1991 240dl Brakes lose pressure when car is started...

blxboarder · Post by **blxboarder** » 13 Jul 2014, 16:42

Hello all, this is my first post to this site, as I have managed to figure out all problems on my car so far on my own with a little help here and there from the internet.

I'll try to keep this as simple as possible. My brake failure light started coming on about a week ago. Today, my father and I replaced the master cylinder, as we were "sure" that this was the issue. Haha. We went through the correct bleeding sequence, and much of the pressure was gained by doing so. Everything feels perfect until you crank the car up. All pressure is lost! It all feels perfect until the motor starts.. my mind is boggled and I have searched this site among others with no probable answer to the issue.

Any help would be much appreciated because we are at a loss. We figure it may be the brake booster but I have no clue how to test it and cant find anything on it. Thanks so much in advance!

93Regina · Post by **93Regina** » 13 Jul 2014, 19:00

blxboarder wrote:replaced the master cylinder...correct bleeding sequence....

Oh...try again: BRAKE SYSTEM

BLEEDING PRECAUTIONS

1) On all models equipped with diagonal split hydraulic
system, bleed either rear wheel first, then opposite front. Repeat
procedure on other side (circuit).

2) On all models equipped with load sensing proportioning
valve, bleed valve before bleeding brakes. If master cylinder is
equipped with a bleed screw, bleed it first.

PS: There are two brake systems on front calipers

blxboarder · Post by **blxboarder** » 13 Jul 2014, 20:32

93Regina wrote:
blxboarder wrote:replaced the master cylinder...correct bleeding sequence....
Oh...try again: BRAKE SYSTEM

BLEEDING PRECAUTIONS

PS: There are two brake systems on front calipers

Yes, I did all of these steps accordingly. The issue is only occurring when the car is started. Most definitely no air in the system.

93Regina · Post by **93Regina** » 13 Jul 2014, 20:50

blxboarder wrote:I did all of these steps accordingly.

All brake booster does is too decrease foot-force required to depressed pedal. Plug its vacuum line, and intake side also.

If both sides of front caliper along with rear calipers were bled by the book, and if nothing is leaking, then ain't nothing wrong with brake hydraulic system.

Again, 240s have a dual front brake system; two separate systems; fail safe braking.

ENGINEERING CHANGES
INTRODUCED ON 1975 VOLVO 240 SERIES

New stepped bore master cylinder to maintain normal pedal pressure during emergency three-wheel braking.

DE from Sweden says - "It has two brake circuits, one for both the front wheels and the rear left, and one for both the front wheels and the rear right. That's why there are dual brake lines and so many air nipples on the front calipers. If one circuit fails due to a ruptured brake line or something else, you'll still be able to stop safely."