Do You Have To Bleed All 4 Brakes When Changing A Caliper?


Car brake line diagram

I ask myself this every time on work on the brakes of an old car, “will I get away with just bleeding one caliper”, because you know the bleed nipples are as rusty as hell.

Do you have to bleed all 4 brakes when changing a caliper? It’s common practice to bleed all four brake lines after opening any one brake line. However, if the brake line you open is an independent brake line, then no, you don’t have to bleed all 4 brakes

This post will cover identifying the type of brake lines you have, brake bleeding procedure and sequence. The type of brake fluids you can mix and the types you must never mix.

A common mistake when working on brakes is to mix incompatible brake fluid types, this simple mistake can be costly as the system will need to be flushed and it’s possible to damage components. I’ll tell you what brake fluids you can mix and what fluids you must never mix

Brake caliper rusty nipple

Brake Caliper Bleed Nipple

I know bleeding all four wheels can be a lot of extra work, especially if the bleed nipples look like they’re really rusted solid. I call it nipple roulette “will they or won’t they shear off”. If they do, your looking for a replacement caliper.

I understand the dilemma, but sometimes you won’t have a choice, you’ll have to bleed all wheels. To figure out if it’s OK to bleed just one caliper, we’ll first need to figure out if the brake line, is an independent line.

Car brake Abs unit

Independent Brake line

So how do I know if it’s an independent brake line? Most modern cars will employ independent brake lines. It’s easy to figure out, if you’ve got ABS unit check and see how many distribution lines. They’ll be marked most likely FL (Front left) FR (Front right) RR (Rear right) and RL (Rear left).

Each of the wheels has its own dedicated brake line, therefore it’s OK to just bleed one brake caliper. (so long as the brake fluid doesn’t or hasn’t drained below the low level mark in the reservoir).

Hydraulic brakes
This independent brake line layout is common to most cars and it’s OK to bleed just one caliper.

If your car was made in the last 20 years, you’ll probably have an ABS system. Early ABS systems were 3 channel, meaning the front calipers had independent brake lines and the rear were paired. This was also a popular pre ABS brake line layout.

If you have a 3 channel ABS system, either of your front calipers will be OK to bleed independently, but if you are working on any one of the rear calipers (or cylinders), you’ll need to bleed both of them. You get idea, you’ll have to bleed which ever brake calipers (or cylinders) are on the same line.

Vehicles older than 20 years will probably have a tandem master cylinder with a diagonal brake line lay out or paired layout front and back.
You’ll need to identify if the brake caliper your working on has an independent line.

Bleeding car brakes

Opening Brake Caliper Bleed Nipple

Opening brake Nipples can sometimes be the hardest part of the whole job. I usually approach them with a wire brush and WD40 well in advance of actually putting a wrench to them.

A wrench is often not much use, as the small nipple head is usually stripped. The vice grips should do the job, unfortunately we can’t use heat to help move it, the caliper pistons have rubber seals. If I can get them out I like to replace them, but be sure that the seat of the nipple is identical to the old ones, otherwise they’ll leak.

Brake Bleeding Sequence

BRAKE BLEEDING SEQUENCE

The process is simple enough. If your bleeding all the brakes, start with the brake line that’s farthest from the brake fluid reservoir. That’ll be the right hand rear wheel on most cars.

If your car or truck has one brake line feeding both rear wheels, you’ll need to bleed both of these first before moving to the passenger side front (next closest). Then finally the drivers wheel. 

Braking System Checklist

  • Check brake fluid level every month
  • Change brake fluid every 3 years
  • Bleed brakes yearly
  • Check brake pad/shoe wear every 3 months
  • Check condition of rotors and drums every 6 months
  • Check for brake cylinder/calipers fluid leaks every 6 months
  • Check and adjust emergency brake yearly
  • Check condition of brake lines and hoses yearly
  • Check operation of brake equaliser yearly

Brake Fluid Types

Brake fluid cap

Most brake fluid types are hygroscopic, they absorb moisture from the atmosphere. Brake fluid should be stored in a sealed container and your brake fluid reservoir cap shouldn’t be left open for extended periods.

