Rob Posted June 9, 2007 Share Posted June 9, 2007 A friend of mine stopped by the shop tonight wanting to know if I had any advice on the problem with his air shift six speed trans. With the air built up you can select the low range and sometimes you're in low, sometimes you are in direct. Reverse seldom seems to be selectable. With the engine shut down, and the shifter in the neutral position, flipping the button gives the seemingly appropriate sounds from the air shift cylinders at the back of the transmission. Every now and again, reverse will fall in and you will have all five speeds. If the splitter is shifted back to neutral along with the shifter handle then both put back into reverse, it is probably going to move the truck forward when you let the clutch out as reverse takes several times to get in. The truck is a DM series, (1986) with a 300+ engine, and is a roll off truck. It has seen some severe duty through the years and runs very well.Any ideas??Thanks,Rob Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment Share on other sites More sharing options...
Lmackattack Posted June 10, 2007 Share Posted June 10, 2007 check the air lines first to see if they are kinked. If they look kinked or badly worn replace them. then look for a bad air cyl ( I belive the cyl is on the top cover?)that selects direct reverse etc.... If the cyl is good it could be a bad shift fork or bad rails again these parts are accessed through the top cover.My experince with air shift 6 speeds was that you would hear a hard grind if you selected a direct or low when rolling backwards or vise versa. also if I shifted to direct from low when rolling along it would grind kinda loud. at a stop the splitter should easly select the desired range with a soft clunk heard.just my .02 Quote Link to comment Share on other sites More sharing options...
Rob Posted June 10, 2007 Author Share Posted June 10, 2007 check the air lines first to see if they are kinked. If they look kinked or badly worn replace them. then look for a bad air cyl ( I belive the cyl is on the top cover?)that selects direct reverse etc.... If the cyl is good it could be a bad shift fork or bad rails again these parts are accessed through the top cover.My experince with air shift 6 speeds was that you would hear a hard grind if you selected a direct or low when rolling backwards or vise versa. also if I shifted to direct from low when rolling along it would grind kinda loud. at a stop the splitter should easly select the desired range with a soft clunk heard.just my .02Hi Trent:That is close to the same advice that I had rendered to the operator. With the engine off and shifting the air splitter, one can hear things trying to operate as they should. There is no sudden rush of air escaping the system and soft clunks can be heard inside the transmission. The owner was going to pull the floor pan in the cab this weekend to gain access to the top of transmission, and both shift cylinders. The problem (to me at least) appears to be blown "O" rings in a cylinder, or a bent/worn shift fork and /or shift rails. It also appears that the problem came on suddenly, and there was no lead up or prior warning.Thanks,Rob Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment Share on other sites More sharing options...
mechmagcn Posted June 10, 2007 Share Posted June 10, 2007 I have run into this problem several times. Before going to any extremes, look for a vent on the rear of the shift housings,(if I remember right, it will be on the lower left side of the shift cylinder) sort of looks like a hole with a screen or rock type filter in it. If this is stopped up, the shifter can't let the air off of the off side of the piston.Jeff Quote 1971 Mack R600 Toterhome "Superdawg" living the life of leisure pulling 1999 NuWa Snowbird 34+2 SE102 "Dawghouse" Link to comment Share on other sites More sharing options...
Rob Posted June 11, 2007 Author Share Posted June 11, 2007 I have run into this problem several times. Before going to any extremes, look for a vent on the rear of the shift housings,(if I remember right, it will be on the lower left side of the shift cylinder) sort of looks like a hole with a screen or rock type filter in it. If this is stopped up, the shifter can't let the air off of the off side of the piston.JeffThanks Jeff, I assume these shift cylinders are of the single acting type with a spring inside to force retraction. If the vent is plugged as you suggest, then there would be a problem most definately. The truck operates at the landfill quite regularly so this is a very viable thing to look at.Rob Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment Share on other sites More sharing options...
Rob Posted June 12, 2007 Author Share Posted June 12, 2007 Thanks Jeff, I assume these shift cylinders are of the single acting type with a spring inside to force retraction. If the vent is plugged as you suggest, then there would be a problem most definately. The truck operates at the landfill quite regularly so this is a very viable thing to look at.RobI took the Hi/Lo shift cylinder apart today and the piston, (aluminum) is scrap. The sealing rings finally gave out not allowing proper travel for the shift fork. This would not reach the neutral gate to allow the reverse gear to engage. Parts are on order, truck is locked in high range and is usable until the weekend when all the parts will be in to repair permanent.Thanks for the help guys.Rob Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment Share on other sites More sharing options...
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