IdleUp Posted December 26, 2008 Share Posted December 26, 2008 (edited) Hello - I just bought a 1990 Superliner Dump truck and it just don't want to go in reverse. If I fuss with it long enough it goes in and works fine but 90% of the time when I move the splitter over to reverse nothing happens. By the way, I hope I'm doing the sequence right. I put the transmission in nutural, then i move the spliter to reverse. Is this correct ?Any ideas on what I might check. Thanks in advance!Mike Edited December 26, 2008 by IdleUp Quote Link to comment https://www.bigmacktrucks.com/topic/7760-intermitent-reverse-problem/ Share on other sites More sharing options...
CML Service Posted December 26, 2008 Share Posted December 26, 2008 A little more info on what trans you have would help. I'll take a guess it's either a 6 or 12 speed with the rotary type air selector. If thats the case is the selector valve leaking? Can you hear air moving when selecting rev? When it does select gears do you hear a distinct clack? Chuck Quote Link to comment https://www.bigmacktrucks.com/topic/7760-intermitent-reverse-problem/#findComment-28091 Share on other sites More sharing options...
IdleUp Posted December 26, 2008 Author Share Posted December 26, 2008 (edited) A little more info on what trans you have would help. I'll take a guess it's either a 6 or 12 speed with the rotary type air selector. If thats the case is the selector valve leaking? Can you hear air moving when selecting rev? When it does select gears do you hear a distinct clack? ChuckI belive it's a 12 speed I drove the truck today and The spliter shifts fine from low to high and back down again. When I shift it into nuteral on the spliter, I can shift the main and nothing happens. Like I said it went in 2-3 times fine and backed up great but like today I could not get it in at all. By the way, there s switch on the dash I think it says dir and low would that have anything to do with it? What exactly does that do?ThanksMike Edited December 26, 2008 by IdleUp Quote Link to comment https://www.bigmacktrucks.com/topic/7760-intermitent-reverse-problem/#findComment-28092 Share on other sites More sharing options...
theakerstwo Posted December 26, 2008 Share Posted December 26, 2008 I think Rob just went thru this with one of his. glenn Quote glenn akers Link to comment https://www.bigmacktrucks.com/topic/7760-intermitent-reverse-problem/#findComment-28093 Share on other sites More sharing options...
IdleUp Posted December 26, 2008 Author Share Posted December 26, 2008 I'm not certain but i think this is the shift pattern - I found this on jpeg on Ebay The spliter on the right and the main tranny is like mine. There is a switch on the dash and when I flip it the tranny only shifts into 1st gear - is that right?I'll try to upload it with this post!Thanks Quote Link to comment https://www.bigmacktrucks.com/topic/7760-intermitent-reverse-problem/#findComment-28094 Share on other sites More sharing options...
Rob Posted December 26, 2008 Share Posted December 26, 2008 I'm not certain but i think this is the shift pattern - I found this on jpeg on Ebay The spliter on the right and the main tranny is like mine. There is a switch on the dash and when I flip it the tranny only shifts into 1st gear - is that right?I'll try to upload it with this post!ThanksBuy a rebuild kit for the "Selectair" valve, and air shift cylinders from your Mack dealer. I'll get the part number if you need it. Also ensure the quick release valve on the transmission top cover is working correctly. It should exhaust when you select the reverse position in the cab.Rob Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/7760-intermitent-reverse-problem/#findComment-28097 Share on other sites More sharing options...
CML Service Posted December 26, 2008 Share Posted December 26, 2008 Could be an o-ring on the actuator cyl for rev. Cooler weather makes them leak internally and any oil or gunk in there will make thins more difficult. Switch on dash is deep reduction for use in 1st gear. Chuck Quote Link to comment https://www.bigmacktrucks.com/topic/7760-intermitent-reverse-problem/#findComment-28098 Share on other sites More sharing options...
