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04 V70 - symptoms of bad brake master cylinder?

kyle242gt

kyle242gt

Still has a Volvo
Joined
Sep 16, 2003
Location
Santa Rosa, CA
Hi all -
04 V70 2.5T - 177K - probably (?) bled the brakes a long number of years ago when replacing pads/rotors. Driven by #1 son, so I've not been in it for a year or more. But it fell to me to get it smogged, and the brakes feel wrong.

Initial pedal application feels normal when gently applied. It then sinks down quite a ways, feels mushy. Car always stops well, but pedal feel is disconcerting. Doesn't feel like the rears are doing more than their share of work, and doesn't trigger ABS (which I'd figure if the fronts were just out to lunch and the rears were overloaded).

Was initially thinking I just need to bleed it, but the more I think about the behavior, the more I'm wondering if the master is just leaking internally top/mid-stroke. Deeper into the travel, master bore is less corroded (or whatever) and gets a better pressure to the calipers.

While I could (and will, absent advice here) bleed and see if that fixes it, just wondering if the symptoms ring any bells.

Thanks!
 
Bad master cylinder, if you lightly push on the pedal with your hand and it goes to the floor bad master cylinder
 
My '78 wagon M/C lasted for 40 years, driving home one day it failed , I coasted home, no issue {was within sight of my house}.
When you get a new M/C , bench bleed it. plug the holes to keep fluid in.
Remove old M/C and plug the lines to the brakes.
Install the new M/C.
Install the brake lines loose 1/2 turn from tight
Have someone gently push down on the pedal to bleed the lines
Once the pedal is down, tighten the lines release the pedal.
Do this 3/4/5 times until no air bubbles come out of the fittings
Tighten the line fittings! you should have a good brake pedal
I have done this many times and have not had to bleed the whole system.
 
^^

What 283SD advises. Just make sure you put something underneath the master cylinder to catch the brake fluid. It will strip paint very quickly. I always put something under the master cylinder and wrap the line/wrench with a rag to catch the fluid that comes out when bleeding the trapped air coming out of the master cylinder.
 
Struggling to get it bled, wonder if anyone has some ideas for me.
I bench bled it by hand, so possible I didn't go full stroke. My bench bleeding was to hook up hose fittings, run the hoses up (to catch air on the return stroke, and cycle it until I didn't hear any more air and had steady fluid from both holes; rereading, I'd never heard of bench bleeding with the ports blocked off.
Installed it, bled at the MC fittings as described.
Then did all four wheels.

Mushy like before, though better - it had gotten to the point that it felt like it had almost no front brakes after initial bite. But the pedal bites initially, then slowly sinks before firming up near the bottom of the stroke. If pedal travel is 3", fist bite is 1/2", then it slowly depresses to about 2 1/2". Not confidence inspiring, but definitely working.

Rebled all four wheels, no air.
Rebled the master fittings, no air; did this several times, full stroke of the pedal, with the engine running to get the booster helping out.

No change on test drive.

Wondering what to do now. Drive it and see if it magically fixes itself? "Bench" bleed the master in the car (rig up a clear hose so I can monitor for air?)?. Pull the master off and bench bench bleed it (since pedal may not actually be full MC stroke)?

Help!?
 
Ooh boy. Going to pull the master and give it another go at bleeding. Is ABS bleeding something that takes VIDA or just something a cut above an ELM27?
 
I have never had to do any sort of valve bleeding in the abs unit on any car until the latest brake by wire unit came out in 2020.

Could you have a soft rubber line? (Sorry I didn't read the entire thread), or a faulty new master?
 
Thanks Jordan - I'm loathe to suspect bad master (ATE from FCP) since that's the typical reflex of someone who sucks at bleeding. Given that it bites/squishes/firms, I think I've got air in the master that pedal stroke is insufficient to chase out (meaning I sucked at bleeding). Picked up another quart of fluid (thankfully it was on sale), so will pull it off and do it again, better. :x:

Never thought to blame a rubber line. I guess anything's possible...
 
Do you have a power bleeder?

Honestly, I only ever power bleed these days, never had a problem changing any component.
 
Yep, I do have a power bleeder (which I used first shot). But (extemporizing here) if the fluid path is res->front of MC bore ->outlet, then it won't chase out air at the back end of the MC bore.
 
I went through this years ago on one of my 940’s and it ended up the master wasn’t the problem at all; I had a seized front caliper pin that was causing the mushy pedal. I’d done pads a year before so hadn’t bothered to even look at that end of the brake system.
 
ortho stice said:
I went through this years ago on one of my 940’s and it ended up the master wasn’t the problem at all; I had a seized front caliper pin that was causing the mushy pedal. I’d done pads a year before so hadn’t bothered to even look at that end of the brake system.
Click to expand...
:nod:
For me it was a seized rear caliper on the S40.
 
I bench bleed by running the lines back into the resevoir and keep them submerged in fluid. The last MC I bought came with some plastic fittings and lines to do this with.
 
HiSPL said:
I bench bleed by running the lines back into the resevoir and keep them submerged in fluid. The last MC I bought came with some plastic fittings and lines to do this with.
Click to expand...
Yep, this is what I did. MC didn't come with fittings, but I had some from a previous job. Had a ton of air in the rear (front brake) port. Good memo for the future to not shortcut this piece of the process.
 
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