So what’s the problem with a little moisture? When brake fluid has a high moisture content, the heat from the brakes is absorbed by the brake fluid, the moisture in the fluid then boils and turns to steam = Spongy feeling brake pedal.

Also, the moisture if ignored will cause rust to form inside the calipers and master cylinder, this can’t be cleaned, they’ll need to be replaced. Moisture will make its way in to the fluid even with a good sealing reservoir cap, so that’s why it’s important to change or flush your brake fluid every 3 years.

bRAKE FLUID CHART

Brake fluid types are coded, and the type to be used will be marked clearly on your fluid reservoir cap. It will be marked Dot 3, 4, 5, or 5.1. I like to keep things simple. You can divide brake fluid into 2 types – Glycol or Silicone based.

Without getting too far into the weeds, Glycol based fluids are compatible but ideally shouldn’t be mixed because they have different boiling points, but you won’t hurt the car if you do mix them. Glycol based compatible family of fluids are Dot 3, Dot 4 and Dot 5.1.

What’s the difference between Dot 3, 4 and 5.1? Basically the amount of heat they withstand before boiling, higher is better. But use which ever fluid is marked on your cap. Also important to note Glycol based fluids will strip paint so careful splashing this stuff around.

Silicone based Dot 5 fluid must not be mixed with Glycol based Dot 3, 4 or 5.1. If mixed these fluids will turn into a sludge in the system and the pedal will feel like a pillow. The mixed fluids will damage your calipers, master cylinder and ABS system, if left in the system.

Dot 5 is used in all military vehicles, and since it doesn’t absorb moisture, it doesn’t need to be changed at regular intervals. It’s excellent in colder climates as the low moisture content prevents freezing fluids and it’s paintwork friendly.

Dot 5 is more compressible than the Glycol types and so the pedal can sometimes feel a little spongy.

Brake Bleeding

Brake bleeding procedure

Bleeding the brakes is traditionally done by two people. I remember sitting in the drivers seat, barely able to reach the brake pedal. I was the brake man, while my father issued the pump and hold commands.

When it comes to bleeding the brakes, you have the option of doing the two man pump, hold and release, and there’s a couple of MacGyver type hacks, but a proper bleed kit is the best option.

A bleed kit is preferred especially on older cars, because pumping the brake pedal can cause damage to the master cylinder seals, as they’re pushed further down into the cylinder than normal.

In my workshop I use a one man kit that pressures the brake fluid reservoir and I simply open each bleed nipple in sequence, you do have to keep a close eye on the fluid level though. A handheld vacuum pump can also be used to draw fluid from each individual bleed nipple, but I prefer the reservoir pressured model.

Brake Bleeding tool

Brake Bleeding Tools

You’ll need a quart of brake fluid, WD40, wire brush, clean rag, selection of small size ring wrench’s, vice grips, 3 feet of clear hose and a container for waste fluid.

A bleeding kit is preferred, the Capri brake bleeding tool is the best I could find on Amazon, it’s a good quality plenty capable. The one man bleed tool isn’t essential but you can do the two man pump, hold and release method.

1

Holding down brake pedal
  • Pump Brakes 5 times
  • Hold Brake Pedal Down

2

opening brake bleed nipple
  • Start With Wheel Furthest From Reservoir 
  • Open Nipple to release fluid
  • Close Nipple

3

Top up brake fluid
  • Top up Brake Fluid

4

  • Repeat The Process For All Wheels
Brake inspection chart

Related Questions

How often should you start a classic car? A classic car should be driven once a week, take it for a 30 minute drive. Just starting a classic car is OK for charging the battery but has a negative effect on the oil and exhaust system, short trips cause condensation which is the enemy.

How do you store a classic car? A classic car should be stored in a garage, preferable heated. If you don’t have a garage, then a breathable car cover is the next best thing, avoid plastic as it traps condensation. Keep your gas tank full and use a gas stabiliser and battery maintainer.

John Cunningham

John Cunningham is an Automotive Technician and writer on Rustyautos.com. I've been a mechanic for over twenty years, I use my knowledge and experience to write articles that help fellow gear-heads with all aspects of classic car ownership, from tires to roof aerials and everything in between.

Recent Content