IdleUp Posted December 26, 2008 Author Share Posted December 26, 2008 When I put it in reverse position, I don't hear anything. If you have the part number that would be great. Is there a post that shows my transmission and the location of the reverse shifter mechanism. I'm thinking it might be a loose airline or something of that nature. Does the switch on the dash have anything to do with reverse. I believe it says direct and something else. when it's in the lower position the transmission only goes in 1st.Thanks Quote Link to comment https://www.bigmacktrucks.com/topic/7760-intermitent-reverse-problem/#findComment-28101 Share on other sites More sharing options...
IdleUp Posted December 26, 2008 Author Share Posted December 26, 2008 Could be an o-ring on the actuator cyl for rev. Cooler weather makes them leak internally and any oil or gunk in there will make thins more difficult. Switch on dash is deep reduction for use in 1st gear. ChuckOk that explains why it locks the shifter in 1st gear!I found this post on this forum - do you think it could be the quick release valve like it was onthis truck? Here's the post:I rebuilt the "Selectair" valve this evening after cleaning everything up using denatured alcohol and the "lube in a tube", (Navy term) to lubricate the new "O" rings and moving parts, All went back together just fine. It would still leak past the seals when the transmission was selected to reverse. Further T/S revealed the QR-1 valve on the transmission was defective, and I replaced the same with a new one on hand. The transmission now works flawlessly. Quote Link to comment https://www.bigmacktrucks.com/topic/7760-intermitent-reverse-problem/#findComment-28106 Share on other sites More sharing options...
fjh Posted December 26, 2008 Share Posted December 26, 2008 Hello - I just bought a 1990 Superliner Dump truck and it just don't want to go in reverse. If I fuss with it long enough it goes in and works fine but 90% of the time when I move the splitter over to reverse nothing happens. By the way, I hope I'm doing the sequence right. I put the transmission in nutural, then i move the spliter to reverse. Is this correct ?Any ideas on what I might check. Thanks in advance!MikeYou may have a brokren snap ring in the split cyl!(The bigger left hand cyl)The shift lid has an interlock pin that will hold out reverse if the spliter does not fully go into neutral.If you have to fiddle with the air shift to get an intermitant reverse this may be the case!loose shift rail bolt is another common thing.Go to the dealer and get a rebuild oring kit and tare into it !The deep reduction is commonly locked out on the 12 speedmeaning it will only work in first gear low high split and reverse. Quote Link to comment https://www.bigmacktrucks.com/topic/7760-intermitent-reverse-problem/#findComment-28139 Share on other sites More sharing options...
fullfuel01 Posted December 26, 2008 Share Posted December 26, 2008 before changing any parts, try to change the filter on the back of your tranny (spin-on filter), look for any air leak and I don't where you're located but is that possible that there is humidity in your line and it start to freeze?? Quote Link to comment https://www.bigmacktrucks.com/topic/7760-intermitent-reverse-problem/#findComment-28141 Share on other sites More sharing options...
IdleUp Posted December 26, 2008 Author Share Posted December 26, 2008 before changing any parts, try to change the filter on the back of your tranny (spin-on filter), look for any air leak and I don't where you're located but is that possible that there is humidity in your line and it start to freeze??Ok, I'll peer around and see what I can find - the guy who had the truck looks like he ran it in the ground - it's a mess. Does anyone have a image of the shifter assembly?I included the image one of the users of this forum provided me (thanks) am i correct in assuming that when the shifter is in reverse that Port # 4 has air pressure and it move the shifer piston forward or do i have it backwards? Quote Link to comment https://www.bigmacktrucks.com/topic/7760-intermitent-reverse-problem/#findComment-28142 Share on other sites More sharing options...
Rob Posted December 26, 2008 Share Posted December 26, 2008 Ok, I'll peer around and see what I can find - the guy who had the truck looks like he ran it in the ground - it's a mess. Does anyone have a image of the shifter assembly?I included the image one of the users of this forum provided me (thanks) am i correct in assuming that when the shifter is in reverse that Port # 4 has air pressure and it move the shifer piston forward or do i have it backwards?You are correct in that assumption.Rob Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/7760-intermitent-reverse-problem/#findComment-28150 Share on other sites More sharing options...
