changing rear end gear

[mrpaintstick]

I have a 76 c30 auto with 410 gears.I was considering changing rear gear ratio to get a little better gas milage. Was not sure which rear end I have and what options would be available. I have the original build sheet. Anyone have any experience with this?

[eray92]

An easy way to tell is count the bolts holing the cover on. Most likely a 14 bolt. But there are 2 types of them. It could also be a 12 bolt. Idk exactly what the c30s came with
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[walkerb]

Its most likely a Dana 70, if I remember correctly

[eray92]

Forgot all about Dana's
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[mrpaintstick]

I will check that. Anyway to tell from the original build sheet and truck plant or did they just use what ever was available at the time?

[donut]

Way I understand it.
14 bolt ff-srw
14 bolt -dual cab and chassis
Dana 70 -dual wheel pick-up

My understanding, may be wrong. By all means, check your build sheet, and/or post up a pic.

[walkerb]

Donut is correct. I assumed, seeing c30, it was a Dually. So do you have a single axle or dual?

[mrpaintstick]

It is a cc dually i will try and post a pic. I am trying to decifer the build sheet I will try to post a pic of it also

[donut]

Don't sweat the build sheet to much. iirc, it'll show gear ratio, not necessarily the rear-end.

How tall are your tires? Rpm at speed?
Personally, On mine, the rpm range was about where I wanted it. In my case, the expense of OD or a gear change wasn't worth it.

[mrpaintstick]

It has 235/85-r16 and 4:10 gears I have never put a tach in it. I figure on nver selling it and I do not forsee gas getting any cheaper. I am in a rural area would be nice to ba able to drive to the city if need be. I just got a line on a good 200r4 for $100.
The drive shaft is the only part fo the swap I would not be able to do myself.

[Keith Seymore]

I would like to see the build sheet if you can post it up.

Thanks in advance -

K

[eray92]

I live in Napoleon and just swapped a 200-4r into my 82 swb and now I'm switching the gears to 4.56s. There is a guy up the road towards greensburg has a farm shop on the left who can put a new tube in your driveshaft. What trans do you have?
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[mrpaintstick]

I have a 350 now. Are you talking about Kunz farm repair? Is the 200r4 a decent trans? Seems most post are about swapping to a 700r4.

[eray92]

200 is a direct swap, just move your crossmember back to the 400 location. That is if its a 6 inch tail shaft. Yes kuntz is the place I think. The 200 has a taller first gear and od. I had 3.08s in there and it would cruise at 1300 rpms. I have a 383 200-4r will be 4.56s and 255/45/20s (29" tire) and my rpms at 60 will be right around 2000, your 4.10s would drop it lower. I like my 200 a lot. If you have any questions on the swap I'm just a message away. I'll tell you everything you need
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[mrpaintstick]

I will keep that in mind thanks a lot

[eray92]

No problem, that's what this site is for
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