Overdrive

[oneluckypops]

The Transmission needs a few sensors for it to work. ECT, TPS, VSS, ISS. The TPS will have to be modified to work with the cummins but doable.
The VSS will have to be in the Transfercase
The ISS is already in the Transmission case


Ok you have a NP205 Which is a cable Driven speedometer, you can still use it you will have to buy a converter so you can send the signal to the VCM. Or you can find a NP241C Passengerside Drop Transfer case from a 90-91 Blazer that has a VSS and the electric Speedo Cluster from the the 90-91 blazer or suburban.

As far as years go for the 4L80E it really doesnt matter to much I would just try to find the best deal.

The wiring is Not a big deal either, you do NOT have to have a harness from a 3/4 or 1 ton the 1/2 tons will work for the 80E also you just have to modify it (which is EASY and CHEAP) I will go into greater details for the wiring on the write up though.

You will need a diesel Torque converter though. which will probably have to be after market, to fit the transmission and still bolt to the cummins flex plate but maybe not not sure what flex plate you are using the buddy that did your conversion can get you in the right direction for that.

 

[Blackdog3]

How do those sensors need to be modified?

It would probably be better to find the converter to keep my truck fully 1 ton. Where would I find this converter.

As for the trans, so 4x4 or 2x4 doesent matter. There are 2 3500HD's in the locale junkyard that had 6.5's in them. I was considering getting the trans rebuilt, any thoughts on that?

As for the torque convertner, i have a 6.2/6.5 diesel one that was put into my turbo 400 when the swap was completed. As for the adapter and flex plate, mine bolts to any chevy trans.


I am interested in knowing more about the sensors and wiring.

 

[oneluckypops]

2wd and 4wd Trans are the same EXCEPT the tail housing and Output shaft you will have to use a 4x4 trans unless you want to run a divorced transfer case.

The flex plate needs to have an 11.5" bolt circle the 4l80E uses 6 mounting lugs.

As for the wiring the 4L80E for a 4X4
1. is the Case connector (20 Pin) But only 11 of the pins are used.
2. ISS has 2 wires
3. Range selector switch (neutral safety switch) This switch is a 2 part switch 1 part communicate with the Instrument cluster the other part sends the current to the starter Relay, I am still studying the Wiring schematics to be able to tell you where exactly the wires need to be hooked up. I will post the diagrams of all the wires incase you get confused later

 

[Blackdog3]

A little update... got the truck back here, leaking atf everywhere. Took it back, guy replaced the trans seal. Called me up said it still leaks with a new seal, need a trans rebuild. Not sure what to believe at this point.... ideas, help would be great! Luke i already pm'ed u about the issue.

 

[oneluckypops]

A little update... got the truck back here, leaking atf everywhere. Took it back, guy replaced the trans seal. Called me up said it still leaks with a new seal, need a trans rebuild. Not sure what to believe at this point.... ideas, help would be great! Luke i already pm'ed u about the issue.

Did he replace the Bushing, and install the ground cable? If not the seal could of already been damaged. causing the leak again. That or he might have REUSED the pump gasket if he pulled the pump to replace the bushing.

 

[Blackdog3]

I do not believe he replaced the the bushing.

 

[oneluckypops]

I do not believe he replaced the the bushing.

That sucks man, Seals dont just go bad for no reason. 9/10 times when a pump seal is leaking it is because of the bushing being worn.

Does the Transmission still operate correctly?

 

[HotRodPC]

Yes, Gear Vendor is high dollar. Why when I seen that burb on CL for $500 I said someone needed to grab it just for the damn Gear Vendor unit. And it was a Turbo 400 Burb.
So I see you have all the options laid out. How do you feel about manual transmissions? The only other reasonable cost situation, is a NV4500. And even then might get costly by the time you acquire pedals, clutch linkage or master and slave cylinders depending on how you do it. Then there is the option of a 4L80-E that is Full Manual Vavle Body, which means its manual shift without a clutch. NO automatic at all whatsoever. You can do that without need for the computer and it will shift pretty firm too. Basically you are taking place of the computer needed to tell it when it to shift and downshift, and you won't have lock up conveter either, unless you hook it up to a toggle switch and do it manually.

 

[HotRodPC]

A little update... got the truck back here, leaking atf everywhere. Took it back, guy replaced the trans seal. Called me up said it still leaks with a new seal, need a trans rebuild. Not sure what to believe at this point.... ideas, help would be great! Luke i already pm'ed u about the issue.

Also besides just the bushing being bad, many times a seal can get hard over years, espeically a 400 since they tend to last so long. The seal can acutally cut a groove in the Torrque converter nose. So to remedy that, you put a washer or 2 in between the flywheel and torque converter, this way the converter nose is riding the new seal in a differant location and it may just fix your leak. But, the guys who did the front seal should have looked for this problem and rectified it.