IdleUp Posted December 26, 2008 Author Share Posted December 26, 2008 You are correct in that assumption.RobThanks Rob - if anyone comes across an image of transmission or shifter please let me know. Regards! Quote Link to comment https://www.bigmacktrucks.com/topic/7760-intermitent-reverse-problem/#findComment-28159 Share on other sites More sharing options...
Rob Posted December 27, 2008 Share Posted December 27, 2008 Thanks Rob - if anyone comes across an image of transmission or shifter please let me know. Regards!Relay the numbers from your transmission. They are located on the left side of the aluminum case in a flat spot. They will be stamped.I am away enjoying "family time" for the next couple of days and am out of the shop so my help will be limited if needed.Rob Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/7760-intermitent-reverse-problem/#findComment-28168 Share on other sites More sharing options...
IdleUp Posted December 28, 2008 Author Share Posted December 28, 2008 Relay the numbers from your transmission. They are located on the left side of the aluminum case in a flat spot. They will be stamped.I am away enjoying "family time" for the next couple of days and am out of the shop so my help will be limited if needed.RobRob,Sorry, I didn't see you message to get the numbers but i did manage to snap a few shots of the top of the tranny. I would presume the reverse shifter is the "Blue" colored module to the rear is that right - if so then i guess the hose in the rear is the one which pushes the shifter into reverse?Thanks Quote Link to comment https://www.bigmacktrucks.com/topic/7760-intermitent-reverse-problem/#findComment-28244 Share on other sites More sharing options...
IdleUp Posted December 28, 2008 Author Share Posted December 28, 2008 Here's the other image - sorry they are so bad! Quote Link to comment https://www.bigmacktrucks.com/topic/7760-intermitent-reverse-problem/#findComment-28245 Share on other sites More sharing options...
Rob Posted December 28, 2008 Share Posted December 28, 2008 Rob,Sorry, I didn't see you message to get the numbers but i did manage to snap a few shots of the top of the tranny. I would presume the reverse shifter is the "Blue" colored module to the rear is that right - if so then i guess the hose in the rear is the one which pushes the shifter into reverse?ThanksThat is backward. The "blue" shift cylinder is for the high/low range selection. The other shift cylinder is the one that routes the transmission to reverse. The .pdf file diagram that was posted gives the air routing as per that chart with the shaded boxes. When the "selectair" valve is positioned to reverse, the air line leading to the back of the reverse shift cylinder is pressurized, and the air line that runs from the side of this same cylinder runs to the "quick release" valve to rapidly exhaust the air from that cylinder. As can be ascertained by the air chart, most of the cylinders have air on both sides of the piston to keep anything from moving except when a selection is made. This effectively "binds" the shifting forks from moving freely.Rob Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/7760-intermitent-reverse-problem/#findComment-28246 Share on other sites More sharing options...
IdleUp Posted December 28, 2008 Author Share Posted December 28, 2008 That is backward. The "blue" shift cylinder is for the high/low range selection. The other shift cylinder is the one that routes the transmission to reverse. The .pdf file diagram that was posted gives the air routing as per that chart with the shaded boxes. When the "selectair" valve is positioned to reverse, the air line leading to the back of the reverse shift cylinder is pressurized, and the air line that runs from the side of this same cylinder runs to the "quick release" valve to rapidly exhaust the air from that cylinder. As can be ascertained by the air chart, most of the cylinders have air on both sides of the piston to keep anything from moving except when a selection is made. This effectively "binds" the shifting forks from moving freely.RobThanks so much Rob, while I was at the lot today, after building up the air, I can hear an air leak somewhere under the cab. It was windy and raining so I didn't pursue it.Right after I started it up with only around 40 lbs of air, It did jump right in reverse. I backed the truck up and the transmission is perfect, however after 40 minutes of playing with it, it never went in reverse again. There's no sequence is there? to get it in reverse right?I also found out today that sometimes I have to shift the splitter a few times to even get it in Neutral. As I move the splitter knob I don't hear any air exhausting when I move to the different positions.Thanks Quote Link to comment https://www.bigmacktrucks.com/topic/7760-intermitent-reverse-problem/#findComment-28247 Share on other sites More sharing options...
