kahall82 Posted April 8, 2011 Share Posted April 8, 2011 Hi all,I have the numbers "354" imprinted on my rear diff housing. What does this mean? Does it mean what centres are in it? Quote Link to comment https://www.bigmacktrucks.com/topic/18660-r-model-diff-housing/ Share on other sites More sharing options...
rhasler Posted April 8, 2011 Share Posted April 8, 2011 Hi all,I have the numbers "354" imprinted on my rear diff housing. What does this mean? Does it mean what centres are in it?That should be the differential ratio. Quote "Mebbe I'm too ugly and stupid to give up!" Link to comment https://www.bigmacktrucks.com/topic/18660-r-model-diff-housing/#findComment-75742 Share on other sites More sharing options...
kahall82 Posted April 8, 2011 Author Share Posted April 8, 2011 Hi,Thanks for your response!Can I change the diff ratio centres to say 4.17 with only changing the centres and not the housing? They are 44,000lb.So we have 3.54 in there at the moment. What gearbox would be best to go behind it to get up to 70mph/100kph+.Or would you change your centre? Which do you change...centres or gearbox to get more speed? Quote Link to comment https://www.bigmacktrucks.com/topic/18660-r-model-diff-housing/#findComment-75743 Share on other sites More sharing options...
b61mack Posted April 9, 2011 Share Posted April 9, 2011 Hi,Thanks for your response!Can I change the diff ratio centres to say 4.17 with only changing the centres and not the housing? They are 44,000lb.So we have 3.54 in there at the moment. What gearbox would be best to go behind it to get up to 70mph/100kph+.Or would you change your centre? Which do you change...centres or gearbox to get more speed?I have never seen 3.54 in an older R model, if you have 3.54 already installing 4.17 would be slower. i have a B61 with 300+ 13 speed overdrive roadranger 3.87 on hi tread 11-22.5 running 2200rpm will run 80 mph. what transmission do you have in it, tire size. Ron Quote Link to comment https://www.bigmacktrucks.com/topic/18660-r-model-diff-housing/#findComment-75749 Share on other sites More sharing options...
slpwlker Posted April 9, 2011 Share Posted April 9, 2011 I'm running 4.11's with an 18 on 11 24.5 rubber it will run mid 90's I'd leave the 3.54's if you want to cruise. It should run if thats what your looking for. Quote Link to comment https://www.bigmacktrucks.com/topic/18660-r-model-diff-housing/#findComment-75753 Share on other sites More sharing options...
Lmackattack Posted April 9, 2011 Share Posted April 9, 2011 somethings seams odd here?a direct drive trans is 1:1 ratio. put 11R22.5 tires / 4.17 diffs behind it and you will be at 62 MPH at 2100RPMthis tells me that if you had a 1:1 trans with your current 3.54 diffs you should already be at 71 MPH at 2100RPMI may be wrong but I have never seen a truck trans that was slower than 1:1? not saying it was never done but...3.54 rears are kinda fast, for example if you had a .78 OD trans (over drive trans) and the same tires and diffs you would be at 100 MPH at 2100RPM.Trent Quote Link to comment https://www.bigmacktrucks.com/topic/18660-r-model-diff-housing/#findComment-75761 Share on other sites More sharing options...
slpwlker Posted April 9, 2011 Share Posted April 9, 2011 somethings seams odd here?a direct drive trans is 1:1 ratio. put 11R22.5 tires / 4.17 diffs behind it and you will be at 62 MPH at 2100RPMthis tells me that if you had a 1:1 trans with your current 3.54 diffs you should already be at 71 MPH at 2100RPMI may be wrong but I have never seen a truck trans that was slower than 1:1? not saying it was never done but...3.54 rears are kinda fast, for example if you had a .78 OD trans (over drive trans) and the same tires and diffs you would be at 100 MPH at 2100RPM.Trent it could be all trans for him like you said. if that is right unless he has a direct that truck should roll out mid 90's to say the least Quote Link to comment https://www.bigmacktrucks.com/topic/18660-r-model-diff-housing/#findComment-75765 Share on other sites More sharing options...
