Reversed Transfer Case for Overdrive?????
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FTE Chapter Leader
Joined: Dec 2001
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From: Crossville, Tn
Reversed Transfer Case for Overdrive?????
I have seen a few post about using a transfer case backwards to act as an overdrive unit. This sounds like something that I may want to try someday, but I am a moron about the whole concept. On my F-5 I realize that it would have to be a custom install and I would have to do a certain amount of fabrication work, and probably have new drive shafts made for it.
There are a lot of them available in the junkyards, but are there only specific ones that would work? I've seen the NP205's from $400 -$1000+ and was wondering what other units might work. Being as this truck is NOT hauling loads (other than my fat butt) and I'm not looking to go 80 miles an hour, if I could at least get the truck up to 55 for very short runs on the Interstate, I would be happy.
There are a lot of them available in the junkyards, but are there only specific ones that would work? I've seen the NP205's from $400 -$1000+ and was wondering what other units might work. Being as this truck is NOT hauling loads (other than my fat butt) and I'm not looking to go 80 miles an hour, if I could at least get the truck up to 55 for very short runs on the Interstate, I would be happy.
Fleet Owner
Joined: Jul 2004
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From: NM
I've heard of doing this with certain divorced xfer cases. I'd be concerned that the thrust bearings wouldn't be adequate for full-time, full-torque reverse operation, but I don't know how they are built inside. One with a chain would seem to have less potential for problems.
Cargo Master
Joined: Aug 2010
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From: Houston
Have you investigated the high speed options available new in your truck? There were optional two speed rear axles. These don't bring much money at junk yards since nobody is looking for them. The other option may be to get the higher speed axle from an F-4. Check the shop manual, it has a very nice chart in the back on axle ratios and tire sizes.
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FTE Chapter Leader
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From: Crossville, Tn
Have you investigated the high speed options available new in your truck? There were optional two speed rear axles. These don't bring much money at junk yards since nobody is looking for them. The other option may be to get the higher speed axle from an F-4. Check the shop manual, it has a very nice chart in the back on axle ratios and tire sizes.
According to the manual, the F4/F5 options were 5.33 or 5.14, the F5/F5Coe was 6.66, I'm not sure which one I have, but there isn't a real big difference between those. As for the 2 speeds, as offered in the F6, they were 5.83-8.11 and 6.33-8.81, as I said, lower rather than higher.
I don't see the chart you're talking about in the manual.
Cargo Master
Joined: Aug 2010
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From: Houston
The manual I am referring to is the 49-51 Ford Truck Shop Manual, with a red cover. The back of this manual has specification charts, and the first one is a page size table of tire and axle options.
The difference in the axle ratios is actually pretty large. I assumed a 34.5 in diameter tire, which should be about a 6.50-20 tire. This gives approximately 584 revs per mile. The r.p.m. at 55 miles per hour for each option is then:
ratio-----r.p.m.
5.14-----2754
5.33-----2856
6.66-----3568
5.83-----3124
8.11-----4346
6.33-----3392
8.81-----4721
As you can see, there is a large difference in r.p.m. between the 5.14 axle and the 6.66 axle. The 5.83 two speed is still quite a bit better than the 6.66 single. It is worth checking what ratios you own. I don't think you want your engine spinning much slower than 2750, you need the power to push that tall truck.
You can also scrounge up the parts to install a Brown-Lipe over-under auxiliary transmission in your truck. I have seen several of these on E-bay over the years, and I think there is a guy who advertises rebuilt units in Hemmings.
The difference in the axle ratios is actually pretty large. I assumed a 34.5 in diameter tire, which should be about a 6.50-20 tire. This gives approximately 584 revs per mile. The r.p.m. at 55 miles per hour for each option is then:
ratio-----r.p.m.
5.14-----2754
5.33-----2856
6.66-----3568
5.83-----3124
8.11-----4346
6.33-----3392
8.81-----4721
As you can see, there is a large difference in r.p.m. between the 5.14 axle and the 6.66 axle. The 5.83 two speed is still quite a bit better than the 6.66 single. It is worth checking what ratios you own. I don't think you want your engine spinning much slower than 2750, you need the power to push that tall truck.
You can also scrounge up the parts to install a Brown-Lipe over-under auxiliary transmission in your truck. I have seen several of these on E-bay over the years, and I think there is a guy who advertises rebuilt units in Hemmings.
Thread Starter
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FTE Chapter Leader
Joined: Dec 2001
Posts: 3,636
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From: Crossville, Tn
The manual I am referring to is the 49-51 Ford Truck Shop Manual, with a red cover. The back of this manual has specification charts, and the first one is a page size table of tire and axle options.
The difference in the axle ratios is actually pretty large. I assumed a 34.5 in diameter tire, which should be about a 6.50-20 tire. This gives approximately 584 revs per mile. The r.p.m. at 55 miles per hour for each option is then:
ratio-----r.p.m.
5.14-----2754
5.33-----2856
6.66-----3568
5.83-----3124
8.11-----4346
6.33-----3392
8.81-----4721
As you can see, there is a large difference in r.p.m. between the 5.14 axle and the 6.66 axle. The 5.83 two speed is still quite a bit better than the 6.66 single. It is worth checking what ratios you own. I don't think you want your engine spinning much slower than 2750, you need the power to push that tall truck.
You can also scrounge up the parts to install a Brown-Lipe over-under auxiliary transmission in your truck. I have seen several of these on E-bay over the years, and I think there is a guy who advertises rebuilt units in Hemmings.
