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Excessive Brake pedal travel before "bite"

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justanotherhumanoid
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justanotherhumanoid

Excessive Brake pedal travel before "bite"

Post by justanotherhumanoid » Tue Apr 02, 2019 4:01 am

My brake pedal feels a little soft in that it takes about 3 inches of travel before I really feel the brakes start to bite. It's been like that a while; the brakes seem to function fine beyond that point, will engage ABS and everything before the pedal goes to the floor, work well in panic-type stops, etc. Thing is, I drove a rental car recently that had that nice new brake system feel to it, and it made me (a) wonder if there might be something wrong with mine and (b) want that feeling of immediate bite that my pedal lacks. Looking for some advice as I'm pretty amateur when it comes to cars.

I did the brakes when I first got the car (2006 S60 2.5T AWD), at about 80k miles, with new Autozone Duralast Gold (the mid-grade) pads and rotors all round, and new brake fluid. I think the brakes felt about the same then, which was an improvement from before, so I didn't think about the pedal feel very much and they seemed to function fine. I bedded them properly and gave them some good hard functional checks, all was well. The car was for a family member so I haven't been its primary driver. No complaints from her but now that the car has come back to me (now with about 96k miles) I can't help but notice it lacks that immediate engagement and bite that I like. I want to restore that immediate bite, even if there might not be anything wrong with the system.

I checked my brake calipers, brake booster, master cylinder, brake lines, and caliper spring installation. No visible issues, brake booster appears to work 100%, no signs of fluid or vacuum leaks, hoses in good shape.

I re-bled the brakes using a LF RF LR RR pattern once (before looking up the correct pattern on the forums) then using a RR LR RF LF pattern twice, got no air the second or third time and hardly any (like 1-2 tiny bubbles from the right front caliper) the first time, I doubt that had anything to do with it since there was no change in pedal feel, still takes about 3" before it bites.

Brake Booster checks fine (used this check method):

Maybe I need a new master cylinder?

At the recommendation of a post I read here, I checked my brake caliper spring installation. They all seem fine to me but figured I'd let some experienced MVS guys weigh in. The rears seem to be sitting a little strangely/at a slight tilt (most obvious in the very last picture) and they lack the rubber bumpers that the fronts have, but I remember that's how they were earlier, not sure if they're supposed to have those rubber bumpers like the fronts do or not, or if that would even matter. Pics below.

So my thoughts are maybe replacing the master cylinder will help, or my caliper springs aren't actually good to go? Any and all thoughts/suggestions are welcome, including those that just tell me I'm crazy and the brakes are fine. Thanks all.

Front passenger side spring:
front pass spring.jpg
Rear passenger side spring:
rear pass spring.jpg
rear pass spring (2).jpg
Rear driver's side spring:
rear driver side spring.jpg
rear driver side spring (2).jpg
rear driver side spring (3).jpg
Front driver's side spring: No pic but looked exactly the same/mirror of passenger side.



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Re: Excessive Brake pedal travel before "bite"

Post by tardcart » Tue Apr 02, 2019 5:28 am

Im not familiar with your year, but soft pedal on earlier Volvos was caused by 1 seized slide that causes the caliper to have to twist before full contact, and then it springs back leaving a large space to bridge before the next stop. You can rule out air since that cant have gotten in since when it was fine.



justanotherhumanoid
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Re: Excessive Brake pedal travel before "bite"

Post by justanotherhumanoid » Tue Apr 02, 2019 6:04 am

Okay, that is one thing that I haven't checked. Doesn't seem like much additional work to remove the pins and make sure they are all in good shape and lubed up... on a related note, man those caliper rebuild kits are expensive, nearly as much as rebuilt calipers from napa. I guess I could save some by just replacing the rubber bits and seals? Or maybe I should just replace all the calipers with rebuilt ones. I'd love to paint them and they'd probably be easier to paint that way... also I've never rebuilt a caliper before.



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Re: Excessive Brake pedal travel before "bite"

Post by June » Tue Apr 02, 2019 6:49 am

One other thing you have not mentioned is a fluid flush. This should be done with a power flush machine to clear the old fluid out of the abs block. At least in my 2004 maintenance schedule it's 2 years or 24K miles. So the brake system must be flushed every 2 years. If the previous owner was too cheap it may not have been done in a long time. Also aftermarket pads feel different depending on the composition. I burned the brakes up in the mountains in 2009 and had no choice but to allow aftermarket pads be installed (4-wheels) on my 2004 and the breaking felt terrible and required more effort. On the plus side the wheels stayed cleaner. When I got home I had Volvo replace them with Volvo pads and a flush in case the shop had used inferior fluid and my breaks were back to normal. So type of pads make a huge difference in petal feel. Whatever the genuine Volvo pads are made if throws dust all over the wheels in as few as 20 miles so it must be a soft material. Also every time my I get the car back after a fluid flush there is a noticeable difference in petal feel. So even 2 years must deteriorate the fluid. June


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Re: Excessive Brake pedal travel before "bite"

Post by XC70Rider » Tue Apr 02, 2019 7:00 am

justanotherhumanoid wrote:
Tue Apr 02, 2019 4:01 am
....
I checked my brake calipers, brake booster, master cylinder, brake lines, and caliper spring installation. No visible issues, brake booster appears to work 100%, no signs of fluid or vacuum leaks, hoses in good shape.

