Quote:
Originally Posted by funkhoss
I did some pretty extensive research on high-geared GM rear ends when I was working on my wagon. At one point, my wagon had a 2.14 rear, .73 overdrive (NV3500 transmission) and the factory 350 motor. It would do 55 MPH at just under 1000 RPM. At the time, I was using a heavy, 4.3 V6 flywheel, which helped with low RPM torque, but yes--the engine pulled that speed/RPM just fine. In fact, I would often cruse at 45 MPH and ~800 PRM.
The highest ratio that is available for the 8.5" 10-bolt in your G20 is 2.41. The 7.5" 10-bolt (which is what I put into my wagon) was available with 2.29 and 2.14 ratios, but that might not be heavy duty enough for your van, depending on how much you haul. (Astro vans had that rear, though, so they're tougher than you think. I don't know if an Astro van would swap into your G20 or not. They have the same wheel bolt pattern, but the differential is off-center and it may be a bit narrower.)
The only other option is a fairly rare 8.75" GM rear, with 12 bolts on the ring gear and 10 bolts on the cover, that came in some cars in the late 70's and early 80's. There was a 2.28 gearset for it, but that gearset only came in Cadillacs from 1977-1979. You could weld spring mounts onto one of those Cadillac rears and bolt it into your van, as it has the same wheel bolt pattern (5x5"), but it would be narrower than your factory rear and the axle shafts and outer bearings would be smaller/lighter duty. If you wanted a rear that was roughly the same width and the same strength (same shafts and outer bearings) as the factory rear in your van, you would need to find one of these 8.75" rears from a late 70's/early 80's B-body station wagon and swap in the 2.28" gearset from a 77-79 Cadillac. I serious considered doing just that with my wagon, before I fulled embraced P&G with EOC and gave up on extremely high gearing.
What is P&G With EOC please??
I hope this helps! Let me know if you have other questions about high-geared GM rears. Unfortunately I know very little about Ford rear ends. 
-Funkhoss |
Well your info is what I am running into with my wanted changes.
Case in point: The problems with going to the super tall gears.
There just is too much cost and problems with them.
I was told by IWE read ends only, that for the Ford, my rear end is a 8.8 carrier with 28 Splines axles. To get to a 2.41 gear set I have to convert the rear end to an 8.5. Of which they never made a posi carrier for. So I have to do some major mods to perhaps get it to fit and then worry if I got it right. AND this set will cost around $500.00+ just for the parts and I still have to make it work. That some machining or slims might be needed etc.
For the Chevy, nearly same deal, I cannot just bolt the tall gears in, again I have to replace the carrier, and as it seems GM is no longer supplying clutches for their posi I am stuck with used or hope to find some NOS parts. And again the cost just to buy the parts to do all of this is also around $500.to $600.00 And I should do a complete rebuild so add another $300.00+.
I was working from the idea of around $200.00 for just the gears, all this extra costs make it less a good deal.
Your information may be an answer. The Chevy rear ends are prone to howling, so far every van I have had howled so it seems to be a design flaw, so I am considering swapping it a different rear end, but need one better made and able or even comes with those gears… and another concern will be finding one that is wide enough to fit the van. Perhaps finding one that the axle tubes can be swapped?? Or Dodge or Ford...like the Ford 9inch...?
So I am going back to my old plan. I am fairly happy with both cars as they are, the Ford is a real jackrabbit jumper off the line and the normal shift points work great under light to moderate power.
The only lack is in a power down shift, which can be a little off, either too low or too tall, lugging a little or over revving, but the main thing I need is a second over drive 5th gear. Adding the old B&W Overdrive looks so very good now.
And the same can be said for the Van.
The best thing of all worlds would be a rear end stronger with less prone to howling with the super gears and perhaps convertible from drum to disk brakes.
Otherwise the Borg Warner OD gives me the deep drop in RPMs at cruse I think I need and if it does not work out I am only out a few hundred of dollars not thousands.
But considering the wright and large front end I truly think a 6 or 8 speed auto would work best in it.
I would very much like to talk with you more.
Thanks for your input and help.
Rich