brakes are fixed

[icanfixall]

Jim, I use the Raybestos Brute stops. They have worked very well for me. They are very expensive but quality costs money. I run them front and back but I do keep my backs manually adjusted up. When my "E" brake peddle sets more than half way down I crawl under and use a brake spoon to adjust the rears. The proper shoe adjustment is 0.025 from the drums. When the brakes are applied the rotation of the drums shift the shoes forwards with the direction of rotation and that acts like a wedge with the shoes. When we back up the trucks the rotation of the drums shifts the shoes causing the adtomatic adjustment. For some engineering reason they don't work very well. My limited knowledge of hydraulics limit what you are stating.. I will be changing my vacuum brakes over to the hydroboost system. I have that system on another truck and have found it to be a very good system. Plus I will gain more room under the hood for other ideas.

 

[jauguston]

Fixall,

Thanks for that. As I posted earlier I have heard good things about the hydraboost. The problem for many is the availability of a donor truck for the needed parts. Around here it is hard to find a auto recycler that keeps anything older than 10 years. And harder yet to find one with any amount of trucks.

The upgrade to the 10 3/4" booster is quite easy and only costs about $75.00 for a rebuilt so for those that don't have access to a hydraboost system or don't want to do a more complex conversion it is a alternative that provides much better stopping ability for a small amount of work.

Tuesday I will start researching the brake lining options posted here by you and Roboto.

Jim

 

[Jeff Dodson]

Ok, I'm not trying to start an argument nor can I say anything about how a hydrolic system works. I do know that I had replaced both front calipers and pads, checked the rear shoes and cylinders and adjusted( good and not leaking nor were they stuck) replaced the RABS valve and for about the third time bled out the whole system, it has clean brake fluid the whole system. Replaced the master cylinder 3 times with what the book called for and with new master cylinders, the only one that would loose fluid was the third one. Finally a friend of mine, a very good and reputable mechanic told me about switching to the F450 master cylinder. I did that, bled out the system again and the brake pedal is great and the truck stops great. The whole system on the truck is new and the brakes work great, thats all I can say. I dont know what the problem the F450 master cylinder could be masking, all the other is new and adjusted.

 

[Mr_Roboto]

Jeff, one thing I would advise is to plumb in a vacuum gauge so you can see ahead of time if your vacuum pump is failing.

With the larger diameter master cylinder, you lose some mechanical leverage on the brakes. Probably not a big deal if your power assist is working, maybe a deal breaker if you lose vacuum. I've driven with a bad vacuum pump (and stock diameter master), stopping power is seriously compromised I.e. you will be standing on the brake pedal just to slow down).

 

[jauguston]

Jeff,

This has been a good discussion, not an arguement.

The ratio between the bore of the master cylinder and the bores of caliper piston and rear wheel cylinders is a simple equation that determines the pressure delivered to the wheels by a given size bore master cylinder with a given amount of force delivered to the master cylinder piston by the pedal.

I have no idea what the bore is for the master cylinder you are using is and this all started with my recommendation that your brakes could be less effective if you have a bigger bore master cylinder than your system was designed for.

What I have gotten from this thread is some good ideas for better brake lining that will provide more aggressive stopping power with the same pressure I am applying now.

Jim

 

[Jeff Dodson]

Jeff, one thing I would advise is to plumb in a vacuum gauge so you can see ahead of time if your vacuum pump is failing.

With the larger diameter master cylinder, you lose some mechanical leverage on the brakes. Probably not a big deal if your power assist is working, maybe a deal breaker if you lose vacuum. I've driven with a bad vacuum pump (and stock diameter master), stopping power is seriously compromised I.e. you will be standing on the brake pedal just to slow down).

I know what you mean here, the belt came off of my vacuum pump once and MAAN it was scarey to stop. As far as putting the larger M/C, its the only thing that would help the pedal. EVERYTHING else is new and the rear brakes are adjusted. I put 3 of the correct M/C and everytime, the pedal would fade. Someone on these sites said it was my RABS VALVE, I spent $200.00 on a NEW RABS valve and the pedal was exactly the same, it would fade. I had to step on my brakes pretty good one time and was pulling my boat. Well I smoked the front brakes because apparently the rears were not helping much and the pedal dam near went to the floor. With the M/C, I can feel the rears working, the truck just stops ALOT smoother and straighter, it does not feel as if one wheel maybe be getting more brake. I pulled my boat the other day and I could stop it a;ot smoother and quicker as well. I feel like the bigger M/C was the best mod I did. The truck is not so intimidating to drive. In saying intimidating, The brakes are the most important thing in my opinion and when they dont work right, IT SCARES THE HELL OUT OF ME.

