saginaw 3 speed with 308 gears, Pro'/Cons

[steveo3318]

Ok guys, I need opinions on anyone that had/has this setup and how its ran for you. I currently have a little over 450 hp in my 7 bolt Saginaw running into my 373's. I do way to much highway driving and the 3000 RPM for 60 to 65 is killing me. I want to keep the 3OTT.

So please let me know any experiences if you have a nice street motor/Saginaw/ and 308's. RPMS at cruising speeds would be huge! I don't race or pull anything

Will I have much problems on take offs with having to slip the clutch to much?

[FrankenCub]

Other than a stock 307 I'm in the same boat, 3000rpm at 65 and not likeing it. I've considdered swapping out the 3OTT for a 5sp but I need to spend money on my engine first. Not sure I'd want to swap for 3.08's because I haul firewood with my truck and looking into a trailor to tow my tractor. Maybe the 3.08's and 4sp with granny gear would work out better ?

[steveo3318]

Also does anyone know how to identify if I have a 3 or 4 series carrier? Or does it have to be taken out!

Yeah mine is strictly a cruiser. I aint pulling anything lol. Pretty sure I am going with the 308's

[Cercious]

Not sure how helpful this is, since my engine is pretty stock and I don't have a tach so I don't know what RPMs I'm running at. I do have a 3OTT with a 350 and 3.08 out back. Around town driving the way I do I get roughly 8mpg, however when I was in the Army driving home to Dallas from Ft. Leonard Wood, MO I would average anywhere from 20-25mpg for a tank, depending on traffic/wind at 70mph.

[EdB]

I have a 70 c10 with a mild 350 (RV cam) with a Saginaw 3 speed and
a 3.08 differential. It was originally a 3.73. I have had it about 35 years and
tried many different things. The gas mileage was greatly impacted when I
built the 3.08. It made a lot of difference. The main problem I have had is
getting the speedometer corrected. It is about 15MPH slow. After a massive
amount of research on the net and other sources I gave up. If I remember
correctly, I needed a green gear in the housing. It was still carried in the
Chevy parts dept. but was unavailable. There was a fellow in Calif. that made
a unit that was guaranteed to correct it. I made a lot of measurements and
ordered it. It made the speedometer 15MPH fast. I don't live far from you.
If you will PM me, I will give you the mileage in distances that you will understand.

BTW, Welcome to the board.

EdB

[steveo3318]

I actually have the green gear in the Saginaw and the speedo gear is green as well

[71sixgun]

Will I have much problems on take offs with having to slip the clutch to much?



Not with 450hp!!

[jjzepplin]

With 450hp I would start looking for my new transmission.

[steveo3318]

Originally Posted by jjzepplin

With 450hp I would start looking for my new transmission.

The Saginaw has been holding up well so far but I am already saving up for a auto gear m22 wide ratio. Going to make a 4 on the tree with a pull handle reverse. I am pretty easy on it with no burn outs or speed shifts. The motor put out about a 100 more hp than expected on the dyno. 472 hp

[jjzepplin]

Doh! Nice.

[67ChevyRedneck]

You seem to have two problems.

1. You want a lot of power.

2. You want lower RPMs.

Those don't normally play well together, that's why we have OD transmissions. If you go from a 3.73 to 3.08 you're going to lose a good bit of the off line acceleration you're used to (why have all that power if you can't "make it go?") But if you don't, you'll have the truck screaming at you. If you don't care about the "power loss" then a 3.08 is a good option. If you want to keep the power you have, you're only real option is some form of OD.

[PanelDeland]

I agree with Redneck. And I wouldn't even consider a swap to the 4 speed.You would only gain a lower gear and a shift since all the transmissions of the era were a 1:1 final ratio or less.I would love to see an option where I could lower the RPM's and keep the TOT without selling my house.I even did a little research on the GV OD and didn't find an adapter for it. Most claim the 700R4 or 200R4 does well with the 3:73 and that makes sense since the non towing package for most was a 3:42 and the 3:73 would give just a touch more grunt at the line.But it's not offered for the original carriers in the 1/2 tons. So far I haven't come up with an option that works for me. Don't forget to consider tire diameter with calculations for speed/RPM when coming up with your plan.

BTW That screaming of the higher RPM's usually stems from people who have been driving the newer vehicles with od and lower Rpms.It was pretty normal back when these were "late model" trucks. Still would be nice to have better mpgs and higher cruise speed.

[steveo3318]

giving up the power is not a problem for smooth cruising to me, Again the motor made a great deal more power than I anticipated anyway. I am going to try the 308's

[steveo3318]

anyone know what tranny color gear sets to use for 308's?

[geezer#99]

Look here for speedo gears.
http://www.transmissioncenter.net/sp...n_______va.htm

If you really do have 450 plus hp your motor won't be happy at a lower rpm.
But you'll find that out soon enough.

[Vintage Windmills]

Originally Posted by steveo3318

The Saginaw has been holding up well so far but I am already saving up for a auto gear m22 wide ratio. Going to make a 4 on the tree with a pull handle reverse.

Consider the MY6 4 spd overdrive. A trick way to get OD. Here is some info on them: http://67-72chevytrucks.com/vboard/s....php?p=3895102

Originally Posted by PanelDeland

And I wouldn't even consider a swap to the 4 speed.You would only gain a lower gear and a shift since all the transmissions of the era were a 1:1 final ratio or less.I would love to see an option where I could lower the RPM's and keep the TOT without selling my house.

Its a little newer, but the MY6 4 spd overdrive is like the 3spd and shouldn't be too expensive?

Originally Posted by PanelDeland

I agree with Redneck. And I wouldn't even consider a swap to the 4 speed.You would only gain a lower gear and a shift since all the transmissions of the era were a 1:1 final ratio or less.

Although more work for stevo,since it involves swapping to 3.08 and trans change, once installed a non granny 4spd may be just as good (if 1st is low, but not granny low) as a trans with overdrive and 4.10 especially and probably 3.73. You gain more than an extra shift (if going to 3.08), you gain closer ratios while having almost the same final drive ratio as an OD truck. I don't know about keeping the column shifter though.