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1991 4L80E upgrade.

6

69Rebel

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Hi all,
The transmission in my 1991 3500HD 2WD has given up the ghost (very low line pressure, barely operable). I have a line on a rebuilt transmission local to me, but it is a '95-'96 unit. I can buy it for about what a rebuild kit would cost. The trans itself was rebuilt by Jake's or Jasper, and has never been installed.
I have rebuilt TH400s and C4s, but I'm not a transmission builder.
As I understand it, to make the swap, I need to use the earlier shift shaft, and a '94-'97 ECM or a standalone transmission controller. Do I have that right, or am I way off? I have already done the wiring harness upgrade.
 
You're better off rebuilding the transmission you have in the 91 than trying to cobble together the support (including a stand alone controller) to run the later model electrically controlled transmission. And Jasper I personally wouldn't trust, either. You're better off buying a good, heavy duty complete rebuild kit with upgraded clutches and steels, and a Transgo Stage 2 valve body kit and Transgo OD valve repair kit. There are many heavy duty TH400 internals that swap right into the 4L80 (the 4l80 family is basically a TH400 with an OD section) such as the 32 element sprag, forged forward drum, etc. You even have options on upgrading the Torque Converter over OEM, too. If you've rebuilt TH400s and C4s yourself, a mechanical 4L80 isn't much harder. There's plenty of how-to videos on YouTube and also manuals available for that transmission.

Just my humble opinion.
 
^^
The more I look into it, I believe you are probably right. The few automatics that I have rebuilt all had one thing in common; they failed due to an internal rubber seal cracking out and causing a large internal hydraulic leak. This one is probably no different.
I was just hoping to press the easy button, but such is never my lot.
 
Nah. The difference in overdrive makes it worth huge effort imo.

Hiway drive ability is so much better. Mpg helps, easier on engine life.—that is if you spend time on the hiway. If not, then stick with the 400.

idk what shifter kits work with what and which controller is the best. I just know the difference of 3 speeds to 4 is big. K5, made all the difference. Same for hmmwvs and hummers. Many military guys hate hmmwvs, then ride in mine or drive it and think that it’s a whole different truck.
 
Yeah, WORLD of difference between an M998 HMMMV or M1008 CUCV with a TH400 behind the 6.2/6.5 and a civilian Hummer with a 4L80E in it - like not going deaf from the motor wrapping out at 65-70 mph on the highway (military tire noise being a whole other issue, as is the noise of the canvas flapping at 70mph in the M998!) and the far reduced engine wear and fear of motor detonation.
 
Heck, my '91 3500HD with the 4L80E would only cruise about 65mph comfortably. IIRC, it has 5.13 gears in the Dana 80.
 
Thats pretty darn close! Hummer/ hmmwv is 5.24:1.

Then the aerodynamics kick in with that windshield which when you engage the GO GO GADGET protractor is 90° to the road, and almost max legal width - that has more wind drag than anything on the road except a shipping container! Haha.

It all depends in your use. If you almost ever hot higher speeds- the th400 is so simple and can be built to last a crazy long life.

Another option could be an under/over drive unit behind the th400 if it ever comes up. Rolling empty on the freeway that 20%-25% could save a lot of fuel. Then if heavy going up some hills, the under drive could help too.

See how easy I can spend your money?!
 
Will L. said:
Most th400 hmmwvs can’t even get to 70 mph.
afaik all new and reconned hmmwvs now get turbo and 4l80e.
Click to expand...
Back in '96 I remember when we'd make the run from Ft. Irwin (NTC) to the old George AFB outside of Victorville, from Barstow to Victorville on I-15 on those downhill stretches the speedometer needle was sitting where 70 would be. Up those hills we were doing good to hold 60 as the cars and semis went whizzing by us. But the most imprinted memory was definitely how damn loud that canvas was flapping at those speeds in the M998!
 
Husker6.5 said:
Back in '96 I remember when we'd make the run from Ft. Irwin (NTC) to the old George AFB outside of Victorville, from Barstow to Victorville on I-15 on those downhill stretches the speedometer needle was sitting where 70 would be. Up those hills we were doing good to hold 60 as the cars and semis went whizzing by us. But the most imprinted memory was definitely how damn loud that canvas was flapping at those speeds in the M998!
Click to expand...

yup! Now, did you know back then how to turn up the fuel screw and adjust the governor for top rpm? Some valuable info right there. That and where to get more padding for the seat! Ever ride fully geared up and try to put on the seat belt? Ha! How do you spell Glass fodder?
 
I actually have a TH400 here, attached to a '89 454. If I could scare up a GV overdrive unit for a reasonable price, I would make that swap in a hot minute. I'd have to figger out what to do for the park brake, but I'm sure there is a solution already on the market for that.
 
