93 Volvo 850 MT Will opening rear brake line drain clutch reservoir?

Post by **JimBee** » 11 Oct 2017, 21:34

I'm considering replacing a rear brake hose and assume I'll lose all the fluid from the reservoir. Will the clutch fluid level also drain?

LOB · Post by **LOB** » 11 Oct 2017, 22:15

By pushing down the brake pedal 3/4 of maximum (with a plank between the seat and the pedal if you are on yourself) you will only lose a few centiliters of break fluid.

Post by **abscate** » 12 Oct 2017, 05:03

You won't drain much, Jim. just put some tape or a rubber glove on it and you will be fine

LOB · Post by **LOB** » 12 Oct 2017, 06:01

abscate wrote: ↑12 Oct 2017, 05:03 You won't drain much, Jim. just put some tape or a rubber glove on it and you will be fine

Or, if you don't want to mess with break fluid at all (except for a few drops) you do it the way I suggested (no fluid can escape the master cylinder when the break pedal is in 3/4 position)....

See this illustration:
http://www.agcoauto.com/content/images/ ... utaway.jpg

Post by **abscate** » 12 Oct 2017, 09:20

If you did drain the reservoir you wouldn't have to do anything with the clutch. The hose to the clutch cylinder would stay full and when you topped up it would burp the air

That's a nice tip from LOB to close of the mc ports!

Post by **JimBee** » 12 Oct 2017, 09:53

Thanks, both, for the good news, but I'd like to understand the logic better. Why doesn't pressurizing fluid at the outlet create more pressure throughout the lines with major fluid loss if a line is opened?

Post by **abscate** » 12 Oct 2017, 09:56

You will squirt out a bit when you crack the line, but then the pressure is relieved and the fluid will just seep a bit

What LOB clever trick does is block the 'refill ports' in the master cylinder, which prevents the reservoir from draining into the mastercylineder and out the wheel area.

Does that make sense?

Post by **JimBee** » 12 Oct 2017, 10:02

Makes sense. Thanks!