95 850 - Low 'bass' resonance when braking

Post by **meine39** » 28 Jun 2009, 14:49

95 850 NA GLT Wagon - 150K
When slowing down at low speed to a near stop, a dramatic low pitched resonance sets off from the brakes throughout the whole car with minor vibration felt as well. If coming to a complete stop, the noise/vibration is not heard/felt. The noise can be 'played' by an exaggerated long slow stop, and seems to be worst just at the threshhold of a complete stop.

Car did this once before, and local indy replaced a frozen left rear caliper, which resolved the probelm (that was about a year ago). I had the car back to my indy last week, and he couldn't reproduce the problem, but confirmed that both rear calipers are functional (not frozen).

Car came back from a 250 mile highway trip yesterday, and now noise is present at nearly every stop.

Brake parts are OEM Volvo at all 4 corners (rotors and pads). I also replaced e-brake cables and shoes late last summer (again Volvo parts only). Any ideas? Frozen front caliper(s) maybe?

Post by **MadeInJapan** » 28 Jun 2009, 15:18

This is a typical problem on the rear brakes when the calipers begin to vibrate against the pads... the solution is to install brake shims and coat them heavily with ant-squeal grease. My druthers are Volvo's own product but www.fcpgroton sell the grease as well as the shims.

Post by **meine39** » 28 Jun 2009, 19:25

Thanks MIJ - the rear pads are OEM Volvo and have the shims and grease installed, so I'm not sure if that's it

I'll clean/regrease the shims this weeks and see if that takes care of it...

valvster · Post by **valvster** » 29 Jun 2009, 05:48

If problem is still there after re-grease, try swapping the inner pad with the outer pad (on the same axle) also check that the pins have been correctly installed...very easy to end up with a pad held in place with only one pin.

cheers....Valvster

Post by **vegasjetskier** » 29 Jun 2009, 08:59

Warped rotor(s)?

Post by **Ozark Lee** » 29 Jun 2009, 16:33

Warped rotor(s)?

That's what I'm thinking. You tend to "feel" them less if it is the rears.

...Lee

Post by **meine39** » 29 Jun 2009, 16:57

Thanks guys - I'll have a look at the pins/clips and rotors as well.

Is there any definitive test or inspection for warped rotors? The rotors are Volvo OEM, and I'd estimate that they have less than 5k miles on them.

Post by **Ozark Lee** » 29 Jun 2009, 18:20

There is a fancy "run out" test that involves a mounted dial indicator. The parts for the test far outstrip the price of a new set of rotors. If they are that new, and you didn't have a stuck caliper then they should be OK. When you said OEM I was thinking original to the car. They usually make it about 3/4 of the way on the second set of pads before they warp but you driving style has an effect. I am real tough on them myself but I have a lot of fun.

Start with cheap and easy and grease the shims.

...Lee

Post by **meine39** » 09 Jul 2009, 21:50

I cleaned and regreased the shims and pad backing plates. I found that the shims were installed upside down (shims are now installed with arrows in direction of wheel travel; the 'cut out' portion of shim is on the bottom half of the pad).

I also installed new pad hardware (pins and spring clips). Noise went from constant to only a few barely perceptible instances on my initial 5 mile test drive - my college driver who puts the vast majority of the miles on the car says the noise is now gone.

It occurred to me that perhaps the only reason a caliper replacement fixed this in a previous instance of this problem (see initial post) was that the pads were replaced at the same time - the groan wasn't fixed, only deferred for a while.

Thanks to all for your help.

Post by **meine39** » 05 Aug 2010, 17:30

HI all - reviving my original thread from late June of last year - it's baaaaaack! Long story short, groaning from rear brakes was solved at that time with a cleaning/regreasing of shims and new hardware (pins and clips). The car is making the same noise again; take note that it was hot then and it's hot now. I will do the ol' clean and regrease, but could it be something else? All brake components front and rear are right from the Volvo dealer's parts counter, so aftermarket components shouldn't be the issue.

TIA