Home » Public Forums » GMCnet » [GMCnet] Disc brake project still in failure mode
| Re: [GMCnet] Disc brake project still in failure mode [message #281991 is a reply to message #281980] |
Mon, 13 July 2015 09:04   |
James Hupy
Messages: 6806
Registered: May 2010
Karma:
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Senior Member |
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Neil, I usually do not even install the ebrake cables until I have debugged
the service brakes and they have enough miles on them to break in the
linings. I do, however adjust the ratchets that move the caliper piston out
towards the rotor. You need to be very diligent in indexing that little lug
on the pad backing plate into the caliper piston. SOMETIMES the caliper
piston will rotate enough so that the detent in the piston will not align
with the lug. If you find this to be the case, the piston must be rotated
back to index with the lug. It is quite difficult to turn. I use a big pair
of channel lock pliers and a piece of gasket material scrap left over from
my bleeders to protect the piston from plier damage. On the ebrake cables,
I make up custom ones of the exact correct length for the outer sheath
instead of the supplied threaded sleeve and jam nuts used with the old
rusty, kinked, original outer cables. Those inner cables need to move
freely with no binding to work correctly.
Jim Hupy
On Jul 13, 2015 4:59 AM, "Neil Fonville" wrote:
> Jim,
>
> I will inspect for the gaps. With one set of the wheels off on one side
> at a time, I don¹t see any gap but will look much more closely.
>
> How important is the parking brake being setup correctly initially. I
> have not done that yet. I was planning on that being the last step?
>
> Thanks,
> Neil
>
> On 7/12/15, 8:19 PM, "Gmclist on behalf of James Hupy"
> wrote:
>
>> Neil, Jack up your coach and remove the wheels and tires. I surmise here
>> that you have the rear/rear calipers with parking brakes. I have found
>> that
>> if the short lug protruding from the inside brake pad is not indexed with
>> the caliper piston that the pad will not sit squarely onto the piston, and
>> there will be way too much space between the components. That pad material
>> should ride in slight contact with the rotor when they are broken in, and
>> there should also be no visible space between the caliper piston and the
>> backing plate on the pad. Same on all disc/rotors. If you broke the
>> retaining clip off the back of the pad and left anything sticking up in
>> the
>> middle of the pad where the rivet is, the pad should be removed and the
>> rivet head ground down. Also you need to pre adjust the parking brake
>> ratcheting mechanism to eliminate all the space. If you have clearance
>> where I have just described, you will use up available pedal travel taking
>> up that clearance before any pressure can build up in the system. Low
>> pedal, and poor stopping is the result.
>> Jim Hupy
>> Salem, Oregon
>> 78 GMC ROYALE 403
>> On Jul 12, 2015 5:20 PM, "Neil Fonville" wrote:
>>
>>> I'm back to working on my brake project and just not getting it done.
>>> Still have soft pedal and it's takes way too much distance to stop.
>>> It's
>>> far worse from where is started with 2 Disc and 4 Drums that were not
>>> working good.
>>>
>>> Here is rehash of what steps I have taken and maybe someone can help get
>>> me back on track. I'm still amazed I can't find a mechanic/shop in the
>>> Dallas area that could help me with my projects.
>>>
>>> First I installed the Manny rear disc brake kit. Install was straight
>>> forward.
>>> Bleed the system with the standard 2 man pump and release fluid method.
>>> Never felt right and the vehicle was not even remotely drivable.
>>> Replaced proportion valve with Disc/Disc model.
>>> Removed OEM MC and replaced MC with new one from O'rilly. Used the P30
>>> (PN
>>> NMC1668).
>>> Did not bench bleed. Bleed with 2 man pump and release fluid. Still
>>> pedal too soft and not drivable. Removed MC and put on bench and found
>>> front chamber not pushing fluid.
>>> Replaced with another new MC from O'rilly same part number. Pedal
>>> pumped
>>> up tighter but it leaked between the fluid reservoir and cast metal
>>> piston. Still not drivable.
>>> Replaced MC with new one from Autozone (PN NM1641 ). Purchased the Hupy
>>> bleeder. Bleed according to his directions which is RR moving to LF.
>>> Removed lots of air and pumped about 1/2 gallon of fluid through the
>>> system. Still not drivable, pedal too soft and vehicle does not stop.
>>> From 30 to zero takes about 1/4 mile.
>>>
>>> So how do I go about troubleshooting the individual components? How do
>>> I
>>> test hydraulic pressure?
>>>
>>> I'm hoping for someone to give me a systematic approach to resolve this
>>> and get this working.
>>>
>>> Yes, I have spoke with Manny and I really don't think any of the
>>> calipers
>>> are defective.
>>>
>>> Thanks Neil Fonville
>>> 1975 GMC II
>>>
>>>
>>>
>>>
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