....
Now it's time to check the brake vacuum pump and it's check valve switch in front of the airbox. My vacuum pump was burnt and had the same symptoms. I replaced the vacuum pump and check valve switch 1 year ago and since then the brakes are very responsive.

https://www.matthewsvolvosite.com/forum ... oft+brakes

The 2.5L engine has low vacuum when cold which is the purpose of the vacuum pump.



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Re: Excessive Brake pedal travel before "bite"

Post by abscate » Fri Apr 05, 2019 5:04 am

Pads and rotors look fine, definitely pull calipers and lube pins and the slides


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justanotherhumanoid
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Re: Excessive Brake pedal travel before "bite"

Post by justanotherhumanoid » Fri Apr 05, 2019 7:08 am

Roger that. I'll try both replacing the vacuum pump (I did already replace the switch which helped fix my poor brakes on cold start), and lubing the pins and slides. Don't have an air compressor or I might consider doing the pistons too, though I guess it wouldn't be a bad time to pick one up. Will report back with results.



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Re: Excessive Brake pedal travel before "bite"

Post by jimmy57 » Fri Apr 05, 2019 7:43 am

The low pedal can also be caused by a failing wheel bearing(hub) also. If the wheel bearing has deflection from excessive "play" then rotor motion pushes the caliper piston much further back and that creates more pedal travel to have that extra fluid volume to push the pistons out before you build pressure.
I also want to comment on bleeding/flushing. The "machine" used to flush brakes is either a tank with a diaphragm with fluid below and shop air above the diaphragm or its a tank that is pretty much a garden sprayer with brake fluid in it that is hand pumped to have air to push it out. The bleeder screws are opened and the fluid flows though from reservoir-mastercylinder-abs hydraulic unit then lines and calipers. There is no high pressure and there is no "power". The very low volume in the hydraulic unit will leave maybe 10 cc of fluid untouched. The accumulators are where displaced fluid goes when ABS is active but the pistons here have springs behind them and are fully extended and have miniscule volume. No fluid flows into those areas during flush and bleed. When you start the car and drive off there is a pump motor and valve cycle test and the residue fluid will get pushed around then and dilutes with the other fluid. The valves can be operated with VIDA but that is not an instruction in VIDA for flushing. If you are doing flushes at 2 year intervals then the fluid is not going to get any contamination that needs any special procedure to remove. The same thing happens every time you change your oil as there are areas, like the oil cooler, that do not drain by removing drain plug and letting oil run out. I'm only mentioning this as you get ZERO additional anything by use of the flush tanks as the source of fluid exchange. A service advisot that says different is misinformed or just lying. The tanks are purely a convenience for the tech. If anything, pushing pedal and keeping some effort on the pedal with bleeder screw closed and then opening the bleeder screw will get more of the old fluid out of the nooks and crannies of the and hydraulic unit. This would have much more pressure than the bleed/flush tanks. That additional fluid is still of no real consequence to the quality of the flush process. When hydraulic unit get replaced or removed where it drains, the system is flushed/bled, the car is driven and ABS is made to be active by braking hard on gravel or other slick surface and if the pedal is thought to be soft then it gets bled again usually a little air is found and the second bleed once pump and valves have been active does it.



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Re: Excessive Brake pedal travel before "bite"

Post by MacNoob » Fri Apr 05, 2019 1:11 pm

A little more on the slider pins:

The sliders run in a rubber sleeve in the caliper body. What happened on my car was that the caliper body rusted around the sleeve, effectively making the hole smaller and making the slider pin bind in the sleeve.
I took the calipers out, pushed out the rubber sleeves, and cleaned out all the rust with a round file. Reinstalled the sleeves and freshly lubed pins and all is good now.

I like Akebono Euro Ceramic for pads - no dust, good bite, last a long time (not the least expensive option though).



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Re: Excessive Brake pedal travel before "bite"

Post by XC70Rider » Sat Apr 06, 2019 8:56 am

justanotherhumanoid wrote:
Fri Apr 05, 2019 7:08 am
Roger that. I'll try both replacing the vacuum pump (I did already replace the switch which helped fix my poor brakes on cold start), and lubing the pins and slides. Don't have an air compressor or I might consider doing the pistons too, though I guess it wouldn't be a bad time to pick one up. Will report back with results.
Test the pump before you replace it. Turn the key to ACC 2 then step on the brake pedal to relieve pressure. You'll hear the pump turn on if it's functioning.

If you don't hear anything then verify the wire is connected. It's underneath the airbox. The link I provided in the earlier post show's how to reach it.



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