The Stovebolt Site Forums The Shop Area Engine Shop Different first gear ratios on three speeds?

Hello all..
After changing the rear end in my '65 C10 (3.73)to a '77 Malibu (2.29?)the three speed in my truck is giving me fits.
It is rough trying to get the truck off the line, and so I was wondering if there is a three (or four/five) speed out there that has a first gear to get the truck moving, and bolts in with minimal hassle.
I sunk some good bucks and time into the three speed, but overlooked the obvious mattter of non compatible gear ratios. :rolleyes:
My other option is to just stick a TH350 in there.
Thanks,
mike

Crowbar,

That 2.29 is a really low ratio for a truck! Cars generally have lower ratios because they weigh less and because they run smaller tires.

You don't say which tranny you have. About the lowest you can get is the SM420 or SM465, which have a "granny" first at 6.55:1. These had a combined lifetime in Chevy trucks of 20 years or so -- they aren't hard to find.

Is it possible to get higher gears for that rear end? You might find that less expensive than switching transmissions.

Brian

Brian,
I switched to the Malibu rear to make a street truck out of the old girl, no loads, just cruising.
I have a three speed from a mid '70's truck.
Don't know which one, but I will be under it this weekend and will get the numbers.
I took a 420 or 465 out of it at the same time I changed the rear.
I don't want the Granny Tranny, just a better first gear.
When my Dad put that monster tranny in his mileage went from 16 to twelve with the 250 six he had.
When I switched to the Malibu rear and 3 speed I went from 13 to 20 mpg with the 350 in it now.
So I guess the 4 speed was great for power, but rotten on mileage robbing parasitic loss.
My whole purpose was to lower cruise rpm's, and due to several factors at the time, this was the best way to go.
If I had it to do again with better circumstances, I would have kept the stock rear and gone with a 700 or a later 5 speed with OD, but hind sight....
I hope the guy that paid 50.00 for my old rear is happy with it.
More later,
Mike

Mike - as for highway cruisin, all trannys have a 1:1 high gear, so the 4 speed is the same as the 3spd for highway mileage - w/ that 2.29 rear, the 4spd 1st wouldn't be a granny, it'd be a real 1st to get ya movin!! shoulda done one swap 1st to see the effect, then the next swap if necessary

best bet now is to change rear gears as that'll be easier and cheaper than swapin trannys till you find that isn't the problem! as said, the 2.29 is waaay wrong for a truck, need more like 3

Bill

I know all the things I should have done, I was in a spot and needed to get something running with no time and fewer funds.
What I need to find out is if the M20 or m21 four speeds have a lower first gear.
More later after I find out which tranny I have.
Thanks,
Mike

The saginaw 4-speeds are cheaper and easier to find. Will probably hold up just as long. You can count the number of rings on the input shaft to determine the first gear ratio.

Mike - look here - towards bottom - looks like if you've got an A suffix Muncie 3spd , you've already got the lowest, which is likely

Bill

The best (for you) first gear ratio in an M20 is 2.56:1 in a 63-65 unit, or 2.52:1 in a 66-74 unit. This is about 1/2 way between 2nd and 3rd in the SM465 you replaced.


What you've done is you changed your starting ratio from 13.35:1 (2nd in the SM465) to 5.86:1!!! I'm not surprised you're unhappy! If you switch your rear gears to 3.08, you'll have a starting ratio of 7.05:1 which is better, but I'm guessing it will still suck. Of course, 3.73 gears will get you back to 8.5:1 starting -- better, but your highway mileage will be exactly the same.

I don't think there IS a cheap transmission swap (except back to the SM465) that's going to work well with your 2.29:1 rear. Interestingly enough, the 2.29 rear end makes the granny first in the SM465 come out to 15.23:1 -- almost exactly where your second was! That would actually work out pretty sweet for ya!

Brian

alright, THIS DOESNT LEAVE THIS THREAD, but I had an F150 in high school with a 3spd + overdrive and a really tall rear, and I had the same problem...you couldn't get teh clutch all the way out until like 10 mph...it was miserable. If I had kept that truck(?) I definitely would have put either a 5 speed, a granny 4 speed, or a 4.55 rear in it. For your truck I would put the SM420 or 465 in like the others are saying. $.02, thank you, come again.

if you do go with a TH350, remember that they have a pretty tall 1st gear too, taller than a 700R4, so it might still be sluggish off the line