69Rebel said:
I actually have a TH400 here, attached to a '89 454. If I could scare up a GV overdrive unit for a reasonable price, I would make that swap in a hot minute. I'd have to figger out what to do for the park brake, but I'm sure there is a solution already on the market for that.
Click to expand...
Check some of the older transmissions, they had the park brake attached to the tail shaft of tje transmission.
Or a line lock would work also too.
 
Those GV ODs were pretty popular for motorhomes, so I'm pretty sure that there is park brake relocation kit. I just haven't researched it yet.
 
Something wild like brakes on the axle where all the normal rakes are. Haha.

Seriously just a cable extension and it’s bracket then new crossmember like bracket behind the gear vendor to hold the brake. The driveline gets rebuilt also, so doing the driveline rotor in that modification is no biggie. Depending what driveline shops are near you -they could do all that stuff. The world famous Adam’s Driveshaft is near me in Henderson Nv (Las Vegas) and they can do that stuff with their eyes closed at a good price. I haven’t swapped my own ujoints in years because of them.

What we lost here was 4 AMAZING transmission shops all sold and magic gone. I used to just drop one off and get back perfection for crazy low prices, could hold bazillions of hp/torque. They all got rich and retired, then moved to greener places- literally. I don’t know a single trans shop here that's good.
 
Will L. said:
yup! Now, did you know back then how to turn up the fuel screw and adjust the governor for top rpm? Some valuable info right there. That and where to get more padding for the seat! Ever ride fully geared up and try to put on the seat belt? Ha! How do you spell Glass fodder?
Click to expand...
Oh yeah. The mechanics in our Support Group's Headquarters Maintenance Platoon had the the pumps turned up a bit on those 6.2s. If you just stomped on it, they'd roll coal like they were laying a smoke screen until the motor was pulling in enough air to clear it up. If you gently rolled into the go pedal, not so bad. The 998's we were using at Ft. Irwin weren't ours, they were the Post's, so I have no clue if the screw had been turned up, but I do know that ours could get out on the highway and hold 70-75 with no problem, the Colonel liked getting places in a hurry.

Now, back in my Enlisted days as a Medic in the Mechanized Infantry, as Medics we had the Medical versions of the venerable Gamma Goat, as well as two M113A1 APCs (Detroit 6V53 powered) with the Armored Ambulance modifications (internal stretcher racks instead of the personnel benches, a pair of hi-intensity surgical lights overhead and a fold-down attendant's seat and small table, as well as the obligatory giant "Aim Here" red cross on the side to designate it as an unarmed ambulance on the battle field, for our Medical Platoon. The Battalion HQ Maintenance Platoon Mechanics got it into their heads with the Medical Gamma Goats and the Armored Ambulances to crank up the IP fueling and modify the governor to take them up to about 200 rpm over the "by the book" factory redline in the 6V53s. Those 3-53 aluminum Detroits I have no idea where they modified the governor to in the Goats, but they flat out screamed and I know for a fact (as I was driving it) that those modified Goats were capable of 80mph against the governor on the highway as I had to rush an injured soldier to the Base Hospital from a training accident. As for the 113s, the theoretical road speed was about 40-42mph. Ours could hold 45-48, fast enough to keep up with the M60A3 Main Battle Tank's 30 mph and out run them, but when the M1's Abrams came out, we found out that while they were factory rated at 48mph road speed, they actually ran more like 50, and as the Brigade Mechanics discovered with the 1500hp turbine engine, it was easy to adjust the fueling to get 60mph on the road out of them!
 
The trick to riding fully geared up and with seat belt on, @Will L., was to unbuckle your pistol belt and slide your LBE around so that your butt pack was to the outboard side and then fasten your belt. Real men didn't need extra seat padding!
 
Husker6.5 said:
You're better off rebuilding the transmission you have in the 91 than trying to cobble together the support (including a stand alone controller) to run the later model electrically controlled transmission. And Jasper I personally wouldn't trust, either. You're better off buying a good, heavy duty complete rebuild kit with upgraded clutches and steels, and a Transgo Stage 2 valve body kit and Transgo OD valve repair kit. There are many heavy duty TH400 internals that swap right into the 4L80 (the 4l80 family is basically a TH400 with an OD section) such as the 32 element sprag, forged forward drum, etc. You even have options on upgrading the Torque Converter over OEM, too. If you've rebuilt TH400s and C4s yourself, a mechanical 4L80 isn't much harder. There's plenty of how-to videos on YouTube and also manuals available for that transmission.

Just my humble opinion.
Click to expand...
What exactly is the overdrive repair kit? Is it a valve body repair kit, or is there more to it than that? Googling around brings up all kinds of different products.
 
The steel check ball hammers the beejeebers out of the aluminum valve body seat and distorts it so it leaks. Also, the kit to replace the valve assembly and repair/enlarge the passage that wears and the valve hangs up in. For specific details/recommendations to build a bulletproof 4L80 you should pick @THEFERMANATOR's brain and vast GM automatic transmission knowledge. He can definitely point you in the right direction for your intended use as far as upgrades/hardening of your transmission.
 
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