I have a 1985 E150 van conversion (to a passenger van). Recently
slightly larger tires (28.9" dia vs 27.1") were put on (due to an
excessive number of blowouts) and this seems to have thrown the final
drive ratio off by quite a bit. Even taking into account the change
in the speedometer and odometer, my mileage has gone down to 11-12
from 14-15 mpg.
Currently, when crusing on the freeway at 60-65, I'm pulling about 10"
of vacuum which drops down below 3 when going up even the slightest
Going 70 on the flat is 7" and on any incline goes to 0.
In gear and at a standstill its 18" and 21" at idle and in neutral.
High rpms in neutral will still pull 20-21" so i dont think i have a
major exhaust restriction, and im not running lean so i dont think
there are any major vacuum leaks.
This leads me to believe that the new ratio (equivalent to putting a
3.25 gearset in) is a bit too tall for the larger diameter tires and
As it is, the engine (5L V8, 2bbl 2150 feedback carb) and tranny (AOD,
not AODE) are stock. The current gearset is a 9" 3.5. Am I on the
right track here? Or should I be looking for something with the
I believe that in order to return the final drive ratio to the way it
was before putting on larger tires, i'll need a 3.72 gearset (actually
3.75, but those are hard to find!). Ive also considered a 3.89 or
If changing the gearset is reccomended, what ratio? I'd like a bit
more acceleration and torque than the original stock set up (with the
smaller tires and 3.5) but I also want to keep the gas mileage
Would using a 3.89 or 4.11 make a big difference? (The van is a
conversion, so its several hundred lbs heaver than the empty cargo van
it was, but i don't tow and i do spend a lot of time on the freeway)
Oh yeah... what sorts of odd tools are needed for this operation
should i try
and do it? Aside from a heavy duty socket set / torque wrench and a
that is. I've seen some people use a press (which i really dont
have), but is
that really necessary?
I know, its a lot of questions, but it helps to keep everything
thanks in advance!