1990 F150 5.0 zf5spd 4x4. When I have my foot to the floor, I can get passed by a school bus. Here's all the work I've had done by a shop (so I know it isnt the problem)
-New transmission seals and shift forks
-Head gasket
-valve job
-machine heads
-cleaning of all disassembled engine parts
-new jasper rear end
-sway bar, ball joints, tires
-all fluids correct levels

So, I think it might be an incorrect gearing between the front and rear axles. The front end was "rebuilt" before I bought the truck. I think it may be a different gear ratio than the jasper rear. Any ideas?

 

It would not matter unless your in four wheel drive. At that point you would know it real quick ....

 

Just a thought,, how are the catalytic converters? Stopped up maybe???

 

It would not matter unless your in four wheel drive. At that point you would know it real quick ....

I mean when its in 4x4, it jumps and bogs down. It will not just drive amywhere near the way it does in 4x2

 

never checked em. Ill give that a shot

 

Jump, turn into scrap steel ( fork in a blender comes to mind) all things that would happen, yes. But in 2wd it would have zero effect on the drive line. Did you match the jasper to the door jam info?

 

If things aren't too rusty just loosen the studs at the manifolds to produce a pretty good leak, or take the pipes completely off the manifolds IF you can get the nuts off the studs with out too much trouble.. Don't forget to use plenty of PB blaster/ or your favorite penetrating oil. if things are really rusty start spraying a day or two in advance. Then drive it and see if there is any change..

 

My son and i swapped the Mazda 5-spd in his 92, for a ZF trans...noticed the gearing difference right away...i was told the ZF is more of a heavy truck trans,thus geared lower and slower...made to haul a load...not haul a**...
That said, if it's only noticeable in 4x4, your diffs don't match, as others have said.

 

There are 2 different ZF's. A close ratio for gassers and a wide ratio for diesels. If you have a wide ratio hooked to a 5.0, I am so sorry.

 

and how would he use a wide ratio behind a 5.0? the bolt pattern wouldnt work at all.


you need to do a few things here. first figure out what gears you have out back and in front. I wouldnt use 4wd until you confirm they are close.

What size tires are you running? also you shouldnt be using first gear unless your wanting to CRAWL. first is a granny low gear similar to the old NP435 4speed trannies. and like mentioned this is a HD tranny geared lower then the m5od you previously had.

 

Could someone have changed the bell housing?

 

Be sure to check the initial timing of the distributor. Should be around 10 degrees BTDC.

 

Could someone have changed the bell housing?

No, the zf bell housing is integrated, and the wide ratio zf would not fit behind a small block. And make sure you remove the SPOUT jumper if you have a tfi control module (cant remember if 90's were)

 

You guys all missed the obvious. It is a 5.0 and that is why it is slow

 

ROTFLMAO