NV4500 swap is underway

[DirtyLarry]

Wow, a S6-650 behind a 6.2L must be like driving a race car engine backed by a dump truck transmission

Glad you like yours….you could have the ZF S6-650 in my 2001 2500HD. I hate the damn thing. Worst shifting manual trans I’ve ever owned with an even worse shift pattern. I’ve own that truck since new and 13 years later it has finally started to loosen up where it isn’t quite as notchy as it was up to this point (It just turned 59,000 miles last week) but I still hate it. The clutch pedal geometry on the GMT900 trucks is also quite funky. There is no slip to it, it works like an on/off switch where it is almost impossible to launch the truck smoothly. Between the clutch operation and the awkward shifting ZF 6 speed is why it has only racked up 59K in 13 years. I don’t like to drive it much.

I still prefer a NV4500 over the ZF any day, but there is no doubt about it the ZF is a much stronger transmission by a long shot.

[K20chevy]

Like I said before and someone else mentioned it before, my S6 650 (and his) shift really smooth, so you must have gotten a bad one. And I have to admit that my clutch linkage and all that is totally different anyways since I jused the duramax hydraulics with the OEM 78 clutch pedal with a home turned and welded mount. so my clutch pedal has about half the throw of the stock one. Takes a little to get used to, but makes for really fast shifts. And together with the 6.2 L92, it makes for a fun and fast combination. The ZF in my truck the way it is set up actually has relatively short throws for a truck tranny and also I think it shifts really nice. You really must have gotten a bad example.

I even think I have an on bord video from a stand still shifting through the gears..that shows how nice it does shift...

Originally Posted by DirtyLarry

Wow, a S6-650 behind a 6.2L must be like driving a race car engine backed by a dump truck transmission

Glad you like yours….you could have the ZF S6-650 in my 2001 2500HD. I hate the damn thing. Worst shifting manual trans I’ve ever owned with an even worse shift pattern. I’ve own that truck since new and 13 years later it has finally started to loosen up where it isn’t quite as notchy as it was up to this point (It just turned 59,000 miles last week) but I still hate it. The clutch pedal geometry on the GMT900 trucks is also quite funky. There is no slip to it, it works like an on/off switch where it is almost impossible to launch the truck smoothly. Between the clutch operation and the awkward shifting ZF 6 speed is why it has only racked up 59K in 13 years. I don’t like to drive it much.

I still prefer a NV4500 over the ZF any day, but there is no doubt about it the ZF is a much stronger transmission by a long shot.

[DirtyLarry]

Glad you are enjoying it. There is no doubt in my mind that transmission will probably last forever. I don’t buy into that I got a bad ZF 6 speed as I have driven several other ZF 6 speeds in GM and Ford Stupid Duties and they shift equally sucktastic, but that is just my opinion. I happened to love the way the NV5600 shift gates and pattern is laid out but there are people that hate that trans and prefer the ZF 6 speed. It’s all in what you like. I still like the NV4500 the best.

[DirtyLarry]

So it’s been almost 4 years and 10 to 15,000 miles since the NV4500 swap and last March coming back from Death Valley the NV4500 really started screaming in 5th gear. With that I knew it was time for a 5th gear cog and fresh mainshaft. Not wanting to cut another mainshaft to make the Advance Adapters kit work I started getting serious about finding a round pattern 205. Once again, birddog Mosesburb found me one with member Ryanroo so coming back from the Overland Expo in Flagstaff last May I stopped by Ryan’s place and picked it up (Mosesburb is like a bird dog….tell him what you want and he can sniff it out, anywhere anytime. He found my brand new in the box front Dana 60 and a few Warn winch bumpers for me).

So the big mystery here is why did the trans defecate 5th gear in the first place?? Well, at first I really wanted to blame the Advance Adapters kit just because I typically really hate aftermarket stuff but once my trans rebuilding friend took it apart, the AA collar that holds 5th gear was tight to my surprise. I figured the AA collar came loose and allowed 5th gear to walk around and knurled the mainshaft. The mainshaft was indeed slightly knurled and the gear did rock a bit but the collar was indeed holding it tight. With that, maybe the naysayers are right about towing in 5th gear eat up NV4500’s. I dunno, I know a few guys that tow like crazy in 5th gear and have never had a problem with them. I also don’t tow but the truck does weight 8,000 lbs. Maybe I overheated it in Death Valley and hauling balls down the mountainious Hwy 160 from AZ to I-25 in Trinidad, CO

Not sure, but this time the 205 will directly mounted to the trans with no adapters and coolers are being added to the trans just for safe measure then we’ll see how it does. If this things craps again, next go around will be something different like an Allison. That would be a tough pill for me to swallow because automatics are against my religion.

Bought this gem from Ryanroo. A round pattern 205


I didn’t get around to ripping into the round 205 until December 2013. It came to me with a slip yoke rear but I used the rear section from another 205 I had laying around with a 1350 fixed yoke. I also traded did some trading with ORD for the long 32 spline input for a short 32 spline input. This picture is just after I gutted it in preparation for sand blasting. The internals were in great shape, almost like new. I only had to replace two bearings in the whole thing.


The rear transfercase section actually came out of the 205 that was in my dad’s ’78 K20 wrecker. No wonder the speedo hasn’t worked in that truck for many years! Look at that speedo cog! The good news is you can still buy new ones from GM.


I also got a new speedo adapter for it as well. There is a seal inside the adapter that isn’t replaceable but you can get new adapters from GM also. The new adapter is not pictured here though.


With getting away from the AA kit also meant I had to find an OEM rear trans cover and modify it to clear the shift rail and idler nut. Argonaut and I were going through the mods at the same time and both of us did pretty much the same procedure to make the clearance holes.


My ain’t that purdy!


I used a wood spade to make the hole . Hey, it worked!


After making an access hole for the range shifter rail and idler shaft nut clearance


As Argonaut pointed it out the trans cover needs to be clearance to allow the 4 NP205 front seal retainer bolts to pass through. This was before I made the mod


It doesn’t take much elbow grease with a rattail file to make a pass through for the tcase front seal retainer bolts. A bit of flat filing on the seal retainer itself was also required as it appeared to be too thick to seat into the transmission cover properly.


Here tis right before I stabbed it in the truck.


Here is the trans all sinched down. One thing new is the Energy Suspension trans mount. The old AA kit trans cover bolted directly to the homemade square stock bracket.


So that is where I am at as of right now while I wait on a few parts. The drive shafts are in town being reworked as the rear is being changed to a 1350 U-joint for the tcase end and I am using a flange mount front shaft this time instead of the old yoke style mount that is a MOFO to install due to only being able to turn the bolts ¼ turn a time. The new front shaft needed to be lengthened and of course the CV needed the full-on replacement. The shafts should be done Monday and the trans coolers should be here Tuesday. That’s it for now!

Here is the old deal buttoned down to a crate ready for a new home.