Home » Public Forums » GMCnet » [GMCnet] Disc brake project still in failure mode
| Re: [GMCnet] Disc brake project still in failure mode [message #281957 is a reply to message #281955] |
Sun, 12 July 2015 20:01   |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma:
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Senior Member |
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Neil,
There are so MANY possibilities that I don't know where to start (and I'm
in the midst of a Hydroboost installation on my 1-Ton+Manny Brakes equipped
23', which has had just about every brake combination you can think of.
I'm just going to mention some items to be sure you've addressed all of
them:
Booster -- what's its' status?
Vacuum seal between the booster and MC -- correct seal, correctly installed?
Push rod length -- have you measured it and set about 0.005" clearance?
Flex hoses (on front, obviously you installed new rear with Manny Brakes).
How much have you driven the coach to break in the pads? It an be amazing
how much improvement occurs in the first 100-200 miles.
Perhaps the most useful tool for you would be one of these:
http://www.amazon.com/SSBC-A1704-Brake-Pressure-Gauge/dp/B003VYVFSS/ref=sr_1_1?ie=UTF8&qid=1436748655&sr=8-1&keywords=brake+pressure+gauge
That kit from Stainless Steel Brakes includes a set of adapters for 'most
any caliper or wheel cylinder to allow you to attach the included 0-1600
psi gauge. With that you can measure the hydraulic line pressure at a
front and a rear caliper. Unless your booster/MC/etc. can provide 600+ psi
of line pressure, you will NOT have good brakes. Having a visual
indication of the results of each action you take will be valuable in
solving your problem. You'd like to have 1000+ psi, but it's rare on a GMC.
HTH,
Ken H.
On Sun, Jul 12, 2015 at 8:19 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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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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