Saginaw 3 speed Transmission - Reasonably Possible to change 1st Gear Ratio?

[Yamariv]

I have an I6 250 with a 3 speed Saginaw transmission which was converted to the floor shifter. Since getting the truck, I've been annoyed at how tall the first gear ratio is. I have to really ride the clutch for what seems to be forever to get going into first gear which just seem ridiculously tall and hard on the clutch.

I've read in a few threads that the gear ratios were different in the 3 Speeds from factory depending on your engine choice. I eventually want to go with a small block 327 or 350 and plan on keeping the 3 speed.

Is it reasonably doable to change the first gear out to something less tall? Is this a common problem or does everyone just live with this really tall gear matted to the I6's?

[kwmech]

What is the rear axle ratio? Would be easier to replace the transmission than rebuild it with a different gear set

[Yamariv]

Originally Posted by kwmech

What is the rear axle ratio? Would be easier to replace the transmission than rebuild it with a different gear set

I'm not sure of the rear axle, I plan on changing out the fluid so I hope to find that info when I can see the gears.

I would hate to replace the entire tranny though, I do like the feel of the 2nd and 3rd gear

[72SB]

1st gear in a truck 3 speed was lower than 1st in a car 3 speed

I agree you would be better off swapping rear gears if it "bogs" or you have to feather clutch in 1st currently. You can jack up rear end, rotate rear tire 1 revolution and count how many times the drive shaft rotates to see what gear ratio you have

I currently have 3:73 in my 250 3 OTT 72, was considering 3:08's as my 1st gear is low enough and the Hwy RPM would be better. YMMV

[Keith Seymore]

Originally Posted by Yamariv

I have an I6 250 with a 3 speed Saginaw transmission which was converted to the floor shifter. Since getting the truck, I've been annoyed at how tall the first gear ratio is. I have to really ride the clutch for what seems to be forever to get going into first gear which just seem ridiculously tall and hard on the clutch.

I've read in a few threads that the gear ratios were different in the 3 Speeds from factory depending on your engine choice. I eventually want to go with a small block 327 or 350 and plan on keeping the 3 speed.

Is it reasonably doable to change the first gear out to something less tall? Is this a common problem or does everyone just live with this really tall gear matted to the I6's?

Saginaws were available with about three different low gear ratios (RPOs M62 and M64 come to mind). Since they all fit in the same case it would be possible to juggle the gearing around, but would probably be easier to swap the complete trans (assuming you can find one). Changing the rear axle ratio would be easiest, but affects your road behavior/fuel economy too.

K

[Accelo]

Stock, non-optioned, gear ratio for your truck is 3:73.
If the SPID is still in the glove box and it doesn't show and option for the differential that is what you should have. As with any 50 year old truck it could be anything.

[Yamariv]

Originally Posted by 72SB

1st gear in a truck 3 speed was lower than 1st in a car 3 speed

I agree you would be better off swapping rear gears if it "bogs" or you have to feather clutch in 1st currently. You can jack up rear end, rotate rear tire 1 revolution and count how many times the drive shaft rotates to see what gear ratio you have

I currently have 3:73 in my 250 3 OTT 72, was considering 3:08's as my 1st gear is low enough and the Hwy RPM would be better. YMMV

So you actually found yours to be too low? If you had 3:08's then mine probably being 3.73's would be super small. Wonder if your first gear was changed out, or maybe mine was

[Yamariv]

Originally Posted by Keith Seymore

Saginaws were available with about three different low gear ratios (RPOs M62 and M64 come to mind). Since they all fit in the same case it would be possible to juggle the gearing around, but would probably be easier to swap the complete trans (assuming you can find one). Changing the rear axle ratio would be easiest, but affects your road behavior/fuel economy too.

K

Gah, that would be a pain to try to find one with the right gearing. Does anyone sell the right gear? Pulling my tranny and adding the right gear seems like less work no?

