{"id":16509,"date":"2015-07-07T11:44:13","date_gmt":"2015-07-07T18:44:13","guid":{"rendered":"http:\/\/www.racingjunk.com\/news\/?p=16509"},"modified":"2016-11-30T15:07:08","modified_gmt":"2016-11-30T23:07:08","slug":"finding-and-fixing-problems-with-master-cylinders-and-brake-boosters","status":"publish","type":"post","link":"https:\/\/www.racingjunk.com\/news\/finding-and-fixing-problems-with-master-cylinders-and-brake-boosters\/","title":{"rendered":"Finding and Fixing Problems with Master Cylinders and Brake Boosters"},"content":{"rendered":"
\"Keep<\/a>
Keep Reading to find out how to save time and money fixing brake problems yourself.<\/figcaption><\/figure>\n

Imagine you’re driving down the road and the light changes. \u00a0You step on the brakes and . . . you\u00a0start<\/em> slowing down and your foot slowly sinks to the floor. \u00a0Then, nothing, you’ve got no brakes. \u00a0But wait, when you check, the master cylinder is full! \u00a0You could take your car to a shop and (sometimes) pay to have it inspected\/diagnosed, but this can be a time-consuming process that often requires an appointment. \u00a0What if I told you that finding and fixing most brake problems that originate under the hood is actually pretty simple and you can normally do it in less than an afternoon? \u00a0Well, it is, and I can. \u00a0Keep reading.<\/p>\n

\"This<\/a>
This is an example of a power master brake cylinder with cast metal body and power booster out of an early model Buick Riviera.<\/figcaption><\/figure>\n

First let’s talk about what I mean when I say master cylinder and brake booster, as not all of us know yet. \u00a0The master cylinder is the brake system component under the hood that sits against the firewall\/bulkhead between the engine and passenger compartment fright in front of the steering wheel. \u00a0On older cars, it’s metal and has a flat metal (cast steels) cover held on by a banjo that snaps over and into grooves on top of the cover. \u00a0On newer cars this is an aluminum body with a plastic fluid reservoir and a cam-lock cap. \u00a0The brake booster is mounted between the master cylinder and the wall on newer or converted\/upgraded cars. \u00a0See the images above and below.<\/p>\n

\"This<\/a>
This is an example of an aluminum-bodied master cylinder with a plastic reservoir.<\/figcaption><\/figure>\n

The Brake Pedal That Slowly Sinks to the Floor<\/strong><\/p>\n

I first have to mention that I don’t mean that the pedal sinks to the floor when you apply your whole to it. \u00a0I’m talking about the pedal sinks to the floor with nothing more than normal braking pressure applied. \u00a0You know that a pedal that sinks to the floor is a sign of a leak in the system and a slowly sinking pedal means a slow leak. \u00a0However, you’ve spent an hour or more under the car looking, you’ve even used a\u00a0leak detector kit<\/a>. \u00a0What’s really got you scratching your head is the fact that the reservoir is full.<\/p>\n

\"Blown<\/a>
Blown up drawing of a master cylinder. A bypassing master cylinder leaks between pressure and return ports for one or both reservoirs.<\/figcaption><\/figure>\n

What I’ve just described is a brake master cylinder that is bypassing. \u00a0One or more of the inner seals on the piston inside have failed and fluid pressure is bypassing that\/those seal(s) and returning to the reservoir. \u00a0The fix for this is either replacing the master cylinder or rebuilding it. \u00a0Neither is really difficult. \u00a0Replacing is in and out with a slight detour, while rebuilding isn’t much different than\u00a0rebuilding calipers<\/a>\u00a0once you’ve got it off and apart in that both require you to ensure the seal mating surfaces are blemish-free. \u00a0I’ll describe the R&R process below.<\/p>\n

