i need help with zf5 issues

[turbo74pinto]

the truck is a 94 with a powerstroke. it has the zf5 and is 4wd. the last few times i used it to pull my landscaping trailer, i had some issues. a few times a day, id downshift into the next gear and it would grind when i let off the clutch. so, hypothetically heres what id do. cruising at 40mph in 4th gear, traffic ahead so i clutch it and grab 3rd. the shifter feels like a good engagement but when i release the clutch, it grinds like im trying to shove it into gear without the clutch. id re-clutch, pull out of third and put back in. then it would work fine.

the other problem is when id be at cruising speed and let off the accelerator, to kinda coast slower with the truck still in gear, the truck would buck. as if the load on the trailer was shifting and slamming forward. but, nothing was shifting. speed change may only be 2-3mph over a good distance. like i said, in gear, cruising rpm/speed, and let off the fuel.

both these happened at the same time. now, i do downshift a lot to let the motor brake the truck. that was the first time the grinding when i was exiting the freeway.

i have since parked the truck (in may) and i am waiting to pull the motor and trans to install a motor im rebuilding and repair the trans. does anyone have any clue what i need to look at? anyone have this problem before? if so, what was done to correct it?

[madpogue]

How many miles on the truck? Original flywheel? If so, your second symptom, at least, is a classic expression of the dual-mass (aka dumb-mass ) flywheel in its last days.

Before pulling the powertrain, pop off the flywheel inspection cover. Truck in gear, engine off, grab the part of the flywheel you can reach. If you can move it rotationally a few degrees either way, then the craptastic little bits that barely hold the two parts of the flywheel together are starting to fail. Word is, if you let it go, and the flywheel comes apart, it can grenade the tranny case, which is not a good day. Recommended replacement is a single-mass, along with a clutch kit replacement; the OEM clutch fork is also known to be wimpy, and this would be an opportune time to replace it.

As for the brand/type of flywheel and clutch, all depends on how you drive. We went with Luk, one made for pretty-much stock power. Lots of other options, though, based on how you're gonna use the truck.

[turbo74pinto]

Thanks for the reply. The truck has 398000 on it. Although the trans was replaced with a used unit with unknown miles. The flywheel is a single mass and the clutch is a HD dual disc set up. I'll look into doing the fork while its apart though. Thanks for the insight on that. Who sells a good fork?

Bob

[madpogue]

IIRC, the latest one from the stealership is an improved design. But call to confirm; this is coming from (eek!) memory.

[turbo74pinto]

OK, thanks!

Anyone else with ideas?? I'll just dig in if need be. But, a starting point or direction would be nice.