Overdrive or Gears

[f.monroe]

I have been driving my 87 3/4 ton a lot lately . It has a factory 4.10 posi rear axle and the little 350 is wound pretty tight at highway speed . (My 05 work truck has a 4.10 rear and turns about 3300 in drive and 2500 in OD . I figure the final drive is around 3.0x with the OD . )I thought of an overdrive 4L80 but have been thinking 3.42 gears would help and is a lot cheaper . I think the 3.42's would still allow it to pull and with the 33x12.50x16.5's would offer a little releif on the highway . What do you think ? 3.42's or a 4L80 ? Also , has anyone here installed a 4L80 in one of these trucks and did you have any problems ? Frank

[cliffsta]

I'd suggest the OD tranny and keep your current rearend. Your 1st gear is gonna be quicker and you'll have the added benefit of OD, as opposed to keeping the average 1st of the TH350 with a doggier rearend.

My truck has a 2.56 rearend, first gear is a beast, and not in a good way.

[MylilBowTie]

4L80E has these gear ratios. 1st: 2.48 2nd: 1.48 3rd: 1.0 Overdrive: 0.75
Its going to be pretty expensive to get the 4L80E they run about 1200-1500 and you will need a transmission controller. I think they still run about the same price as the transmission or right at it. I think the driveshaft may need to be shortend also.

The overdrive would be better but cost is alot more. With the overdrive you would want to keep your gears. The tall tires and the weight of the truck will need help to get moving. Then you have overdrive for the highway and it wont lug the engine locking and unlock the convertor all the time.

3.42 gears will lower the rpm some. The gears don't cost much but the labor does to get them installed. Have you thought about different tire sizes? I take it you have a th350 or th400?

[gmcman7202]

also can you get a 4l80e that will bolt up since the lsx motors use different bell housings, iirc.

[gmcman7202]

what about a gear vendors unit? i think it might be better in the long run, as then you would have overdrive throught all gears. alot more versitility doing everything such as driving, pulling, towing, mudding, ect.

[75sierraclassic]

Why can't you just put in a earlier 700R that bolts up to the SBC?

[MylilBowTie]

The 700r4 and even 200r4 will bolt up but its hard telling how long either would last. They are pretty much stand alone transmissions other than the lock torque convertors. If there is a 9in tailshaft th350 currently installed then the 700r4 will go in without driveshaft mods. I believe that the 200r4 will also. These transmissions can be built up but its right around the cost of the 4L80E maybe a little more.

Then you are around what the stock 4L80E will handle. If you are talking about a 4L80 then those pretty hard to find. I cant remember what you have to look for to find one. Maybe someone else know, I'm thinking it was a early 90's Suburban with a big block. 4L80 doesn't need a transmission controller and still has overdrive.

[f.monroe]

Thanks for the input so far . It currently has a TH400 . The reason I dont want a th700 is the massive low first . A friend of mine had 4.10's in his 93 half ton and first was way low . I looked at gear vendors as an option . I may look for an early 4L80 also . I would install the gears myself so the cost is just the gears ,lube ,etc. The truck only has 54,xxx miles so the posi is in good shape . No rebuilding there . Has anyone had a Gear Vendors unit installed for a long period of time . I wonder if they ever start to howl or anything . I agree that that is probably the way to go since I could remove it if I decided to sell the truck. Frank

[MylilBowTie]

The 200r4 doesn't have the low first gear if that helps any. It has a .67 od ratio vs the 700r4s .70 overdrive. You would also need a uni-case 200r4 if you went that way. The gearvendors unit is only .78 overdrive but will make your 4.10s to be 3.20 gear while in od. Those taller tires will bring that number down even more to id say about a 3.08 or so.

Board member Lemield has an gearvendors unit with th350 that he uses. Might want to give him a pm or something and see how he likes it.

Here is a gearvendors link
http://www.gearvendors.com/cg2wd3s.html

[magnethead]

The 4L80E will not bolt up to our generation of trucks without modification. Said modification involves a large hammer and about 2" of clearencing of the floorboard i am told.

I too have looked at gearvendors..seems like the better option.

[MylilBowTie]

What is supposed to stick out and two inches? I really dont see how it wouldnt fit in all the pictures Ive seen. Looks like a normal th350-th400 on the top and sides of the case for the most part. Only thing I can see that might be a problem is where the inspection cover mouts. There is a spot on each side that sticks out a little farther than normal. But shouldnt be a problem. It wouldnt take much to clearence them and not hurt anything if that was.

http://www.donneysaab.com/FDT/4l80epics.htm

http://www.novak-adapt.com/knowledge/th400.htm

[edman87]

Are you wanting for gas mileage or engine longevity?
If only for mileage reasons, I say deal with the expensive fillups. You aren't going to make it much better.

[75sierraclassic]

Originally Posted by edman87

Are you wanting for gas mileage or engine longevity?
If only for mileage reasons, I say deal with the expensive fillups. You aren't going to make it much better.

Edman 87 has a point.
If you assume 10000 miles/year driven, and gas stays at a constant $2.50 (I know, constant gas prices ha ha ha). I'd assume you may get an average of 12 MPG with your current setup. I would also guess that the overdrive will only gain you a lot of mileage if you drive at highway speeds most of the time, but lets assume it gives you 2 MPG. At that mileage (14 MPG), gas price, and miles/year, you only save $300/year.
I'm not sure how much a 4L80 or gear vendors overdrive is, but if it is $2000 then it will take a little under seven years to even break even and start saving money.
And if you are curious, yes I am bored at work

[kevinr1970]

I remember looking at a '90 or '91 1-ton 2wd crew cab dually that had a deisel a while back. It was a navy surplus truck.
It had an overdrive tranny and I was told by someone here that it was the 4l80e. He said that for that year (not sure if the deisel had anything to do with it) that they didn't use a seperate controller. He said that would be the tranny to get and rebuild if you were looking to upgrade to a 4l80e.

[gmcman7202]

the e stands for the electric controler thats why the 700r4 is now refered to the 4l60

[kevinr1970]

It might have been a 4l80 then? All I really remember was that he said that was the tranny to get.

[MylilBowTie]

Yeah that would be the one to get. Its right around those years, and I would look in the HD stuff. 3/4 - 1ton diesel or big block in trucks and suburbans.