Overdrive Transmission Help Again

Ho Boy, where to begin? This whole gear ratio, and ordering the parts is a nightmare, each time I call ( reputable company referred to) gives me different rates, extremely different, each time I told you can do this, you can't do this?? Weve been through the whole " I don't know what I have routine" still I have had "what size are your tires" your good, what is stamped on the axel, your good, then someone else says that won't work, the mechanic here in my town won't do it, the mechanic in a city where it would take me 2 hours to drive, and "specializes in rear ends, doesn't want to gurantee anything should I order the parts and this is a long long nightmare, a month later and I am spinning my wheels AHHHHHHHH!!!!

Ok, so here we go AGAIN>>>>

Overdrive transmission.

It is obvious people have done this, I searched the "search words".

How about some imput, NOW we don't have to know what gears I have Exactly ( I presume) and perhaps I can move on so as to LOWER THESE SONS OF BITCHES RPMSSSSSS....

Ok, frustration, ( non mechanic)

What kind?

How much?

New? Used?

What else does it affect?
What else will it change?
How does it work?

I'm a pain in the arse, but I still need help?

Bill

Automatic trans with overdrive. You basically have 2 choices, a 700R4 or a 200R4. I have the 700 myself combined with a 350 V8. They work well with the 12 bolt RA gearing what ever one you have, 3:73 or 4:11. Both will give you a lower first gear that would be good for a 6 banger. You still will be at or about 2000-2200 RPM @ 60 mph with 26" tall tires. But you may not gain gobs of mileage as the Overdrive will also take a little more engine power. You should gain a couple with normal driving conditions tho. The 700 you may have to lower your engine cradle an inch. Not sure on the 200? Both will need a custom transmission mount. The guys seem to be using units bought from Speedway. Specs I do not know. You would have to shorten your driveshaft approximately 2 inches with a 700 install. The 200 I believe will work with the same length but either one you may have to change out the front yoke? Cannot help you with the cost numbers as those depend on your resources. If you look for used try to get one from a running vehicle. The " Yeah, It worked fine when I took it out 3 years ago" will be a rebuild job. There are some other details involving shifters and some linkage and electrical also. Somewhat involved but to me would be worth the effort if needing to stay with the 12 bolt RA. Easiest way to get a few extra MPGs would be to get a hold of a 10 bolt VAN RA with a 3:36 ratio, that should get you in the 15-16 range. They are out there just need to broaden your contacts and gain some resources. Good luck.

Put a 200r in mine. Didn't have to change nothing on the driveshaft, just a custom made, home made, crossmember. My van cruises 65 mph at about 2100 rpms. Keep in mind that if you put in a overdrive transmission you also need to change the geometry on the carb where the transmission cable hooks up, which wasn't to hard to do either.

i can understand your frustrations with your mpg's, and your want to just hop into an overdrive trannyt to try and solve it. with that being said, when we spoke on the phone, your mileage numbers were in the 11's. I wouldn't ignore that it may need tune up items as well as a tune on the carb to help with this. I would hate for you to spend lots of money doing this, and end up with little or no results.
afterall , there are lots of guys on here that have overdrive trannys that get between 10 and 14 mpg's. I hope that somebody on here can get you fixed up, and enjoying your van more.

Scott wrote:I put a 200-4r in mine, replaced a Powerglide.

I had to drop the engine mount 2" so the Bellhousing on the transmission would clear the rear of the doghouse and still keep it all level. I also had to had a crossbeam to support the transmission.

The splines on the driveshaft were the same as the Powerglide, and the Powerglide is so close to the same length of a 200-4r that I didn't have to do anything to the driveshaft.

Also, I had to add a little kit that disconnects the overdrive when the brake pedal is pushed, and the cable from the transmission to the carburetor will have to be connected and adjusted.

It's really not that difficult once you get into it.

Is there any additional benefit of using an 700r4 over the 200-4 since it seems the 200 fits more readily without cutting down the driveshaft?

Im going with the 700R4 trans. got to be built anyways & stronger when built also!! Must lower either trans too. Much more for the 400R too.

Not sure what your setup is, but your avatar shows a first gen so I'll assume six cylinder....My 66 GMC handivan got 17mpg everywhere it went in the mid seventies with the 230 and three speed stick.... Gas was cheap back then, so I swapped in a 396 and never got over 10 after that.....The national speed limit was 55mph, so not having freeway gear was not an issue!
35 years later, the two major interstates that go past my locale have 75mph speed limits, so I now consider a overdrive/lockup trans a necessity for being able to travel at reasonably modest RPM.
Think about this: These vans were built and marketed for plumbers, electricians, public utilities, dry cleaners BEFORE MANY FREEWAYS EXISTED, AND they were meant for local surface street use.... NOT meant for the highway.....Choosing an Overdrive/lockup trans is about making your engine comfortable running at faster speeds without having it work harder from a dead stop....Increased fuel mileage is an expectable byproduct of lowering the rpms, as you will be travelling farther on the same motor revolutions....The higher overall final drive ratio WILL put extra load on your engine, so fuel mileage improvement might not be that much in the absence of other improvements.....

I don't believe that a six cylinder van can get only 11mpg unless there is a tuning problem...

.I'd start with a compression check to check that all the cylinders have about 130-150 lbs of compression and all are within 10% of each other. Next, I would order up a new HEI distributor (sixes had them in the late seventies), make sure your six has the right carb and do a careful rebuild, and then do a full tune-up, paying special attention to the timing curve. I'd be willing to bet that your advance mechanisms are frozen or your carb is overfueling (or both). Worn engine, cam lobes, timing gears, and weak valve springs can also diminish fuel mileage substantially, and I'd make sure the engine was A-1 before doing the trans swap if funds are a consideration....

With the engine tuned and running right, you should be able to extract 15-17 mpg easy, while doing as much as 75mph at a somewhat modest RPM with an overdrive trans installed.....The improved driveability is the reason to do the OD conversion, but if you require an improvement in fuel mileage to justify it,it's possible you could end up disappointed.