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dragging brakes?

Discussion in 'VN - VP Holden Commodore (1988 - 1993)' started by VPRob, Nov 7, 2019.

  1. VPRob

    VPRob Active Member

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    My VP has VT front brakes with slotted rotors and VT master and booster. Upgrade has been in the car for a few years. In the last few days I have experienced a disturbing strong vibration or shudder for a second or 2 when accelerating after releasing the brake pedal. This has happened 3 times. It feels like it is shaking the whole car and then stops. I am interpreting it as a brake problem.
    Front of car is currently lifted and wheels off. Rotating the front wheels it is clear that the driver's side wheel is dragging and feels worse on some areas of the rotation. I have been experiencing some vibration under braking recently and the whirring from the (straight) slotted rotors has seemed to be getting more noticeable. Stopping power has still been good but all 4 rotors were hot after a relatively short drive yesterday.
    I'm pretty sure I've got free play in the push rod but that's an obvious candidate.
    Any tips on how to proceed?
     
  2. Davo_vx

    Davo_vx Member

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    I had a similar problem on my vx that I fixed by replacing the master.
     
  3. _R_J_K_

    _R_J_K_ Well-Known Member

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    Based on that and the shuddering you describe the first place I would go I would be looking at would be the rotor to see if it's warped. I know you say it's straight but I reckon the slotting would amplify it significantly if it were even slightly bent.

    Has a bleed done anything? Z-bar bushes up to scratch too? Uneven/slanted wear on the pads?
     
    Last edited: Nov 7, 2019
  4. VPRob

    VPRob Active Member

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    My next step is to rotate the rotor up to have a look at the pads. With a bit of gentle levering with a screwdriver the pads retract further and the rotors rotate freely. That seems to indicate the pistons are free in the calipers and the pins are free also. When I run the motor to charge up the vacuum assist the pads stay retracted and the rotors are free but when I apply the brake pedal and release it the driver's side will rotate but with a noticeable amount of drag compared to the passenger side.
     
  5. VT2Commie

    VT2Commie Active Member

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    Please check your drive shaft centre bearing carrier rubber, disturbing vibration /shudder under acceleration for a short second is drive shaft related.

    As for the brakes, when applying them at speed, the caliper slide pins may feel/look like they are free but I would remove, clean and relube them and make sure the rubber guide pin boots are not torn or split.
    Do a brake fluid flush by bleeding them. With the correct fluid type of course.

    And go get the brake rotors machined or replaced if under spec.
     
    Last edited: Nov 11, 2019 at 1:53 AM
  6. VPRob

    VPRob Active Member

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    Thanks for the responses everyone. I will check my centre bearing but I had dismissed that as I completely rebuilt the driveshaft about 5 years ago.
    The Gregorys flags a blocked or partially blocked port in the MC so I am thinking a bleed is a good way to go.
     
  7. vc commodore

    vc commodore Well-Known Member

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    Does sound very much like the caliper pins are starting to seize on the right hand side....I'd pull them apart, clean the pins and pin slot up, re-grease them and see how that goes.

    I'd also check the rotor isn't warped, as a result Good chance it will be if the brakes have been dragging on them....
     
  8. VPRob

    VPRob Active Member

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    what's the appropriate grease to use on the caliper pins?
     
  9. Davo_vx

    Davo_vx Member

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    I use the bendix high performance synthetic stuff.
     
  10. losh1971

    losh1971 Well-Known Member

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    Yeah Synthetic caliper slide grease Rob. I reckon Repco now stock it. I normally buy it from eBay. I buy a tube once every 8 - 10 years. The Bendix satchet stuff is good but might need to get it from a brake place.
     
  11. losh1971

    losh1971 Well-Known Member

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    Did you get a gen centre bearing Rob. The aftermarket stuff is pretty poor as found out when mine went bang a second time less than six months of having the original one replaced.
     
  12. Davo_vx

    Davo_vx Member

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    Yeah nah they sell it at supercheap losh.
     
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  13. MikeC

    MikeC Active Member

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    If you have a problem finding caliper grease, I've used Castrol HTB in its various versions on caliper pins and front wheel bearings since disc brakes were introduced to Australia in the late 1960's. Never had any problem with it melting, even on FWD's towing large unbraked boat/trailer combinations through the mountains- which would be totally illegal these days.

    The brake stickling could be your driver's side brake pistons are not retracting due be a dirty caliper bore or the O rings on the pistons have lost their elasticity and not returning the piston .

    The shudder when accelerating after braking could be caused by something in the front suspension or engine/gearbox mounts moving when the forces on the car body reverse- I'd look at all rubber components and if the car has had a hard life look for cracking around things like the front suspension strut bearing.
     
  14. Trevor loves holden.

    Trevor loves holden. Well-Known Member

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    I don't think a slight warped rotor would make it shudder. I be looking at your front suspension or even a hub bearing.

    If its bad as you say its not brake related.
     
  15. vc commodore

    vc commodore Well-Known Member

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    A slight warped rotor does make a shudder under braking.....If it's through the steering wheel, it's the front rotors.....If the brake pedal pulsates under braking, the rear rotors are slightly warped....
     
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  16. FXST01

    FXST01 The Grey Man

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    Rob, check that your calipers are on tight.
     
  17. MikeC

    MikeC Active Member

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    Isn't the problem accelerating after releasing the brakes? - " strong vibration or shudder for a second or 2 when accelerating after releasing the brake pedal."
    That's why I think the cause is something that is affected by the change in forces from braking to accelerating- like the suspension.
     
  18. Trevor loves holden.

    Trevor loves holden. Well-Known Member

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    Not on take off for a few seconds after taking your foot off the brake, besides your not even doing 40k's yet, it could be bad engine and transmission mounts or tail shaft issues or a rough engine due to bad spark.
     
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  19. vc commodore

    vc commodore Well-Known Member

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    If you read the first post, it is described that the right hand front wheel is dragging, when it is being rotated, with the weight off the wheel. So to me, this would indicate a caliper slide pin is sticking and a sticking slide pin will cause a rotor to become warped.

    It is also mentioned, the Op has noticed some vibration under braking recently, which to me, is another indicator of a warped rotor, caused by a sticky slide pin.


    Where I am right or not, I don't know.....It's somewhere for the OP to check to help solve the issue
     
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  20. Trevor loves holden.

    Trevor loves holden. Well-Known Member

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    Car will not vibrate upon take off and shudder the car from a brake rotor at such low speed. Like I said suspension or mounts or tail shaft even motor could shake the car on take off if its lagging due to spark breaking down when loading up the engine, I would expect shudder upon braking with a buckled rotor and at speed which may also be a bad tyre or rim but not at take off, that is a load issue you know power (torque) related until you level out the speed hence the reason it only last for a few seconds upon take off. Well that's my understanding from the message.


    Maybe the brake pads rubbing but can also be the hub bearing..
     
    Last edited: Nov 11, 2019 at 4:15 PM
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