Pulsating Brakes

  • Thread starter Thread starter Randy G.
  • Start date Start date
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Randy G.

Paul Colini said:
I have a '91 240 with 100 000 miles on it and feels like I'm riding on
square tires when I brake. I had the front rotors changed but the problem
persisits. Wheels were balanced-no difference. The front end is tight and
it's not so much a vibration at the steering wheel (although there is some)
but you can feel it in the seat of your pants. It does it only when the
brakes have warmed up so I suspected a warped rotor but the new ones do it
too. I tried braking with the emergency brakes and the problem is gone.
What else could cause the shaking other than what I've mentioned?
Also whenever it is cold it lets out a groan whenever I go over a bump.
Doesn't feel like something is loose but either a shock or other suspension
component is worn out and metal is scrubbing metal. Not as bad once the car
has been driven for a while. Difficult to isolate if coming from front or
back. Any help is greatly appreciated.
Confused
Click to expand...

If it is only when the brake are warmed up then I too would suspect a
bad rotor. Any good suspension shop should be able to rule out most
other causes such as bad steering rack, bad tie rod ends, worn
suspension bushings, etc.

Although unlikely, it could be dripping brake fluid on the drums, but
that is a stretch of the imagination.

New rotors do warp, and this is more likely with cheap after-market
rotors and those which have been improperly installed or over- torqued
wheels.

You might want to try cross-drilled rotors which dissipate heat more
efficiently and reduce the chances of warping.

__ __
Randy & \ \/ /alerie's
\__/olvos
'90 245 Estate - '93 965 Estate
"Shelby" & "Kate"
 
Paul Colini said:
I have a '91 240 with 100 000 miles on it and feels like I'm riding on
square tires when I brake. I had the front rotors changed but the problem
persisits. Wheels were balanced-no difference. The front end is tight
and
it's not so much a vibration at the steering wheel (although there is
some)
but you can feel it in the seat of your pants. It does it only when the
brakes have warmed up so I suspected a warped rotor but the new ones do it
too. I tried braking with the emergency brakes and the problem is gone.
What else could cause the shaking other than what I've mentioned?
Also whenever it is cold it lets out a groan whenever I go over a bump.
Doesn't feel like something is loose but either a shock or other
suspension
component is worn out and metal is scrubbing metal. Not as bad once the
car
has been driven for a while. Difficult to isolate if coming from front or
back. Any help is greatly appreciated.
Confused
Click to expand...

If you feel it in your ass and not really the wheel it's from the rear end
most likely. You mention replacing the front....but don't mention the rear.
If the rear is disk as well it could very well be warped or have a heavy
ridge. The ebrake uses a mini drum inside the rear disk.
 
Paul said:
I have a '91 240 with 100 000 miles on it and feels like I'm riding on
square tires when I brake. I had the front rotors changed but the problem
persisits. Wheels were balanced-no difference. The front end is tight and
it's not so much a vibration at the steering wheel (although there is some)
but you can feel it in the seat of your pants. It does it only when the
brakes have warmed up so I suspected a warped rotor but the new ones do it
too. I tried braking with the emergency brakes and the problem is gone.
What else could cause the shaking other than what I've mentioned?
Also whenever it is cold it lets out a groan whenever I go over a bump.
Doesn't feel like something is loose but either a shock or other suspension
component is worn out and metal is scrubbing metal. Not as bad once the car
has been driven for a while. Difficult to isolate if coming from front or
back. Any help is greatly appreciated.
Confused
Click to expand...


Check the rear discs, if they're warped you'll get exactly those symptoms.
 
I have a '91 240 with 100 000 miles on it and feels like I'm riding on
square tires when I brake. I had the front rotors changed but the problem
persisits. Wheels were balanced-no difference. The front end is tight and
it's not so much a vibration at the steering wheel (although there is some)
but you can feel it in the seat of your pants. It does it only when the
brakes have warmed up so I suspected a warped rotor but the new ones do it
too. I tried braking with the emergency brakes and the problem is gone.
What else could cause the shaking other than what I've mentioned?
Also whenever it is cold it lets out a groan whenever I go over a bump.
Doesn't feel like something is loose but either a shock or other suspension
component is worn out and metal is scrubbing metal. Not as bad once the car
has been driven for a while. Difficult to isolate if coming from front or
back. Any help is greatly appreciated.
Confused
 
Wheel bearings? Worn/distorted spindles?
Probably not the cause, but to eliminate a factor did you replace the pads
when they did the rotors?
 
Be careful if tempted to use drilled discs - they have a nasty habit of
cracking around the holes.
If you do want cross drilled discs use ones where the hole is cast in as
opposed to driled as they have much higher resistance to cracks.
Alternatively try using grooved discs - much the same effect as drilled but
with none of the cracking problems.

As regards the issue reported, look at the discs to see if there are spots
of dark material on the disc... this is known as pad transfer and can cause
the same problem you were describing.
There is a very good discussion of brakes and pads at
http://www.stoptech.com/tech_info/wp_warped_brakedisk.shtml#

Alastair.
 
I had a persistent problem like this on my "91 940, and it didn't go away
even after I replaced all the brake parts. What did seem to make it go away
was being absolutely sure the wheels themselves were tightened to the
specified torque. On my car, at least, the specified torque is surprisingly
low, and unless you call that to the attention of whomever is installing
your wheels (which I switch twice a year to install mounted snows/summers),
they tend to tighten randomly (apparently). Since I've been insisting on
the correct torque in foot-pounds as stated in the owner's manual, I've not
had the shuddering problem.
 
I believe that you will find the correct torque stamped into the dust
cover over the front wheel bearings.



mdrawson said:
I had a persistent problem like this on my "91 940, and it didn't go away
even after I replaced all the brake parts. What did seem to make it go away
was being absolutely sure the wheels themselves were tightened to the
specified torque. On my car, at least, the specified torque is surprisingly
low, and unless you call that to the attention of whomever is installing
your wheels (which I switch twice a year to install mounted snows/summers),
they tend to tighten randomly (apparently). Since I've been insisting on
the correct torque in foot-pounds as stated in the owner's manual, I've not
had the shuddering problem.
Click to expand...

__ __
Randy & \ \/ /alerie's
\__/olvos
'90 245 Estate - '93 965 Estate
"Shelby" & "Kate"
 
That is so Randy and it is quoted as 85Nm (63lbsft). It is exactly the same
for my caravan wheels (UK 1992 Lunar Clubman 400/2)

All the best, Peter.

700/900/90 Register Keeper,
Volvo Owners Club (UK).
 
Thanks to everyone for all your input-I guess I'm off to buy a torque
wrench!
 
I saw that stamp on my 960 when I pulled the wheels to go through the
brakes (check and clean calipers and sliding surfaces) shortly after I
bought it three years ago. I had a really tough time getting the lug
nuts off since the PO had the tires done at a *Mart store and they
used the air wrench to tighten them. I suppose that they are not
required to read or think there.



Peter K L Milnes said:
That is so Randy and it is quoted as 85Nm (63lbsft). It is exactly the same
for my caravan wheels (UK 1992 Lunar Clubman 400/2)

All the best, Peter.

700/900/90 Register Keeper,
Volvo Owners Club (UK).
Click to expand...

__ __
Randy & \ \/ /alerie's
\__/olvos
'90 245 Estate - '93 965 Estate
"Shelby" & "Kate"
 
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