Dudley Posted March 3, 2019 Share Posted March 3, 2019 I lust purchased a 1990 Midliner CS 250P. The transmission is a six speed and is hurt so I am putting in a 13 speed. I am trying to figure out the rear gear ratio but have been unsuccessful to this point. I have a spec sheet for the truck and it shows the rear ratio as 13x41 which I believe is a 3.15 but it also has the planetary ends and I can't find any info to help me figure out the total gear ratio. I do not think that 3.15 is the final ratio but I do not know how to figure out what is without taking it apart and I do not want to do that. I also found that it is a P1021-01-05. I scratched around on it and found some numbers cast into it but nothing that looked like gear ratio numbers. Can anyone tell me where to look or possibly help me figure out the rear ratio. I am trying to figure out whether to leave the 13 speed as single overdrive or flip it around to double over. Thank you for your help! Quote Link to comment https://www.bigmacktrucks.com/topic/55925-midliner-rearend-ratio/ Share on other sites More sharing options...
kscarbel2 Posted March 3, 2019 Share Posted March 3, 2019 Does your truck have a planetary hub reduction axle? (which I think the P1021 is) You want to attach a 13-speed Eaton Fuller transmission??? Quote Link to comment https://www.bigmacktrucks.com/topic/55925-midliner-rearend-ratio/#findComment-417057 Share on other sites More sharing options...
Dudley Posted March 4, 2019 Author Share Posted March 4, 2019 First thank you for your time to reply to my question! It does have the planetary hub axle. I am guessing it is maybe 2:1 ratio and maybe the ring and pinion are 13x41=3.15 which would make it 6.3 total reduction. I should have mentioned this will be a farm truck for personal use so my goal is to get more low gear where I can spread gravel better in low gear and also easier to get moving in soft ground but of course I don't want to be stuck at 50mph road speed. It does in fact have the BDSL-181 which I think has 6.70 low and 0.75 OD. It is hurt now. I don't know what is wrong with it as the previous owner removed it because it was locked up. I understand parts are hard to get plus expensive so I chose to upgrade to 13 speed. I have a RTO-9513 that I am rebuilding now and I am trying to decide whether or not to turn it around to double over. If the rear ratio is in fact 6.30 then I will turn the trans around. 5.20 rear ratio is kind of my breaking point. 5.20 or less and I will leave it at RTO. RTOO is 9.27 low and 0.64 OD so will be better on both ends plus better splits all the way up through the gears. I know this has been debated many times on here and other sites but I counted the teeth on every gear and figured out all the ratios for both RTO and RTOO. Splits remain the same but low gear moves and OD moves. Thanks again! Quote Link to comment https://www.bigmacktrucks.com/topic/55925-midliner-rearend-ratio/#findComment-417236 Share on other sites More sharing options...
Dudley Posted March 4, 2019 Author Share Posted March 4, 2019 Rob, Thank you. The 5.45 puts me right on the edge of a good overall low gear with the turned around over drive. The 5.45 with 9.27 low of turned around double over drive gives me 50.6 overall reduction in low gear which is much better than 36.5 overall with the BDSL-181. I read that the loggers like 60 overall ratio so that is kind of my target but maybe 50.6 is still ok for small dump truck and the turned around double over gives me a good road gear at 0.64 over drive. But if I leave the trans like it is I would have two good low gears (low and first) and maybe a decent road gear at 0.87 over drive. Truck would top out around 67 mph and 55 mph should be about 2100 rpm. I probably won't get more than 25 or thirty miles away from the farm so maybe leave the 13 alone is the best answer. Quote Link to comment https://www.bigmacktrucks.com/topic/55925-midliner-rearend-ratio/#findComment-417253 Share on other sites More sharing options...
Dudley Posted March 4, 2019 Author Share Posted March 4, 2019 Thanks Rob! Quote Link to comment https://www.bigmacktrucks.com/topic/55925-midliner-rearend-ratio/#findComment-417258 Share on other sites More sharing options...
brettj3876 Posted April 27, 2019 Share Posted April 27, 2019 If it helps any you can take the aux off an old RTO like we did with a 14613 and put it on a RTX14609B giving you .62 Quote Link to comment https://www.bigmacktrucks.com/topic/55925-midliner-rearend-ratio/#findComment-421471 Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.