I've been researching this since I had my '54 (so for the last year and a half or so) and I've seen a handful of posts with the same question I have but, there are never any details in the answers that follow. The '54 was a 3 speed with 3.70s. It started out good in 1st and pulled strong in 3rd. When I started collecting my t5 swap parts, I got a '57 rear with 3.70 gears to keep everything the same but obviously have the steeper 1st and OD. Well, now that I have my '51 PG it has the 3.55 in it. I've been using gearing calculators so much, I have the rpm's burned into my brain for life haha. Why did Chevy put lower gears in the manuals? Was it because the autos could slip the torque converter (multiplier) so it seemed like the motor made more power with the higher gears where as the manual was direct drive? Of course we all know about putting auto rears in manual cars for freeway driving but how did THAT affect steep grades? I have a line on a 3.36 third member but don't wanna go too high for my stock 235 to be able to pull it. At the same time, I don't wanna put the 3.70 in and wind the motor out and throw a rod through my block (easy to find) and fender/hood (not so easy to find). Btw, my 235 is the origional, un-rebuilt motor. Where I live, you need to drive through mountains to get anywhere out of town so going up long grades is a concern for me. With the 235/3.55/PG/27" tire combo I have now, I was driving up the mountain the other day. My motor was heating up but it was cruising along just fine (in high gear) at about 2000 or so. I've seen some say the 3.36 will work fine with the 235 but they never say what type of area they live in (flat, hilly, mountains) so this is where this post comes in. Of course I can always downshift going up but will that make enough difference or should I stick with the 3.70 rear. The goal is about 2000 rpm at freeway speeds, give or take a couple hundred. According to about 5 different gearing calculators, the difference in speed (for about 2000 rpm is an increase of 3 mph from 3.70 to 3.55 and 6 mph from 3.70 to 3.36. It seems pretty straight forward on paper but as far as real world numbers, it's never that easy. The entire rpm range of all 5 gears needs to be taken into consideration. Anybody with a 3.36 rear, .76 OD t5 and 27" tires have any mountain driving experience? Sorry for the 1000th post on gearing but specifics are needed and all that's out there currently are generalizations. Thanks guys and gals.
3rd gear in the 3 speed and 4th gear in the T-5 is the same ratio. I don't think the 235 has enough beans to pull a 3.36 in overdrive. Personally, I'd recommend staying with the 3.70.
I think if you want really get a great match in overall gearing, you may want to first review all the T5 gear sets that were available. Go to www.britishV8.org for a comprehensive list. To get the optimum combination for all driving conditions, the rear end ratio is but one component. The T5 variants have 1st gear from about 4.03 or so thru about 2.95, as I recall. And 5th gear OD ratios from about .72 thru about .82. But with your data of tire size etc. taken into consideration, you should be able to calculate a good balance. Downshifting to 4th (or lower) on some grades may be necessary. But, if it weren't, what would be the point of having 5 gears to chose from. As a ball park estimate, I tend to agree with Montanl above on the 3.70 axle. Ray
My only concern is the rpm range of my dipper 235. I read somewhere that they were governed (in trucks) to a max 3200 rpm but that was 60+ years ago. I looked into a rebuild but, at $4500 I'd like to make this one last as long as possible. It still has perfect oil pressure and good compression having an original 70 some thousand miles but I don't want to over do it. As it is now, I'm at about 2200 at 50 (according to gps) and I'm concerned to take it much over that.
I run a 261 same as a 235 with bigger bore. I have a 235 cam in it so bore is the only real diffrence. I have the t5 with .72 od. I have this in a 38 chevy coupe might be lighter than you. I run 3.00 rear gear in a 8 inch ford. This set up will cruise at hwy speed and never need to come out of od. I do not live in mountains however we have some pretty big hills never had a problem. I like tall gears.
Let me ask this than...with my engine being 65 years old but in fairly good condition, what's a safe rpm (not short duration but, hours at a time) to maintain? I know if it had a fresh rebuild with aluminum pistons that would change everything but unfortunately I have iron pistons. I used to run my '54s 235 at 3000 with no worries but I've heard alot of horror stories about the dipper motors. I plan to drive to Tennessee for ink and iron in august which is about a 9 hour drive, Chicago for another show, OC for their cruise week and plenty to Carlisle and back.
QUOTE="StefanS, post: 11447731, member: 232342"]Let me ask this than...with my engine being 65 years old but in fairly good condition, what's a safe rpm (not short duration but, hours at a time) to maintain? I know if it had a fresh rebuild with aluminum pistons that would change everything but unfortunately I have iron pistons. I used to run my '54s 235 at 3000 with no worries but I've heard alot of horror stories about the dipper motors. I plan to drive to Tennessee for ink and iron in august which is about a 9 hour drive, Chicago for another show, OC for their cruise week and plenty to Carlisle and back.[/QUOTE] "My only concern is the RPM range of my dipper 235" Even back in the day, a 216 or 235 engine was more than likely rebuilt, before 70,000 miles. You are choosing to go with the 60 plus year old dipper engine, as is. Not a good plan, in my book. Creating low RPM's now, is a band aid, not the solution. Either rebuilding the dipper and/or replacing the dipper engine is the solution. The "heart" must be strong, for the patient to survive. Being that you want to use a T5, with a . 07 overdrive, you'll have your lower RPM's, and lower torque, but LOW RPM's will not give you necessary torque to climb your mountains, unless you're downshifting ..... which then raises your RPM's. You're pulling 3,300 lbs of car, there's more needs to be addressed, not only low RPM's More attention needs to be placed on a rebuilt or an updated, full pressure engine. A 3:70 gear would be my thought, along with an engine refreshing.
