Mack Rears

[b61mack]

I have a 72 R model it came with 3.86 rears, i have a 76 and a 77 with 3.87, i was wandering why they stopped making 3.87 and went back to 3.86 , are the 3.86 better than the 3.87. thanks Ron

[mackcl96]

I have a 72 R model it came with 3.86 rears, i have a 76 and a 77 with 3.87, i was wandering why they stopped making 3.87 and went back to 3.86 , are the 3.86 better than the 3.87. thanks Ron

Ron,

3.86 are just fine but mack found the 3.87 to more durable. I thought 3.87s came in the 1980s

4.64 and 5.02 etc are bullit proof

Jim

[David]

Mack's theory is slow rears and fast transmissions. This allows for lighter drive shafts and longer life from the rears.

[therabbittree]

so your saying most macks have heavy overdrive ratios in the trannies and really low rear gears?..ie 4:30 plus..?..many of the r moels i have driven't maxed out 45-50 if i was lucky but they were dm and rm.. mummn the only "fast " ones i've seen were new ch or cls... I think my B81 has 5.50 or low rear gears and quad box..i guess 50 mph is about all i'd get..i would leik to try some 4;30 or sos but i think with 58k rears 460 or so is the highest you can go?..any idea. what about 65k rears how high can the ratio go?..... how much overdrive does a 20speed quad box have in it?.

Thanks

Deo

[Lmackattack]

I think what David is saying is that if you have a "slow" 5.73 rear ratio with a double overdrive trans you get a bullet proof drive train. Top speed is not the objective.

It was explained to me that the "slow" ratio rear ends have more teeth on the ring and pinion to spread the power across more aera.. also a faster spinning drive train (to an extent) will allow for smoother starts under large heavy loads.

Over the road trucks can get away with a low 3.55 rear ratio and a overdrive trans becase they dont get down in the mud like dirt trucks.

that sound right david??

Trent

[rsmartyn]

I think what David is saying is that if you have a "slow" 5.73 rear ratio with a double overdrive trans you get a bullet proof drive train. Top speed is not the objective.

It was explained to me that the "slow" ratio rear ends have more teeth on the ring and pinion to spread the power across more aera.. also a faster spinning drive train (to an extent) will allow for smoother starts under large heavy loads.

Over the road trucks can get away with a low 3.55 rear ratio and a overdrive trans becase they dont get down in the mud like dirt trucks.

that sound right david??

Trent

Don't know about David but I'd say you hit the nail right on the head with that reply. Bob

[David]

Trent, I agree. We had a local brick manufacturer with 4.17 rears in pit trucks. They were always tearing up ring and pinions. After switching to 4.42 and 4.64 rears there problems disapeared. Of course they would be slow as hell on the road, but they never went out of the pit. You can have the best of both worlds ( slow rears and good road speed) with a fast transmission. When making a comparisson, if you multiply the high gear ratio of the trans by the rear ratio you get a final drive ratio. So you can see how you can reduce the rear end speed, increase the trans speed and keep the same top end speed with acceptable rpm's. In the 70's we saw a lot of 6 sp directs (1.00 to 1) and 4.17 rears. Thats a final drive ratio of 4.17 (1.00 X 4.17). With the T2090, 9sp (.71 overdrive) you can run 5.73 rears and be slightly faster (.71 X 5.73=4.07) than the direct with 4.17's. The 9 speeds I have (or have had) came with 5.02, 4.64 or 4.42 rears. That's final drives of 3.56, 3.29 and 3.14 respectively and never any rear problems with on /off road use. The Mack T200 5, 6, 7 and 8 speeds are even faster transmissions (overdrive ratio of .6 to 1) That means the engine turns 6 tenths of 1 rev for each full turn of the driveshaft or another way of looking at it is the driveshaft is turning 167% faster than the engine. I think these are the fastest transmissions on the market. You can run 5.73 rears and still have a final drive ratio of 3.44. Now you know why I'm looking at putting a T2050 behind a 2 stick direct. I don't know the ratios of the quad boxes but they were posted on another website at on time. I'll see if I can find that list.

[therabbittree]

mumn thats explained it well..i understood the idea..but i didn't know macks were speced this way inparticular.

cool

thanks

Deo

[Lmackattack]

just wondering a little here....why does mack say to only use "low low" in the first gear position? could you just use a T200 6 speed trans in the low range(1-5) and then flip it to "direct" to get that hwy gear? got to thinking again about your "new idea" Dave, and it makes perfect sence now..

