Rob Posted February 2, 2012 Share Posted February 2, 2012 What do you guys think a set of known good Mack 3.87 carriers would be worth? Is the engine speed difference enough to justify going from 4.17 down to these?Thanks,Rob Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment Share on other sites More sharing options...
mack mhe9 Posted February 2, 2012 Share Posted February 2, 2012 looks to be 100rpm lower with a .71od if that helps Quote Link to comment Share on other sites More sharing options...
daveigou Posted February 2, 2012 Share Posted February 2, 2012 I would think $1,000 with known history. Quote See my Flickr photostream page http://www.flickr.com/photos/96692978@N05/ Link to comment Share on other sites More sharing options...
Bollweevil Posted February 2, 2012 Share Posted February 2, 2012 I don't think you would benefit much, maybe as much as 3.5 mph at 1600 with tall rubber. Even if the cost was 0 there is a lot of labor for a hobby truck. Send me an email, I am having a problem contacting you. Quote Link to comment Share on other sites More sharing options...
Rob Posted February 2, 2012 Author Share Posted February 2, 2012 I don't think you would benefit much, maybe as much as 3.5 mph at 1600 with tall rubber. Even if the cost was 0 there is a lot of labor for a hobby truck. Send me an email, I am having a problem contacting you.Yes I'm looking at hobby truck usage. My Cat powered truck has 4.17 rears and I was wondering, (given how hard on fuel a 1693TA is) if the swap would be feasible or not. I haven't driven this truck over 60mph when driving it home from KY when purchased, and it hasn't been off the property since. I know these rears as I've driven the truck shortly before being turned over/wrecked, and written off.I'll get in touch with you shortly. My email is: robsautoaffair@gmail.comRob Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment Share on other sites More sharing options...
Bollweevil Posted February 2, 2012 Share Posted February 2, 2012 Yes I'm looking at hobby truck usage. My Cat powered truck has 4.17 rears and I was wondering, (given how hard on fuel a 1693TA is) if the swap would be feasible or not. I haven't driven this truck over 60mph when driving it home from KY when purchased, and it hasn't been off the property since. I know these rears as I've driven the truck shortly before being turned over/wrecked, and written off.I'll get in touch with you shortly. My email is: robsautoaffair@gmail.comRob They would be good to have in reserve, they certainly won't rot, I don't think you would see much of an Rpm drop at 60mph. Quote Link to comment Share on other sites More sharing options...
Rob Posted February 2, 2012 Author Share Posted February 2, 2012 They would be good to have in reserve, they certainly won't rot, I don't think you would see much of an Rpm drop at 60mph.Thanks much James. 60mph is my target road speed with anything for figuring. That truck is on 10.00RX20 tires and will most likely be the one that is hauled to shows in the future. Appreciate the guidance guys, I can get them priced right and certainly won't let them go to scrap as I don't think they have 100K on them since being remanned.Rob Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment Share on other sites More sharing options...
slpwlker Posted February 2, 2012 Share Posted February 2, 2012 Since it is just a hobby I would go higher geard. mid to Lower 3's if your not pulling anything. You'd get lower Rpm's, maybe better mileage If your not lugging it and still have enough power to get on it and get out of the way bobtail Quote Link to comment Share on other sites More sharing options...
rick harper Posted March 14, 2012 Share Posted March 14, 2012 Dropping from 4.17 to 3.87 will increase your speed approx. 6MPH. This is how you figure road speed. tire factor x gear ratio x direct drive or overdrive, divided into the rpm's. EG. for 11.00R24.5, 4.17 ratio and Mack T-2090 transmission. 7.93 x 4.17 x .71=23.48. Now divide that number into the RPM's. Lets consider 1800RPM. Your speed is 76.6MPH. The tire factor for a 11.00R22.5 tires is 8.25. 7.93 and 8.25 represents brand new rubber height. Quote Link to comment Share on other sites More sharing options...
rick harper Posted March 14, 2012 Share Posted March 14, 2012 I forgot to say that mechanical speedo's can be as much as 5MPH off. Fast or slow. Quote Link to comment Share on other sites More sharing options...
theakerstwo Posted March 14, 2012 Share Posted March 14, 2012 Rob if you go that way i know a man that has good 3:88 carriers he wants to change to 4:17 and as for as i know they are good ones.Keep him in mind. Quote glenn akers Link to comment Share on other sites More sharing options...
Rob Posted March 15, 2012 Author Share Posted March 15, 2012 Rob if you go that way i know a man that has good 3:88 carriers he wants to change to 4:17 and as for as i know they are good ones.Keep him in mind.Hi Glenn, see if your buddy can get a photo of his carriers to ensure mine are the same mounting as his. I have a couple sets of known good 4.17's as I've driven both trucks.Rob Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment Share on other sites More sharing options...
bubbamobilin Posted March 15, 2012 Share Posted March 15, 2012 Hey Rob. I didn't change rears but I did swap tranny's. Went from a 12spd. to a 2180 (.78 to .71 od) and I lost 200 rpm's @ 70 mph. Just my $.02 worth. Quote Link to comment Share on other sites More sharing options...
theakerstwo Posted March 16, 2012 Share Posted March 16, 2012 Wish i had the 12 speed Quote glenn akers Link to comment Share on other sites More sharing options...
