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Pulsing brake pedal...why?
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shorepig
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PostPosted: Tue Apr 26, 2011 7:12 pm    Post subject: Pulsing brake pedal...why? Reply with quote

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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joetiger Premium Member
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PostPosted: Tue Apr 26, 2011 7:14 pm    Post subject: Reply with quote

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.
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syncrodoka
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PostPosted: Tue Apr 26, 2011 7:21 pm    Post subject: Reply with quote

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.
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IdahoDoug
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PostPosted: Tue Apr 26, 2011 7:28 pm    Post subject: Reply with quote

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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BushChicken
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PostPosted: Tue Apr 26, 2011 7:57 pm    Post subject: Reply with quote

IdahoDoug wrote:
A shot of brake fluid would fix this one.

DougM


Well....maybe brake clean would work better... Wink
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EvilDNA
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PostPosted: Wed Apr 27, 2011 12:26 am    Post subject: Reply with quote

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.
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BayrischerGTI
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PostPosted: Wed Apr 27, 2011 6:48 am    Post subject: Reply with quote

BushChicken wrote:
IdahoDoug wrote:
A shot of brake fluid would fix this one.

DougM


Well....maybe brake clean would work better... Wink


LOL would work MUCH better I think Laughing
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IdahoDoug
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PostPosted: Wed Apr 27, 2011 7:17 am    Post subject: Reply with quote

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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Captain Pike
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PostPosted: Wed Apr 27, 2011 7:17 am    Post subject: Reply with quote

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
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insyncro
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PostPosted: Wed Apr 27, 2011 7:22 am    Post subject: Reply with quote

Captain Pike wrote:
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


So true!
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climberjohn
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PostPosted: Wed Apr 27, 2011 11:14 am    Post subject: Reply with quote

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
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Syncronoid
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PostPosted: Mon Sep 03, 2012 9:04 pm    Post subject: Reply with quote

Anyone know what the front spec torque is on a '90 Syncro Westy?
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morymob
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PostPosted: Tue Sep 04, 2012 3:33 am    Post subject: Reply with quote

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.
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Syncronoid
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PostPosted: Tue Sep 04, 2012 7:31 am    Post subject: Reply with quote

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.
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markz2004
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PostPosted: Fri Nov 16, 2012 2:07 pm    Post subject: Reply with quote

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
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markz2004
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PostPosted: Tue Nov 27, 2012 1:17 pm    Post subject: Reply with quote

- bump -
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presslab
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PostPosted: Tue Nov 27, 2012 1:55 pm    Post subject: Reply with quote

markz2004 wrote:
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


Over-torquing distorts the hub, and the brake rotor is mounted to the hub so that distorts too. I'd say that if you have over-torqued the lugs and run it long enough, the rotor will take a "set", so even if you fix the torque and machine the rotor, the rotor is still messed up.

Junky rotors can also warp a lot easier than good ones. The "frozen" rotors (cryo treated) supposedly don't warp. Another thing that causes pulsations is that the brake pad material can transfer to the rotor. The rotor isn't really warped in this case but turning the rotor cleans it up.
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morymob
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PostPosted: Wed Nov 28, 2012 5:58 am    Post subject: Reply with quote

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.
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KLSteward
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PostPosted: Wed Nov 28, 2012 11:14 am    Post subject: Reply with quote

morymob wrote:
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.


^ This. If all he can tell is you is to not worry about he obviously has no clue what he is doing..
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Cygnus
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PostPosted: Wed Nov 28, 2012 2:39 pm    Post subject: Reply with quote

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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