The master cylinder went out recently on my 89 vette. I have never replaced a brake master cylinder before, any trick or tips on accomplishing this task?

FYI: I purchased a remanufactured master cylinder that doesn’t have the reservoirs attached

 

It's pretty straight forward. Getting your reservoirs onto the rebuild is probably going to be the hardest part. Once they're on, bench bleed the master. The rebuild should come with 2 hoses and fittings and instructions on bench bleeding.
Re and re is as simple as removing the 2 lines and the 2 nuts holding master. Once installed, you will have to bleed the brake lines of air.
Start at the left rear then right rear then left front and right front.
My info is for 86 (single res), but the technique for res install may work for the double, also.
http://members.shaw.ca/agent86/Master%20Cylinder.pdf

 

The reservoirs (at least for me) are a pain and frankly I'd go new. Also check the caps and make sure the diaphrams aren't leaking - when full, nothing should be coming out of the vents. Diaphrams are servicable - Dealer or NAPA.

 

If you don't have a set of line wrenches, I would get a decent quality set. They will be much cheaper then dealing with a rounded brake fitting.

I was surprised how easy it was to change the master cylinder in my 86'. It was my first time doing the job, and it took me less than 2 hours, and I like to go slow and careful.

 

Well neither had I till a few years ago and it was "an experience", especially on getting the old resevoirs onto the new MC...

There is, of course, a "special tool" to install the resevoirs & seals, which I did not have. So I used a large C-clamp and sockets to "persuade" the resevoirs over the seals and onto the MC.

Then came the bench bleeding which was a pita as the rear chamber didn't want to give up it's trapped air very easily.

My rebuilt MC kit came with some tubes and instructions on how to install the parts and bench bleed the chambers.

I also took the opportunity to bleed the entire brake system (at each wheel cylinder), fush out all old fluid and replace with frsh DOT 3.

It's a bit of a tedium but good luck with it.

 

Before the guys come in here and start telling you to buy gadgets....Below is what I have posted before. The Cups are hard to pull and pres on

They say the Bench bleed is helpful.....I did this one time and it seemed like a waste of time.

You have to take the hoses off to install the line don't you?

The vacuum pump is pricey for a once every three or four year job

Gravity feed? This will take days when it should take 20 minutes.

Anyway. Get a coke bottle, and a piece of 2' vacuum hose from Kragen. Get the size hose that will just fit over your bleed nipple.

Make sure you have a nice closed end wrench for that nipple.

one person inside the car and the other at the Bleeder. Start at the RR Bleeder.

The Box end goes on the bleeder, then the hose on top of that, run the hose so that it goes down into the Coke bottle all the way to the bottom.

You yell, "Pump" to the person inside, they push the brake pedal......You "crack" open the bleeder valve just enough to let some fluid out then you quickly shut it again. Once it is shut you yell "release"

Repeat this process over and over. You are looking for a few things things.

1. you'll hear the bubbles as they squeeze through the small opening of the bleeder, This is why I said Crack open the bleeder, you don't want to open it up wide. To get a idea of what it sounds like, squeeze some spit between your teeth with your mouth closed.

2. you'll see the bubbles in the Coke bottle. Make sure the hose stays down in the bottle. You WANT to see the bubbles...this tells you that you almost done. If the hose is tight and the end is down into the old fluid in the bottle, how can you suck air back into the nipple?

3. You'll start to see new clear brake fluid coming into the bottle. This means that fluid from the MC has made it all the way to the caliper you are working on. If you keep the hose down into it, you'll see the clear fluid at the bottom as it forces the old brown stuff upwards.

The RR Caliper will be the worst one as it has the longest hose for the fluid to travel.

The pedal will feel exactly the same way until you finish the fourth caliper. This is the part where everyone gets messed up....they keep bleeding one or two calipers thinking that there should be a change yet the pedal continues to go all the way to the floor. Until you get the air out of the last caliper...the Front Left one... the pedal will not change and you'll have no breaks.

You must constantly be vigil about the fill level. If you let it run dry, you've screwed yourself and you have to start all over.......Completely start over.

Lastly, make sure you have a patient person inside. They must be wiling to sit for 20-30 minutes and be ready to follow commands of "Pump" then "Release" and understand that "Pump" means push the brake pedal at a steady slow rate and HOLD IT DOWN until you yell "Release" No exceptions

If they let go while you still have the bleeder valve open, there is a chance to re-introduce air into that system.

This is a 20-30 minute job.

If you ask me, the hardest part of that Job was getting the Plastic fill cups off of the old MC. That part was a real bugger as I didn't want to break them yet they were stuck.

Bleeding is a breeze compared to those cups.

 

on the removal of the m/c resovoirs however, i found it a little more difficult in putting them back onto the new m/c body....i wound up using a short piece of 2x4 across the top and, after wel "lubbing" the bore of the m/c and seal and extended part of the resovoir, it went in rather easily....

 

You're correct that you want to start with the caliper farthest from the master cylinder, but with ABS it doesn't work the way you've described. Your '86, and all Corvettes after, has factory ABS. Since the ABS motor is (essentially) in the center of the car, the correct sequence is Right Front, Right Rear, Left Rear, Left Front. This ensures that all old brake fluid and air is removed from the ABS motor.

(Source: FSM)

 

Source 86 Factory Service manual

 

wait, the furthest from the MC is the Right Rear.....

 

If I plan on bleeding the system, do I have to also bench bleed the new master cylinder?

Thanks

 

Since the rear chamber of my MC bleed down much more slowly than the front I did the bench bleed before a complete system bleed & flush on the car.
You can do it either way, your choice.

 

Speed Bleeders allow you to do the job without the help of an impatient person and work GREAT.
I now have 3 vehicles with them and will never bleed the brakes any other way.

 

So no impact to the ABS system if i don't bench bleed the master cylinder

 

If you bench bleed, put the M/C on the car and use the pedal to pump. Just use the tubes to make a closed loop system.

Understand, once you take the plastic pieces out to put your lines in......where are you now?

 

Struggling with getting reservoirs back on MC - I'm pressing with all my might (which isn't all that much)

What's the trick?

Thanks

 

Take the base and coat it a thin film of heavy gage motor oil....I have some 90w gear oil around here for what ever reason.

You think they are going to break but they don't. I was just like you...feeling like it was impossible to it to go on but it goes eventually