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Re: [GMCnet] Maintaince [message #288864 is a reply to message #288857] Fri, 16 October 2015 17:01 Go to previous messageGo to previous message
powerjon is currently offline  powerjon   United States
Messages: 2446
Registered: January 2004
Karma:
Senior Member
As I have the Dave Lenzi brake layout on my stretch coach with 80MM front, 80MM with 12 1/2” Ford rotors (Leigh Harrison Brake setup on Mid bogy) and Stock drums with 15.16” slave and carbon metallic shoes, I run with the reversed lines as the rear re has a larger volume than the front along with the longer rear stroke. You have to see the demo that Dave does with the Master cylinder and it does in deed have a longer stroke! I also have the sensitized booster and matched master cylinder by DL along with the pressure sensor adapter that allows to see only the brake booster pressure and the new Ford hi-volume vacuum pump. I run my pressure switch at 18 in vac, I may reset for 20” vac in the future after I cure some vacuum leaks in the HVAC side of the vacuum system. I have the best brakes that I have ever had in 18+ years in 2 coaches and the avion with also have this system upgrade.

Now for the adapters to swap the lines on the master cylinder.


or
http://tinyurl.com/pjwj4br

and


or
http://tinyurl.com/pzbl8mw

This is my results, yours may vary.

JR Wright
GMC Great Laker MHC
GMC Eastern States Charter Member
GMCGL Tech Editor
GMCMI
78 GMC Buskirk 30’ Stretch
1975 GMC Avion (Under Reconstruction)
Michigan
> On Oct 16, 2015, at 4:14 PM, Emery Stora wrote:
>
> However the front and rear have different size fittings at the master cylinder so they cannot be reversed.
>
> Emery Stora
>
>> On Oct 16, 2015, at 1:38 PM, KB wrote:
>>
>> another theory: the lines were reversed front to rear at the master cylinder during the swap. As Albert B, Dave Lenzi,
>> and others have recently demonstrated, the capacity of the piston in the master cylinder is different in the front vs rear
>> (not just the reservoir, the volume available in the piston itself).
>> It's possible to bottom out one half of the piston (and hence have low pressure on one half) while still having
>> functional brakes on the other half. More an issue with all-disc systems, but could happen in other circumstances.
>>
>> Just a wild guess, which may not apply here. As JR suggested, it could also be that the rubber brake lines were changed at
>> the same time and that those were the real problem. Bulging, spongy, or collapsed lines will play havoc with your brakes.
>>
>>
>> Karen
>> 1975 26'
>>
>>
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J.R. Wright
GMC GreatLaker
GMC Eastern States
GMCMI
78 30' Buskirk Stretch
75 Avion Under Reconstruction
Michigan

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