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Differential Calc

To: MGList <mgs@Autox.Team.Net>
Subject: Differential Calc
From: Michael Graziano <mgrazian@ltcm.com>
Date: Mon, 22 Jun 1998 18:12:26 -0400
Hello all.  I'm still trying to figure out why my Midget is
topping out at 50 mph at 4500 rpm.  THanks for all the
suggestions so far.  While none have solved the problem
yet,  you have all moved me along the learning curve quite
rapidly.

I've narrowed down the problem (I think) to my
differential.  

The car still has plenty of pep at 50 mph,  so I know it's
not something like carb, valves, exhaust, etc.)  It's simply
bound by the little red section on my tach.  

The clutch isn't slipping (it's new,  and I'd be able to
tell if it were slipping that much).  

And I've made sure my gauges are correct by having a friend
driving next to me to check the speedometer, and by using a
tach/dwell on the tach.  Right on until 4000 rpm when the
meter tops out (the gauge increases steadily after 4K).  

SO it must be in the drive line.  I thought maybe it was
possible for someone to have rebuilt the tranny with the
wrong gearing (thanx Bob for straightening out that
misconception).  What's left?  The differential.

I know the PO (quickly becoming an ignorant DPO) changed the
differential because one of the bearings (somewhere) had
worn, but he didn't know what gearing the new (used)
differential was.  Yes,  I called him this weekend.  I even
called the mechanic who installed it, entertaining a slight
hope that he might have a) remembered where he got the used
one (it was only 6 or 7 months ago), or b) he actually kept
records.  Negative on both (duh!).  

Now the question ..... How can I tell what the gearing in
the differential is?  I tried jacking up the car by the base
of the differential (so both rear wheels were free) and had
2 friends turn the wheels at the same rate while I counted
how many times a little white dot moved around on the drive
shaft per wheel revolution,  but either they were inept at
turning the wheels synchronized, or I was inept at counting
the white dot.  End result:  Aggravation and a wide range of
results.  I wasn't even close.  THere has to be a better
way?  

Any insights on any of this?  My next step is a mechanic
(God Forbid) because I HATE watching grandma in her 85ish
corolla with blue smoke coming out the tailpipe giving me a
dirty look as she passes me like I'm going in reverse, (True
story, BTW).

Mike


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