Dear Fellow Brickboarders,

Hope you're well. After inspecting all four wheel brakes and correcting a stuck caliper pin, I still can't end a slow, rhythmic "whump-whump" when braking.

This is not likely drive-shaft related: the noise's frequency does not increase with speed. The drive-shaft center support seems to be in good order: there's no play.

Noise frequency does increase with brake pedal pressure. The car does stop, but more pedal pressure is required to get that done, than used to be so.

The ABS warning light stays-off after start-up. The steering wheel does not "twitch" when this noise is present.

A car-smart neighbor opined, having been a passenger for a test drive, that the noise comes from the rear.

Could the brake booster be the source of this worrisome noise?

Thanks for the benefits of your insights!

Yours faithfully,

Spook

If you had a stuck caliper slide pin, it's possible that you may have warped the front brake rotor. Did the front brake rotor get (really) hot when the caliper stuck??
It happened to me on a 93 940.

Steve

Dear HillBilly,

Hope you're well. Good point!! While I know that a seized caliper can cause the car to pull to one side, in this case there was no such result. Thus, I never suspected the caliper slide pin was stuck and so no reason to check for over-heating.

I'll swap in a factory-new rotor and see if that helps.

Thanks for the suggedstion!

Yours faithfully,

Spook

Spook

Hope you are well. On one of the 940's I've had similar pulsating when braking for as long a I can remember, about 8 years. I gained a lot of experience trying to figure out the problem (sliders, pads, rotors, calipers). The condition never changed. So I just have been living with it. Once in a while I think I should try the control rod bushings

https://www.brickboard.com/FAQ/700-900/Brakes.htm#BrakeShudderingandSuspensionBushings
--
89 240 wagon, 94 940, 300K, 94 940, 141K

Dear Spook,

Check the tires for flat spots (prolonged parking) or uneven wear (caused by worn absorbers).

Side note: Sometimes I wonder when is the time to replace absorbers. Replaced both rear ones early last year getting only slight improvement in ride comfort compared to 10+ years old part. Planning to do the fronts next.

Regards,
Amarin.

Dear Amarin,

Hope you're well. Thank you for your insights. The tires (Michelins) have 6,000 miles (10,000 km) on them.

Shock absorbers can be tested by placing a foot on the bumper cover at the corner, pressing down hard, and then quickly removing one's foot. If the shocks are serviceable, the bumper will instantly and "crisply" spring back to its normal height. If the shocks are not serviceable, the bumper will bounce a couple of times, before motion ceases.

If a shock is weak - and the tire hits an obstacle, the tire will not stay in contact with the road. Rather, the tire will bounce away from the road surface. That loss of contact - however brief - is worrisome.

Hope this helps.

Yours faithfully,

Spook

Are you confident the rotors are all true?

Randy
--
Any twenty minute job is just a broken bolt away from a three day ordeal

Dear rstarkie,

Hope you're well. Thank you, for your comment!

The front rotors have about 3K miles use; the rears, about 2K miles. Both sets of rotors were made by Brembo.

I installed these rotors and torqued lug nuts to spec (63 pound/feet).

Even so, I can't be sure that the rotors are still true.

A rotor swap - easily done - will resolve the issue. But I'll wait to see if someone has had a similar problem and - with some luck - learn how they solved it.

Yours faithfully,

Spook

Spook,
Were the pads replaced when the rotors were replaced and if so, were the pads genuine Volvo? I had problems years ago with aftermarket pads being too hard and not dissipating the heat which warped the rotors. I have never used any pads but genuine Volvo since and have not had a problem with warped rotors. The genuine Volvo pads are softer and there is more residue on the rims/hubcaps.
I assume your calipers are good (even pad wear) and the front pins are free.
--
Mine:3-940s running; 1-740, 3-940 parts; dtrs:3-940s running

Dear jd620,

Hope you're well. Thanks for your reply.

"Yes" to both questions. I replaced pads, rotors, and calipers. I used Volvo pads (made in Denmark).

Yours faithfully,

Spook

Your remark about the aftermarket pads causing the rotors to warp reminded me of another cause. If the flex line is restricted, pads of any sort will spend too much time and pressure in contact with the rotors. The clue is the pulsation doesn't happen until you've driven a mile or so, or when retracting the pistons you need to use muscle. And, of course, replacing a rotor will greatly reduce the pulsation until it is worn thin like the old one. I'd put money on Spook using genuine Volvo pads like you and I do. Just not real money. :)
--
Art Benstein near Baltimore

“Expertise in one field does not carry over into other fields. But experts often think so. The narrower their field of knowledge the more likely they are to think so.” – Robert A. Heinlein

Old rubber brake lines and overheated rotor. Doesn't take too much heating to wrap metal.

Dear Art Benstein,

Hope you're well. Thank you for your insights! I indeed used genuine Volvo brake pads (on the rear, Volvo #271824-5, made in Denmark).

By "flex line" I presume you refer to the rubber-sheathed brake hoses. Those seem to be in good order.

As to retracting pistons, I use a standard plate-and-screw tool. When I checked the rear brakes, it took only a few taps with a plastic mallet to free the calipers from the rotor. I didn't need to use this tool to re-install the calipers: with a couple of gentle mallet taps, they slid into place.

Yours faithfully,

Spook

Hi,

“By "flex line" I presume you refer to the rubber-sheathed brake hoses. Those seem to be in good order.”

You can’t determine if they are good by looking at them. If you don’t know how long they’ve been on there, they might be bad. They can deteriorate internally and still look “good” on the outside.

Dear c1800,

Hope you're well. I do know how long they've "been on there". They are factory-original. While I bought this car "used", it was one-owner, and she left all of the records in the glove-box. Thanks to a broken glove box lock, the records came to me with the car.

You're correct that brake hoses - as do all other hoses - fail from the inside out. So, I agree totally that external inspection is not helpful.

I have spare hoses, so will await warmer weather to do this work. At 27 years old, these hoses don't owe me a penny.

Yours faithfully,

Spook

+2 on flex lines

They normally deteriorate on the inside. A few years ago I had to replace the front flex lines on my 95 850 GLT. The brakes had become unsafe. Thumping, more pedal pressure required then eventually they started pulling. If yours are original it could be time to replace them.
--
Will I buy another Volvo??? We'll see....