Brakes: Bleeding the System - System Component Descriptions & Function

[FrankinBaltimore]

Sent: 5/5/2004 9:31 AM

I just started here and have a few questions about brakes, please. I just acquired a 1975 Winnebago Chieftain. Been setting a few years. The brakes (hydraulic) are worthless. Air in the line, I am sure. Two questions, please.

1) What are the components of the brake system? I see a master cylinder and the lines that go to the cylinders and drums. Are there boosters and other components? How does the sytem work and vary from car brake systems?

2) How do I bleed, step by step the brake sytem? There is definitely air in the lines. Practical step by step easy way to bleed with tips. Thanks.
Frank in Baltimore

[denisondc]

Sent: 5/5/2004 1:54 PM

Besides air in the system you will have some water mixed in with the fluid at the wheel cylinders and calipers, scary rusty water. With luck a member with a 75 Chieftain who has real knowledge will answer. Here is my guess meanwhile:
The brakes are mostly similar to a 1975 car with bigger parts. I don't know the brake setup your chassis has, you will have to let us know after looking underneath. Let us know if it is an M400 or M500. You have seen the master cylinder; there are 3 possibilities for the power assist scheme. 1. A large cylindrical vacuum chamber with the master cylinder bolted to it, like cars have. 2. A pair of remotely mounted boosters, called hydrovacs, each consisting of a large cylindrical vacuum chamber with a hydraulic cylinder attached - like a master cylinder but with no reservoir on it. 3. A smaller cylindrical item growing out of the master cylinder and with high pressure hoses running to it from the power steering pump. This is called a hydroboost system, and uses the power steering fluid to assist your foot. Its an excellent system assuming your power steering belt and pump and those hoses are in good condition.
The Winny brakes are a split system, also like cars. There would be a brake warning switch mounted on the frame rail somewhere. You probably have dual piston calipers on the front axle. The rear axle could have a wheel cylinder on each brake backing plate, or it could have two wheel cylinders on each side. The parking brake could be integral with the rear brakes, or it could be a separate little drum on the end of the transmission. Have a look and tell us.
Before I started to bleed the system I would put penetrating oil on all of the fittings and bleed screws for a couple of days or longer. If you have the hydrovac boosters, each of them has a bleed screw on top too.
You would start bleeding by cleaning the murky fluid out of the master cylinder, then filling the reservoir, and keeping it pretty full. I have my wife assist me by pushing the pedal down and holding that pressure till I have opened and re-closed each bleed screw. After doing the boosters, if you have them, then do the calipers and wheel cylinders. I don't think the order of doing the four corners is a big deal. Don't let the reservoir on the master cylinder get empty, or you get to start over. Refilling the master cylinder is a miserable chore. I always take the drivers side front wheel off to help. I also drilled a strategic hole in the floor in front of the drivers seat, so I can pour fluid down into the master cylinder - one of my best moves ever.

But for safety I would advise dismantling the brakes to clean the rust out of caliper pistons and to buff out the piston bores - they will look scabrous inside I imagine. The same thing for the rear axle; to clean and hone the wheel cylinders, and make sure the linings aren't worn down, that the self-adjusters are freed up, no springs broken. Before you decide you do not want to go to this much trouble, price out replacement rotors, replacement drums. $$
And check whether your hand brake cable or cables work freely and fully relax. Usually they get sticky and stiff unless frequently used; then once applied, they wont fully release and are wearing out your brake shoes and drums. The cost of new cables isn't great compared with replacing a set of brake shoes that wore out in a week.
There were two kinds of handbrake's. One type was combined with the brakes on the rear axle, like most cars. The other type was a smallish drum mounted on the end of the transmission. This type is really only a parking brake and is very susceptible to wearing out from dragging shoes. I would not try to stop a moving RV with it.
I would avoid applying the handbrake at all until I had made sure the cable was free and slippery; especially with the type that operates on the rear axle brake shoes! If it sticks it becomes Much harder to remove the drum/hub! Report back to us how it goes

[Rick Shaw]

Sent: 5/5/2004 2:54 PM

Frank,
Someone else might be able to explain the brake system better than me so I will just concentrate on bleeding.   It is always easier to have someone work with you while bleeding brakes.   They do have a kit available that suctions brake fluid for the person doing it alone.  Either way you must always start with the wheel farthest away from the master cylinder.   This is the right (passenger side) rear.   Then you move on to the left rear (driver side).  Then to the passenger side front and then the driver side front.   I don't know if you want the basics or not but I will include them here.   You have someone sit in the drivers seat and pump the brakes while you are getting your wrench ready.   Usually the bleeders come with a 3/8 inch nut.    When you are ready you have the person pumping stop and hold the pedal until you loosen the bleeder and allow fluid and air to run.   You then tighten up the bleeder and when it is tight you tell the person on the brake pedal to let up and start pumping again.  Repeat the procedure until the brake fluid runs without any air bubbles coming out.   When you have accomplished this wheel you move to the next until you are done with all wheels.   I hope this helps you.
Rick

[Lefty]

Sent: 5/6/2004 9:10 PM

As an added note to Ricks post: Be sure to check the master cylinder. fluid level after each wheel. If you run it dry, you get to start all over. Lefty