SWalters Posted May 10, 2015 Share Posted May 10, 2015 Hello Guys, I have a 18 speed Mack trans that will not stay in high side range! It will slip out and grind when accelerating then reingage when u let off pedal. I can get it to do it in the shop brakes on wheels chocked, in high gear. I change selector control on top of trans thinking it might had an internal issue, I didn't put gauge on air supply to it but there seems to be plenty of air, everything is shifting as it should. There. Is no air coming out of trans to suggest the selector/actuator that shift to and from high side is leaking internally. Any help is appreciated! I like to diagnose issue and fix problem not throw parts at like my Peterbuilt dealer. My Mack guy passed away this past winter at a very young age, and we miss him dearly! Quote Link to comment Share on other sites More sharing options...
Macktech689 Posted May 10, 2015 Share Posted May 10, 2015 Sounds like the synchronizer is worn out if the clutching teeth disengage. It can be replaced without pulling the transmission out but requires special tools to do so. I would take it to a Mack dealer to get it repaired. Its also possible the bolt in the range fork has come loose, tightening the bolt probably wont fix the problem but its something that can be tried. If the bolt is found loose it should be replaced. 1 Quote Link to comment Share on other sites More sharing options...
SWalters Posted May 10, 2015 Author Share Posted May 10, 2015 Can I see range fork bolt if I take off top cover on trans? I have to take top off anyhow if I have to pull rear of trans off, that where the special tools come in hand to hold the 3 shafts in place. Right? I have 580,000 on trans Mack put a bearing kit in it at 250 300 thousand should I just pull it and go thru the hole thing? Quote Link to comment Share on other sites More sharing options...
Kansas farmer Posted May 10, 2015 Share Posted May 10, 2015 I just deleted the pictures off my phone. I had an issue where it wouldn't shift into the high side when cold. I did the work myself new forks and rebuilt the range cylinder. You can see the forks by taking the top cover off. One will come out with the top cover. To get the range fork out you need to pull the cylinder off the back. I did hear that the set screw could come loose they need to be torqued to 52lbs I believe and loctited. Quote Link to comment Share on other sites More sharing options...
SWalters Posted May 11, 2015 Author Share Posted May 11, 2015 My trans shifts fine even in winter, but it doesn't really get cold here. If the range cylinder is not working corectly it wood leak internaly? Quote Link to comment Share on other sites More sharing options...
Td713001033 Posted May 11, 2015 Share Posted May 11, 2015 when you make the range shift does it grind or shift smoothly. did you drain the oil and check plug for filings . what happened that you needed bearings at 300,000 miles seems premature. how old is your clutch. we have ten of these transmissions and we just pull them and go with mack reman. 2 year unlimited mileage warranty. tried the patch it here and there method before never lasts long. at 580,000 you must have wear on sliding gears and shift fork ends. I do not know what you do or how hard you work the truck but I would go with reman T 2180 B. Quote Link to comment Share on other sites More sharing options...
SWalters Posted May 11, 2015 Author Share Posted May 11, 2015 Shifts smooth. I didn't get that far, but I will tomorrow night. I had a bearing cage come apart in trans. my speed sensor broke I changed it, then broke again few days later if that. did a little checking there was pieces of a bearing cage floating around in there keep breaking speed sensor. so Mack suggested bearing kit. so I let them do it. Clutch is brand new I took engine out last winter and sent to Allentown Mack to rebuild. Truck works hard always 80,000 plus. young drive as well, he not bad just alittle rough I think. I don't have a problem takin trans out and swap with rebuild. just don't want to if its a simple range cylinder rebuild or change shift fork and bolt. Just want to diagnose the problem correctly. thanx for your help Quote Link to comment Share on other sites More sharing options...
gearhead204 Posted May 11, 2015 Share Posted May 11, 2015 if air pressure is good, i agree with the fork or syncro issue as mentioned in earler post Quote Link to comment Share on other sites More sharing options...
turckster Posted May 11, 2015 Share Posted May 11, 2015 Sounds like worn high range clutches/sliding clutch teeth. Its can be caused by incorrect range pre-select technique, worn/damaged range interlock pin, driveline angle/balance issue, incorrect rear susp. ride height, etc. Replacement of the synchronizer is possible in chassis but it is quite a job. Without the correct tools, pulling the trans and replacing the assly out of chassis would be your best option OR letting a dealer replace the assly. If you remove the rear shift lid, the range fork is right there. Check it for being loose which is common. Inspect the high range clutches(high range to the front , low range at rear). The clutches for high range will most likely look black and have a lot of play. You can pry the sliding clutch back and inspect the range engagement teeth, more than likely they will be damaged and require replacementThere are constant parts updates with these transmissions and service updates. If you decide to do the work yourself, make sure you install and have the correct current parts. The range fork pinch bolt and output yoke bolts are replaced every time--never reuse those bolts. Make sure you torque the range pinch bolt at least 45-50 ft/lbs. Replace all range/spliter o-rings, lube those o-rings with Eaton/Fuller O-ring silicon lube (this stuff can be used for bunches of other things too). They make a synchronizer complete kit and a rebuild kit, use the rebuild kit unless the synchro housing has damage or pin bores have excessive wear. I wouldn't cut corners on this repair because it will be expensive the first time. good luck Quote Link to comment Share on other sites More sharing options...
SWalters Posted May 16, 2015 Author Share Posted May 16, 2015 Thanx for all the input. I removed rear shift lid and checked fork hoping it was lose. But it wasn't so I got to use my brand new trans jack! Allentown Mack rebuilt for me going to pick up Monday AM and install. Quote Link to comment Share on other sites More sharing options...
slingblade Posted May 23, 2015 Share Posted May 23, 2015 on alot of other transmissions with many hard miles ive seen the stack shims wear causing excessive clearance between the gears which will cause it to jump out of gear also,,most transmissions call for 005 to 011 clearance at the end of the gear stacks on the shaft, Quote Link to comment Share on other sites More sharing options...
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