[Yamariv]

Originally Posted by Accelo

Stock, non-optioned, gear ratio for your truck is 3:73.
If the SPID is still in the glove box and it doesn't show and option for the differential that is what you should have. As with any 50 year old truck it could be anything.

Yeah, doesn't say anything about gearing on the glove box. I'm guessing 3.73's but hope to confirm when I do the axle gasket and fluid change

[72SB]

beyond the different gear ratios offered for a Saginaw 3 speed, it is my understanding the trucks got the 2;85 1st gear (aka no lines) vs the 2.54

Saginaw 3-speed 1st 2nd 3rd n/a n/a
Saginaw 3-speed – 1 Line 2.54 1.50 1.00 n/a n/a
Saginaw 3-speed – 2 Lines 3.11 1.84 1.00 n/a n/a
Saginaw 3-speed – 3 Lines 3.50 1.89 1.00 n/a n/a
Saginaw 3-speed – No Lines (grooves) 2.85 1.68 1.00 n/a n/a

IDK to what extent the cases or other internal parts are different, if they even are, other than the gear ratios

You would have to pull trans, put in 1st and rotate input shaft and count the revolution of output shaft to see

[Steeveedee]

A better way to go is to substitute a different trans, as mentioned. Should be cheaper than gutting the old one, because it's going to take a different cluster gear as well.

[72SB]

another way of checking 1st gear ratio without pulling trans.

remove DS. put in 1st. Use a FW/Flexplate wrench to turn the motor 1 turn. Count how many times tail shaft turns. Or have a helper rotate engine by damper bolt and you count tail shaft turns

[Yamariv]

Finally go around to doing my rear diff oil change today and did the tire spin while counting the axle spins to try and figure out my diff gearing.

I tried the one full rotation of the rear tire and counted my drive shaft rotations which didn't even get around twice which I thought was weird. I then googled a video and one guy said you have to rotate the rear tire 2 full turns to find your gear ratio which seemed to work much better. By using the 2 full turn method, my drive shaft rotated 3 full turns plus a sliver. I'd guess that to be 3.08 or 3.10 gearing. Is the two full rotation the proper way of doing it?

That's pretty low rear gearing but it would explain my having to feather the clutch a lot to get going in traffic as well as the PO putting on larger tires making this worse.

I was hoping for something more in the 3.73 range but don't think it's worth changing the gearing out now cause I just put $60 worth of Royal Purple in there and the diff gears looked really really nice when I opened it up.

[72SB]

well maybe someone swapped them to 3:08 or you have a higher gear ratio 1st gear Saginaw than the 2.85 truck saginaw

I have 3:73 and would like to swap to 3:08's but my understanding is 3:73 use a 4 series carrier and 3:08 use a 3 series carrier so I would have to find a 3 series to go 3:08

[Yamariv]

Originally Posted by 72SB

well maybe someone swapped them to 3:08 or you have a higher gear ratio 1st gear Saginaw than the 2.85 truck saginaw

I have 3:73 and would like to swap to 3:08's but my understanding is 3:73 use a 4 series carrier and 3:08 use a 3 series carrier so I would have to find a 3 series to go 3:08

The PO also put larger tires on the truck so all that in combination isn't helping lol

[Steeveedee]

Originally Posted by Yamariv

Finally go around to doing my rear diff oil change today and did the tire spin while counting the axle spins to try and figure out my diff gearing.

I tried the one full rotation of the rear tire and counted my drive shaft rotations which didn't even get around twice which I thought was weird. I then googled a video and one guy said you have to rotate the rear tire 2 full turns to find your gear ratio which seemed to work much better. By using the 2 full turn method, my drive shaft rotated 3 full turns plus a sliver. I'd guess that to be 3.08 or 3.10 gearing. Is the two full rotation the proper way of doing it?

That's pretty low rear gearing but it would explain my having to feather the clutch a lot to get going in traffic as well as the PO putting on larger tires making this worse.