 

[bucket]

No matter how you slice it, it's gonna be spendy. A 4l80E is expensive to buy (even as a core usually), expensive to have rebuilt, plus the needed controller and other nickle/dime stuff that all adds up in a hurry. It would end up costing nearly as much as the GV unit.

I would pick the GV unit. I'm no expert, but I believe a TH400/GV is about as strong as you can get, and less work needed for install. Shorten the rear shaft, and that's about it, as far as I know.

 

[hirschdalechevy]

That sucks man, Seals dont just go bad for no reason. 9/10 times when a pump seal is leaking it is because of the bushing being worn.

Does the Transmission still operate correctly?

I agree XXXXX2 ^^^^^^^^^, sometimes if you are not careful you can damage the seal when stabbing the converter as well (it has happend to me before). And I have also seen the bushing go bad and screw up the snout of the converter , (got extemely hot) and distort the snout .Just had to replace the pump , bushing and converter on my ford service truck (all because of that bushing) , and the rest of my tranny was ok , but the pump had shavings from that bushing in it , (I am sure that it did'nt do it any good though)

 

[Blackdog3]

Sorry Gang i did respond. First officail work day of the 2011 landscaping season. The Transmission still operates as it did before. As for a NV4500, i was consdering, but with plowing snow etc, i figured an auto would better suit me. Plus I am not the greatest stick driver ever. As for the 4l80 E swap, not sure what i want to do. I just need the truck back at this point. I have another 400 at my shop i could just put in but I dont want to have the same issue again.

 

[HotRodPC]

Sorry Gang i did respond. First officail work day of the 2011 landscaping season. The Transmission still operates as it did before. As for a NV4500, i was consdering, but with plowing snow etc, i figured an auto would better suit me. Plus I am not the greatest stick driver ever. As for the 4l80 E swap, not sure what i want to do. I just need the truck back at this point. I have another 400 at my shop i could just put in but I dont want to have the same issue again.

You're not likely to have the same issue. Its not common for that bushing to wear badly in a T400. After a humpteen thousand miles, sure, it can wear some. And if someone just replaced the seal and didn't at least inspect the bushing when the old seal was out, they were idiots. Also if they did not check the snout on the TC to see if it was grooved from a hardened seal edge. As I suggested, you might be able to correct your issue by putting a couple of washer between the flywheel and TC mounting holes. This will push the TC the thickness of those 1 or 2 washers back into the trans, giving a new place on the snout for the TC to ride the seal and it not being worn there, may fix the leak. Just be sure the use the same thickness washers on all 3 holes.

 

[oneluckypops]

You're not likely to have the same issue. Its not common for that bushing to wear badly in a T400. After a humpteen thousand miles, sure, it can wear some. And if someone just replaced the seal and didn't at least inspect the bushing when the old seal was out, they were idiots. Also if they did not check the snout on the TC to see if it was grooved from a hardened seal edge. As I suggested, you might be able to correct your issue by putting a couple of washer between the flywheel and TC mounting holes. This will push the TC the thickness of those 1 or 2 washers back into the trans, giving a new place on the snout for the TC to ride the seal and it not being worn there, may fix the leak. Just be sure the use the same thickness washers on all 3 holes.

Actually hotrod the pump bushing has been a notoriouse problem, I talked with blackdo a few times in PM and explained it to him somewhat but ill spill it here for you to.

The pump bushings are known to prematurely wear for a couple of reasons.
1.) is because they are not a wide bushing you can correct that with an aftermarket bushing.

2.) Ok if the engine is not PROPERLY grounded then it tries to ground thru the transmission which causes an ARC, the arc can wear the bushing aswell as harden the pump seal. Another reason is from the moving parts inside the Transmission causes static electricity.

The proper way to fix it is to install the updated bushing, AND install an additional Ground from the bellhousing to either the Frame, known good ground, or direct to the battery is the BEST.

I have seen this condition MANY MANY times.

 

[HotRodPC]

hmmmm, I've not see it many times. But I do know the bushing I replace it with in the rebuild kits its wider but never knew it to be a common problem at all. I didn't know what caused it, but I was aware SOME, T400 can get the hardened seal edge and actually cut a groove in the TC snout, and why I suggested using the washers so the TC would ride in a differant portion of the snout where the current position maybe grooved from the previous hardened seal. I have actually fixed leaking front seals by doing the washer trick. It can actually buy you 10-20K miles and by the time maybe its time for a trans rebuild or, at worst, pull the trans anyway and fix it right with new bushing, and seal, then do the washer trick with 3 washers. I suggest that cuz he said he already had the seal replaced and its still leaking. Likley cuz of a ridge in the TC snout from the previous seal. Intersting to learn a ground strap is what causes the seal hardening. Now you know that seal had to get pretty damn hard to cut a groove in a TC snout. And we're talking a rubber seal getting that hard and sharp. But, the same thing also happens on pinions seals too, cutting a groove in the pinion gear. The fix that is an oversise seal and a bushing slid over the pinion gear shaft. Good as new again.