The Brake Pedal That Feels Like a Weak Spring<\/strong><\/p>\n

This is the brake pedal that goes farther than normal and then feels like it wants to bounce back a little. \u00a0Braking force applied to the wheels is lower and you have to step on the pedal harder to stop the car. \u00a0This is air in the brake lines. \u00a0Air is compressible, while fluid isn’t. \u00a0This property of brake fluid is what makes it ideal for use in automotive brake systems, while air is pretty bad. \u00a0The fix for this is to bleed the air out of the hydraulic system, bleeding the brakes. \u00a0I describe bleeding the brakes at the end of this article.<\/p>\n

The Brake Pedal That Stays Hard but Doesn’t Stop the Car<\/strong><\/p>\n

\"This<\/a>
This is a photo of a non-power master cylinder from an early model Pontiac Grand Prix. Notice the bleeder kit at the bottom of the image.<\/figcaption><\/figure>\n

Your car has power brakes but it feels like you have to stand on the brake pedal to get your car to stop, even at city street speeds. \u00a0It’s worse than the days before power disc brakes if you’re old enough to remember them. \u00a0The technical diagnosis for this condition is “gunk in the lines and orifices”. \u00a0You see, brake fluid is hygroscopic, which means it absorbs water (even in a sealed system) which causes rust and sludge buildup. \u00a0The combination of “gunk” can clog up the small orifices in the brake system as well as the small brake lines, reducing system efficiency.<\/p>\n

You can verify this by scraping the tip across the bottom of the fluid reservoir and seeing if anything sticks to it. \u00a0The fix for this is to suction the old fluid out of the master and flush the system, preferably with denatured alcohol and then fresh fluid. \u00a0This process is described in Step 7. \u00a0If you have drum brakes I would highly recommend cleaning out the wheel cylinders also, which I’ll describe in a later article. \u00a0Also, use only denatured alcohol as anything else will deteriorate the rubber seals in the system.<\/p>\n

You Hear a Hiss When You Step on the Brakes<\/strong><\/p>\n

There you are coming to a stop light or sign. \u00a0 You apply the brakes and as you’re coming to a stop, you hear a hiss that sounds like air escaping from a tire or balloon or the sound a snake makes. \u00a0Chances are you’re also thinking to yourself that the pressure you’re applying is more than normal for power disc brakes.<\/p>\n

What you’re describing is a power brake booster that is suffering a leaking seal, either inner or outer. \u00a0A brake booster outer seal that’s leaking is likely to be accompanied by signs of wetness between the master cylinder and power booster because it will cause the piston seal on the master cylinder to fail\u00a0due to being put under a vacuum. \u00a0Your only repair option here is to replace the power booster. \u00a0If you’re seeing signs of leakage from the master, you’ll also either have to rebuild or replace it.<\/p>\n

Removing the Brake Power Booster and Master Cylinder<\/strong><\/p>\n

\"Retrofit<\/a>
Retrofit master and booster for an early model Cadillac. The black thing on the side is a combination vacuum inlet and check valve. Braking power is boosted by using engine vacuum.<\/figcaption><\/figure>\n

You’ve got to remove the master cylinder in order to get at the brake booster. \u00a0If you only need to replace the booster, you don’t need to pop open the brake lines on the master, so all you’ll need is a wrench to remove the master (usually 5\/8″ or 9\/16″) and a socket (same size) and extension(s) and maybe a swivel universal. \u00a0If you’re not taking the master out of the car to work on or replace, skip to step two below:<\/p>\n

    \n
  1. Loosen and remove the brake lines at the master cylinder. \u00a0These are usually either 3\/8″ or 7\/16″. \u00a0It is best if you use line wrenches, especially if the fittings look rusty as they’re designed to not round the corners of the fitting. \u00a0A little WD-40 can make this easier.<\/li>\n
  2. Use a wrench to remove the two nuts that secure the master cylinder flange to the brake booster by turning them counter clockwise. \u00a0WD-40 again.<\/li>\n
  3. Once you’ve got the nuts off, if you’re going to work on the master, remove it from the car and put it on your work bench or the ground for the moment. \u00a0If not, simply move it forward enough to slide off the booster studs.<\/li>\n
  4. Inside the car and under the dash you will find either two or four (usually four) nuts or bolts securing the brake booster to the firewall\/bulkhead. \u00a0This is easier with the socket and swivel.<\/li>\n
  5. Disconnect the brake booster piston from the brake pedal. \u00a0This might be a nut and bolt connection or a pin through an eyebolt secured with a cotter pin or locking pin.<\/li>\n
  6. Remove the booster from the car from the engine compartment.<\/li>\n<\/ol>\n

