08-26-2018, 02:09 PM
I know this thread is a few years old , but it's applicable to what I have going on with my 86 coach with 8V92TA . Back in July I tried the Jake brake for the first time , got no response . After researching this deal , I think that the two times I actually tried the Jake I wasn't going fast enough , probably only 35 or 40 mph , coasting in drive. In any case I have been going over the electrics of the system and have found the following: With console switch on , I have battery voltage (12.7 ) going into the lower (common) terminal of the buffer switch.
The wire going to the driver's side valve cover is connected to the center ( N.O.) terminal of buffer switch . The wire to the other valve cover was disconnected.
Using a thin strip of metal between the buffer shaft and switch plunger I was able to trigger the switch , sending power to the N.O. terminal. Therefore the switch was working.
I removed the micro switch only , leaving the actual buffer screw unchanged so the adjustment will not be affected . The micro switch is held in place with two machine screws on a slotted bracket .
While cleaning the switch I managed to tear the protective boot on the plunger so I went in search of a replacement switch . The original is an Omron , Z-15 series . Jacobs only sells an upgrade which requires removal of the whole buffer screw , a little more than what I want to get into at the moment. Ended up finding a replacement on Ebay , a Pacbrake unit p/n PO 1218 , identical switch , not Omron.
The buffer screw is hollow with a spring loaded plunger to activate the switch . The plunger is very close to flush with engine off .
I installed the switch using Prarieschooner's method of adjusting it. I can't see why this won't work provided the mechanical parts are working , but I worry about premature activation due to the very short travel of switch (.010") before it clicks .
I am wondering if there is gap that should be set between the switch and the plunger . Also wonder if anyone might know the travel of the plunger when the governor moves it in a no fuel condition .
Appreciate any and all input ,
Thanks, Chris
The wire going to the driver's side valve cover is connected to the center ( N.O.) terminal of buffer switch . The wire to the other valve cover was disconnected.
Using a thin strip of metal between the buffer shaft and switch plunger I was able to trigger the switch , sending power to the N.O. terminal. Therefore the switch was working.
I removed the micro switch only , leaving the actual buffer screw unchanged so the adjustment will not be affected . The micro switch is held in place with two machine screws on a slotted bracket .
While cleaning the switch I managed to tear the protective boot on the plunger so I went in search of a replacement switch . The original is an Omron , Z-15 series . Jacobs only sells an upgrade which requires removal of the whole buffer screw , a little more than what I want to get into at the moment. Ended up finding a replacement on Ebay , a Pacbrake unit p/n PO 1218 , identical switch , not Omron.
The buffer screw is hollow with a spring loaded plunger to activate the switch . The plunger is very close to flush with engine off .
I installed the switch using Prarieschooner's method of adjusting it. I can't see why this won't work provided the mechanical parts are working , but I worry about premature activation due to the very short travel of switch (.010") before it clicks .
I am wondering if there is gap that should be set between the switch and the plunger . Also wonder if anyone might know the travel of the plunger when the governor moves it in a no fuel condition .
Appreciate any and all input ,
Thanks, Chris
1986 #89
VIN 007
Detroit 8V92 TA 475 HP
Allison four speed
Chris and Sharon Hand