planetary overdrive

[tatersalad]

I've seen articles on a rancho overdrive that used to be available for broncos. Just curious why a planetary overdrive unit wouldn't work with our stock c4 trannys for a simple overdrive upgrade without having to change out all the stock stuff. Anyone tried this?

 

[garberz]

The biggest issue is, it will make the drivetrain too long.

 

[tatersalad]

doesn't the black box being used as an underdrive have the same issue. Or is it put in place of the intermediate housing?

 

[garberz]

The black box adds minimal length because about a third of it fits inside the D20. It still bolts up to the C4 adapter. I would guess the Rancho unit isn't as slim as the Black Box "I". Once your drive shaft gets shortened to about 26", your gonna have problems on the highway. True Hi-9 time.

Mark

 

[Broncobowsher]

Having personally seen a couple of those old overdrives, packaging is really an issue. Don't even think of putting a lift on it. There is also strength issues as it has to handle all the reduction with the transfer case is in low range.

There is also issues with the C4. Without a lockup torque convertor it is too easy to get into a low RPM, high torque demand situation. Same as over tired/under geared. This will slip the convertor horribly generating excess heat. Not a good idea.

A transmission with the overdrive built in and a functional lockup convertor packages and functions much better. And you can run some lift as well.

 

[00gyrhed]

sorry this got long but I loved these stupid things but I strongly recommend you spent your money somewhere else. They are old technology and not very strong.

The unit is a Borg Warner OD unit, quite popular in the late 50s and early 60s, before automobiles made a lot of HP and were geared low because of the lack of HP.

Not only did they make the driveshaft too short and at a steep angle, it WILL be the weak link in your drivetrain. the main shaft in those things is pretty small. I twisted one off in my 55 chevy with a 235 inline six and all I had done to it was put headers and a small 4bbl on it. I doubt they would be up to taller than stock tires or heavy HP.

My 55 chevy had a different out put shaft than stock and when I twisted it off I paid a premium. I bought everyone I could find after that at swap meets. Still have one in the barn.

Just cant bear to part with it they are really cool to drive. In town with 4:11 R&P you could start in second and the planetary in low and let it upshift and down shift as needed, the only time you use the clutch is when you come to a stop. Problem is everyone did that and it wears the transmission main bearing because it is really meant to see 3rd gear every once in a while and get a rest. Most every mainshaft I ever saw had wear in that bearing. the internet may have helped the situation but back before Al Gore invented the old interweb the only way to get parts was to buy old junk at swap meets.

There is a spring that wraps around the shaft to slow it when it shifts and it is easy to break taking it on and off and it wears. The fix is to squeeze it, problem is you might break it. That spring was impossible to find and I actually ran one I welded heated and quenched for 30,000 miles.

I did see build one time where the guy had located one of these things including a shaft that he claimed would bolt it directly to an NP435. He claimed an adapter was actually available to allow the unit to go between the transmission and transfer case. I spent a ton of time trying to find anything on the internet with no luck, other than I did find BW did make a bigger heavier unit for trucks and busses so who knows.

Just buy one of the modern planetary units that go in between the transmission and the t case. They don't add much if any length to the set up. There was a thread on here just a few days ago, I just cant find it and need to go right now.

 

[tatersalad]

Im not in the market for one. I saw the article on the rancho unit years ago and badabing it crept back into the old memory again today so I thought I would see what ya'lls thoughts on it are.

 

[NYLES]

ZF=OD all im gonna say good read 00

 

[tatersalad]

ZF means going back to a clutch.

 

[garberz]

How about the 4R70w? How much could that cost, just for one more gear?

Mark

 

[Broncobowsher]

How about the 4R70w? How much could that cost, just for one more gear?

Mark

On the surface its only one gear. But with a wider spread of ratios the first 3 gears are already better than a C4. Yes, the overdrive is another gear. Now add in that lock up torque convertor that can be as good as yet another gear. Which means it is better than just tacking an overdrive onto a drivetrain that shouldn't otherwise have one.

And most of the time the overdrive can't be used as is, the axle gearing is too high to accept an overdrive. So figure in lower gears in the axles to be able to use the overdrive.

 

[76Broncofromhell]

Swap in a modern overdrive transmission. You will be money and time ahead.

 

[tatersalad]

an Aode or 4r70w are eventually on the bucket list but I'm cool with my c4 for now. The mileage hasn't ever been an issue. I have just seen black box builds and wondered why they don't do an overdrive the same way. If that unit is strong enough to lower your gear ratio it seems plausible that it would work the other way around too.

 

[garberz]

I just don't think there's a market for a black box type overdrive, since there are so many overdrive transmission options out there.

Mark

 

[NYLES]

ZF means going back to a clutch.

if ya crawlin you dont need it!

 

[tatersalad]

I don't crawl. I did have a beat up 75 that I was going to not worry about but when I converted to efi, 351W and rebuilt both tranny and engine I had to make a choice due to $$$, so I sold the 75 to a guy building with his 13 year old son to help keep my driver on the road.