So I have been doing so research into overdrive options and rear-end gear ratios for my Model A for about 2 years and in the last couple of days partook in Hot Rod Tour where the speeds were about 65-75 constantly. Now I have a hot model a engine, balanced crank and rods, Riley Two port, and two Stromberg, and was staying in the leaders of this tour for the first 100 miles or so. Unfortunately, my engine stopped pulling and now has a knock, but that I can fix. My question is a question that has been asked many times over the years and a question that should be reasked every so often to get the most up-to-date info; What Transmission and rear end gears should I use for a comfortable 65-75mph? Currently, I have a fully syncrod model A 3 speed and the stock 3.78 gears. So far I have these options for Transmission upgrades: Mitchel OD 26% or 36% Tremec T170 4 speed From 70s-80s Ford trucks Tremec TK series 5 speed And for Gear Ratios: 3.25 3.55 3.78 (Stock ratio) 4.11 From my googling it seems 4.11 is used with most OD setups but that seems to be for a lower speed 55mph model A, essentially Model A tours type of build. Since I want to do both Model A club and normal Hot Rod tours what should I run? I was thinking to complete my Mitchel order and get a 3.25 gear set but now I don't know. The 4 and 5 speed conversions sound good but would require other work, Brake rebleed, and torque tube to open shaft conversion/tube shortening. Also if y'all got any ideas on handling upgrades I'd love to hear them as well.
Hi Matt , l have a all stock model A with a 3.78 in a Columbia twospeed witch is a about a 20% overdrive. For me this is the perfect set up. Good cruising speed,only have to downshift on large hills.
There's a couple of threads on T5 to t/tube conversion's worth searching. I think there's a link on the first post of the monthly banger meets.
Check out @Mart 's videos on installing a Volvo gearbox and Laycock de Normanville overdrive in an early Ford. Brilliant stuff.
I have a 36% Mitchell in my 40 with the 3.78 gears and 65mph is ~1700 rpm with 30" tall tires. That might be a little too tall for you but the 26% might work. Call them, they're very helpful. It might take a wheel/tire change to dial it in but for the price the workmanship is top notch and it bolts right in.
The thing you have to think about first is the engine you have thats gonna drive the trans. Lots of the old conversions were done with flathead V8s which probably have more power and torque. You have to be able to drive the overdrive gear in a 5 speed without lugging or over reving your engine. You have to pick an rpm thats likeable/usable/desirable when running 75 mph. Generally a V8 is happy somewhere between 2100/2500 and not overly noisy. The question is whether your banger will produce sufficient power at a similar rpm. My wifes 4 cyl SUV will run 80mph operating in that range. Again, probably more hp than yours (I think 180) but also much heavier than your avataur. Anyway, you first have to have enough power available at say 2300 rpms...........then I would use a late model 5 speed.........then see what each rear gear/tire size gives you 75 mph. If the combination does not work well in touring, then either change the rear gearing and add a few rpms or find a way to develop more power.
Should've given some context, this is the car, currently the engine is cappable of 75 mph but I beleive its running at 3500-4000 rpms to do it. I have the stock 30 inch tire diameter and a syncroed 3 speed. I can safely assume that I am prodicing atleast 80ish HP. Ned, I'll check Mart out, but I feel like a volvo transmission might be a harder find than a s10 5 speed. Texas loves its trucks afterall. Rak, I have actually had a OD from mitchell on hold for awhile and they are the kindest people. Just unsure if I want to go that way or a trans swap. Trying to get for info and opinions on both.
So for now I think I am going to get the 3.25 gears for my rear end as I have the power to pull them. As for trans options I'm still on the fence. I have definitly ruled out the mitchel, I'd like to keep any extra buttons and levers out of the "cabin" as I can. The volvo transsmsion looks promsing as recomeneded by Ned, Marts videos are really good so far, the T170 4 speed with its .78 od sounds pretty good and it keeps it all ford, but the Tremec 5 speed not only has the best conversion parts but actual parts for the gear box seem to be plentiful. Still looking and researching. If y'all have any more options let me know.
Here is what I think you should consider. First while the 4 speed od may sound like a good option, you should consider that the spread between gears is something thats important. Think about the old Muncie 4 speeds that came in "close ratio" and "wide ratio" as an example. Its not just the number of gears, but how much ratio spread they have. Generally, the more gears..........the closer they are together. I'd look for a transmission that has a reasonably low first and second gear, and an overdrive that is not too high. Not all overdrive ratios are the same. Personally I'd look for a 5 speed and maybe even a 6 speed from something outside the normal choices if you are good at adapting things. What I'm trying to say is that at various times you need more gear choices to meet different driving conditions. Since you are looking to get on the xway and drive 75 mph, you also need to be able to accelerate on the on ramp. By the way......Nice Car !
