buffer screw lenghth question

[Larry B]

When I bought jake brake parts, in the box was fast idle air cylinder and buffer screw not connected together. The buffer screw would operate jake without air cylinder. Would prefer to keep fast idle option. Do buffer screws come in different lenghth or numbers as per desired use? Tried sending picture but it says file is too large. Will try sending picture without words.

[thomasinnv]

as has been discussed here before, there are a few different options available to you. When using the fast idle, there is no buffer screw. The fast idle cylinder replaces the buffer screw. When installing jakes, the fast idle cylinder is usually removed and replaced with a buffer switch, which disables the jakes in any position other than no fuel. If you want to retain the fast idle with jakes installed, there are a few ways to tackle this. 1) probably the least desireable, is to leave the fast idle cylinder in place and simply not use a buffer switch. Most engines the jakes won't engage below 1000 to 1200 rpm anyway because there is not enough oil pressure. 2) replace the fast idle cylinder with the buffer switch, and install a king cruise, which will give you not only cruise control but also a fast idle that you can set at any rpm you choose. This option is slightly less expensive than number 3) replace the fast idle cylinder with a fast idle buffer switch, which is around $750 or more, if you can find one.

And yes, in answer to your original question, the buffer switch is engine specific. Get the setting wrong and wave goodbye to your engine as you run away screaming.

[wg4t50]

You bet, run away if you get the buffer screw in too far and start it up 
I setup the Jake with a switch at dash to use as needed, stayed away from the fast idle / Jake combo, worked great on both 71 & 92 engines.  Gotta tell you the 12V-71 Jake would scare the heck out of cars behind you in a tunnel, Oh what fun !!

[Larry B]

My engine is an 8v71. The air cylinder I have , there is a bracket that is designed for a jake micro electric switch to be mounted on. I maybe used the wrong word. Instead of screw, I should have said buffer spring assem. When the center pin of the buffer spring pushes back in the no fuel it trips the lever on the air cylinder to witch the micro switch is connected. Is this not a reliable set up? I believe the buffer spring I have is for micro switch only-that is the switch mount it came mounted too.The air cylinder was separate in box of parts. I have manual trans, is this cruise workable with manual? Is ther a site to explain cruise?     

[luvrbus]

Ok your fast idle buffer switch cylinder should be 7 inches long with the screw in part it has a place for 4 screws on the bracket for the switch mounting then a pin with 2 rollers and a small lever between the 2 rollers, then at the top of the bracket then there should be 2 slots for attaching the micro switch and for adjustment of the switch

If you have all that it is a fast idle buffer assembly and if the diode and rubber boot are missing or the boot is torn from the micro switch replace those and be sure to adjust the holding cylinder or off to the races when you engage the fast idle and that adjustment is in your DD bible forgot but there a small cover plate that goes on the bottom to keep junk out of the assembly  

good luck

[eagle19952]

http://miscpartsmanuals3.tpub.com/TM-9-2815-224-34-P/TM-9-2815-224-34-P0502.htm

just keep clic next in the center of the page top...lotsa help here....
good luck.

[Larry B]

I have all the pieces that Luvrbus talks about and purchased new micro switch. It is the piece from the air cylinder to the governor that I believe to be wrong lenghth. The 3"  long piece has at least 2" of running thread, a jam nut and a larger nut to hang air cylinder from. In the center of 3" piece (only 3/8" dia)is 1/8" shaft. I mounted only 3" piece first. Started engine and turned in slowly. You could feel it touch the link arm(believe that correct name) I stopped turning. The governor end of 3" long piece has a small spring that took the roll out of engine at idle. Took engine up to 1500rpm and then moved to no fuel position on throttle. During this time of returning to idle the center pin moved out 3/8". When back in as soon as engine resumed idle. All this happened in 1/2 second. My problem (I believe) is that the center pin is too short to activate the mechanical linkage on the air cylinder that controls closing of micro switch. I repeted everything with air cylinder  mounted no switch and tried a couple times, the linkage does not move. Held finger on trip linkage to check for movement. There are too many unknowns for me to machine a longer center pin and I do NOT want an overspeed.It is the small 3/8" dia shaft that goes to governor that I want to know if they come in different lenghths or numbers. I have a picture of all the pieces but I can't get it to go with reply   

[bevans6]

It actually sounds exactly right to me.  It sounds exactly the way my similar switch setup is. Another way to make the pin operate is to turn the engine stop lever to stop.  As it gets to the full no-fuel setting the pin will extend fully and the switch should operate.  I can try to take pictures later today, I can take the switch/air cylinder off the buffer screw part and show you how much the pin sticks out on mine (which is stock and hasn't had the switch off).  I read the instructions about how to never mess with the switch adjustment and how to use a factory tool to set up a new switch as well, that is in the MCI manual I think, not the DD manual.  Do you have that information yet?

Brian

[luvrbus]

That pin is 3-1/8 inches long and has a step down make sure to install the step down towards the governor then adjust the switch

good luck

[bevans6]

here is the page from my MCI manual that says how to adjust the position of the switch.  Of course it presumes you have the special tool, which I bet no one has.  On my switch, it operates just as the stop lever reaches it's maximum travel, you could adjust for that.  You don't want it to ever operate while the engine is receiving fuel, only at no fuel.

Brian

[Larry B]

Went to the local junk yard yesterday and found a different buffer mount screw for air cylinder. I got the correct one this time. He wished me a Merry Christmas and said if I take it off I could have it. It was still on engine.  Sometimes a person get lucky.