The Stovebolt Site Forums The Shop Area Driveline Transmission gear swapping

I recently swapped a saginaw 3 speed overdrive transmission from a 67 Chevy pickup into my 58 Suburban. It is a synchro first gear tranny with the 7 bolt side plate. The last transmission was the original 3 speed trans with the 4 bolt side plate.

The trans and overdrive work great. The problem is that 1st gear and reverse are too high. They are much "taller" than the old trans. Its too hard the get the truck moving. I have seen lots of conflicting/confusing information about the gear ratios of these trannies. I know there are different first gear and reverse ratios depending on the year and engine size of the vehicle it came out of. My Burb came with a 6 cylinder engine. The truck I got my overdrive trans out of came with a V8 (283).

I still have the old transmission that I took out. What I am wondering is whether or not I can take it apart and pirate the 1st and reverse gears and install them in my new trans.

Anybody know if the gear sets are interchangeable? If not, how about buying replacement gears for the new trans?

Hy Larry_58_Burb, as far as I know there are no interchangeable parts between those two transmissions, hope that helps.

3B is right. They are 2 different animals. What rear end ratio do you have. It doesn't seem like there should be that much difference in the ratios. I wonder if it is trying to start out in o-drive or if that is possible.

The truck has the original 3.90 rearend. Other than being too high in 1st gear it drives great. Nice cruising and comfort. If I could just pick up a little lower 1st gear, I'd be all set.

standard original 3 speed would have a 2.94:1 first gear according to the books [regular 3 speed or Muncie OD] and in 58 an OD would have come with a 4.11 rear, I believe the Sag SM326 has a 2.85:1 low gear, not really much difference - if you have a hard time getting rolling that's not the problem, maybe the OD is malfunctioning as George says, or maybe your rear gears aren't what you think, 58 was the start of 'mileage minder' rear ratio options

Bill

Bill;

Ok. I jacked up the rearend a while ago and followed someones advice to determine the gearing. I'm pretty sure it's a 3.90.

I didn't have a problem with the old transmission. I only noticed the problem once I did the swap. I still have to fix the fuel sending unit. That will require a drive shaft drop. Maybe I'll take the tranny back out and turn the input shaft to check the gears. I'll compare it to the one I have.

I'll keep you posted.

3.07 gears were available in a spicer 45 rear. Does that burb have a round cover on the rear, or a somewhat octagonal shaped cover. Round would indicate an Eaton rear, Octagonal would indicate a Spicer rear.

Daddy;

I'll crawl under there during lunch and take a look. It's parked right outside my office.

I read in your other thread that you have the trans set up to through a toggle switch. Is the switch wired directly to the solenoid on the trans? Or do you have it going to a relay that grounds out through the governor?

The synchro low tranny did not come stock in the '67 pickup, that year was the last of the "crash boxes". It was probably put in by a previous owner. The all synchros had a 2.85 low gearset, and a 2.5something low gear set (for V8s?). Some four speed saginaws had a 3.11 low gear set that probably wont swap into the three speed saginaw.

Agreed, the all synchros and the older "crash boxes" wont swap gears. You could replace the gear set in the new tranny-but today's transmission gear prices are out of this world- and you would have to replace three gears, the main gear (the one with the spline for the clutch disc), second gear, as well as the cluster gear.

In the late '50s/early '60s those three gears were (with a friend behind th' counter) approx $75. The old "crashboxes came with 2.94, 2.54 (or so) and the three speed 'Vette 2.20 low gear sets. How does the heavy 'Burb like the o/d on the road, how does it take to the hills?

Daddy;

It's got a round cover.

Bill;

The wiring is per the instructions (including relay, governor, solenoid and kickdown switch). The only change I made was to put a switch in line between the kickdown switch and the solenoid. The change did not effect the "takeoff" problem. It is just hard to get rolling in 1st gear.

Idsky;

Thanks for the input. The truck runs great on the road. It will run 55mph at 2000rpm in overdrive. It will run 70mph at around 2600rpm. It does ok on the hills. It's relatively flat here in MO so I haven't run any real big hills.

The truck that my new tranny came from had a V8 (283) in it. Most likely it has the 2.5X 1st gear. I'd like to have the 2.85 1st gear.

When I come through the security gate to get to my house, I have to stop at the gate that is on an incline. When pulling away from the gate, I have to walk a fine line between revving the truck and easing the clutch out or I get a violent bucking in the engine and trans. I have a real hard time getting the truck up onto some wheel ramps that I have. There isn't any problem once the truck gets rolling, it's just getting it to move.

I was hoping to be able to find a Saginaw trans of similar vintage that came out of a 6 cylinder truck. I thought I could just take the 1st gear out of that and put into mine. Sounds like that is not an option.

Is there something I can do with clutch selection to make this better? I also need to coax as much power as possible out of my 250.

Bottom line is I like the trans. It makes for a good overall driving experience. My concern is how the truck will perform if I have it loaded or am towing something. If I can't change the 1st gear, what can I do to make the situation better??

As edski pointed out you can't just take a gear out of something and put it in to change the ratio. Gears come in matching sets. If you were to find a lower 1'st gear you would need the cluster gear to match it. The cluster would also have to match 2'nd & 3'rd gears as well. Any gear changes will require a complete disassembly of the transmission. I'll be happy to trade you straight across for a rebuilt (4 bolt) OD trans. It has the same ratio as the trans you took out. Transportation would be the only issue.
Fred

Fred;

Thanks for the input. I appreciate your offer, but I'm not ready to trade it away quite yet. I really like the full synchro 1st gear.

According to all the spec sheets (Truck and Passenger) the overdrive syncro 3 speed has a 2.85:1 first gear. However, is the overdrive is engaged in first, it will make the overall gearing a 1.995. The description of the problem you're having almost sounds like that's the most likely problem. Have you tried it with the overdrive locked out to see if there was any difference?

I'm with Bill, and I really don't see how changing from 2.94 to 2.85, or even 2.5 would make it hard to get rolling, even on a slight incline, on level ground you should be able to start out in 2nd by slipping the clutch a bit .... as for it 'bucking' on letting the clutch out, are you sure all your motor mounts have good rubber and are tight?

Bill