If I had a 2050 I would have a huge final drive... .60 x 4.17 = 2.5 final drive!!!!LOL

thats over a 100 mph at 2300RPM HA ha.. little to fast but would be nice

here is that link with the info on B model transmissions ratios etc...

http://www.oldmacksrus.com/trannys.htm

Trent

[David]

Trent,

You could cruise to truck shows at 70 mph and only be turning about 1600 rpm. A T2050 is an easy find. I have 2 I can't give away. They only weigh 468 lbs. and don't bring much for scrap.

[therabbittree]

hey did you save that link to the tranny info before the web page stopped working?..every time I try to go to www.oldmacksrus.com and go to info area, it has only a empty box with a red x in it next to the b model stuff. ie cab info, trans inf etc..if you click on the empty box no info comes up. The only info I am able to read is the photos page, and the links page...the link you posted above works ..but I don't know why it works..as I used to visit that page often, a few years back..i wanted to look up stuff for my mack and was upset when it wouldn't work. I figured that the web page was down...but when you posted a link that works,.. I scratched my head..any one know if its down or what?

Thanks

Deo

[Truck1536]

hey did you save that link to the tranny info before the web page stopped working?..every time I try to go to www.oldmacksrus.com and go to info area, it has only a empty box with a red x in it next to the b model stuff. ie cab info, trans inf etc..if you click on the empty box no info comes up. The only info I am able to read is the photos page, and the links page...the link you posted above works ..but I don't know why it works..as I used to visit that page often, a few years back..i wanted to look up stuff for my mack and was upset when it wouldn't work. I figured that the web page was down...but when you posted a link that works,.. I scratched my head..any one know if its down or what?

Thanks

Deo

Page worked fine for me at 1:40pm

[Lmackattack]

sence on topic what are the full range ratios for the T200 sieres trans

..........Edit..

found a book tonight at the shop with many diffrent trans ratios

[Superdog1986]

Trent, I agree. We had a local brick manufacturer with 4.17 rears in pit trucks. They were always tearing up ring and pinions. After switching to 4.42 and 4.64 rears there problems disapeared. Of course they would be slow as hell on the road, but they never went out of the pit. You can have the best of both worlds ( slow rears and good road speed) with a fast transmission. When making a comparisson, if you multiply the high gear ratio of the trans by the rear ratio you get a final drive ratio. So you can see how you can reduce the rear end speed, increase the trans speed and keep the same top end speed with acceptable rpm's. In the 70's we saw a lot of 6 sp directs (1.00 to 1) and 4.17 rears. Thats a final drive ratio of 4.17 (1.00 X 4.17). With the T2090, 9sp (.71 overdrive) you can run 5.73 rears and be slightly faster (.71 X 5.73=4.07) than the direct with 4.17's. The 9 speeds I have (or have had) came with 5.02, 4.64 or 4.42 rears. That's final drives of 3.56, 3.29 and 3.14 respectively and never any rear problems with on /off road use. The Mack T200 5, 6, 7 and 8 speeds are even faster transmissions (overdrive ratio of .6 to 1) That means the engine turns 6 tenths of 1 rev for each full turn of the driveshaft or another way of looking at it is the driveshaft is turning 167% faster than the engine. I think these are the fastest transmissions on the market. You can run 5.73 rears and still have a final drive ratio of 3.44. Now you know why I'm looking at putting a T2050 behind a 2 stick direct. I don't know the ratios of the quad boxes but they were posted on another website at on time. I'll see if I can find that list.

in my new superliner i hav 4.64s and a 9sp transmission and i can pull at 80mph i dont know why but its not slow but its nothin compared to my other superliner with 4.17s a 12sp and the e9-500

Chad

[mudslut28]

Remember the slower (higher number) the rears the stronger the gears....

[maxidyne237]

trent i dont anyone who ever payed attention to the "only use low in first" decal in trucks with six speeds. I even know guys who would split them like a duplex, (even though there isnt any gain) they are bulletproof. The best way i have found to shift a six speed is 1st through third in low, then wind out third and shift aux into high and proceed into 4th and 5th. hope i wasnt too off topic

[Lmackattack]

Not of topic my friend, thats what the message board is for!!!

funny you bring that up because thats how I like to shift the 6 spd if I ever need the low hole on the street. (i.e hill)makes the progressive shift RPMs closer and gets the truck rolling to a faster pase to grab direct in the aux box. Just wondered if there was a reason other than "close over laping" ratios.

Trent