 

[Guntherx]

Fixall,

Thanks for that. As I posted earlier I have heard good things about the hydraboost. The problem for many is the availability of a donor truck for the needed parts. Around here it is hard to find a auto recycler that keeps anything older than 10 years. And harder yet to find one with any amount of trucks.

The upgrade to the 10 3/4" booster is quite easy and only costs about $75.00 for a rebuilt so for those that don't have access to a hydraboost system or don't want to do a more complex conversion it is a alternative that provides much better stopping ability for a small amount of work.

Tuesday I will start researching the brake lining options posted here by you and Roboto.

Jim

Is the 10 3/4 just a bolt on, or is there other mods to do the job?

Also, what is the procedure to test the RABS, and will it just fail at once??

 

[TLBREWER]

Jeff

Glad to see you got it figured out. I've come to the conclusion that every one of us looks for a different "feel" when it comes to brakes, turbo's, seats, etc. The important thing is that you've found a combination that works for you in your truck.

The mixing and matching of both mechanical and hydraulic combinations in brake systems could go on forever. Every person that crosses this bridge eventually finds a combination that works for them.

Tom

 

[Jeff Dodson]

Is the 10 3/4 just a bolt on, or is there other mods to do the job?

Also, what is the procedure to test the RABS, and will it just fail at once??

You just have to elongate the mounting holes to the inside a little. Everything else was a direct fit.

I dont know if there is a test for the RABS valve, somebody told me on here that it was bad so I changed it. It probably was because after I did change it, I could feel the brakes working more in the rear instead of just the front.

 

[icanfixall]

When I change to the F450 master cylinder I will be going to the hydroboost system so things should work better. I do have the large vacuum booster now but I'm really not that pleased with the braking system overall. I know its not a Vette when it comes to stopping power but my truck seems kinda lazy when it comes to the braking...

 

[jauguston]

When I upgraded to the 10 3/4" booster there were two modifications. The bolt holes in the MC had to be slotted a little with a rat tail file and the pushrod that goes to the pedal was too long. I cut it down to the same length as the old one and welded it back together. Cut just behind the pedal pin hole on the flat part of the rod.

Jim

 

[datkinsonsr]

A lot of interesting thoughts have appeared here about the hydraulics of the larger master cylinder. Yes, a larger cylinder will move a larger volume of fluid. However, at the end of the brake shoe travel, no more fluid will move. At this point, the pressure begins to increase do to your foot pressing on the pedal, evidenced by the pedal becomming harder. Because the surface area of the master cylinder piston is greater, the same amount of force being applied to the piston will create a greater pressure than it will with the smaller piston. Volume is not giving you the stopping power. It is the pressure of the fluid acting on the wheel cylinder piston creating a force against the brake linings that is giving you the stopping power. And because you have increased the amount of pressure you can create by the bigger system, you have greater stopping power at the brakes. The math will prove this with this formula......Force = Area x Pressure, Pressure = Force / Area.

 

[tuckerd1]

The math will prove this with this formula......Force = Area x Pressure, Pressure = Force / Area.

Your formula just proves what others have been saying is true. If you increase area and do not increase force then pressure goes down.

 

[Mont91]

jauguston you went from a '93 van to an '86 van.
I am guessing your rod length issues came from going across chassie redesign years? Somebody remind me what year they redesigned the van. "88 was a major redesign for the F series and many things do not fit. Electricaly '92 was a major change.
Jeffs fix would drive me crazy because the base problem was never corrected.
My brake pedal improved recently after I replaced my destroyed rear axle speed sensor with a used one from a '92 and the quality of pad/shoe material does make a big differance in pedal travel. Elcheapo pads require more leg muscle to stop so they compress more allowing the pedal to travel further.

I also aree that the bigger MC works because it moves more fluid per stroke thus "masking" a fluid volume issue. This does not mean it is a bad fix. Hopfully the volume issue does not get worse.

 

[jauguston]

Mont,

After you get the slack out of the brake lining to drum and pad by moving the pedal there is basicly no movement of fluid, you are just transfering force (pressure), nothing moves more than thousands of an inch.

Jim