Lmackattack Posted March 16, 2012 Share Posted March 16, 2012 Wish i had the 12 speedditto...I need a 12 speed also...Rob I think it will all depends on your transmission. Yes its a hobby truck but you will pull a trailer someday...some of the Mack End Dumps with 300/ 6 speeds and 3.87 rears were dogs in the top 2 gears and found I needed Low Low alot more. Its a minamal Road speed change but if your heavy and dont have a good selection of transmission gears or the HP to pull. it can be a downfall. If you have a 13 speed and a big cat motor you will be fine as you can just downshift if its lugging or you stick it in OD and get home fast.something us 6 speed owners cant do LOL!!!! Quote Link to comment Share on other sites More sharing options...
Rob Posted March 16, 2012 Author Share Posted March 16, 2012 ditto...I need a 12 speed also...Rob I think it will all depends on your transmission. Yes its a hobby truck but you will pull a trailer someday...some of the Mack End Dumps with 300/ 6 speeds and 3.87 rears were dogs in the top 2 gears and found I needed Low Low alot more. Its a minamal Road speed change but if your heavy and dont have a good selection of transmission gears or the HP to pull. it can be a downfall. If you have a 13 speed and a big cat motor you will be fine as you can just downshift if its lugging or you stick it in OD and get home fast.something us 6 speed owners cant do LOL!!!!Hi Trent, that truck does have a RTO-12513 transmission. I am not certain which way I will go, (if any) on this truck. It is all original and prolly won't see another 10k miles in the balance of my lifetime. Never have pulled anything with the truck and it will hardly pull itself with the clutch being completely shot. The engine will run away from the driveline bobtailing.Rob Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment Share on other sites More sharing options...
Lmackattack Posted March 16, 2012 Share Posted March 16, 2012 only 10k in its life? I put about 1500 on the RS evary year just in shows and around town.. you got to get out more LOL... Quote Link to comment Share on other sites More sharing options...
bubbamobilin Posted March 16, 2012 Share Posted March 16, 2012 Wish i had the 12 speedSorry guys but the 12spd is still hanging around in case of an emergency. Quote Link to comment Share on other sites More sharing options...
Lmackattack Posted March 16, 2012 Share Posted March 16, 2012 Sorry guys but the 12spd is still hanging around in case of an emergency.why did you switch to the 18? just a more modern and easy for parts? Quote Link to comment Share on other sites More sharing options...
Rob Posted March 16, 2012 Author Share Posted March 16, 2012 only 10k in its life? I put about 1500 on the RS evary year just in shows and around town.. you got to get out more LOL...I will prolly haul it most places of any distance on the drop deck. I may use it occasionally to keep it clean. All depends.....Rob Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment Share on other sites More sharing options...
Lmackattack Posted March 16, 2012 Share Posted March 16, 2012 Trailer Queen!!!! LOL Quote Link to comment Share on other sites More sharing options...
Rob Posted March 16, 2012 Author Share Posted March 16, 2012 Trailer Queen!!!! LOLMost likely that and local parades. Everything around here has to run and be usable in one fashion or another.Rob Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment Share on other sites More sharing options...
bubbamobilin Posted March 16, 2012 Share Posted March 16, 2012 why did you switch to the 18? just a more modern and easy for parts?I just wanted the 18spd for the .71 overdrive. I have 3:87 rears on big rubber and with the 12 speed @ 70 mph I was turning 1700 rpm. Now with the 18spd @ 70 mph I'm turning 1500 rpm. I love a 12spd tranny but the 18 is nice too. I think one day I still want to go to a 3:65 ratio. Most of my runs are in the south were the speed limit is 65-70 mph. Quote Link to comment Share on other sites More sharing options...
Josh3599 Posted March 24, 2012 Share Posted March 24, 2012 I'd like to have the 417's Quote Link to comment Share on other sites More sharing options...
slpwlker Posted March 24, 2012 Share Posted March 24, 2012 Heres some food for thought. Gear it as high as you can get it. In Mack carriers idk if you can get much past 3:87's. put a direct drive trans as the Od will make it work harder. you can keep the rpm's lower if you keep the speeds around 58 to 60 or since your mostly bobtailing with it 62. keeps the rpms around 13 to 1400. Now with the older motors I know they like to run in the higher ranges. Alot of people trying for the optimum fuel mileage are going to 3.23's and 2.90's but not using the last 2 gears in the 18 speed. seems to be a waste of a trans. Doing that they keep it in Direct,Keep it lower rpms, and get fuel ,mileage. Quote Link to comment Share on other sites More sharing options...
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