ZF 6 speed

2WD or 4WD? I have been doing them same, looking for a 6 spd for my '00 7.3 4WD. Can also try car-part.com.

IDT-572 wrote:4x4, hard to find............

I know what you're saying, looking for a 6spd to replace mine in my '00 F250 7.3 4x4 w/ 303K(getting a slight input bearing whine, probably not slight if I can hear it above the "regular" diesel noise), best I found was a rebuild for $1800. I have found a dozen used 2WD models but only a few 4WD 6 spds(on Craigslist from FL to N. Carolina to E. Texas). I will keep an eye out, what are you looking at spending(if you don't mind me asking), total with shipping of course. What is happening to yours to make you want to replace it?

The gear roll-over noise is typical in a ZF trans, had the same noise in my ZF5 spd behind an EFI 460. When I changed my factory clutch(pressure plate, flywheel, TO bearing, actuating arm(the stock ones sometimes crack) and block to a South Bend CON-OFE set-up, it came with a Kevlar input shaft bushing, the noise was gone....for a while. The end of the input shaft was chewed up(fairly typical on these manuals) a bit due to the factory pilot bearing failing. The SB clutch only lasted 80K, I figured for a $1000 clutch it should have lasted longer than the supposedly POS factory clutch that lasted 175K. I have since installed a cheaper CARQUEST clutch and re-installed factory flywheel along with an input shaft repair kit. When first installed the roll-over noise was once again a bit quieter, but ultimately came back. I then removed the thin auto trans fluid and now use 5w-40 Mobil 1(roughly the same low temp viscosity but much higher vis. when hot as compared to ATF) with a 1/2 quart of 75-140 synthetic gear oil, this REALLY quieted down the trans and has been in there for 47K miles(the bearing whine was there before I changed the fluid). I put small rare magnets on the drain/fill plugs and have checked and no bearing or gear debris at all. The trans shifts fine due to the low vis. 5w-40, a higher vis oil or more 75w-140 would or could cause low temp shift issues. Hope this helps.

Glad to help if possible.
I can tell you the first gear or L on my ZF S6-650 6 spd is almost too low(kinda hard to shift from L to first gear due to the large "gap" between the gear ratios), I only use it when pulling our tandem axle trailer when loaded near or over 20K. This info may give you an option and possibly be cheaper and/or easier to find.
http://www.dieselhub.com/trans/zf-5-speed.html
A wide ratio S5-47 or a better option(IMO) is a close ratio S5-47 will give a lower first gear without being a "granny' low or for the most part, useless 1st gear for traffic driving. I have actually run mine in 4WD low in town(less than 35mph)when towing heavy while not locking in the manual front hubs (got rid of the vacuum actuated hub crap), really helps with get-up and go but the shifting goes fast.
Here are some specs for the ZF S6-650.
http://www.dieselhub.com/trans/zf-6-speed.html
Hope this also helps. Good luck with your search.