EWB555 Posted March 25, 2018 Share Posted March 25, 2018 I have a 95 RD688s with the 12 speed air shift. The extended range switch on the dash bleeds air when it's in direct. It's so bad we switch it into low in the am to allow it to air up. Everything works fine, I'm just wondering how to I determine if it's the switch or something causing air to bleed back? It is not leaking from the lines to the switch, its coming from the exhaust ports. I appreciate any suggestions. Quote Link to comment https://www.bigmacktrucks.com/topic/52915-12-speed-extended-range-switch-leaking-in-direct/ Share on other sites More sharing options...
Lmackattack Posted March 25, 2018 Share Posted March 25, 2018 sounds like the dash switch is bad or the inversion valve is bad . the dash switch has 2 ports that one or the other has pressure going to it depending on the position of the selector on the stick. if the inversion valve is sticking it may be stuck half open and exhausting when it should not be? someone just posted this pic the other day 1 Quote Link to comment https://www.bigmacktrucks.com/topic/52915-12-speed-extended-range-switch-leaking-in-direct/#findComment-395056 Share on other sites More sharing options...
EWB555 Posted December 24, 2018 Author Share Posted December 24, 2018 Been a while since I posted this. Call me crazy but as soon as temperatures went up during spring & summer this air leak went away. Now here we are in December and it's back again, I replaced the switch today and that was not the problem. I moved the switch on the shifter and that did I not seem to change the air bleed from the dash. The only thing I did realize is that when I switch to low, the leak doesn't go away, it moves to a union in the air line down under the cab. Isnt the inversion valve what steps down the air pressure? Maybe it's letting too much air to my dash switch. Quote Link to comment https://www.bigmacktrucks.com/topic/52915-12-speed-extended-range-switch-leaking-in-direct/#findComment-411850 Share on other sites More sharing options...
Mack Technician Posted December 24, 2018 Share Posted December 24, 2018 (edited) Not a bit uncommon for aged shift cover soft parts to lose elasticity in winter and begin to leak. For an o ring to seal it has to be willing to distort into the shoulder of its land. Edited December 24, 2018 by Mack Technician 1 Quote Link to comment https://www.bigmacktrucks.com/topic/52915-12-speed-extended-range-switch-leaking-in-direct/#findComment-411855 Share on other sites More sharing options...
mrsmackpaul Posted December 25, 2018 Share Posted December 25, 2018 (edited) On 12/24/2018 at 1:51 PM, EWB555 said: Isnt the inversion valve what steps down the air pressure? Maybe it's letting too much air to my dash switch. No mate, I'm pretty sure the air regulator number 13 drops the pressure Should be around 50 - 60 psi Paul Edited December 25, 2018 by mrsmackpaul 1 Quote Link to comment https://www.bigmacktrucks.com/topic/52915-12-speed-extended-range-switch-leaking-in-direct/#findComment-411898 Share on other sites More sharing options...
fjh Posted December 26, 2018 Share Posted December 26, 2018 The low switch is plumbed exactly the same as number 4 (thats reverse they show there) deep reduction has its own circuit same plumbing How ever! The orings in the cyl are very suspect!Unfortunately the cyl is hard to get too you must remove the pass side floor panel ! not so bad in a newer or garage kept unit But if its been used in a salt mine watch out! also there is a line that also goes to the puff limit when Low on the stick is selected to limit Torque output! Quote Link to comment https://www.bigmacktrucks.com/topic/52915-12-speed-extended-range-switch-leaking-in-direct/#findComment-411968 Share on other sites More sharing options...
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