Hello to all,

I have a 79 F350 4X4 with some brake issues. The problem is when the brake pedal is pushed it will travel a normal distance to stop the truck then if keep the pressure on the pedal it will continue to slowly creep to the floor and the brake light will light. If I pump it the same thing will happen just a lot quicker. The rear brake reservoir in the MC will empty out to the front brake reservoir so much that if I take the cover off the MC brake fluid will spill out from the larger reservoir.

This weekend I did a complete brake job. I replaced the pads, shoes, Master Cylinder (Third one) and even the proportioning valve. The pads and shoes showed normal wear. Now my brakes are rock hard for a few seconds and then my pedal will slowly creep to the floor. (Still)

I'm not new at this, what else could be going on here? I have a few ideas but I would like to get some input from the forum. Also my parking brake has always been bad but now there is no improvement. I don't think its related but you never know. Here's a photo of the drivers side rear brake assembly after I installed the new shoes.

Any input would be a big help.

 

If you have no leaks at the wheels or brake lines, then the master cyl is failing.

 

Are you making sure to bench bleed the master cylinder on a level surface before installing it in the truck?

 

The shoes are backward.The leading shoe needs to be mounted to front of the backing plate.X2 on the master cylinder bench bleed.Are you using a new master cylinder or rebuilt?New cylinders are not that much more expensive,and are a better investment.

 

Shoes are backward! What a stupid mistake. I installed the replacement shoes in the same direction as the previous owner and I didn't check the book to make sure I had the correct orientation. That would certainly explain why my parking brake didn't work very well since I purchased my truck 4 years ago.

FMC400 I did not bench bleed the MC, I never had too in the past. I just bleed out the entire system with me and 2 of my kids. One pumped the break, the other filled and I was underneath the truck. What is the correct proceedure to bleed the MC?

 

Bench bleeding is a must in order to get the tiny pockets of air out of the cylinder itself. This is done with the master cylinder placed in a vise, before it's installed in the truck. Did the master cylinder not come with the plugs and instruction sheet?

 

No documents where included with the MC. I did Google bench bleed of the MC and gained knowledge on how to do it. How would I push the MC actuator on the bench?

 

I have a pry-tool that is shaped just like a flat-head screwdriver, but is rounded off on the edges where the blade would be. That has worked fine for me. Anything that you can fit down in the bore and comfortably exert force without damaging the casting. A little ways into the process, it will get harder and harder to push in the cylinder, so make sure to use something strong.

Clamp the MC in the vise by its flange (not the body) so that it holds steady.

 

Thanks FMC400, you've been a great help. I will work on it this weekend and post my results.

 

And I have an old push-rod from a manual brake truck that I added a grab handle to, and I use that to bench bleed my master cylinders.

Also, if after bleeding everything again, you still don't have a firm pedal you may have to pressure bleed your system. One time I had an F250 that would not give me a firm pedal until I had it pressure bleed, it seems there was some air trapped in there somewere.

 

The shoes look correct to me. The parking brake cable enters from the front which would be the left of the picture. The parking brake lever that the cable attaches to goes to the rear which would be the right in the picture. The larger secondary shoe is towards the rear (right) and the smaller primary shoe is in the front (left) like it's supposed to be. The primary lining doesn't look as thick as the secondary though, but that may be an optical illusion from the angle of the photo.

 

He said that it was the driver side shown in the picture.The shoes are not correct as the primary shoe is shown on the rear of the backing plate.It belongs on the front of the plate.The parking brake cable housing enters the plate from the rear as it should.When the cable is pulled taught,it moves the acuator the cable end is connected to,turns a pivot to open the brake shoes against the drum.Take another look at the picture.

 

You guys are good!

What's the difference between the primary & secondary shoe? All the shoes in the kit I got look the same other than two have a little more pad than the others & I installed the bigger shoe towards the front... just by chance, but the drum was a BEAR to slide back on.

The only things left I have to replace in my brake system are the front calipers & the pedal is still very soft. I did get a big improvement by bleeding the brakes using 3 people - 1 to keep the MC full, 1 to press the brake pedal, and myself under the truck with a hand vacuum pump using the process like you would without the hand vac.

I have a very similar problem on my 78 F250 supercab.

 

The photo shows the drivers side rear brake so the front of the truck would be to the left.

After doing some brain storming with some buddies and reading up on your replies I think the primary (The one with the most pad) should be on the front of truck side of the drum assembly. This would mean the P.O. had installed the old set not only backwards but all shoes would be reversed and when I installed the new set I just followed what he had done. In other words to get the correct orientation I would need to swap the shoes from the left to the right and visa-versa. Lesson learned, When servicing your truck always check to be sure the previous work was done correctly.

Any thoughts?

I will also check the factory book when I get home tonight.

 

The primary shoe (least, shortest lining) goes in the front (left in picture)

The secondary shoe (most, longest lining) goes towards the rear. (right in picture)

Here's an illustration
http://www.2carpros.com/forum/automo...3_brakes_1.jpg

and another
http://image.customclassictrucks.com...um_removed.jpg

and another
Drum brakes image by dodgese on Photobucket