Master cylinder replacement

[faof2]

91 240 station wagon, 102,000 miles.

Brake pedal creeps down as I push on it to stop, so I am planning to replace the master cylinder. After reading the Bentley Publisher "240" manual, it looks like an easy job. I looked at the "Repair Database Categories" in this forum and found nothing on "brakes".
The manual is unclear about bleeding the brakes, giving confusing instructions. Do you have a reference on this forum or elsewhere that gives specific details for bleeding the brakes?

Is it correct that I must use DOT 4 fluid?

How much should I bleed from each bleeder valve? I understand there are six valves in front and two in the rear, a total of eight bleeder valves. My book recommends one pint from each caliper. Is each bleed screw location to be treated as a a caliper, or do I bleed less from each caliper when there are multiple screws?

Given that my pedal can work its way down to near the end of its travel, I presume that this means fluid is leaking past the piston and possibly ending up in the booster. Is there a way to clean out any fluid that may be in the booster?

Do you have a suggestion for a place to buy parts on the internet (good quality, low price)?

Thanks in advance for your advice.

[lummert]

Here are two good websites:

www.fcpgroton.com
eeuroparts.com

[billofdurham]

ABS/non-ABS have different bleeding procedures. The attached has both.

240 Brake Bleeding + ABS.pdf

(512.46 KiB) Downloaded 3316 times

DOT4 is used in both applications.

There is no fixed amount of fluid to be bled out. Bleed the system until no air bubbles appear in the jar.

It is unlikely that fluid will find its way into the booster due to the seal set up in the master cylinder. Have you needed to top up the master cylinder on a regular basis since this problem showed itself?. If not then there will be no fluid in the booster.

Bill.

[faof2]

Follow up question:

1. Does it matter if I buy a reconditioned master cylinder, versus new aftermarket, versus new genuine Volvo?

2. What are the pros and cons of buying with and without a new reservoir?

3. Is it necessary to remove the wheels to bleed the system? Can it be done by crawling under (all wheels on the ground)?

thanks again

[billofdurham]

1. Who is doing the re-conditioning? If it is a reputable company there is no problem. I am not a reputable company but have re-built several master cylinders which have given long service. The main thing is that the bores aren't scratched, everything is done in dust free conditions and new seals are used. Also be aware there are different cylinders for ABS and non-ABS systems.

2. The reservoir is a push fit into the top of the cylinder. It sits in two sleeves to make an airtight seal. You may be better off obtaining two new sleeves to get the best fit.

3. It is possible to bleed the system with the wheels in place but it is a great deal easier to remove them. Remove one wheel at a time and replce it after bleeding that wheel.

Bill.

[rgk]

I have to disagree with Bill about the wheels here. Coming from someone who had to bleed his brakes for MONTHS because of inexperience, as well as from someone who has a pretty thin build, taking the wheels off creates more work than slipping in behind and wrapping your arm around them, especially if it takes you many tries before getting it right.

On another note, I have heard that you should bench bleed the new master cylinder before putting it in, but don't know much about that.

As Bill mentioned to me last year, investing in a hand pump or power bleeder will pay off 1000% as bleeding the brakes using the brake pedal is incredibly tedious. Do yourself a favor and shell out the 40 or so dollars to get it. But remember that bleed order differs whether you are using the hand pump or brake pedal method, as one method pushes brake fluid, while another pulls (or more appropriately, sucks) it out. Bill recommends raising your rear axle when bleeding the back. Check the link at the bottom of this post.

Please be aware that, if you've never done it before, bleeding the brake fluid can be incredibly time-consuming and infuriating. There are many things that can affect the pressure in the brake line. Even the tiniest hole can introduce air into the system and ruin your process. In other words, you have to be very careful to make sure everything is just right. Sometimes you know something is wrong but simply don't know what.

One thing I wish I would have known when first bleeding my brakes is to use thread tape on each and every bleeder screw, especially if using a hand pump, because air can easily sneak in through the threads on the screw. I bled my brakes for days without success, not understanding why I constantly had so many air bubbles. Well, it was because air was being sucked in from the atmosphere around the thread on the bleed screw and right back out into my hand pump. In other words, I was circulating air on the surface and unable to produce enough pressure to pull the fluid (and the air with it) from deep inside my brake line system. Remember this: air residing in the brake line comes out at the same speed as the fluid. Air coming in through the bleeder valve comes in quickly and looks a lot like soda pop fizz. Thread tape will eliminate this annoyance.

A small amount of tape - once and a half times around the screw will do. You want the tape to stick to itself around the threading, but you don't want excess tape to make a mess inside your caliper. However, remember that each time you open the bleeder valve you cut into the tape a little. If you tighten and open the screw too many times you will destroy the tape and have to start the process anew. It's quite a delicate process.

Another important thing to remember is that calipers are essentially two halves screwed to each other and it is of the utmost importance NOT TO UNSCREW THEM. This might seem obvious to some, but was never clearly stated to me until I actually did it. Even though at the surface it looks like you can screw them back together correctly, it takes specialized equipment to do so just right, and you definitely don't want to take such a chance with your brakes.

I've also had to replace some of the rubber brake hoses through which the brake fluid travels. For some reason most of the gunk in the brake lines ends up in these, effectively clogging them. If nothing is coming out of your bleeder valve, first try detaching your caliper and spraying brake cleaner into each one of the holes. Sometimes hand pumping gets the clog out, but other times you might have to physically replace parts of the copper line. Due to a leak, I also had to replace the little block that takes the fluid from the master cylinder and splits it eight ways - four lines to the front and four to the rear. It has an electric connection and tells your BRAKE FAILURE light to come on if it senses that the pressure going to your brakes is out of whack. Due to its complexity this cannot be fixed and can only be replaced.

In short, it's a complicated process. If you have the time and the money, it's a good challenge. But if you can't risk not being able to drive your car, just have a mechanic do it.

To view my full story, check out the thread https://www.matthewsvolvosite.com/forums ... =2&t=19355

[billofdurham]

I have to disagree with Bill about the wheels here............... as well as from someone who has a pretty thin build,

My wife describes me as "portly" and my 13 years old granddaughter reckons I am "cuddly". It is easier for me to take the wheels off.

Bill.

[Choguy03]

I have to disagree with Bill about the wheels here............... as well as from someone who has a pretty thin build,

My wife describes me as "portly" and my 13 years old granddaughter reckons I am "cuddly". It is easier for me to take the wheels off.

Bill.

ROFL.

[asg1986]

I realize this is an old thread, but if someone is reading there is another bleeding method that you never hear mentioned on these DIY sites- and it's the easiest way! I took a brakes class at the local community college, and the unmentioned method is simple "gravity bleeding." All you have to do it loosen the master cylinder reservoir cap, then open the bleeders on the brake calipers. You might have to wait a half an hour, but there is no pumping, vacuuming, or partner required. Sure, you are exposing brake fluid to air for longer than with the other methods (brake fluid absorbs moisture), but I doubt its significant. Be sure to make sure the fluid level stays above the line.

My teacher said he used to open the bleeders while doing oil changes just to get some fresh fluid into the calipers... Not a bad idea.

Also, if you're doing the master cylinder you should bench bleed before installing. This is easily done.

[rgk]

The above post is terrible advice and will surely result in air being introduced into your brake lines.

Only the hand pump or the brake pump methods are acceptable. This is because downward pressure associated with these methods do not allow air to be exposed to the lines.

Using these methods, the operator opens the nipple only after the pressure is applied and closes it before the pressure is relieved. This ensures a one-way street of pressure.

I repeat: No air should EVER be allowed to move into the lines.