I have a ZF-5 in my 351 4x4, Shifts great, even stays in reverse, new clutch. This was a boneyard-running truck find.
The only issue is loud "chatter" at a high-way speed only when there is no "load" on the drive train.
If I lay off the gas at highway speeds, and before the truck starts to slow You can hear lots of "gear slapping"
Very quiet accelerating, (it has a load) and very quiet decelerating (under a load). Just in that sweet spot does the gears slap around.
Is this a warning sign of impending doom? or could this be this way for years?
I've been thinking about this. Is this the same tranny I had in a 1988 F250 with the 7.3 IDI diesel?
A ZF S542 is what I believe it was.
It was a tough tranny but didn't shift like most manuals I was used to. Could be the miles on it, over 200k. I would start it in the "slot" for the gear and wait to feel it sync up, then ease it into gear. Like it wasn't syncro'ed.
I put Amsoil ATF in there and it helped a lot. Especially when it was cold.
I did have one breakage, I pulled up to a stop and was in second, Reached over to put it in first when traffic cleared and couldn't find the shifter. Looked over and it was laying on the floor. The shift tower broke. Made it home in second gear.
Yes, basically the same tranny. Different gear ratios and different case to accommodate the different bell housing bolt pattern, but still the "42".
Synchros appear to be a weak point on these. They are a truck transmission and weren't designed to speed shift. And they were designed for Type H ATF, which is explained on the Evolving Specifications tab on the Specifications/Lubricants page.
You didn't say which Amsoil ATF you used, but they recommend any of their three ATF's for the ZF5, as shown here on the transmission tab. Apparently they all meet or exceed the Type H spec.
Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/soon-to-be ZF5/3.55's & EEC-V MAF/SEFI
I don't remember which type of Amsoil ATF it was, probably what Amsoil recommended on their website.
I've had good results with their tranny fluid, our Suburban would "hunt" while driving, shifting up and down and in and out of lock up. Found a GM Service Bulletin that said to use synthetic. It cleared it up.