If you are heating and pulling along just fine with the gears you got now I am going to suggest that a taller gear is going to kill you or you will be pulling it in a lower gear. If you got to an AD I am going to suggest that you go to a deeper gear than a 3.7 behind the 235, you really want a 4.11 or so. You are not going to be pulling the grades in 5th gear either you will be dropping to 4th. As for your question about automatic v manual gearing the older school of thought was that you need to taller gear to over come slippage, they didn't have the technology that we do today with automatics and they were no where near as positive under load as a manual so they used a taller gear to overcome it. There is a reason that an automatic was called a slush box and a power glide was called a power slip. That school of thought has pretty much gone the way of the Dodo these days, current tech has made the automatic on the same lever of performance as a stick and in some cases better than a stick. We normally are not dealing with that type of box here so I guess the older argument is the best in our case.
So essentially, the 3.70 without slippage will kind of be equivalent to the 3.55 with slippage as far as rpm's go?
I'm over 100k miles on a '56 235, 848 head, Fentons 2x2 Edelbrock intake with 2-2bbl Carter-Webers. I have that mated to a '69 3sp+od. The rear end is 3.90, the od is .70, so that's 2.73 in 3rd od. The smartest move I ever made was to install a vacuum gauge with the color bands that indicate optimal efficiency, I spend a lot more time in third gear now rather than od. I do live in the piedmont foothills and she pulls strong over the Afton mountain pass in third gear at about 67mph. I make 3-4 1k round trips per year and got 18.9 mpg on a highway trip going my normal 60-75 mph, I don't baby her I drive her. Oh yeah, dd/only vehicle '49 Chevy 1/2 ton. I 've heard idiots claim that the 235 's are gutless and I have more miles in reverse than they have in forward gears, please stick with what you think you know.
Cosmo49, that's the info were looking for right there. With the 3.7 gears, the .76 OD gives me a 2.81 ratio. The slightly higher ratio should compensate for me having less power than you do lol...hopefully
If your engine is a 54, it wouldn't be a dipper. There is way too much thinking going on here. Just go with the T-5, the 370s and don't worry about the little shite. Go and enjoy the ride!
Stefan, I should mention that I am running 215 85R 16's on stock wheels no tubes. You are doing a great job with the chart plugging in the numbers, after that it's all seat of the pants. For me the 3.90 around here in the foothills is optimal, I chase rice rocket bumpers coming over the reservoir and up the hill on the other side. Honestly, that vacuum gauge has paid for itself. In addition I'm a firm believer in more gears for the 235, kind of like going from a one speed bicycle as a kid to your first 3 speed, then 10-15-18 gears! Sure there's overlap, but mating engine efficiency with terrain is the name of the game. At 2700-2800 rpm's is the sweet spot of these engines, it sounds like it's working harder because we're conditioned by almost silent engines nowadays, my vacuum gauge tells me this is where the engine is working MOST EFFICIENTLY. That's a damn nice car you have there! Good luck with your decisions!
It's a '51 235 in a Bel Air but you're absolutely right, I am overthinking it. I'm going with the 3.70s. I just bought a pair of almost new looking grille horseshoes for $200 to replace my rust hole filled ones on the car. That was my 3rd member money so, even though I decided to use the 3.70s before that, now I have to use them by circumstance. Thanks everyone. Hopefully this'll help someone in the future who's in my position.
Thanks alot, I love it. There are alot of responses from alot of people who's advise I've learned to trust in and they're all saying 3.70s.
I think you are going to like the 3.70's. I run a 3.42 in my 52 with a .82 OD and I have not had a lot of wheel time due to winter. The shake down cruise was great, but with that said, I am in flat land compared to you. The extra gears mean more shifting, but the car seems so much more responsive, it is definitely worth it. Here is a quote from Tom Langdons stovebolt 6 page showing that what you are planning is just right, if you have not been to his site, it's worth a visit. He has been playing with the 6 bangers for a long, long time. Gear Ratios General guidelines would recommend about 12:1 1st gear overall driveline ratio (1st gear x axle ratio) for a good ‘take off’ gearing for a 235 Cu. In. engine. Below 10:1 will require clutch slipping and in excess of 15:1 will be an aggravation similar to a ‘granny gear’. Final drive should be between 3.0 and 2.50. If overdrive is .73 and your axle is 3.73, your final drive will be 3.73 X .73 = 2.72 (perfect!)! Have fun, Jim
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