I was hoping for something more in the 3.73 range but don't think it's worth changing the gearing out now cause I just put $60 worth of Royal Purple in there and the diff gears looked really really nice when I opened it up.

If you haven't put the diff cover back on yet, the tooth count for the ring and pinion are stamped in the ring gear.

[special-K]

I never liked a 3spd transmission due to the high first gear, as well as such a wide range between gears. Making some turns in 2nd can mean lugging or slipping the clutch a bit. I just always felt they were a bit below minimal gearing, a bit deficient. Not a hater, but that has always been how I have felt. The best thing and first thing I'd do is slap a 4spd to get proper gearing. I keep a 4spd Saginaw around for just that reason, in case I end up with a 3spd truck. You already have the shifter moved to the floor, so visibly there is no change except way better driveability. The best part about it is a 4spd slips right in as if the truck already had one

[Yamariv]

Originally Posted by special-K

I never liked a 3spd transmission due to the high first gear, as well as such a wide range between gears. Making some turns in 2nd can mean lugging or slipping the clutch a bit. I just always felt they were a bit below minimal gearing, a bit deficient. Not a hater, but that has always been how I have felt. The best thing and first thing I'd do is slap a 4spd to get proper gearing. I keep a 4spd Saginaw around for just that reason, in case I end up with a 3spd truck. You already have the shifter moved to the floor, so visibly there is no change except way better driveability. The best part about it is a 4spd slips right in as if the truck already had one

I was thinking of upgrading to a 4speed originally but after a bit of research it seemed like there was no point to go to a 4 speed because guys were saying the 1st gear was useless for daily driving. So you're saying then that second gear in the 4 speeds makes the difference?

You're definitely right about the 3 speeds being wonky on some turns! Lol. I don't mind mine, its kinda fun to drive but having a better 1st gear would be ideal

[HO455]

You might look to see if at some point in the past someone swapped a car transmission in. I'm no expert on these transmission (Or any transmission really) but there should be a way to determine what version you have without pulling the transmission. Casting numbers probably won't tell you what gear set is installed but there should be a tag or some stamped numbers/letters to indicate how the transmission left the factory.

[geezer#99]

A pic of the drivers side of the transmission will help.
Could be a Saginaw or a Muncie.

[RichardJ]

>>................ because guys were saying the 1st gear was useless for daily driving. <<

They were talking about a truck 4-speed such as a SM465 with a granny low.

Special-k was talking about a car 4-speed.

[72SB]

Originally Posted by HO455

You might look to see if at some point in the past someone swapped a car transmission in. I'm no expert on these transmission (Or any transmission really) but there should be a way to determine what version you have without pulling the transmission. Casting numbers probably won't tell you what gear set is installed but there should be a tag or some stamped numbers/letters to indicate how the transmission left the factory.

See post # 10

yeah OP may have a passenger car 3 speed

[Accelo]

"want to go with a small block 327 or 350 and plan on keeping the 3 speed."
I would consider ignoring the transmission issue for now. Make the motor change first.
The extra torque may make the whole thing mute.

A modern truck five speed may be your best answer. Gets rid of the clumsy linkage and you get an overdrive.
A win win.
Cheers

[HO455]

Originally Posted by 72SB

See post # 10

yeah OP may have a passenger car 3 speed

I'm afraid I don't know what you're referring to when you say "lines". Are the lines machined on the gear sets?

[72SB]

My understanding is the grooves (marks) denoteing what gear ratios are on the input shaft so you would need to pull the tranny to see them.

Saginaw three-speed transmissions featured gear ratios of 2.85:1 for first, 1.68:1 for second and 1.00:1 for third when matched with L6 in-line six-cylinder engines. For small-block V-8s, like the 350, the three-speed used 2.54:1, 1.50:1 and 1.00:1. The four-speed matched with the straight-sixes were 3.11:1, 2.20:1, 1.47-to-1 and 1.00:1. For V-8s, it was 2.54:1, 1.80:1, 1.44:1 and 1.00:1.