1978 Eagle 05 Differential

[gpzzdrm]

Bill, I traded my 4.10 or 4.11 from my MCI 5C for a 3.38 from a Eagle. I can find the # if you are intrested.  Not sure he still has it, as I did see it on Ebay. Let me know if you are intrested.  Tom Y

Tom,
Saw this after my last response. I am no longer chasing the 4:10 diff. The world trans. deal fell apart. I am no going back to plan 1 which is the HT740 I had, but replacing the 3:73 with a 3:36.
Bill

[David Anderson]

Bill,

Do you already have a 3:36 rearend?  I'm pretty sure my 1985 Houston Metro 10 has a 3:36 because my speedo shows 80mph at 2100.  I got these numbers as per Jim Sheppard.

I think his metro 10 has a 3:73 since he was surprised as to my numbers I'm getting on mine considering it is a bus from the same fleet as his.  Of course that assumes my speedo and tach are correct. 

David

[TomC]

3.36 with 11R-24.5 (478rpm) will give you a 1600rpm cruise of 60mph, 1873 at 70mph.  If you could find a 3.08, that would be better.  That would give you 1600rpm cruise of 65mph and 1840rpm at 75mph.  Much better!  It's to bad the HD4060 or B500 didn't work out.  With the 4.11 you'd have a 75mph cruise at 1571rpm and a rocket ship off the line.. Good Luck, TomC

[David Anderson]

Tom C.

I've got a question.  On any given differential, is the rpm to speed proportional when in  1 to 1 ratio, 4th gear lockup? 
Ie., 1600/60mph    1873/70mph   2100/80mph

The rpms for each equation are slightly different, but are they close enough for accurate computations?  They are all in the 26rpm +/- per each mph.

David

[TomC]

No- try 478rpm with 5.29 ratio.  At 60 you'd be turning 2528 and at 50 you'd be turning 2107 for a difference of 421 or 42.1 per rpm.  Each ratio will have different rpm splits between speeds.  Good Luck, TomC

[David Anderson]

Thanks Tom,

I never thought about the formula, but I assume anyone can compute their gear ratio by  looking at their tachometer at 60 mph and dividing by 478 (24.5" tires) then can get engine rpms for any mph by computing rpms for each mph from the above formula.  I drove my bus yesterday and my rpms were just a tad off the mark at 60 mph, thus the computation below:

1606/478=3.36  1606/60=26.76 rpm per mile per hour.  26.76x70mph=1873 engine rpms at 70 mph and so on, and so on.

It's simple math, but my "light bulb" never turned on till this thread was written.  That's the way it goes sometimes.

Thanks,
David