Ok, maybe I shouldn't have done this but, oh well! I was tinkering with my truck checking fluids etc. And decided to take her for a spin. Got her on I44, turned off OD, ran her to 4800 rpm, turned OD back on and ran wot to 4500 rpm. Of course I buried the speedo. So out of curiosity I looked up a speed calculator and put in the forth gear ratio, rear end ratio and tire size. Calculator says 148MPH !!!!! could this be wrong. I figured the truck was governed!

 

Older models do not have speed limiters, but I seriously doubt you were doing 148. My 90 had the 5.8 engine and could come nowhere near that. As these are nothing but big heavy bricks you are trying to push through the air, I would bet less than 115. Probably lower.

 

Well either the calculator was wrong. Or I was wrong about the input info. I entered 4th gear at .71:1 with 3.55:1 rear with 235/75/15 for tires @ 4800 rpm. Can someone confirm these numbers?

 

Edit**** 4500 rpm in fourth not 4800. I ran 4800 before turning OD back on.

 

You can actually EDIT your post instead of making another post - just click the EDIT button in the lower R corner of your post.

The math is correct - the numbers obviously aren't. Not only would the truck flip before getting to 148mph, the tires would explode. So unless this is a HEAVILY modified truck & engine, there's no way it was doing what you posted.

And if it was, you could be thrown UNDER the jail for doing it, so I wouldn't post again about illegal activities. It's against the user agreement on this forum (& most others). Next time, go to a TRACK or a runway or some other non-public place.

 

Ok advice much heeded, thank you. As far as the edit thing, I'm using the mobile version of this site and I haven't found the edit button. Apologies for the extra post.

 

Does your truck have an AOD or an AOD-E? A 90 should have an AOD but the way you describe switching the OD off sounds more like an AOD-E.

The reason I ask: the AOD will not upshift from 3 to 4 at WOT, it will only upshift if you release the throttle and it will shift back down again if you bury it. 4th gear in an AOD is designed simply as a cruising OD not as a performance gear

 

It has neither AOD or AOD-E. its an E4OD. The only reason I even used the button was to build more rpms in 3rd before allowing to go into overdrive( foot on the floor, OD on, shifts at 4200 rpm) I understand that fourth is not a performance gear. but it is still possible to gain rpm especially after running third so high. now I've come to the conclusion that this truck isn't completely stock. I know for sure that the trans is not stock(added clutches etc) but the engine I'm not sure. I can only see what's on the outside. actually I have been pretty impressed by the way it runs. a few bugs here and there but hey its a 90. I have owned the truck since October. It had just received a trans build and engine rebuild. the engine is extremely stong for a 302. i can only guess that it has a mild cam (it sounds like it) k&n fipk, msd ignition goodies. I've tried to reach the previous owner several times to no avail. I bought the truck from a used dealer and found the receipts for a lot of work done to it, mostly trans work and for certain engine parts. I wish I knew exactly what was in this thing. I bought this truck looking for just a good daily driver, and ended up with little more.

 

Any chance that the PO swapped rear end gears?
With 3.55s you should be right around 1960 RPM @ 65 MPH
If he put 4.11s in it you'd be turning about 2280 RPM @ 65 MPH and 4500 would be about 128 MPH which is way more believable than 148.

 

I don't know. but what I can do since I know the speedometer is correct (roadside speedbox) is see if can get a pic up of the gauges at 65 mph. I really don't think I have 4.11's, wouldn't have been able to negotiate the recent snow we had here very well with that gear.

 

Just look at the tach when you're at 65.
The difference between 1960 and 2280 should be pretty obvious

 

Will do.

 

Alright 65 mph = 2000 rpm. its not the 1960 you were quoting but i guess its close enough. i imagine there could be differences in tires, im not even running LT tires. they are 235/75/15 Hercules MRX Plus IV. so the actual diameter may differ from the LT 235/75/16. thus the difference of 40 rpm. this is just what i think. i could be wrong.

 

Read this caption:



To confirm the gear ratio, chock at least 1 front tire fore&aft, jack up ONE rear tire, put the trans or t-case in N, mark the yoke/companion flange to the rear axle, then rotate the lifted tire exactly 2 revs while counting the d'shaft revs. If it goes around ~3 1/2 times, the gears are 3.55; if it goes slightly more than 4, they're 4.10s.

Another way is to pull the fill plug on the front of the diff housing & rotate the d'shaft (tires chocked, rear lifted as above) so you can read what's stamped into the edge of the ring gear.

 

Factory tachometers are notoriously inaccurate. 1960 RPM vs. 2000 RPM is not a difference that they can display. Also my figures were based on 720 revs/mile. Some 235/75-15s have lower revs/mile, some higher. That's merely the number that Ford uses in calibrating their late-model PSOMs.

You have 3.55s