m16ty Posted April 15, 2016 Share Posted April 15, 2016 I've got a RD822 with a 12 speed and I'm getting ready to install a Spicer 1241, 4 speed auxiliary. I don't recall the rear end ratio but it's low and the truck tops out around 60 mph right now. What I'm wondering is if I can run the truck safely in 12th gear on the main box and OD on the auxiliary? I'm worried it would spin the rears too fast. I'm mainly installing the auxiliary for the lower gears but the double OD would be nice out on the highway, Quote Link to comment Share on other sites More sharing options...
terry Posted April 15, 2016 Share Posted April 15, 2016 Nothing I would be concerned with. terry Quote Link to comment Share on other sites More sharing options...
AZB755V8 Posted April 15, 2016 Share Posted April 15, 2016 Got an overdrive 9 speed with a 3speed brownie OD for double overdrive and 5.77 rears. It's been running since 1953 with no issues. Quote Link to comment Share on other sites More sharing options...
m16ty Posted April 15, 2016 Author Share Posted April 15, 2016 Checked the rear ratio today and it's 5.88. I'm also running 11.00-24 tires. Quote Link to comment Share on other sites More sharing options...
david wild Posted April 18, 2016 Share Posted April 18, 2016 4 spd aux will not take a lot of input torque, they really don't like being run in the high side loaded. 2 spd will do better at holding up, they come either over or under. I have extra 1202 in storage, very low miles air shift. Quote Link to comment Share on other sites More sharing options...
m16ty Posted April 18, 2016 Author Share Posted April 18, 2016 David, I was worried about that and the overdrive gear is quite a bit narrower that the rest. I'd say it would be wise to stay out of OD during heavy pulling. I might would do some dealing on the 1202 but I've already spent $1,600 in parts to rebuild this one. I've got a KW that could use a some more gears also so I'll keep you in mind if I ever get around to that project. The guy a bought the box from has run these 1241s for years and probably the most knowledgeable heavy haul person in this area. I don't like to throw out names without people's permission but any heavy haul truckers in the middle TN area will know who I'm talking about. He said, if you treat it right, this box will hold up to anything you throw at it and the driveshaft will fail before the box does. He also said that what gets most boxes is running in lower transmission gears with the auxiliary in OD. Quote Link to comment Share on other sites More sharing options...
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