fasteddyT5 Posted June 19, 2007 Report Share Posted June 19, 2007 I am thinking about buying a new master cylinder to swap into my '95 855T, and curious if there are any hints or things to watch or avoid in doing the job. I've never pulled a master cyl. before, and this one seems to be a little hard to access all of the fitings. I've got a good brake bleeder, a set of flare wrenches, etc., just looking for hints. the reason for the swap is a long term low brake pedal. For some years, the pedal goes down quite a ways before any effect, and then brakes work fine. Car has had new rear calipers and all other rear parts, new front rotors, pads (but original calipers), has original brake lines (at 108k), original proportioning valve. Pumping the pedal has no effect - always the same "long" pedal travel, then solid stops, and it has been doing this for at least the last 60K if not longer. The master cylinder is about the only thing left that I can think of as a culprit here, although it passes the normal checks like holding pressure on it (no drop in pedal regardless of how long you hold it). Any hints, suggestions, or thoughts of other things to try before swapping the MC? Thanks Link to comment Share on other sites More sharing options...
matt b Posted June 19, 2007 Report Share Posted June 19, 2007 I've done brakes for as long as I've owned cars and it sounds like you should adjust the rod rather than replace the entire thing. There are settings you should mess with before swapping out the part.Replacing a MC is anything but fun and unless you have clear signs of failure, you should try to adjust things first.Just my $0.02 Link to comment Share on other sites More sharing options...
mbsl98 Posted June 21, 2007 Report Share Posted June 21, 2007 Any other suggestions or hints? I don't believe that it is just a rod adjustment, because there seems to be some slight brake action initiated early in the pedal travel. I know I said that there was no braking action until the pedal was well down, but on really paying attention to the motion while sitting in the driveway, and carefully listening with the motor off, it actually seems that there is some very slight pressure created in the early part of the pedal travel (Sorry to have possibly misled here). Problem is that pedal goes a long way further before firming up and stopping well. If I could adjust rod, it would always be into the first part of the travel where there is sense of some slight braking. Once the pedal starts to create pressure, it just takes too much added pedal travel before full pressure is established, as if the pistons were being allowed to retract too far whenever pedal pressure is released, so they have to be pushed out further to reach calipers. Unfortunately, I don't know the innards of a MC so don't know it there are actually any sort of conrtol valves in there.If it does sound like a MC rod adjustment, how is that rod actually adjusted on an 850? I looked at that area a while ago, but didn't find anything that looked adjustable. Done from interior or under hood?Barring rod adjustment, hints on actually removing and replacing MC?thanks to all,Mike Link to comment Share on other sites More sharing options...
Guest Guest_whilst_* Posted June 22, 2007 Report Share Posted June 22, 2007 Any other suggestions or hints? I don't believe that it is just a rod adjustment, because there seems to be some slight brake action initiated early in the pedal travel. I know I said that there was no braking action until the pedal was well down, but on really paying attention to the motion while sitting in the driveway, and carefully listening with the motor off, it actually seems that there is some very slight pressure created in the early part of the pedal travel (Sorry to have possibly misled here). Problem is that pedal goes a long way further before firming up and stopping well. If I could adjust rod, it would always be into the first part of the travel where there is sense of some slight braking. Once the pedal starts to create pressure, it just takes too much added pedal travel before full pressure is established, as if the pistons were being allowed to retract too far whenever pedal pressure is released, so they have to be pushed out further to reach calipers. Unfortunately, I don't know the innards of a MC so don't know it there are actually any sort of conrtol valves in there.If it does sound like a MC rod adjustment, how is that rod actually adjusted on an 850? I looked at that area a while ago, but didn't find anything that looked adjustable. Done from interior or under hood?Barring rod adjustment, hints on actually removing and replacing MC?thanks to all,MikeMike,with engine off,is pedal "high & firm"? If so, it's pointing to a bad Brake Booster.HTH.Jeff Link to comment Share on other sites More sharing options...
mbsl98 Posted June 22, 2007 Report Share Posted June 22, 2007 Thanks Jeff. Unfortunately, the pedal feel is about the same with motor off (as far as the travel distance). Link to comment Share on other sites More sharing options...
Ozark Lee Posted June 22, 2007 Report Share Posted June 22, 2007 Barring rod adjustment, hints on actually removing and replacing MC?I haven't had to change one on my Volvo but I have on just about every other vehicle I have had. Normally the new MC must be bench bled before it is installed. I note that the method in Haynes is to mount the MC and leave the brake lines loose. They then say to fill it with brake fluid and leave the lines loose until brake fluid is running out of the line connections.The only sage advise I can give you is that the MC itself must be bled before trying to bleed the rest of the system or it will never work....Lee Link to comment Share on other sites More sharing options...
drlava Posted June 22, 2007 Report Share Posted June 22, 2007 how is that rod actually adjusted on an 850?I'd like to know this as well. Link to comment Share on other sites More sharing options...
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