Pulsating brake pedal

Post by **V8Patrol** » Wed Mar 17, 2004 10:22 am

Ok so it sounds weird but thats exactly whats happening.....

Every time the brakes are applied be it either gentle or hard,
the brakes operate as per usual, ........ but...... about 5 secounds after the brakes are applied I get a distinct "pulse" back through the brake pedal, this pulse then happens untill the rig comes to a complete stop.

The pulses are about 1 sec intervals and get progressivly stronger as the rig comes to the stopped position..... the final pulse "feels" to push my foot up about 10mm !!!.

Ive checked ......
pads ................ replaced while I was at it.
fluid ................. dumped the old stuff and flushed and then refilled.
lines ................. checked for kinks etc .... nil to be found !
booster.............. swaped with 3 other rigs, still no change !
brake pedal........ fitted new hinge bolt and greased
master cylinder... replaced, and still no different

rig is a 1980 Nissan MQ diesel..... dead stock standard !!!

any ideas ?????????????????????

Post by **-Scott-** » Wed Mar 17, 2004 10:35 am

Any chance someone fitted a dodgy ABS system while you had your back turned?

Post by **antt** » Wed Mar 17, 2004 10:50 am

sounds like the brake discs need machining

Post by **PRZOOK** » Wed Mar 17, 2004 10:52 am

I had the same problem one time, was warped brake discs. A quick machine and it was all fixed.

Post by **lay80n** » Wed Mar 17, 2004 5:13 pm

Sounds like brake shudder. Have you got drum rears. If yes, and the pedal pulsates and ya steering wheel dont shake, id say that the drums out of round. If wheel shakes then either rotors warped or both rotors warped and drums out of round. Machineind rotors and or drums would fix this, but make sure that they are still legal. All discs have a minimum thickness and all drums have a maximum inside diamiter. If these are not adhered to the system is ilegal, and wont dispurse heat properly. When brakes applied hard (emergency stop from freeway speed) they can shatter. NOT GOOD!!!
If ya pads low as well, it is best to change them at same time, They can also contribute to shudder. Anyone who owns VS/VT/VX commadore has probably had this problem(shudder). Its pretty common in them.
hope this helps
layto....

Post by **ozy1** » Wed Mar 17, 2004 5:50 pm

lay80n wrote:Sounds like brake shudder. Have you got drum rears. If yes, and the pedal pulsates and ya steering wheel dont shake, id say that the drums out of round. If wheel shakes then either rotors warped or both rotors warped and drums out of round. Machineind rotors and or drums would fix this, but make sure that they are still legal. All discs have a minimum thickness and all drums have a maximum inside diamiter. If these are not adhered to the system is ilegal, and wont dispurse heat properly. When brakes applied hard (emergency stop from freeway speed) they can shatter. NOT GOOD!!!
If ya pads low as well, it is best to change them at same time, They can also contribute to shudder. Anyone who owns VS/VT/VX commadore has probably had this problem(shudder). Its pretty common in them.
hope this helps
layto....

What he said!

Post by **bazooked** » Wed Mar 17, 2004 8:55 pm

what they all said... :finger:

Post by **-Mandy-** » Wed Mar 17, 2004 9:07 pm

I agree.
Had the same problem with my zuk,turned out to be the rear drums.
Just simply had them adjusted (screwdriver),6 mths on,no problems.

Post by **Beastmavster** » Wed Mar 17, 2004 9:57 pm

possible also tyre/wheel balance, flat spot or out-of-round tyre, or wheel bearing.

I'd be checking these as well, but suspect discs.

Post by **oozuk** » Wed Mar 17, 2004 11:49 pm

I had this problem too once, trust me it will be the front rotors and rear drums need machining and then the rear's reajusted

there warped due to overheating

Post by **high n mighty** » Thu Mar 18, 2004 6:01 am

The rotors/discs overheat if you are using the brakes late and hard, thus heating them up. Making this worse is heatin them up and sitting at lights with the brake held on, it warps them easily. Having worked in a mechanic shop in sydeney and one in newcastle I can tell ya they get this problem more down there.(or alot more ppl any way due to the constant stoppin)

Post by **BeZeRK** » Thu Mar 18, 2004 6:05 pm

Wheel bearing play, check it, could cause it, or yopur disks are warped, get them machined and whack some new pads on.. grease your wheel bearings at the same time.

Post by **Ruggers** » Thu Mar 18, 2004 6:55 pm

it sounds like brake shudder you can get you disc machine on the car now which is a lot easyer than have to pull then all apart. i do at least 1 to 2 commodores a day with the smae problem

Post by **Bluey** » Thu Mar 18, 2004 8:30 pm

dad's jeep has brake shudder too. started when did trip up to n.t. and back, has had discs machined couple of times, replaced pads, now new slotted discs and new pads. still cames back

might get him to check wheel bearings, thanks for the idea bezerk

Post by **Ruggers** » Thu Mar 18, 2004 8:37 pm

im not sure of jeep discs but if they are full floating like the new commodores you have to make sure that the hub face is clean and dial the disc rotors back in when refiiting or it will come back

Post by **Bluey** » Thu Mar 18, 2004 8:58 pm

thanks ruggers. not sure about whether full floating myself.
and, what do you mean about dialing in? is this like running motor in, no hard braking for first so many kays?

Post by **Ruggers** » Thu Mar 18, 2004 9:15 pm

its where you set up a dial indicator and spin the rotors aournd and make sure the run is exceeded its normally. .05mm for the front and .08mm for the rear

Post by **Bluey** » Thu Mar 18, 2004 9:27 pm

cool thanks. so i know this wasnt done as dad and i replaced the discs and pads in my garage

they were dba slotted discs and something or other :armsup:

pads. worked real good till emergency braking manouver when found oncoming car on hill crest, other car was going wrong way on divided road :bad-words:

now they shudder

Post by **the_smoo** » Mon Apr 26, 2004 10:01 am

did you end up sorting this problem out?

Post by **V8Patrol** » Mon Apr 26, 2004 10:52 am

yep !

there was a crack in the firewall that allowed the brake booster to flex a bit when the brakes were applied !!!, solution was easy...... weld it !

Outer Limits 4x4 Board

Pulsating brake pedal

Pulsating brake pedal

Who is online