Last week, it seemed like the master cylinder was going out not more than a year since it was replaced. I replaced it again under warranty but have had no luck at all getting the brakes to work again. I thought that I might have gotten a bad new unit so I was able to swap it with a new one yet again.

I'm on my third MC in just one week and I'm pretty sure by now that this isn't my problem

Car off, I can press the brake pedal almost all the way to the floor. Car running, I can floor it with some effort. It gives all the indications of air in the system but I swear that I know how to bleed the brake system properly and have gone through two large bottles of brake fluid. I tried several methods of purging the air including vacuum through the wheel end.

The only thing I'm not sure about is if a bad brake booster could cause this. I tried YouTube-ing it but can't quite get a satisfying explanation of what's not right.
--
signature

I suggested to a friend that I was gonna take it to a professional to get it done. He then commenced the necessary scathing ass chewing about the simplicity of the brake system and how I would be wasting time and money on something I can do myself.

So, I got out the big tools and after a couple hours I finally realized that I had a rusty seized caliper guide pin on the front right brake. To be honest, I don't recall greasing those things the last time I replaced the pads. The caliper had been trying so hard to overcome the problem that the guide pin is now bent and will need to be replaced. Not expensive but it could have been avoided altogether with the proper preventive maintenance.

Lesson to ya!
--
signature

Did you bench bleed the master cylinder?

You can do this after it is on the car simply by taking a section of brake line from each of the two fittings and route them back to the reservoir (submerge each one in the reservoir fluid and slowly pump the pedal)

This effort will purge any air from the master cylinder and then reattach the brake lines. Then bleed the brakes in the correct order as described in the FAQ's (https://www.brickboard.com/FAQ/700-900/Brakes.htm#BrakeBleedingSequences).

Good luck,
Randy

If you want to be sure your brakes are properly bled, get a pressure bleeder. I have used the Motive Products one for some years now. Homestly, it's one of the best 50 bucks I have ever spent on a tool. It's especially good with ABS with its nest of plumbing or the old Volvo with the dual caliper bleed screws before they went to ABS. You won't regret the purchase. Never got it right with the pump the pedal or vacuum method. Hope this helps. Mike

From the 700-900 FAQ (click FAQ at the top of each brickboard.com page):

Non-ABS Brakes
https://www.brickboard.com/FAQ/700-900/Brakes.htm

Or ABS?
https://www.brickboard.com/FAQ/700-900/BrakesABS.htm

If you are bleeding brakes using the brake pedal, if you press to far, even on a new ATE (or Girling?) Brake Master Cylinder, you can displace seals in the piston bore. (Or the seals are on the piston?)

Are you bleeding the brakes yourself? Like with the fluid dripping down the caliper, or with a hose between the caliper bleed nipple and a container of old brake fluid? Either way, air can get suck back in through the thread interface of the bleeder nipple and the brake caliper body.

Else, use a Motiv Power Brake Bleeder or the like. These use a container full of your fave DOT 3 or DOT 4 NEW brake fluid, you pressurise it with a pump of spare tire air (if this was 1967 and we're working on your VW Bus), and open and close the bleeder valves as the clean fluid comes out the (hopefully transparent) hose connected to the brake bleeder.

If no ABS, you have to pay some special attention to the two brake check valves at the rear of your 1989 740-series Volvo. Something about raising the rear of the car up a little higher. Or, as you power bleed the rear brakes, gently tap the brake check valve to dislodge any air bubble in there.

If you have ABS, you may want to run the ABS brake pump after you have clean fluid coming out the furthest brake bleeders so as to remove old brake fluid in the ABS pump.

There may be a more efficient way to do this using a power brake fluid bleeder whether you have ABS or not. You may want to call around to see if you can rent or borrow a brake power bleeder. It has to be clean, if it is not new.

Use at least 91% anhydrous Isopropyl alcohol to clean away the spent brake fluid in your power bleeder tool and let dry before storing again. You do not want the brake fluid to remain anywhere inside the power brake bleeder tool.

Other more qualified than I shall chime in with better suggestions, I'm sure.

How are them rear wheel bearings on that 1989 Volvo 740 doing for grease pack? They need some NLGI-2 grease pack love, also, like the front wheel bearings.

Questions?

Hope that helps you.

Sundae's MacDuff - Hangin' Out up by the Brickboard.com!
--
The Volvo 164: The Mightiest of All Volvo Automobiles in Perpetuity

All good info. Thanks for the list!
--
signature