(I’m gonna assume you have juiced brakes) that being said it looks like your running stock suspension I have a stock 28 Tudor and have driven it as fast as 50 mph I would be scared to death to drive it at 75 mph my steering and front end is tight but the way the car rolls and leans, if I had to make a fast maneuver at that speed there would be no way I could avoid a roll over. Nice A by the way
Yeah I do have juiced brakes, and will be converting to disks in the front, I also plan to box and add a k member to the frame and then test the stock suspension again. If I still feel the shimy I was feeling I'll work back to front spliting wish bones, modern tubular shocks and so forth. I am trying to keep as stock looking as I can afford.
The question becomes this: are you looking for good highway cruising or do you want to go drag racing. I am not a big fan of OD, especially on a banger powered car. I was running a T5 from an S10 behind an S10 banger that I tweaked. The OD was .83. Now the banger in an S10 stock is considerably more stout that the banger in an A bone even a tweaked Model A banger. Now with a 4.10:1 rear gear even on a moderate grade I was running in forth. The last paragraph while OT is just for reference sake. If I was running an A bone that I wanted to run on the highway I would first decide where the engine is comfortable. Next I would take the diameter of my drive tires and calculate what gear I could run/find that hits my target. Forget the OD.
The 325 gear set might be all you need. I have a 31 high boy with a Riley 4 port, b trans with 40 gears. Was running a stock 378 rear and at 65 mph I was at 2800 to 3000 rpm. I put a Halibrand quickchange in with 333 gears and at 65 mph I now do 2100 rpm. I run a tach so rpms are accurate. Can cruise with traffic with no problems. Nice thing is you can change gearing to suit your needs. Bad thing is mine is straight cut gears so it does whine like hell.
I'm only looking for a good "backroads" cruiser. Unfortunetly many of the backroads in texas are used by gas and oil trucks so the speed limits are basicly 65-75. I can run that speed but its definitly to many RPMs for my motor. The tour I was just on was about 65 mph for the entire thing and I made it only 100 miles on the tour before a "knock" started coming form the engine. @62pan I'll look at the halibrand quick change but something tells me a junkyard OD trans and adapter will be cheaper to aquire. But honestly you are right at 65 a gear ratio change should be all I need. @porknbeaner since it is the OG 3 main block with a counterbalanced crank my engine seems to be comfortable around 2500ish RPM. I have no tach but a stock model a I beleive made peak power around 2200, with all the mods that were made to it it should be capable of 2500-3000 rpms with 2500 being the sweet spot.
No Model A, but a thought. I went to a faster gear in my Buick, from 4.10 to 3.36. Really like it for road speeds. Miss the slower gear in town. I think if I was doing another and could afford to do so an overdrive of some sort would satisfy me better. In a car with a floor shift already a 5 speed [ T 5? ] would be MY choice. Ben
No experience, but I have read that babbit bearings don't like sustained high rpm use. Anyone else know any more about this?
I beleive you are right, they can and have been used for land speed cars way back when but a ton of model a have been updated to insert bearings. From the custom work I see on my crank and the fact there are no shims in my mains or rods I can safely assume that I have inserts, that and based on facts my grandfater and father have said.
My otherwise stock ‘31 coupe has a 6:1 head and Mitchell OD and I love how it cruises at 55 - 60 mph.
Then the question becomes.........how long will it take you to get to 65 mph. Its like the old Chevy V8s that were backed up by a 2 speed powerglide. Modern technology has small engines (and even large ones) using transmissions that have 8 and 10 speed transmissions. They easily keep up with the traffic and exceed the posted speed limits. Granted the engines have advanced technology even though they may be small, but the provision of many gears allows them to move seamlessly at freeway speeds and they are pretty perky accelerating up to that speed. Just saying that while you don't want that level of technology, you might want to look at the general theme that more gears are a good thing.
I have been thinking about this topic quite a bit lately. I figure a well built balanced insert bearing A or B should be able to maintain 3000 RPM all day. An A with a 3.54 differential in 3rd gear(1:1) with a 30" tire at 3000RPM mathematically will be at 75.67 MPH. A better gear spread than an A transmission would be beneficial and can be remedied by installing a later V8 transmission. I do think a T5 would be nice by adding an extra gear and an overdrive. Although I'd like 5th gear to be relatively close to 4th, somewhere near .80. It comes up to how much you want to spend and ease of installation. I'm going to try the V8 toploader route and go from there.
@ekimneirbo The problem becomes that most modern transmission have a intergrated bellhousings. Besides the transmssions I listed the only other one that I know could be used is the nissan CD009 that already has a way to cut the bellhousing and enough bolt locations to make an adapter. Unless you have some recomendations I can look at.
[Well the older T5 is probably a good choice. Might post a picture of what the back of your engine looks like. Here is some info that may help. If you go with a T5 I would buy a copy of this book, as it will save you money. Amazon bout $25
I'm using a T 170 RTS in my '41 Ford p/u . It took 6to 8 weeks to find a new 4th gear. Normal rebuild parts,brass blocker rings,bearings, gaskets are pretty available but hard parts can be scarce. I think a Columbia would be a good choice . If you're interested, PM me.
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