Kerr

So, I think i have sold my car and im going to have a 2 speed gear vendors over drive kit left. It was attached to the TH400 that was in the car. I was wondering if i could reattach that to the suburban. It a 4x4 so if im thinking correctley that will mount to the transfercase, which i have no clue what it is. I have that junk auto 4wd crap..

So anyway any of you looked into this or have you seen it done?

Leroy_454

I would contact gear vendors. Also PM James B. on here. He is knowledgeable with the gear vendors and various tranny combos.

kbracing96

iTrader: (26)

I'm pretty sure GV makes an adapter to bolt it to the back of the transfer case. You do have to wire it up so it can only be engaged when you are in 2wd.

GMCtrk

iTrader: (27)

wait, I thought you had the allison behind the 8.1L?

So you can effectively make a 4l80e a 6 speed?

cttandy

iTrader: (12)

4l80E with a 2 spd overdrive unit, that would be an 8 spd, unless 2 ratios match at some point.

hog

It makes a 4 speed and 8 speed. Its an over/underdrive unit. very strong. Dont think it can be used on 4wd truck due to teh transfer case. Contact Gearvendors for sure.

peace
Hog

Kerr

yea mine is just a over drive unit. The way it work on the TH400, was i had fist, second (overdirve) 3ed ( over drive)

So if this will work on the suburabn ( they have the 4L80E ) then i would have
1st= 2.48
2nd=1.48
3ed=1.00
(gear vendors)
4th =.75
(gear vendors)

That is if i work it the same as i did on the other car. However i have seen some guy spilt each gear...

What im thinking about doing is moving to a lot steep ring and pinion gears, like 4:56 or 4:88's then with 33.5" tires and GV over dive i could sill have a low rpm crusing range and be a LOT stronger down low when i have the trailer behind me..

Found this on the web page. This is for the hole kit. Im not sure if they jst sale parts.

Part #3D0205I
NP 205 Transfer Case with Fixed Yoke, 4L80E Transmission.
Replaces 1 1/8" output case housing.
If a slip yoke 205, requires output shaft replacement with GM #458499 (not included).

kbracing96

iTrader: (26)

Ya you can use them on 4wd, I installed a few back in the day when I worked at camping world. They have a safety switch that when you put it into 4wd, it kicks it out of overdrive if it's in it, and won't allow the GV to be engaged while in 4wd. Basically it will only work when your in 2wd.

Just a FYI for the rest of you guys, iirc, you can't really split 1st and 2nd, because the GV needs to be going at 40mph for the internal pump in it to make enough pressure to engage the unit. So really can only be used effectively like Kerr said in 3rd and 4th.

BlackGMC

iTrader: (31)

That is pretty sweet idea!!

James B.

iTrader: (1)

I don't know about the Allison, but the adapter for the 4L80/85-E is available. In order to buy the adapter from GearVendors they will require that you return your existing TH400 adapter. I'm not clear on why they do it like that, I suspect it helps them keep third-party parts availability under control. I had to turn in the 4L60-E adapter when I upgraded to the 80.
The Overdrive has only one weakness - reverse. Basically, when the unit is disengaged there is an overrun clutch that's held under spring tension. Reverse input torque (and even engine braking when the O/D is not engaged) is held by the overrun clutch. The limit to that clutch's torque handling can be exceeded under certain circumstances. For example, if you had to back a boat with surge brake up an incline to park it you'd be asking for trouble.
Behind a transmission that already has overdrive it'll provide double-overdrive. I use that on the highway above 60mph since I have 4.56:1 gears and only 29" tires. It does make for some scary-fast driveline RPM at 130MPH, I try not to think about it. Any installation of a GV is going to require a custom driveshaft anyway, so if you're combining the GV and a really low rear end ratio, tell the driveline shop you need it balanced to 7000+ RPM.