David Posted April 9, 2011 Share Posted April 9, 2011 Are you sure it's a 3.54? I've never seen that ratio before. Quote Link to comment https://www.bigmacktrucks.com/topic/18660-r-model-diff-housing/#findComment-75766 Share on other sites More sharing options...
slpwlker Posted April 9, 2011 Share Posted April 9, 2011 IDK if it is right but could it be 8.54? just can't see the other half Quote Link to comment https://www.bigmacktrucks.com/topic/18660-r-model-diff-housing/#findComment-75767 Share on other sites More sharing options...
rhasler Posted April 9, 2011 Share Posted April 9, 2011 My carrier chart, which is kind of old, shows the fastest ratio at 3.65, the slowest at 9.15. The only one in the 8's is 8.24 Quote "Mebbe I'm too ugly and stupid to give up!" Link to comment https://www.bigmacktrucks.com/topic/18660-r-model-diff-housing/#findComment-75771 Share on other sites More sharing options...
Rob Posted April 9, 2011 Share Posted April 9, 2011 My R model with a single over 13 speed on 11RX24.5 tires and 3.87 rears will bury an 80 mph speedometer but I don't know how fast it will run wide open. Rob Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/18660-r-model-diff-housing/#findComment-75785 Share on other sites More sharing options...
kahall82 Posted April 9, 2011 Author Share Posted April 9, 2011 OK looks like I don't have 3.54 in my rear housing from the sounds of what everyone is saying.The truck has a 5 spd box and the max speed we got it up to before we pulled her off the road was 70kph!Guess we will have to crack her open to see what is in there! Quote Link to comment https://www.bigmacktrucks.com/topic/18660-r-model-diff-housing/#findComment-75788 Share on other sites More sharing options...
fifth wheel Posted April 9, 2011 Share Posted April 9, 2011 Hi all,I have the numbers "354" imprinted on my rear diff housing. What does this mean? Does it mean what centres are in it?The numbers on the rear of the sumps are the models such as SWD 573, SWD* 574 etc.The carrier housings have the numbers on the right front, model and ratio etc.Most drop-ins will interchange,and I am sure 3.65 is the fastest. And you don't have to go in to check ratio, roll the truck and piece of chalk will do it.Just trying to help.FW Quote Link to comment https://www.bigmacktrucks.com/topic/18660-r-model-diff-housing/#findComment-75789 Share on other sites More sharing options...
b61mack Posted April 9, 2011 Share Posted April 9, 2011 OK looks like I don't have 3.54 in my rear housing from the sounds of what everyone is saying.The truck has a 5 spd box and the max speed we got it up to before we pulled her off the road was 70kph!Guess we will have to crack her open to see what is in there!I bet you have 3.87 if you can run close to 68-70 mph, 4.17 and 3.87 were common that era. Quote Link to comment https://www.bigmacktrucks.com/topic/18660-r-model-diff-housing/#findComment-75790 Share on other sites More sharing options...
Lmackattack Posted April 9, 2011 Share Posted April 9, 2011 yea. 4.17 would put you in the low 60 MPH depending on tires. 3.87 got you up to the 68-70 MPH mark. Most macks with the 5 speeds pulled better with 4.17s but some of the OTR guys put the 3.87 in to get the faster road speed and lower RPMs Quote Link to comment https://www.bigmacktrucks.com/topic/18660-r-model-diff-housing/#findComment-75799 Share on other sites More sharing options...
leversole Posted April 9, 2011 Share Posted April 9, 2011 Hi all,I have the numbers "354" imprinted on my rear diff housing. What does this mean? Does it mean what centres are in it?The diffs I have seen have the ratio stamped on the machined plate on the front side as shown below, also, it should read #.##, the ratio with the decimal point, such as 4.42, or 5.73 (like mine!) Quote Link to comment https://www.bigmacktrucks.com/topic/18660-r-model-diff-housing/#findComment-75827 Share on other sites More sharing options...
spud Posted April 23, 2011 Share Posted April 23, 2011 kahall are you in austrailia of kiwi land? Quote Link to comment https://www.bigmacktrucks.com/topic/18660-r-model-diff-housing/#findComment-76531 Share on other sites More sharing options...
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