Re: [Amc-list] Early 80's 4-cyl bellhousing

[Frank Swygert <farna@xxxxxxx>]

BAD IDEA!! That little four (a 2.5L GM "Iron Duke" in your case) doesn't have the torque to pull an OD. It probably doesn't have enough to pull an OD five speed either. The OD gear in most five speeds is similar to that of the old ODs, so if you do go this route do yourself a favor and find a T-5. In either case you'll need a lower rear axle ratio to pull the OD.

A common misconception is that OD adds a higher gear -- it does just the opposite. Check the books for any old car with a three speed and OD and you'll find that it used a much lower rear axle ratio than a car with a standard three speed. OD reduces rpm in a street/strip car that's set up to run on the strip without using OD, that's why people think it's such a great thing! That's not the case in a pretty much factory stock car though. 

All OD actually does is add another gear. OEMs add OD to an auto trans to get a fourth gear without having to completely retool all the hard parts of the trans -- same with a five speed manual, really. 2/3 of an auto trans has to be reengineered (maybe 3/4!), but there is still a substantial savings in using existing 1-3  internal components. 

It really doesn't matter how they add the fourth (or fifth) gear, it's the spread between the gears that matter. The rear axle ratio is adjusted accordingly -- more gear for less first gear, less rear axle gear if first gear is low. 

------------
Date: Tue, 7 Oct 2008 22:13:04 -0400
From: "oldcars@xxxxxxxxx" <oldcars@xxxxxxxxx>

I have an 81 Concord 4 cyl 4 speed, which has been laid up for a long
while. 
I have to fix the clutch master cylinder and slave cylinder, and replace
the windshield.

However, I came across a T-86 with overdrive

I would love to team up the overdrive with the 4 cylinder, so it would have
good
crusing mileage. 

Are there any other patterns likely to be drilled into the bell, or only
the SR4/T4/T5?

-- 
Frank Swygert
Publisher, "American Motors Cars" 
Magazine (AMC)
For all AMC enthusiasts
http://farna.home.att.net/AMC.html
(free download available!)

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