    Installing the New Brake Booster and Master<\/strong><\/p>\n

    Installing the new power brake booster is just removing it in reverse, unless you’ve either worked on the master cylinder or replaced it.<\/p>\n

      \n
    1. Slide the booster piston through the large hole in the bulkhead. \u00a0Align the bolt holes and push until the booster is flush to the bulkhead.<\/li>\n
    2. Install and tighten the nuts\/bolts securing the booster to the bulkhead and connect the piston to the brake pedal.<\/li>\n
    3. If you’ve disconnected the master cylinder, you need to bleed it. \u00a0New masters come with bleeder kits which are nothing more than rubber tubes attached to plastic fittings. \u00a0If you’ve only rebuilt it, you can buy a\u00a0bleeder kit for cheap at places like Autozone<\/a>. \u00a0I’ll describe this later.<\/li>\n
    4. Slide the master cylinder over the studs on the brake booster. \u00a0Install and tighten the nuts.<\/li>\n
    5. If you’ve removed the brake lines, reinstall them and tighten them using a line wrench.<\/li>\n
    6. Bleed the brakes following the directions in Step 10 of the linked article.<\/li>\n<\/ol>\n

      Bleeding the Master Cylinder<\/strong><\/p>\n

      After attaching the new or rebuilt master cylinder to the brake booster, thread the plastic fittings of the bleeder kit into the cylinder ports and route the hose(s) into the reservoir(s). \u00a0BY HAND, slowly depress the brake pedal. \u00a0have someone watch and let you know when no more air bubbles come out of the hoses. \u00a0Remove the bleeder kit and reattach the brake lines to the master cylinder. \u00a0Bleed the brake lines completely, rears first then fronts. \u00a0If you have a vise mounted on a solid workbench and a large Philips screwdriver, you can mount the master on the vise to bleed it. \u00a0This is easier.<\/p>\n","protected":false},"excerpt":{"rendered":"

      Mike Aguilar gives tips on how to identify and fix brake problems.<\/p>\n<\/div>","protected":false},"author":28,"featured_media":16513,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[5009,11,9],"tags":[318,281,461],"class_list":["post-16509","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-brakes","category-how-tos","category-tech-tips","tag-brakes","tag-how-to","tag-tech-tips-2"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"https:\/\/www.racingjunk.com\/news\/wp-content\/uploads\/2015\/07\/X05AR_CO004.jpg","jetpack_shortlink":"https:\/\/wp.me\/p42YSK-4ih","jetpack_sharing_enabled":true,"amp_enabled":true,"_links":{"self":[{"href":"https:\/\/www.racingjunk.com\/news\/wp-json\/wp\/v2\/posts\/16509","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.racingjunk.com\/news\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.racingjunk.com\/news\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.racingjunk.com\/news\/wp-json\/wp\/v2\/users\/28"}],"replies":[{"embeddable":true,"href":"https:\/\/www.racingjunk.com\/news\/wp-json\/wp\/v2\/comments?post=16509"}],"version-history":[{"count":3,"href":"https:\/\/www.racingjunk.com\/news\/wp-json\/wp\/v2\/posts\/16509\/revisions"}],"predecessor-version":[{"id":16518,"href":"https:\/\/www.racingjunk.com\/news\/wp-json\/wp\/v2\/posts\/16509\/revisions\/16518"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.racingjunk.com\/news\/wp-json\/wp\/v2\/media\/16513"}],"wp:attachment":[{"href":"https:\/\/www.racingjunk.com\/news\/wp-json\/wp\/v2\/media?parent=16509"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.racingjunk.com\/news\/wp-json\/wp\/v2\/categories?post=16509"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.racingjunk.com\/news\/wp-json\/wp\/v2\/tags?post=16509"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}