850 brakes any suggestions?

Anyone any ideas and comments about this one. 1996 volvo 850 2 litre 20
valve. Sent it into the mechanic, brakes very spongy becoming harder with
the next press of the pedal. Mechanic bled the brakes but pedal still low
and although less spongy and more efficient depressing about a third of the
pedal travel and not hard. Mechanic said it needs new discs as they are
warped (I will agree with this as there is the classic symptoms of a warped
disk) and once the discs are replaced with new pads they should be as I want
them. Also he says that the calipers become 'lazy' with age and they should
also be replaced. In other words nearly all of the system replaced except
master cylinder, pipes vacuum and abs unit. I always understood the 850
brakes were exceptional, they certainly were when i bought the car 2 years
ago. Any comments and suggestions gratefully accepted. - Roy

 

Spongy Calipers? That's a new one on me. Any "sponginess" in the
caliper would be (IMO) not moticeable at the pedal. Now, if the
pistons are really worn and not holging their position well and the
seals are pulling the piston back into the caliper i suppose that is
possible, but it seems a stretch of th imagination compared to the
other forces involved.

Flexible brake lines can become spongy and I have experienced that on
a motorycle, increasing feel after replacing those.

Test the rotors this way: with the engine running, pump the brakes up
so they feel solid again. Without movign the car, wait a minute or two
and see if the pedal sytays where it is or whether it needs pumping
again. If it stays solid then suspect just the rotors (and suspect the
mechanic as well).

Warped rotors should be done first if they are bad enough to push the
pistons far enough to necessitate double-pumping. That is a safety
issue.

__ __
Randy & \ \/ /alerie's
\__/olvos
'90 245 Estate - '93 965 Estate
"Shelby" & "Kate"

 

The symptoms you describe are in my experience the signs of a failing
master cylinder. Volvo brake system hydraulics seem to last a very,
very long time if the fluid is completely flushed and replaced with
correct new fluid once every two years as the maintenance schedule
requires. However, at least in the US, many people neglect this bit of
maintenance.

John

 

In an earlier contribution to this discussion,

I suspect that you've got some water dissoved in the brake fluid and that
this locally turns to steam when the brakes get hot. If the fluid hasn't
been changed, renew it *all* - don't just bleed. That will probably fix it.

If the discs *are* warped, they will need to be skimmed - if within
thickness limits - or renewed. But get the runout checked against acceptable
limits with a dial gauge *before* doing anything. Many perfectly serviceable
discs - in the UK at any rate, and probably elsewhere too - get replaced
unnecessarily.

 

car has had new front brake hoses and the brake fluid is brand new.

 

Master cylinder!