Pulsing brake pedal...why?

shorepig · Posted: Tue Apr 26, 2011 7:12 pm Post subject: Pulsing brake pedal...why?

My 1985 west went in for a pre purchase inspection which included checking the wear on the brakes. When I picked the van up and pressed the brake pedal I could feel a pulsing in the pedal that was related to the rolling speed of the van. I brought it back to the mechanic and he said everything looked fine and the pulsing was nothing to worry about .

What could he have done that would cause this? I'm not happy with his response and would like to return to him with armed with more knowledge.
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85 Westy
92 Mitsubishi Mighty Max 4x4 V6
74 Honda CB500T cafe racer
2013 ktm 690r
Sector nine pintail

joetiger · Posted: Tue Apr 26, 2011 7:14 pm Post subject:

He might have over-torqued the front lug bolts, which would cause the discs to warp.

Loosen them and re-tighten to spec ASAP and see if that works.
_________________
Joe T.

'86 NAHT Vanagon GL Syncro/ supercharged ABA 2.0 "Pigpen"
'04 GTI 1.8T
'04 Golf R32

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syncrodoka · Posted: Tue Apr 26, 2011 7:21 pm Post subject:

Drive slowly and pull up the emergency brake lightly with your thumb on the release button. If the handle rises and falls them the rear drums are warped- not a uncommon problem.
Loosening the lug nuts and retorquing to the proper spec wouldn't be a bad idea either.

IdahoDoug · Posted: Tue Apr 26, 2011 7:28 pm Post subject:

If the test involved a braking test and the brake rotors were thin, or drums, then they may warp when subjected to a test stop. I don't know if that's part of the test.

Also, if the mechanics hands were greasy or similar, then a bit of grease or oil in the drum brake surface or the rotor brake surface will make the brakes pulse until it's burnt off. A shot of brake fluid would fix this one.

DougM
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1987 2WD Wolfsburg Vanagon Weekender "Mango", two fully locked 80 Series LandCruisers. 2017 Subaru Outback boxer. 1990 Audi 90 Quattro 20V with rear locking differential, 1990 burgundy parts Vanagon. 1984 Porsche 944, 1988 Toyota Supra 5 speed targa, 2002 BMW 325iX, 1982 Toyota Sunrader

BushChicken · Posted: Tue Apr 26, 2011 7:57 pm Post subject:

EvilDNA · Posted: Wed Apr 27, 2011 12:26 am Post subject:

I had this EXACT issue happen and the culprit was improperly tighten lug nuts. I simply loosened and retightened the offending wheel and Bob's Your Uncle.
_________________
1990 4 Speed Orly Blue Multivan

BayrischerGTI · Posted: Wed Apr 27, 2011 6:48 am Post subject:

IdahoDoug · Posted: Wed Apr 27, 2011 7:17 am Post subject:

Heh, indeed. Meant brake cleaner - just spray it on the front rotors liberally with the engine idleing and immediately drive off with the brakes applied for a hundred feet or so. That will get the product around the rotor under and on the pads before it dries, which it will do in 20 seconds. Won't edit my post just on general principle.... Heh...

DougM
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1987 2WD Wolfsburg Vanagon Weekender "Mango", two fully locked 80 Series LandCruisers. 2017 Subaru Outback boxer. 1990 Audi 90 Quattro 20V with rear locking differential, 1990 burgundy parts Vanagon. 1984 Porsche 944, 1988 Toyota Supra 5 speed targa, 2002 BMW 325iX, 1982 Toyota Sunrader

Captain Pike · Posted: Wed Apr 27, 2011 7:17 am Post subject:

If the (wrench) used a hammer to loosen the drums he most likely distorted one or both. Common mistake for a non Vanagon savvy wrench.
Do the above tests esp. the parking brake test. If all else fails then .....well....you paid to learn about not hitting the drum. Sad

_________________
LEARN TO SELF RESCUE
59 Panel bus, 1966 Single cab. 73' 181. 73 Westy. 91' H6 Vanagon 3.3L.
.....................All Current.......................

insyncro · Posted: Wed Apr 27, 2011 7:22 am Post subject:

climberjohn · Posted: Wed Apr 27, 2011 11:14 am Post subject:

FYI, here's one more thread on this topic:

(Samba search tip: search on: brake + pulse )

Pulsating Brakes

http://www.thesamba.com/vw/forum/viewtopic.php?t=428491&highlight=brake+pulse

-CJ
_________________
'86 Westy, 2.5 Subaru power
Know your limits. Exceed them often.

Syncronoid · Posted: Mon Sep 03, 2012 9:04 pm Post subject:

Anyone know what the front spec torque is on a '90 Syncro Westy?

morymob · Posted: Tue Sep 04, 2012 3:33 am Post subject:

For sure i wouldn't trust anything or even go back to that 'mech ??' A tire out og bal and run in the front will cause a rotor to wear uneven ending up with a pulsing pedal, tire can cause same. Awhile back it took awhile to convince mgr of a courier i worked 4 of the circle u can get into with tires/rotors and NOT correcting BOTH tire and rotor problem at the same time.

Syncronoid · Posted: Tue Sep 04, 2012 7:31 am Post subject:

I had/have this problem right from the start with brand new, machined, Audi (VanCafe) big discs and new16" tires/wheels. Are big-discs more susceptible to this tightening-induced warping??

UPDATE: I loosened and re-tightened the front lugs to spec (123ft lbs)… nice and smooth braking now.

markz2004 · Posted: Fri Nov 16, 2012 2:07 pm Post subject:

Can anyone explain to me why or how over-torquing the lug nuts would cause a rotor to warp?

I have the VC big brake kit. A few thousand miles ago, I had a rotor turned due to the pulsation, but it has now returned...

thanks,
Mark
_________________
87 Westy, 250k GW 2.4 - 2.0 Wink

, 16" wheels

markz2004 · Posted: Tue Nov 27, 2012 1:17 pm Post subject:

- bump -
_________________
87 Westy, 250k GW 2.4 - 2.0 Wink

, 16" wheels

presslab · Posted: Tue Nov 27, 2012 1:55 pm Post subject:

morymob · Posted: Wed Nov 28, 2012 5:58 am Post subject:

China rotors can and will wear uneven in normal use, hard ?, soft? spots in material??, chicken/egg choice, too bad U. S. rotors hard to find.Out of bal tire WILL cause rotor to wear uneven,replace bad tire and pulsing pedal from uneven rotor will do same to new tire, gotta do both at same time.

KLSteward · Samba Member Joined: November 28, 2012 Posts: 11

Cygnus · Posted: Wed Nov 28, 2012 2:39 pm Post subject:

On my 85 I had exactly the same thing - pulsing on braking. Fronts were fine - turned out that it needed the rear wheel bearings replaced and the rear drums were wasted beyond turning as well. replaced all and its good as new.

-B
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'86 Syncro Timbertech Hightop "Cygnus"


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