4.17 Gears Behind A Quad Box

[fordguyhey]

I'm putting together a B75T and I really want to make it a tandem truck. I have the opportunity to buy a set of 38k rears with 4.17:1 gears at a decent price. I also have an older 285/237 maxidyne with TRQ7210 quadbox in the truck. I'm wondering if anyone else has run a setup similar to this. I know I won't be using overdrive very often with those gears, but I'm also wondering if I'll be frying the clutch trying to get moving on the low end. Its not very nice for the tranny to shift from 1stLL to 1stLo split because the jump is huge, I've done it in other B models but I don't think I want to be doing it every time.

[ThaddeusW]

I'm putting together a B75T and I really want to make it a tandem truck. I have the opportunity to buy a set of 38k rears with 4.17:1 gears at a decent price. I also have an older 285/237 maxidyne with TRQ7210 quadbox in the truck. I'm wondering if anyone else has run a setup similar to this. I know I won't be using overdrive very often with those gears, but I'm also wondering if I'll be frying the clutch trying to get moving on the low end. Its not very nice for the tranny to shift from 1stLL to 1stLo split because the jump is huge, I've done it in other B models but I don't think I want to be doing it every time.

Doubt you are going to fry the clutch if you are gentle with it. Are you going to load it or just bobtail around to shows? If bob-tailing you should not worry. If loaded just take your time and shift gently. A 285 has allot of Torque, something like 1050 ft/lbs Vs. the 237's 820 ft/lbs. So maybe sticking with a 237 will be better for the Quad and will make installation easier.

[Lmackattack]

you will be fine if you drive it the right way. if the quad is double overdrive you will have a geared top speed of around 100MPH tho LOL

[fordguyhey]

I plan on using the truck to haul mostly antique tractors but realistically I can't see myself hauling much over 10 to 15 tons. And yes I know it will probably do over 100mph in 5th but i guess to avoid speeding tickets I won't be using 5th very often. LOL

[Superdog]

I plan on using the truck to haul mostly antique tractors but realistically I can't see myself hauling much over 10 to 15 tons. And yes I know it will probably do over 100mph in 5th but i guess to avoid speeding tickets I won't be using 5th very often. LOL

My B-83 wrecker has 4:17's behind a double over Triplex,and is on 11R24.5 rubber.In 5th direct at 1700 rpm I had it up to 107 mph according to the car I had following me.It's geared way,way too fast,even in low it's geared too fast,making it very hard to use.The lo-lo of a quad would help a bunch,I'm sure,but I couldn't tell you how much.

[vanscottbuilders]

You should do a little math and get the real numbers, if you haven't already.

Go to a gear ratio calculator online and plug in the required data - tire diameter, max rpm and final drive ratio to get the top speed.

Then run a calculation at 1,650 rpm or so, for a nice cruise engine speed, to see what you have.

Running around 70 mph at 1,650 is a real nice, easy cruise.

I think the TRQ-7210 is a .69 overdrive, which gives you a 2.88 effective final drive with the 4.17 rears,

probably way too fast as Mike has said earlier. Excellent for going downhill though.

Would you consider trading with someone for a single over triplex or quadraplex?

The 4.17 rear gears are great with a single overdrive Mack transmission with a .86 or so overdrive, for a 3.58 effective final drive in high gear.

I'm sure there are a lot of guys who could use the double-over box.

Keep us posted,

Paul Van Scott

[Rob]

I have figgered out that my B67 has 5.73 rears and a single overdrive duplex transmission. This truck in low range still backs too fast for my comfort level. If the truck is at idle and in reverse, I'll bet it will mosey along about 2-3mph. I'm sure a 4.17 ratio would be much too fast and be hard to start a loaded trailer at 10 tons.

Rob

[Lmackattack]

his only saving grace is that he has a maxidyne to pull the now faster low gears. I think even at 10 tons he may be safe in the LO LO range of a quad even in slight off road conditions. We need to figure out what a 5/6 speeds first gear is with 4.17s and compair it to his first gear with a quad and 4.17.

I dont have ratios handy to compare

[Rob]

his only saving grace is that he has a maxidyne to pull the now faster low gears. I think even at 10 tons he may be safe in the LO LO range of a quad even in slight off road conditions. We need to figure out what a 5/6 speeds first gear is with 4.17s and compair it to his first gear with a quad and 4.17.

I dont have ratios handy to compare

I don't have ratios either but it sure seems that anywhere from 8.5, to 11:1 reduction ratio is common in low gear without extra low reduction.

Rob

[Lmackattack]

looks like the TRQ7220 has a 13.8ratio in the lowest forward gear 1st LO LO and 6.52 1st low split.

a quick search here found an old thread by "block" with this message

" Mack made 2 different 2 stick 6 speed Transmissions. the first one part number TRXL 107 had the following gear ratios. Low range 14.10 in first, 8.20 in second, 4.65 in third, 2.72 in fourth, and 1.64 in fifth. High range as follows 8.59 in first, 4.99 in second, 2.84 in third, 1.66 in fourth, and 1.00 in fifth. And the following ratios in reverse. 36.66 in first, 21.32 in second, 12.11 in third, 7.07 in fourth, and 4.27 in fifth. The second was part number TRXL 1071 The gear ratios in low range are as follows 23.08 in first, 13.42 in second, 7.62 in third, 4.45 in fourth, and 2.69 in fifth. The gear ratios in high range and reverse were the same in both transmissions. There were also air shift verisions of both transmissions part numbers TRXL 107A and TRXL 1071A. Hope this helps out Blocl"

looks like the quad with 4.17 rears in 1st LO LO would crawl at 3-4MPH at full throttle? a 6 speed in LOW LOW 1st is 3-4 mph also. At that point I would be more concerned at the stress the trans would see in that gear with the maxidyne.

Ok I did my part. we need solid numbers to move forward... Who is good at math LOL!!!

Trent

[HK Trucking]

If it was mine I'd leave the quad box as is, and swap out the 4.17 diffs for a set of 5.73's, and set it up so it'll work the right way.

[Freightrain]

I working on a similar project, but I'm going with 4.10 gears and my single OD Triplex. I agree, even with my 4.62 gear now, it's kinda fast in Reverse. It will be worse with the change to 4.10.

With my 14K trailer, I usually start in 2nd LO(very easily), but likely need 1st LO with the change out back. With the added length in my frame a Brownie would really be an asset giving me a deep first when needed. THREE sticks......Ya boy!