Fastduramax Posted July 26, 2018 Share Posted July 26, 2018 Ok 12 speed Guru's please help me out ! 88 RD688S 350 12spd pulled tranny out today and my replacement tranny is different in this way... It has a spring loaded plate against the housing that the input shaft passes through that the clutch brake presses against, the tranny I pulled out does not, the housing "snout" is actually longer making up for the space the spring loaded plate takes up on the rebuilt tranny so the clutch brake on my tranny presses against the housing instead of a spring loaded plate in other words.... Both TRTXL-1070B trannys, both have equal distance from either the spring loaded ring or housing snout on my tranny to the end of the input shaft... So million dollar question are they interchangeable with no other modifications? Thanks guys !! Quote Link to comment https://www.bigmacktrucks.com/topic/53914-need-12-speed-help-asap/ Share on other sites More sharing options...
fullfuel01 Posted July 26, 2018 Share Posted July 26, 2018 picture worth thousand words Quote Link to comment https://www.bigmacktrucks.com/topic/53914-need-12-speed-help-asap/#findComment-403103 Share on other sites More sharing options...
Fastduramax Posted July 27, 2018 Author Share Posted July 27, 2018 I agree Fuel unfortunately I don't have access to either tranny until tomorrow... UGH ! Quote Link to comment https://www.bigmacktrucks.com/topic/53914-need-12-speed-help-asap/#findComment-403105 Share on other sites More sharing options...
turckster Posted July 27, 2018 Share Posted July 27, 2018 Trying to remember since its been so long but I think what your talking about is an old design. Everything is the same as far as clutch brake adjustment. They used a spring loaded pad instead of a solid type to extend clutch brake life (?). Could be wrong as far as reason. Like I said, been a while since I've seen one. Quote Link to comment https://www.bigmacktrucks.com/topic/53914-need-12-speed-help-asap/#findComment-403127 Share on other sites More sharing options...
Fastduramax Posted July 27, 2018 Author Share Posted July 27, 2018 Thank you Truckster I believe (praying) you are correct as most of the feedback I am getting around here says the same... Just hoping the clutch fork, throw out bearing and clutch brake ect are all the same spec old style and new style ! Quote Link to comment https://www.bigmacktrucks.com/topic/53914-need-12-speed-help-asap/#findComment-403131 Share on other sites More sharing options...
fjh Posted July 27, 2018 Share Posted July 27, 2018 It will work fine! Quote Link to comment https://www.bigmacktrucks.com/topic/53914-need-12-speed-help-asap/#findComment-403141 Share on other sites More sharing options...
Fastduramax Posted July 29, 2018 Author Share Posted July 29, 2018 Ok here is the skinny for those who may run into my dilemma... As Truckster said old style versus new style... From my research yes the spring loaded clutch brake saves on wear and tear but when the springs break with nothing else wrong its a 16 to 20 hour job to pull a 12spd out of a tri-axle to fix not good ! I unbolted the spring loaded housing from my rebuilt tranny and bolted on the solid casting from my smoked tranny and good to go just replace the existing seal... One other thing to check is to make sure you have a splined countershaft if you plan on running a rear mount PTO don't get the new tranny in and find out after the fact or you're looking at another $1800 plus for a side mount PTO and they SUCK in a Mack tranny ! Anyway all good in the Peru hood should be dumping dirt by Monday... 2 Quote Link to comment https://www.bigmacktrucks.com/topic/53914-need-12-speed-help-asap/#findComment-403248 Share on other sites More sharing options...
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