Use a Motive or like power bleeder.

As Mr. Yount describes, some plastic like food cover plastic wrap is best under the reservoir cover.

I forget whether I remove the sieve (strainer) under the cap.

Replace the cap.

Perform your repair. Study the method and know the caveats. Corrosion at the copper / nickel hard lines at any union.

As Nahtanha says, inspect the rear flexible brake line. The outer rubber line cover by this date and miles may be well cracked and you may be able to see the nylon line inside. If in an auto safety inspection state, you may not pass.

Use Blaster, Kroil, Liquid Wrech on the flexible brake line unions. Unless you have these you may want to obtain Snap-On or maybe S&K (maybe not S&K, not the same in the modern era) line or flare wrenches.

Though I've been able to use regular open-end spanners.

ATE is OEM for flexible brake lines. There may be other brands of quality or all 240 flexible brake lines are made in the same factory someplace.

(I have to replace the two rear flexi brake lines on my 1990 240 before MO-state safety inspection Dec 2020. Yet the inspection station failed me for the front line outer rubber line covers were cracked.)

You do not indicate ABS or non-ABS 240 brake system. If not ABS, the left and right rear ATE caliper are each connected to the two (primary & secondary) different circuits. Brake fluid loss for such a repair would best be treated by a full flush of new DOT-4 using a Motive brand or like pressure bleeder.

If the brake fluid is black or very dark, yes, you want to flush.

Brake fluid contaminates do move through the system through dilution as the brake fluid ages and through use, pickups of ambient moisture and corrosion forms.

The Motive brand high pressure vinyl line from the top of the pressure bleeder burst (conveniently) at the end of the flush on my 1990 240 non-ABS. So take care. Maybe the tenth or twelfth time I'd used the thing.

Do not use the brake pedal, or, if you must, place some wood sections under the pedal to limit pedal travel. An assistant coordinates with the one at the brake pedal. Open after starting the stroke, closed before brake pedal stroke finish.

The issue is the gap between brake bleeder nipple you turn open and closed and the caliper at the thread interface. On brake pedal release, air is drawn into the caliper through the brake nipple bleeder to caliper threaded bore interface. The other reason why we do not use a vacuum method to replace brake fluid.

If ABS on your 1991 240, you may be able to get away with one 32-ounce bottle of DOT-4. Walmart SuperTech DOT-4 is fine.

Your 240 service manual should include the brake bleed order for both non-ABS and ABS brake systems. I'm unsure, yet the 700-900 Series FAQ here seems to relate the brake bleed order on 700-900 series for non-ABS is different.

240 Non-ABS Flush Order:


I'd suggest organic (non-metallic) brake pads. Rotor quality from after market outlets has greatly improved. Bosch gets the best reviews for pads and rotors. Though a rear set on one 240 and a front set on another 240 are all AutoZone or Advanced Auto or maybe O'Reilly auto parts. I forget. Receipts are filed.

My shrill write-up on a recent brake fluid flush on my ABS-240 about 15 months ago.

https://www.brickboard.com/RWD/volvo/1662538/220/240/260/280/new_pads_resurface_rotors_hows_brake_fluid_black.html

With rotors removed, you may want to inspect the parking brake works at the hub. At this age and miles, the brake shoes can begin or have already de-laminated. As I have to do on the 1990 240, yet the car left rear parking brake shoe is gone. The rusty back plate remains. The car right side parking brake shoe remains, yet I'll replace that. Several ways to replace the parking brake shows. Can be a (In Old Duke Parlance) a 7F job or more. May also want to inspect and repack the rear wheel bearings, yet that is a task to perform carefully and in the event you have other transportation options should the parking brake shoe or rear wheel bearing taska go terribly wrong.

Else, I guess that does it.

Questions?

Antihistamine (makes me more goofy) Boyeeeeeee
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Jonathan Harshman Winters III: The Mightiest, Greatest, & Most Powerful North American Comedian & Comedic Actor in Perpetuity

Replace your rubber lines while your doing the calipers.

Define “doing” or we’re all just guessing about what’s going on.

The answer to both questions is YES. Bleeding all 4 corners is usually called a flush.

Brake fluid does not move through the lines while operational. However, water vapor getting into the system is the real problem. And typically, the water comes in through the reservoir, and percolates to the lowest point of the brake system. So, when you do a partial bleed, you will be moving contaminated fluid down the line. Not the best scenario.

I have replaced rear brake calipers without flushing the entire system. Not a problem. But, I like to flush the fluid every few years.
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Keeping it running is better than buying new