midship overdrive for 7.3 & allision auto trans

[mf8n]

I have a 1993 7.3 non turbo with a 545 allision 4 speed automatic trans. I have contacted us gear and gear vendors they do not have an overdrive for this transmission. does anyone know of a midship overdrive that i could use?

[fish36991]

I thought gear vendor units worked on anything...you just have to have the adapters and shorten the drive shaft. I don't know how hard it would be to have the adapters built your self. I know they're selling GVs on Ebay for way less and they're brand new (so the ad says) but if they're not, they're pretty bulletproof anyway unless you're turning 1000+ HP. If you save money using ebay, you may be able to afford custom adapters. Just a thought,

Josh

[huskyhauler]

if i was going to do it. the gear vendors really would not be my choice. to much hydraulic-electric dependency. i would really choose a us gear unit. they come in both a true overdrive OR underdrive. the gear vendors is really just an overdrive(25%). the us gear is a good old fashion auxillary gear box, and you can underdrive or overdrive any gear at ANY speed (by 25% 4.10 become 5.15, or 3.09, etc). yes the GV will overdrive any gear over 28 mph, but most of the time an underdrive is what you want while towing. it will eliminate the spot between 2nd and 3rd (or 3rd and 4th). you know that point between where 3rd is to slow, and 2nd is to high. the allison i believe is rated at 36k lbs, it is the same unit my father has behind his 32' deisel pusher 5.9l. i will need to pull my book out on it, but i am going to guess that the number is right. the gear vendors and us gear are both rated around 35k, which would not meet the specifications of the tranny. neither company makes one for the allison. your best option might be to place a 3 speed "brownie box" in. this will give you underdrive (1st gear) direct drive (2nd gear) and overdrive (3rd gear)all in one unit. this would be my choice if i was to run one. the old brownie boxs are a self contained divorced auxillary transmission similar to a divorced transfer cases of the olden days. a good used one will run you in the $750-1500 range, but will run circles around both the US Gear as well as the GV. keep your eyes on ebay, and you can find the LD and MD units with the 1350 u joint in the $400-500 range. or call around to the local heavy equipment salvage yards and ask about a light duty or medium duty brownie box with the small u joints. most yards are more than willing to help, as there is no longer a call out for them. most are taking up good shelf space. in the days far gone, it was the only way to make those old N/A big diesels go down the road faster than 35. now with electronics in the diesel, turbos and all the other goodies, there is no call out for more than 9 forward gears. think about having 30 forward gears [img]/ubbthreads/images/graemlins/shocked.gif[/img] in an old 10 speed road ranger, now thats a shifting nightmare!!

[mf8n]

thanks for the info. this sounds like the way to go, i do have a couple of questions what is the difference in the LD and MD units? and also you said the small u joint, is the 1350 the small one? do you know what % over is?

thanks again you are the first person that had any answers

[EDWARDWD]

Saw a 10-Speed RR replacing a plain 5-speed that had a 3-speed twin screw. Now what gear am I in????
EDWARD

[huskyhauler]

most of the ld units had the 1350 or 7290 joints. some of the md units had the same, and others had the mid size spicer joints (cant recall the numbers). i would take what i could find, and have the driveshaft built around the joints. the rear will have to be shortened, so place a new yoke there with the correct size for the output of the brownie. the front shaft (trans to brownie) take the old yolk of the front half of the shaft and place it there. if you find one in a salvage yard, look for the smallest joints, and try to find an old driveshaft to go with it. this will save you on the 2 yokes you will need. the drive shafts will run you around $300-500 built and balanced. still cheaper than the GV units. as for the OD and UD it depends on the box. i have seen them as low as 100% and as high as 20%, depends on the box. also there are two types made, the manual shift units, and air shift units. easy to figure which is which. either will shift like a US Gear box. heavy throttle, back off, shift, will take a bit to get use to it, but will do you fine once you get it figured out. i have seen the air shift boxs in non air brake trucks, they usually run a small 12v compressor, a 90 psi switch, and a small air tank. keeps the pressure at 90 and you have a storage unit for frequent shifting. unit needs at least 65 psi to shift, or at least thats what the air solenoids in the RR need to shift. the box you are looking for is a 5831 spicer. thake a look at www. 6066gmcguy. org/spicer-5831-b.htm . just remove the spaces, and it should work. type in 5831 spicer, and you will see alot of info on these boxs. they are real popular units, and millions were made. for some reason they got popular with the LD trucks. neater than a GV or US Gear unit. hees one for sale "74 Ford rear end, 3/4 ton, 4.10 ratio, $200; 5831 Spicer Brownie gearbox, 3 speed, $700; 73-80 Chev PU or Blazer 1/2 ton rear end, 4.10 ratio, $200; LW pickup toolbox, indestructible, 1/8” steel, sliding drawer, lockable, $170. 505-281-2288." heres another link to an outfit that has them www. classicantiquetrucks.com/Engines_trans. html

[aceohearts]

[ QUOTE ]
now with electronics in the diesel, turbos and all the other goodies, there is no call out for more than 9 forward gears. think about having 30 forward gears in an old 10 speed road ranger, now thats a shifting nightmare!!


[/ QUOTE ]

I'll have to disagree with you. My truck has a 10 spd and the previous one I drove had a 13 spd. I really miss my overdrive gears, especially when I'm climbing hills. Sometimes that 500 rpm shift is a little too much if you're loaded heavy.

[huskyhauler]

yeah, the older guys do miss the twin sticks, or lots of gears. give a newbie anything but a super 10, and he is lost. give him an old mac with a twin stick, and he is likely to shoot himself dead before hitting the key. you have to admit though, the new cummins l10 stock will outperform an old "small cam 855 na", and nearly outpull an old 375hp big cam. that was the biggest reason for having lots of gears. a few under, and a few over. now a days, most driver have not a clue what to do with 13 gears let alone 39 or 52 in the 4 speed brownie boxs. remember those. double under, 2.0-1 in low-low , 1.55 in low, 1.0 direct, and .87 in od, couple that with a RR 13 speed, and you got your self hornests nest of gears. yikes, that would even confuse me...

[aceohearts]

I'm not THAT old school...LOL But I do like a few half gears in the mix. Give a good strong 13 or 18 any day. Better yet, I'll be happy to trade anyone my perfectly good 10 spd Autoshift for the 18spd Autoshift... [img]/ubbthreads/images/graemlins/biggrin.gif[/img]