Carsten here, has anyone some advice what gearbox to use behind a Poncho straight eight? it would be nice to ged rid of some rpm's . my car is technically stock, there were no longer gears than the one i have, installing an overdrive is bound to some frame mods that i don't want to. When my 1942 Pontiac was built there were no Hydramatics in sight, so there isn't much extra space for huge gearboxes. the best would be to replace the old 3-speed by a 4-speed box, what do you think? any experiences for a change without modifying too much? Thanks folks, let's hear your thoughts.
Most four speed transmissions have a 1 to 1 top gear. As do most 3 speed transmissions. So changing will not result in any difference in the finial drive ratio. You could look for a Ford top loader four speed that has an OD fourth gear. But in Germany I would think some European car would make a better doner. That straight eight isn't going to make enough power to hurt most transmissions.
I know nothing of the engine you're using but there are some things to consider. A 4 speed won't have any effect on your cruising rpm's as 4th gear is 1to1 unless you find an overdrive version. Rearend gears and vehicle weight should be part of the equation also. For instance if using a rearend with gears in the 3.08 range in a heavy car; a transmission with a first gear in the range of 2.52 to 3.00 will better help get the car moving, plus it will increase clutch life. An example is the GM Muncie M21 ( close ratio) with a first gear of 2.20, and the M20 (wide ratio) which has a 2.56 first gear, the M20 will get the car rolling from a dead stop easier. The aftermarket also has quite a range of transmissions with many ratio options.
I have a 4 spd in an OT Dodge pickup that has 3 spd/od 4th. These were 80's vehicles. But why not go 5 like a lot of guys on the forum? Sent from my LG-TP450 using The H.A.M.B. mobile app
thanks all, yep you're right, i forgot about the highest gear is nearly always 1 to 1, so the solution would be to mate an OD gearbox to my engine or look for another rear axle gear. i have to take another look for the ratio of my rear end, i just red that Pontiac offered an economy version with 3.90 : 1, the standard which i suppose to have was 4.30 : 1 for the streamliners. i'm sorry for the dumb question, but would it make a huge difference? on ebay there are two 3.90 rear end gear sections for not much dollars. Thanks for all advice, i just don't have experiences in changing any ratios.
DDDenny, thanks for that, but do you think that the aftermarket has some that fits this old Pontiac rear end?
RichFox, the straight eight is a reliable and smooth engine, but, as you write, there's no chance that it will pulverize ANY gearbox it still goes strong upwards the most hills, but not more. Thanks.
Pontiac and Oldsmobile used the same rear differential from around 39 to around 53. Especially some of the later Oldsmobiles with Hydromatic transmissions will have a better hiway gear that fits your case.
Did't the first Hydramatics come out in 1939? I believe the third members for the rear end, with better/higher gears, were the same up to 1956; may give you a better range of years to look for. You could also go with a larger diameter tire, but that also requires speedometer recalibration. Typical change one thing, you have to change another, then another................ I am Butch/56sedandelivery.
I put a m40 Volvo 4 speed behind my ford banger.They make overdrive m41 as well.Seems like they would be easy to find over there.
Your question is a little wonky but it will take some creativity no matter what route you take. "If it was easy, everybody would be doing it".
Carsten, I have a 3.63:1 third member in my -40 Olds who had a 4.30 from factory and it's a huge different. All 39-56 carrier will work in your axle. Try to find a carrier from a -54-56 Pontiac
I've had several 40s Pontiacs and I always change the third member. You don't have to change the entire rear axle, only the gear set and it simply unbolts and comes out the front of the axle housing. I always seem to come up with 3.23 gears from a 55-56 Pontiac with the hydramatic trans. It's a straight across swap into a 40s Pontiac housing. I remember I had to use 2 special length bolts from the 55-56 rear and that's about it. I also used tall 16 inch rear tires to help get the gearing up and I drove my cars all over the U.S. on interstates. I could cruise at 60-65 MPH comfortably with the stock flathead engine. The third member in the photo is a 56 Pontiac. Your 42 flange will interchange ok on the 56 gear...37-55 gears all used the flange like you have on your 42. Olds third members of the same years will interchange but Olds use a different spline count on the axle shafts...you'd have to use your old Pontiac spider [side] gears in an olds gear set. I know of no 4 speed that will bolt up to a Pontiac straight 8. Keep your transmission and change the rear gears
Rocky, Olds use the same spline (10) on the axle shaft up to 1952, later on they use 16 spline. I have a Pontiac carrier on my -40 Olds and it bolts right in.
Aside from being more "comfortable" to drive, I can't see any advantage in swapping rear gears under the old Pontiac. Last year I swapped rear ends in my OT '76 GMC Dually, from 4.56's to 3.73's. I had hoped to make a small improvement in fuel "economy" (a difficult word to use when talking about that truck), but that made no difference at all. What it DID do was make it much more pleasant to drive, it's not like driving around in low gear now. I'd have to say the trouble and expense was worth it just for that.
Thanks Rocky and Per, that was what i wanted to hear! so i will look for another third member and will leave my gearbox alone, that is a good and cheap solution to save some rpm. Thanks guys, all your advice is very appreciated!
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