again, Mikebai1990 contributes another great article for our
website. In October '06, he showed us how to drain the
transmission fluid and replace the transmission strainer. Then, in March of '08, he
showed us how to replace a worn A/C belt tensioner.
This month, he's going to show us how to replace the Vig's brake master cylinder.
Go for it, Mike...
A faulty master cylinder, unfortunately, is not easy to
diagnose. However, if you are in doubt, the relative low cost and relative ease of
removal/installation makes this a no-brainer. The following are possible scenarios that
may point to a faulty master cylinder.
|Brake pedal feels spongy and does not offer precise
response based on pedal height, despite a proper brake bleeding.
||Brake pedal sinks towards the floor during constant
||Car drags to one side under braking. The brake system is
set as a criss cross setup, so that if one piston is faulty, it affects a front wheel (ex.
left) and the opposite rear wheel (ex. right), while continuing to provide braking (albeit
reduced braking power) to the front right and the rear left wheel. With a faulty cylinder,
more pressure could be applied to one piston, causing uneven braking and potential veering
under braking. Of course, faulty calipers, brake lines could also cause dragging to one
There doesn't seem to be a hard-set diagnostic
procedure for a potentially worn out master cylinder. The Acura Vigor Service Manual
procedure is as follows: With the engine stopped, depress the brake pedal several
times, then depress the pedal hard and hold that pressure for 15 seconds. If the pedal
sinks, the master cylinder, brake line or a brake caliper is faulty.
With the diagnosis and background out of the way, let's move on to the replacement! I have
numbered the parts in the pictures so you can cross reference to pinpoint the exact part
||Brake master cylinder. Purchased New Beck
Arnley brake master cylinder from rockauto.com for $94.49, Part number 072-8877.
||Line wrench. Helps to provide better hold on
the brake lines bolts. Using a open ended wrench is possible but not recommended, as the
bolts are likely to strip if one is not careful, resulting in a lengthy (pun intended)
replacement of the entire brake line and $40+.
||Assorted sockets and extensions (10,12,14mm)
||Aquarium hose with 7/16in and 1/2 in outer
Estimated time: 2-3 hours
First we need to bench bleed the new master cylinder. Just
like we sometimes bleed the brakes to purge the air in the brake lines, we need to bleed
the new master cylinder to purge air out of the cylinders. Without doing this, the brake
pedal will feel spongy due to the compression of air in the master cylinder.
Bleeding the New Master Cylinder
1. As shown in the photo at right, connect old brake
lines (preferred) or aquarium hose to the two openings (PART #1 and PART #2) on the new
master cylinder and route them back into the master cylinder. For the smaller opening, we
snugly fit a 7/16in aquarium hose. For the larger opening, we used the same hose, but had
to apply constant pressure or else the fit wasn't airtight. I would recommend getting
larger hose for the larger opening.
2. Fill the master cylinder with new DOT3 or DOT4 fluid and secure the hoses so that they
don't fall out during the bleeding process.
3. Using a block of wood on the piston area (pictured) press in on the piston to start
routing the fluid. Another option is to place the block of wood against a secure surface
and push on the other side of the master cylinder. Keep pumping the piston in and out
until you can see fluid without bubbles coming out from both openings. If fluid isn't
coming out of the hoses, the openings are not airtight. Readjust and continue. It takes
about 10-15 compressions to bleed the master cylinder.
4. Take the plugs that were originally on the openings, and plug them in place of the
aquarium hoses/brake lines. You will take these plugs off when you install the brakes
lines on the car. Put the strainer back in if you took it out earlier, and put the cap on.
Make sure the "FRONT" marking on the cap is pointing towards the front of the
Club Members can also read Heimonator's
excellect write-up in the Files
Section of the Clubhouse.
Second, we will remove the old master cylinder from the
Remove the Old Master Cylinder
1. Remove the old master
cylinder cap and either siphon out the fluid or use a turkey baster and remove as much
fluid as you can. Then remove the reservoir to reveal what's in the photo at right..
2. Disconnect bolts holding the EVAP (PART #3) to clear out some space to access the
master cylinder bolts. Do not remove any hoses/wires on the EVAP. Open the plastic holding
(PART #8b) clip allow movement of the blocking hoses.
3. Using a 10mm line wrench, break loose and disconnect the brake lines connected to the
master cylinder (PART #10 and PART #11).
4. Remove the two nuts (PART #6 and PART #7) that attach the master cylinder to the brake
booster. Then remove the bolt (PART #8) that holds the black bracket (PART #9) which is
between the master cylinder and the brake booster. (See photo on next page. Move the
bracket out of the way and remove the master cylinder module.
- Top -