Home » Public Forums » GMCnet » [GMCnet] Disc brake project still in failure mode
| Re: [GMCnet] Disc brake project still in failure mode [message #281958 is a reply to message #281955] |
Sun, 12 July 2015 20:19   |
James Hupy
Messages: 6806
Registered: May 2010
Karma:
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Senior Member |
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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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