208 to 205 Swap Question

[Doppleganger]

My 85 K20 has a 208C. 100k and was rarely used. The motor and trans are coming out in the Spring for a built vortec 350 and 4l80e. I located a 205 - I have heard that the drive shaft lengths are different between the 208 and 205. Since I'll have a custom shaft made for the 4l80 swap, what else do I need to collect (or fab?) to make this work?

Been looking online for some time but get conflicting claims. Kind of hoping someone here did exactly what I'm planning and has a cheat sheet.

Thanks fellas.

 

[Arkansas_V8]

Remember reading a 2wd 4l80e was the way to go with the adapter. I will check on that.


Stole this from Pirate-

"total newb said"-Credited

Ok, these are the 2 combos you want to find. That way you won't need to do any unnecessary dismantling.
2wd 4l80. Fig 8 th400 adapter and short input 32spl 205
4wd 4l80 stock or th400 round 6 adapter long input 32spl 205.

One benefit of the 2wd is the VSS is in the trans. No need to run a 4 low switch.

 

[Doppleganger]

The 2WD part confuses me. I saw several postings on Pirate as well as several different scenarios.

Whats the deal with the VSS switch? The 4WD doesn't have it? I had intended on getting a Painless controller for it.....or something along those lines.

 

[eskimomann209]

He shouldn’t need vss as he has an 85. It’s mechanical the 205 can handle that.

 

[eskimomann209]

This is mind blowing... I had no idea this cheat for the 4l80 existed... in fact I’m kinda pissed I never seen it.
ok I see you’re response now. Your old 4x4 didn’t have it because it was a mechanical trans. The 80e is electronic. Since you plan on putting the 205 behind it you run into the issue that your t case doesn’t have the ability to tell the controller how fast you’re going. As a result the 80e has no idea when to shift.

on the 2wd versions they never had a t case so the vss bung is in the tailhousing. The trick here is to adapt the tailhousing to take the t case that you want and not have to worry about the vss in the t case because the tranny itself has that taken care of. But usually you run into issues when in 4 low. Transmission has no idea the t case is spinning at a different ratio

 

[Arkansas_V8]

That was everything I have bookmarked on the swap. Sorry man. The computers and wiring have steered me clear, and closer to a 6BT.


This is the page I saved. I liked his keep it shorter stance.
https://www.pirate4x4.com/forum/che...ing-2x4-4x4-4l80e.html#/topics/2018010?page=1

 

[Doppleganger]

Thanks for the info...but I'd be a liar if I said it made any sense to me. lol

I have seen how they make 2wd 4l80s into 4wd versions....and would have no issue with it if I thought there was any shops around here who could/would do it.

What did the late 90's use? The 4l80's were out - were the 205's not used by then? My 350 is a 97 vortec with Edelbrock FI. Was just gong to use an aftermarket controller for the trans. Wasn't aware the transfer case would be such an issue.

 

[bucket]

The only trucks that got a 4L80 and a 205, were the '91 V3500 crew cab trucks.

 

[Doppleganger]

I've heard the early 4l80's weren't that great. ?! Dunno. Might have to live with it. Will start looking into the 91 3500. Thanks.

Interesting find.....

http://www.northwestfab.com/4l80E-to-TH400-NP205-AdapterSpacer-Kit_p_98.html

"All 2wd and some 4wd 4L80E have VSS Sensors built into the transmission. If your transmission does not have functional VSS Sensor we do sell a VSS Rear Output Kit for the NP205."

 

[SquareRoot]

Dopple,

What trans do you have in it currently? Why did you decide on the 4l80 option?

I also have an 85 K20 and have gone back and forth on an overdrive option for a couple years now. I have every single piece to convert to the 4500 from my th400.

However... I've recently changed my mind and have decided to add a Gear Vendor OD instead. I was wanting a 4l80 as well but after multiple analysis, the GV makes the most sense economically and labor wise.

This opened a can of worms regarding the vss. The GV comes with a vss in the unit. My issue is if it will also drive my Dakota Digital guages? I also have a 205 with a vss drive that was machined by ORD but that piece gets replaced with the GV adapter.

Head scratcher....lol

 

[Doppleganger]

Dopple,

What trans do you have in it currently? Why did you decide on the 4l80 option?

I also have an 85 K20 and have gone back and forth on an overdrive option for a couple years now. I have every single piece to convert to the 4500 from my th400.

However... I've recently changed my mind and have decided to add a Gear Vendor OD instead. I was wanting a 4l80 as well but after multiple analysis, the GV makes the most sense economically and labor wise.

This opened a can of worms regarding the vss. The GV comes with a vss in the unit. My issue is if it will also drive my Dakota Digital guages? I also have a 205 with a vss drive that was machined by ORD but that piece gets replaced with the GV adapter.

Head scratcher....lol

The original TH400 is still in it. I'm leaning towards bailing on the 4l80 idea simply because every step of the install is $500+ extra....harness, controller, speedo...all in addition to the trans. I get half answers and no one with a bona fide 'list' and set cost of putting one in. If there was a way to take a factory controller and adapt it (or buy one thats been modded) affordably, I might consider that. Just leery at this point of an aftermarket (chinese?) electronic device that could strand the truck completely and without warning.

Talked with a few guys who are running the 'monster built' 700r4's behind 500++ ft lb torque motors and 2 of them have Vettes that have them in it that they drag race with every weekend for 3-4 yrs. The local guy who builds trans said he's put several 700's in 3/4 ton trucks - ones that are pulling trailers - and had no issues.....but he said they are built with that in mind. I have also read that 90-92's were the strongest of the lot from the factory.

Its becoming a money pit quick.

 

[SquareRoot]

Same here. I'm not willing to pay $3k for a new trans, a core charge, controller, tq convertor etc just to get OD.

I have less than 1k miles on my rebuilt 400. I didn't realize how simple the 400 is and why it's so damn tough.

I paid $800 for the rebuild with quality parts. They even opened the TQ, straightened the fins and hand brazed them. Better than factory.

That trans had 153k miles on it and still had the original parts inside.

I've done so much work to the truck the past two years I'm tired of working on it. If I go with the 4500, the dash has to come out, pedals installed, hydraulic clutch installed, driveshaft mods, etc. I'm using a Lokar floor shifter ( the tall one with the bend for bench seats) with the 400 and I LOVE it!

If I go Gear Vendor, all I got to do is swap the tail shaft housing on the trans and bolt it up. The rear shaft needs a slip joint installed for the fixed output of the 205, so it can be shortened at the same time.

Almost no more money out of my pocket. Should be a one day task and I'll have a bombproof setup with NO electronics to worry about.

 

[Doppleganger]

My 400 has <100k on it. Would love to figure a way to keep it. The GV option was on my mind too. Heard a couple places with issues on 4wd's.

Dunno.