2001 v70 soft pedal

[agruenberg]

Hi everyone. The brake pedal in my v70 has been getting progressively softer, and the pace of decay has picked up in the past couple weeks, so I dove into it. I checked all four calipers for leakage and found none, so I figured the culprit would be the master cylinder. I put one in and bleeded it extensively with a pressure bleeder. It made no difference. The replacement cylinder was a new ATE unit, so I doubt it's bad, and even if it is, I doubt it would be bad in the exact same way my old one was. So, my next thought was hoses. I blocked them all off, and the pedal was a tad harder, but would still gradually sink to the floor.

I wonder if all the hoses are just old and soft rather than one of them being acutely bad.
I'm sure the pads and springs are properly installed; I open and clean my brakes every summer, so I'm well used to installing them.
I have stability traction control, but not dynamic stability traction control.

I can't get the brakes to skid or even activate the ABS system they're so soft.

Any ideas?

[MoVolvos]

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It could be a soft spot, crack or bulge in the hose. The part about sinking to the floor? When I replaced our S80 T6 with stainless hoses on all corners the pedal feel was much better. Yours still most likely the Master Cylinder though it's a new ATE. If there are no leaks and the reservoir stays full then it's most likely the Master Cylinder piston seals.

I recently rebuilt the MC on our 05 GS430 with a piston kit. Used assemblies are around $300 and the sinking to the floor didn't seem like anything else in the ABS system. Not wanting to go used I decided to take it apart. Couldn't find any issues till I used a magnifying glass and the found a sliver of O-Ring on the side of the Plastic retainer and O-Ring in the bottom of the piston groove. The two are in the same groove side by side. The piece was from the inside curve and sheared loose after 240K miles and you could tell it was not form solid from the tiny pitted air pockets in the material.

The piston kit was $150. Not knowing if the sliver was the problem looked for and found a replacement O-Ring slightly larger from Lowe's but for plumbing. Decided to put it in for testing and no more petal to the ground. Before the new O-Ring the car would stop fine then all of sudden it would go lower till it hits bottom. After some more research discovered the material was not compatible with brake fluid as it would swell by 20 to 40%.

https://www.lowes.com/pd/Danco-33-O-Rin ... 5013060231

After mulling over whether the 30 cent O-Ring would swell under pressure in the cylinder bore I decided it was best for my Son and others in case it gave way and caused an accident. After typing in a different area code I found the same kit half price from a dealer in Jersey. Although the seal had fixed the problem and it worked fine it was night and day compared to the entire rebuild assembly. Now the pedal is high and rock solid.

Before you go about replacing the new ATE try a reverse bleeding procedure. Start with the shortest run of brake line, so bleed the driver's side first and then passenger. Take a test drive and see if it made a difference. Afterwards, bleed the driver's side back then finally the passenger. I had to bench bleed the MC on the car rather than when it was out. That's a another procedure on its own.

If possible get someone to depress the pedal rather than using the pressure bleeder. Make sure the helper does not let the pedal up before you secure the bleeder screw. Removed the MC 3 times and as I reverse a part in the assembly and fluid gushed into the foot well . Almost got rid of the car thinking I somehow damaged the MC besides the new Piston Assembly. Be patient keep at it.
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GS430 O-Ring.png (192.23 KiB) Viewed 421 times

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[MoVolvos]

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Here's the part in red I reversed in the kit so pay attention to details including your procedures and bench bleeding of the MC. It's a leak, air or seal. Hope it's not the pump even though there are no codes.
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The cap has a wedged O-Ring. If installed properly it looking like it will spread when the piston is coming up. In reversed it pushes flatter so fluid was coming out at the bore.
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Piston CAP.jpg (509.21 KiB) Viewed 414 times

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[vtl]

Hook up DiCE/VIDA, start bleeding a caliper (with a vacuum pistol type pump), trigger ABS inlet/outlet valves of that caliper. You'll see a large air bubble escaping eventually.

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[jonesg]

Hook up DiCE/VIDA, start bleeding a caliper (with a vacuum pistol type pump), trigger ABS inlet/outlet valves of that caliper. You'll see a large air bubble escaping eventually.

1.png

going to have to grab my laptop and look at that feature.