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Old 03-21-2017, 02:34 PM
NJTy180 NJTy180 is offline
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Join Date: Jul 2016
Location: Manahawkin, NJ
Vehicle: 85 745 D24T
Posts: 34
Default Differentials, Ratios, Speeds and RPM's

I've been doing a lot of research on this forum and around the internet for the past few months learning about the diffs that came in these cars and trying to figure out what ratio would be best for my project.

The car I have the most experience driving when I was younger was the 745 w/ ZF Auto that I'm currently working on, but I don't plan on using the ZF when I put it back on the road. I would like to retain the driving/cruising characteristics that transmission provided, just with the ability to row gears.

The other two diesel powered Volvos that were in my family growing up wer a 84 244 w/ 3 speed auto? (that car sucked) and a 245 w/ M46. It wasn't until I started reading the comments on this forum did I remember how short 1st gear actually was on that trans.

I picked up my 83 760 will intentions of doing a full drivetrain swap into the 745, but I really don't think Ill be happy with the M46 and after seeing all the T-5 swaps, that got my gears turning on my own trans swap.

It's really been bugging me not knowing what gear ratios were in the 3 cars I have so today I set out to answer that question and here's what I found.



1983 760 D24T/M46
1031 Housing - 3.54 Ratio - Non-Locking

1989 745 B230FT/AW71
1030 Housing - 3.73 Ratio - Non-Locking

1985 745 D24T/ZF22
1031 Housing - 3.91 Ratio - Non-Locking

I already knew none of the cars I had were locking diff equipped, but I will hopefully remedy that in the future, the ratios were the important thing for the day, now I could calculate gear ratios, final drive ratios, speeds and RPMs based on OE tire sizes.

The ZF/3.91 combination provides the following results;
ZF Ratios - 1st: 2.48 - 2nd: 1.48 - 3rd: 1.00 - 4th: 0.73
Final Drive Ratios - 1st: 9.70 - 2nd: 5.79 - 3rd: 3.91 - 4th: 2.85
Speed @ 3000 RPM - 1st: 22 MPH - 2nd: 37 MPH - 3rd: 55 MPH - 4th: 76 MPH

The M46/3.54 combination provides the following results;
ZF Ratios - 1st: 4.06 - 2nd: 2.16 - 3rd: 1.37 - 4th: 1.00 - 5th: 0.79
Final Drive Ratios - 1st: 14.27 - 2nd: 7.65 - 3rd: 4.85 - 4th: 3.54 - 5th: 2.80
Speed @ 3000 RPM - 1st: 15 MPH - 2nd: 28 MPH - 3rd: 45 MPH - 4th: 61 MPH - 5th: 77 MPH

Now that I have some numbers to work with, I can figure out what diff will work best for me. Just figured I'd post this now because this was the information I was looking for when brainstorming the project, hopefully someone else can find it useful in the future.
__________________
Morgan

1985 745 GLE D24T ZF22 || 1983 760 GLE D24T M46 (Parts Car) || 1989 745 Turbo B230FT AW71 (Parts Car)
1993 GMC Typhoon #0180 || 1993 GMC Typhoon #1579 || 1992 GMC Typhoon #1068
2007 Chevy Trailblazer 3SS || 2001 Chevy 2500HD 4x4 || 1952 Cadillac Series 62 Coupe

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