4L80E or GV Overdrive for my '90 Suburban?

[idahovette]

In his first post the OP says he wants it automatic, NO switches to work. To me that says 700R4, 4L60E or 4L880E?

 

[BigDaddy72]

Lmbo!! Ya clear as mud now huh!! He’s probably more unsure now than he was before he posted the thread.

 

[Matt69olds]

Obviously a 700 isn’t the best choice for heavy towing or big block power. That’s why I mentioned if no big power increases are planned, a 700 will live just fine behind a small block.

It could be argued that a 700 might live behind a small block doing do heavy towing. Or behind a mid big block cruiser, but definitely not the right choice for both. The problem with a 700 is when you have enough hydraulic integrity and the friction material to clamp and hold big power is about the point where expensive hard parts start to break. Sure, there are plenty of aftermarket support for the 700, but by the time you spend the money for all that fancy stuff you could have easily installed a inherently stronger 4l80 and have zero worries, with money left over.

It’s just my opinion, but if you absolutely have to have overdrive with more than 450-500 hp, use a 4L80. Only reason that makes any sense to use a 700 is if the bigger transmission just won’t fit. Since the op said his suburban has a small block, the 700 will basically bolt in with easy to find parts.

 

[TPISly-C10]

A gear vendors would probably end up being more expensive than a 4l80. A rebuilt 2wd 4l80 is only $1400-1800 out here. A controller is $400 and your rear driveshaft may work.

rebuilt mine for $1600

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[90Saburban]

You've all given me lots to think about. Seriously, I don't think any of it is bad advice. It seems it will all come down to price/performance for what I need. I currently do absolutely no towing, but I may one day. If I ever do, it will be an occasional car trailer either carrying a project vehicle home, or 3 to 4 four-wheelers. I think a 700/4L60E would be just fine for my needs when it comes down to it. I've got an anemic 350 TBI that made 190hp stock (170,000 miles now) I don't think there's much danger in blowing up a 700/4L60E from too much HP. That said, I'm going to be keeping my eye open though for good buildable cores, or rebuilds of any kind from a project that didn't get finished. I have a good transmission shop nearby (@idahovette I live in southeast Idaho) and have had a few 4L60Es built by them in the past and have been very happy with them.

This is my first 3/4 Suburban, or actually any truck of any kind. I've had several half-tons. I know the 4L80E will take more horsepower to spin - should that be a factor at all in my decision?

Thanks again everyone for the great input! I'm not doing anything until summer or fall so I'll just keep getting input and shop around until I'm ready.

 

[rt66paul]

Unless you are on the highway for more than a couple of hours each way, I would leave it be. It is really hard to beat a TH400. The weak point on a 4L60 is the OD and it is expensive to rebuild. You could always get taller tires next time.

 

[Matt69olds]

If you go with a 4l60, make sure the shop installs a Raybestos Z Pac 3-4 clutch kit. The best 3-4?clutch kit from the factory had 7 friction discs, the Z pac uses 14 single sided friction. The input shaft will break off the input housing long before those clutches will slip. Combine that with the wide 2-4 band and your overdrive problems will be solved.

The lower first gear of the 700 will help get the heavy Suburban moving from a stop. The 700 has a 3.06 first gear ratio, the 400 is 2.48. I’m too lazy to do the math, but assuming your suburban has 3.42 gear, it will accelerate like you installed 4:10 with the 700.

The obvious solution is to install 4:10 gears WITH the 700. Then it will feel like you swapped in big block accelerating, combined with the same freeway friendly cruising you have now. Best of both worlds!

 

[SquareRoot]

The GV still won't fix the slippage from the torque convertor. The 4L80 is a better overall choice. IMO. I was going this route until I opted for the NV4500 swap. It furthered my opinion of how much I hate automatics in general.

 

[SquareRoot]

The obvious solution is to install 4:10 gears WITH the 700. Then it will feel like you swapped in big block accelerating, combined with the same freeway friendly cruising you have now. Best of both worlds!

LOL. That's funny right there.

 

[90Saburban]

The Sub has 4.10 gears in it right now. I’m very happy with the way it drives currently around town - the 4.10s help it move from a stoplight and I prefer the 1-2 shifts in the 400 versus the huge RPM drop you get with a 700/4L60e from 1st-2nd gear. Every 700/4L60e has always slammed into 2nd gear too. The TH400 is truly a joy to drive in this rig. Just wish it had the overdrive. I don’t regularly drive on the freeway, just occasional trips, so it’s more of a luxury item. It’s the OCD in me that get’s bothered by the high RPMs. Overdrive has spoiled us in recent years!

 

[Matt69olds]

Sonnax makes a gearset that changes the first gear ratio from 3.06 to 2.84. But the cost is pretty high, more than the cost of a controller for the 4L80.

The 700 or 4L80 is the only automatic overdrive transmission that’s easily adapted to a square body.

 

[MikeB]

R2500 = 2wd, right? If so, why not take the simple route and change the ring and pinion to something like a 3.42, or whichever ratios are available for a 3/4 ton diff? RPMs would drop around 17%, and you'd still have converter slip to get you moving in first gear.

I know my old SWB square didn't weigh nearly as much as yours, but it wasn't a dog even with a 2.73. Then again, its 355 probably made close to 400 lb/ ft torque.

 

[Daveo91Burb]

The Sub has 4.10 gears in it right now. I’m very happy with the way it drives currently around town - the 4.10s help it move from a stoplight and I prefer the 1-2 shifts in the 400 versus the huge RPM drop you get with a 700/4L60e from 1st-2nd gear. Every 700/4L60e has always slammed into 2nd gear too. The TH400 is truly a joy to drive in this rig. Just wish it had the overdrive. I don’t regularly drive on the freeway, just occasional trips, so it’s more of a luxury item. It’s the OCD in me that get’s bothered by the high RPMs. Overdrive has spoiled us in recent years!

FWIW, I'm hoping to have the OEM 4L80e that's currently in my '91 for sale soon. You'd need the PCM for it, but I'll be selling that as well. Zero wrong with it, shifts great, no funny noises, fluid stays clean, etc. I'm actually upgrading to a 4L80e from a '97 and the only reason I'm doing that is to be able to use a later model PCM. (can't run an early model 4L80e with later model PCM and vice versa) the early PCMs don't respond well to tuning for modified/higher output engines but it would work just fine for your stock TBI 350.

Not sure where you are in Idaho, but if you want to make a road trip to Vancouver, WA in a month or so, PM me!