamiliar with the Ford brake system and assumed the lack of fluid in the forward half of the MC meant that the front brakes must be the cause. A quick look at the lines made me think the cause was a leaky front wheel cylinder. As you know, this thinking was wrong. After replacing the front brakes, I noticed a puddle in the rear while bleeding the fronts (and filling the MC). Now I know that the problem is actually a bad line in the rear system.

Anyway, my question is....
Shouldn't I have at least some amount of good pedal even without the rear brakes? I KNOW that the front system is tight and adjusted properly but there still is very little braking. I thought the reason for the dual system was so if one half failed the other half would still operate. Is this normal or do I have another problem somewhere?

Thanks!

Larry
http://larryscars.com/70fordpu.html

 

It's my understanding that the first brakes to touch are the rear, with the front then coming on and taking the major load.
Check to see that the rear brake shoes are adjusted correctly first.


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You're right Dennis-

The rears engage first because they are adjusted tighter than the fronts. There is no "proportioning" valve so the brake pressure is applied equally between the front and the rear.

Any type of leak needs to be repaired- period. Then you can properly adjust your brakes and go on from there.

Joe

 

Thanks guys!

Yes, of course I'll be fixing it tomorrow.
I was just surprised to see how the system reacted with a leak only in the rear half. I always thought the failure of one half would still leave you with adequate but diminished braking power.
Since that is not true right now I thought I may have another problem.
Basically, I'm just asking if this is a normal phenomina with a rear leak so I don't have to worry about it all night! Sounds like it is normal especially if the block is just a distributor rather than a proportioning unit.

Thanks!

Larry

 

It could be that the cups are worn in the master cylinder as well. Probably cheap insurance to put on a new/rebuilt one.

mike

 

I belive it has some to do with the fact that it is all drum braking. If the fronts (for instance) were disc, the phenomenon you are refering to may allow more braking pressure. I am not sure however. I know that when a rear wheel cylinder went bad on me I had virtually NO brakes. It was a really bad situation.

I was helping my brother move to Eureka Springs AR. If you have never been there it is Smack in th emiddle of the Ozark Mountains. There is no staight or flat road going to from anywhere. I was in my truck which was loaded full and I was pulling a 18' ski boat also. It was the first time I had ever really worked the 390 under the hood. I was so happy i could pull hills with no problem. I was goin along following my Bro. Tapped the brakes and I didnt' slow down at all. I pushed them harder still nothing. Got them all the way to the floor and the fronts I guess were starting to slow me down. It was a night mare to say the least. I had to down shift going down hills to keep from runnig people over. Wan't fun. Then My brother about got rearended by me. I asked, after we stopped and figured out what was wrong, how far into town he lived? He said not far. I said good cuz these brakes aint going to work for much longer. We are getting close to town. There was alot of traffic. And I didn't wanna go to fast, but I also didn't anyone getting In between us. We are going along and all of a sudden he just stops on a dime. I lock em up to keep from rearending him. I was pissed to say the least. Well everything ended up working out though. I had to leave my truck there for a week til I could get the parts. Then came back installed wheel cylinder and was on my way. But I hated not having my truck for that week.


Sorry for the really long post.


Scotty

 

Looks like it is normal.
I fixed the rear leak and I now have good brakes.
Thanks!

Larry

 

Hello I have a 1970 sport custom with manual brakes, and I experianced many problems with my brakes. It had sat for 8 years and the wheel cylinders were leaky and the master cylinder was about useless. I too had virtually no pressure untill the pedal got to the bottom. In my case I think the seals in the master cylinder had worn allowing the fluid to slip past, causing poor braking not to mention irratic pressure. I replaced it. Completly. It cost me about $80 and was a very good Idea. I also pulled the wheel cylinders out, and used a cylinder hone to refurbish the corroded cylinder. I bought a wheel cylinder kit with new cups, springs and dust boots the cost me about 20 each, available from raybest. I did this with all 4 wheelcylinders. I also replaced the pads and had the drums ground ad the pads had been biting the drums due to the leaky wheelcylinders. I then bled the brakes and pressure tested the lines by simply standing on the brake pedal as hard as I could (not while moving!)to ensure the lines held. Also you may want to properly adjust the park brake to make sure the rear brakes dont drag. The adjustment is underneath, where the cable is split just tighten the bolt to adjust. My truck also has a brake warning light, the switch is below the steering box, all the brake lines intersect their. If the pressure fails front or rear the switch flips illuminating a light on your dash, in the bottom left corner. If you bleed the brakes you can bleed the front or back in order to center the switch and shut off the light. I DO BELEIVE THIS IS A PROPORTIONING VALVE. I will check a manual I have and get back to you tomorrow but if that light is on you had best check this valve. Thats most everything I know about brakes, I made mine work by myself, did all the work myself. PS brake fluid melts paint, you really don't want to spill it on your truck, Ifound out the hard way (got a bit on the inside fender, oops.) TTYA l8ter. Scott

 

"I DO BELEIVE THIS IS A PROPORTIONING VALVE."

Hello Scott-

I have a breakdown of the "pressure differential valve"- It is nothing more than a "4-way" to get brake fluid to 4 locations from two sources with an electrical switch and a piston that slides back and forth in the event of a loss of pressure. So therefore, Ford does not call it a proportioning valve as it does not regulate brake pressure.

This is why brake pressure is applied evenly between all the drums. On a car with disc brakes, there IS a proportioning valve that supplies a larger percentage of pressure to the front discs, and less to the rears.

Hope this helps you in your understanding. Even if you never use this knowledge, it's good to have in case someone else has a question

Joe

 

Ok I beleive you thanx for the clarification.

Scott