Rob Posted December 28, 2008 Share Posted December 28, 2008 Thanks so much Rob, while I was at the lot today, after building up the air, I can hear an air leak somewhere under the cab. It was windy and raining so I didn't pursue it.Right after I started it up with only around 40 lbs of air, It did jump right in reverse. I backed the truck up and the transmission is perfect, however after 40 minutes of playing with it, it never went in reverse again. There's no sequence is there? to get it in reverse right?I also found out today that sometimes I have to shift the splitter a few times to even get it in Neutral. As I move the splitter knob I don't hear any air exhausting when I move to the different positions.ThanksThose packings are needing replaced on both the shifter selectair valve, and shift cylinders and are not worth wasting the time to troubleshoot. The problems you are experiencing will be eliminated with the refurbishment. You will have gray hair by the time you are finished troubleshooting, and then need to replace them anyways. The rebuild is very straight forward after the top of the tranmission is removed. Be sure to mark your air lines for orientation prior to removal to ease the reassembly.There is no sequence that must be followed. You can have the shifter in a gear position and flip the handle from a forward, to reverse position and it should slip right into gear. You drive that transmission like a two speed rear axle and with good seals, it will shift instantaneously for you. Rob Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/7760-intermitent-reverse-problem/#findComment-28248 Share on other sites More sharing options...
IdleUp Posted December 28, 2008 Author Share Posted December 28, 2008 Those packings are needing replaced on both the shifter selectair valve, and shift cylinders and are not worth wasting the time to troubleshoot. The problems you are experiencing will be eliminated with the refurbishment. You will have gray hair by the time you are finished troubleshooting, and then need to replace them anyways. The rebuild is very straight forward after the top of the tranmission is removed. Be sure to mark your air lines for orientation prior to removal to ease the reassembly.There is no sequence that must be followed. You can have the shifter in a gear position and flip the handle from a forward, to reverse position and it should slip right into gear. You drive that transmission like a two speed rear axle and with good seals, it will shift instantaneously for you. RobThanks Rob - as soon as I close the deal I'll pick up the rebuild kit and the quick release air valve & filter.Thanks Quote Link to comment https://www.bigmacktrucks.com/topic/7760-intermitent-reverse-problem/#findComment-28249 Share on other sites More sharing options...
Rob Posted December 28, 2008 Share Posted December 28, 2008 Thanks Rob - as soon as I close the deal I'll pick up the rebuild kit and the quick release air valve & filter.ThanksI for some reason thought the truck was yours already. Be sure to have the vin number for the truck, and the model number of the transmission ready for the Mack dealer. The Selectair valve is the same throughout production, but there are a couple different kits for the shift cylinders.Having those numbers will half way ensure you get the correct parts!Rob Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/7760-intermitent-reverse-problem/#findComment-28250 Share on other sites More sharing options...
IdleUp Posted December 28, 2008 Author Share Posted December 28, 2008 Thanks . . . . Quote Link to comment https://www.bigmacktrucks.com/topic/7760-intermitent-reverse-problem/#findComment-28251 Share on other sites More sharing options...
theakerstwo Posted December 28, 2008 Share Posted December 28, 2008 Here's the other image - sorry they are so bad! They are bad , i got dirty looking at them lol glenn Quote glenn akers Link to comment https://www.bigmacktrucks.com/topic/7760-intermitent-reverse-problem/#findComment-28252 Share on other sites More sharing options...
IdleUp Posted December 28, 2008 Author Share Posted December 28, 2008 (edited) Here's the other image - sorry they are so bad!I just noticed but it looks like this line is right up against the exhaust pipe _ I wounder if it's burnt and leaking air? Edited December 28, 2008 by IdleUp Quote Link to comment https://www.bigmacktrucks.com/topic/7760-intermitent-reverse-problem/#findComment-28260 Share on other sites More sharing options...
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