The difference in the axle ratios is actually pretty large. I assumed a 34.5 in diameter tire, which should be about a 6.50-20 tire. This gives approximately 584 revs per mile. The r.p.m. at 55 miles per hour for each option is then:
ratio-----r.p.m.
5.14-----2754
5.33-----2856
6.66-----3568
5.83-----3124
8.11-----4346
6.33-----3392
8.81-----4721
As you can see, there is a large difference in r.p.m. between the 5.14 axle and the 6.66 axle. The 5.83 two speed is still quite a bit better than the 6.66 single. It is worth checking what ratios you own. I don't think you want your engine spinning much slower than 2750, you need the power to push that tall truck.
You can also scrounge up the parts to install a Brown-Lipe over-under auxiliary transmission in your truck. I have seen several of these on E-bay over the years, and I think there is a guy who advertises rebuilt units in Hemmings.
As I said in my original post, I'm a moron at this, so i have no idea how you got the figures for the engine rpm at 55mph, especially since my truck won't go 55mph.
Phantom of the Phorum
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More Turbo
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From: Cincinnati, OH
A transfer case ran backwards will be a *very* tall overdrive. Most transfer case are in the 2.0 range reduction, so that means it would be a 0.5 OD ratio.
You would be better to get a real OD unit, either an old BW 3-speed with the OD or an add-on unit.
You would be better to get a real OD unit, either an old BW 3-speed with the OD or an add-on unit.
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Thread Starter
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FTE Chapter Leader
Joined: Dec 2001
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From: Crossville, Tn
Thanks EffieTrucker. I guess what I really need to find out is which ratio I actually have. Based on 38 coupe's info, if I could find the 7 tooth pinion and the 36 tooth drive gear,(the 5.14 setup) that would make enough of a difference for me. From the looks of the cases, I would probably have to pull the rear end out of the truck to change them.
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FTE Chapter Leader
Joined: Dec 2001
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From: Crossville, Tn
Well, I'm still pretty confused here. Scarped and wire brushed the rear end housing looking for numbers and hopefully the axle ratio.
on two spots I found metal tags stamped 0160 (one on the right case and one on the left) and stamped in the left Case was BB (could be 88) 4182C.
Any ideas?
on two spots I found metal tags stamped 0160 (one on the right case and one on the left) and stamped in the left Case was BB (could be 88) 4182C.
Any ideas?
Cargo Master
Joined: Aug 2010
Posts: 2,927
Likes: 135
From: Houston
Your best bet on axle ratios is to jack one side up and count revolutions. Spin the rear wheel twice (because of the spider gears) and count the number of times the drive shaft spins. It helps to put a chalk mark on things.
Thread Starter
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FTE Chapter Leader
Joined: Dec 2001
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From: Crossville, Tn
Well, I talked to Bill (number dummy) and he said there should be a tag on the rear end. I have scraped and wire brushed the whole thing down to bare metal and no luck. He also told me that my truck has the Ford/Timken B150 rear end, so the gearing is either 5.14 or 5.83. I never really pushed this truck before, I guess with the noise from the broken exhaust manifold, when it got so loud, I just backed off. Before today, I never had the truck over 42 mph. O took it out on the state hwy today and actually had it over 50. I'm sure I have the 5.83 gears in it, but I will take your advice and jack it up and figure it out someday when I have a helper nearby.
Fleet Mechanic
Joined: Aug 2009
Posts: 1,771
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From: Western Washington
Now this is interesting, I've heard of transmissions being turned around and used as overdrive gearboxes, but hadn't though of using a transfer case. If anyone here has done it, can you shift into over-drive while moving, or do you have to be stopped to get into it?
It's a neat idea, but I think I'm sold on the idea of using a second four speed, just turned around and put behind the main box. You'd get 16 selections using that! Think about it, granny on the auxillary box would turn into a VERY steep overdrive, as would the other gears (except 4th, it'd still be 1:1) Of course, a few of those ratio combo's would be the same, but still, you could give those 5-speeders a serious case of gear envy! Just don't tell them how much shifting you'd have to do.
One forum member has actually done it: https://www.ford-trucks.com/forums/5...ed-w-3-od.html
Sam
It's a neat idea, but I think I'm sold on the idea of using a second four speed, just turned around and put behind the main box. You'd get 16 selections using that! Think about it, granny on the auxillary box would turn into a VERY steep overdrive, as would the other gears (except 4th, it'd still be 1:1) Of course, a few of those ratio combo's would be the same, but still, you could give those 5-speeders a serious case of gear envy! Just don't tell them how much shifting you'd have to do.
One forum member has actually done it: https://www.ford-trucks.com/forums/5...ed-w-3-od.html
Sam
Elder User
Joined: Jun 2008
Posts: 694
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From: Vashon, WA
Now this is interesting, I've heard of transmissions being turned around and used as overdrive gearboxes, but hadn't though of using a transfer case. If anyone here has done it, can you shift into over-drive while moving, or do you have to be stopped to get into it?
So far it's worked fine for what I need.
Fleet Mechanic
Joined: Aug 2009
Posts: 1,771
Likes: 9
From: Western Washington
Nice job, very professional looking! I'm looking forward to that build thread..
I wonder, could you still use the PTO port on the transfer-case? I was thinking it's rotation would be reversed, but I don't know enough about PTO systems to know if it would make it unusable or not.
Sam
I wonder, could you still use the PTO port on the transfer-case? I was thinking it's rotation would be reversed, but I don't know enough about PTO systems to know if it would make it unusable or not.
Sam