Auxiliary Trans aka Brownie

[Michael Dimock]

Have been looking at different alternatives to get more out of my travelette and am interested in what y'all think of an auxiliary transmission. I have a 73 1310 travelette 2wd with a 4.88 Dana 70 rear end, 304, and a 727 automatic. I'm turning 3000 rpms at 55 and 2nd is just really geared too low. So I've been doing some searching in my newly acquired free time and have been pondering about 3 speed brownies: under/1:1/overdrive. Since I'm 2wd, driveline issues won't be a problem. The one thing that is a cause for concern is the amount of power the brownie will rob from the engine. With a .73 overdrive my 4.88's will become 3.56 gears which will be significantly better on fuel economy. I'll be doing about 2300 rpm's at 55 instead of 3000. I'm not worried at all about fabricating mounts and know that I will have to modify the drivelines. Besides that, what are your opinions? Yay/nay?

 

[stu simpson]

have been looking at different alternatives to get more out of my travelette and am interested in what y'all think of an auxiliary transmission. I have a 73 1310 travelette 2wd with a 4.88 Dana 70 rear end, 304, and a 727 automatic. I'm turning 3000 rpms at 55 and 2nd is just really geared too low. So I've been doing some searching in my newly acquired free time and have been pondering about 3 speed brownies: under/1:1/overdrive. Since I'm 2wd, driveline issues won't be a problem. The one thing that is a cause for concern is the amount of power the brownie will rob from the engine. With a .73 overdrive my 4.88's will become 3.56 gears which will be significantly better on fuel economy. I'll be doing about 2300 rpm's at 55 instead of 3000. I'm not worried at all about fabricating mounts and know that I will have to modify the drivelines. Besides that, what are your opinions? Yay/nay?

My own personal opinion is that the 304 and especially the slushbox would perform poorly with a b-l auxiliary in od. You can't shift on the fly so I would think it would struggle to get off the blocks in od. I would think it would be especialy hard if you were towing. Are d70 rears really hard to find in 4.10? I guess you know what you have, but are you sure you have a d70 and not a ra15? The ra15 was available with 4.30 gears and isn't too hard to find in mid 60s 1 tons. Drop out pumpkin.

If you only want to run in od completely empty, and you already own the od, have crossmember material/mounts etc I say why not, you can always just keep it in direct.

Why do you need the ud? Plan on pulling big loads?

 

[Michael Dimock]

Looking at my gear options, I was thinking that the close ration (if you will) brownies with a 1.25/1/.75 ratios would be good to operate. .75 all the time empty, 1 when towing, and then shift down to low (1.25) when climbing hills. Or, low coulld be used when pulling out firewood and the like. But, if they can't be shifted on the fly, then that makes it a little bit less appealing. I figured that with the automatic, I could just let off the gas (to idle) and be able to shift the brownie up/down. As this would basically be the same as pushing in the clutch. so, there is no possible way to shift one on the fly?

Oh, it is a Dana 70 rear end, and no, it isn't that hard to find one in 4.10's. I have a ra-15 and you can definitely tell the difference betweeen the 2 as the ra-15 dwarfs the Dana 70! I might end up swapping in a 4.10 rear end later if this can't pan out...

 

[stu simpson]

The b-l boxes have spur gears and are unsynchronized. It's not like shifting on the fly absolutely can't be done....lots of truck drivers have had to shift 5+3, 5+4 etc unsynchronized combos (there is a reason you don't see those around in use much anymore...). There are a number of things working against you---you have an automatic transmission, I am assuming you don't have a lot of experience driving an unsynchronized transmission, and the truck will only see few situations where you will need to shift the box. Its just going to be really difficult to get a feel for shifting the auxiliary, even with a lot of practice and especially with an automatic in front. I think it would be much easier to do with a manual transmission, but you would have to drive it a bunch to get it down. It is just going to be a brutal learning curve, one you don't want to be on the uptick while towing.

 

[Michael Dimock]

The Scout has an unsynchro first, and I have managed to shift it into first double clutching.... Have driven the Scout by not using the clutch a couple times just to see if I could do it, but no I haven't driven/shifted an unsynchro trans for any real length of time. would have definitely preferred a manual trans, but the auto was what the truck came with, so I'll be sticking with it for now. Hmm.... Still liking the od for unloaded driving though.... Stu, do you have any idea how much hp the brownie would rob, as I know it will need a bit of go juice to keep all the gears spinning.

 

[Robert Kenney]

If the bl od was mated to a manual gear box you could learn to shift on the fly, not easy but do able.

On the other side behind an auto I seriously doubt it. Matching speeds with a converter and no clutch......oooohaaaaaaa.