Ya, I'm beating a dead horse here. I landed an OD truck trans and a 9" but the 9" has 2.75 gears and the OD trans is a 4spd. I really only have driven the truck around the yard so I don't have much of a frame of reference. I'm keeping my flathead and just trying to "get my ducks in a row"

option 1 keep current 4.25 rear and just swap in the srod trans 3.07, 1.72, 1.00, 0.70 I have it here, I'm thinking that's very close to the light duty trans ratios I have now.

option 2 swap in the 9" rear I have try out the 2.75 ratio and if I don;t like it I can get a 3.25 or 3.50 for $100 use original trans

option 3 wait for a S10 t-5 to show up and swap that in. I may have a line on a V8 trans but then I need to source a tailshaft. I do not see an advantage with getting the S10 gear set...

Again I live in the north east, so my main goal for driving is back roads, some highway, 10-30 miles max. occasional trips to work. The flathead will remain mostly stock with just headers and duals.

My main concern with the flatty is being in between gears all the time. That's the main pull for the T5 but I must admit it's the most costly option. The rear I have needs to be put back together but it's all there, and in good shape. I will have to get new wheel cylinders and brakes. spring plates and U-bolts. The Srod needs the same work as the T5 - less the tranny. And to me it's a little more traditional aka old school.

please chime in,

 

Messing around on the axle calulator your best bang would be the 9 inch. For me my first choice was the 3.25 ratio than a 3.50 came along so that's whats going in. I can always put the 3.25 in later. A point of referance was when I had a S-10 with a 4 banger and T-5 about ten years ago. I wish I knew the axle ratio, but living in the foothills above the mile high city never had any problems getting around. I'm hoping for the same results from the T19 I'm hooking up to my flattie. I may have posted this before but t-5 and t-19 have the same gear ratios 1-4.

 

Personally, I wouldn't waste my time or energy with the SROD. You'll still have to source adapters and clutch parts, so you still have some expense involved there, which you'd have to do over again if/when you decided to go T-5.

I would be concerned with the 2.75 ratio being too high to work with the flattie, not having the HP or torque of a more modern engine, and being a total dog "off the line" or struggling in your back woods roads and hill climbing. That was the reason for the low gear ratios in older vehicles, to keep the revs up in the power band at lower speeds. It doesn't sound like ultimate top speed is your main criteria. If your original diff is in good shape, I'm not sure what you'd be gaining with a 9" swap, big picture.

My vote would be to wait for the right trans to come along. I think you'd be happier in the long run. That's my 2c, anyway.

 

You'll burn out your clutch with the 2.75. The SROD is intriguing, but do you have column shift now? It's not quite as much work as a T5, but close.

Are you sure your stock rear isn't a 4.11?

Assuming your existing trans is in good shape, I'd try the 9" with 3.50 gears first, with fairly tall tires. You should only be out about $300, but it's an easy, quick swap (compared to the alternatives). Save your old rear end in case you decide to do a T5 later.

 

All good points, and I do appreciate the discussion. No doubt, the 2.75 is too high but that's what came in the 9" and it was too good of a deal to pass up, knowing where I can easily get a better ratio pumpkin.

I'm sure my original rear is 4.27, glove box, rear casting, and spinning the tires confirm that. I wish it was the 3.90 I would know what to do then.

Cross country travels is not my plans just local stuff, but I don't want to get run over on the highway if I need to travel it.

I guess, I'm trying to avoid changing both the trans and the rear. and my rear is in good shape. Will the brakes stuff swap over?

The srod is the same swap as a any other toploader, so yes a little less work and cost over the T5.

I really don't want to do the T5 swap unless it's from a V8 car because of the gear ratios I would only be gaining a 4:1 first that I really don't need with my 4.27 rear.

 

What direction would you go with a 3.92 rear? I will likely be swapping out my 3.92 for a 3.50 - 9". I am also saddled with some tires that I bought to get it rolling, that are small diameter. I want to end up with 3.50/9", tires about 39 - 30" true rolling diameter, and the stock 3-sp.

The brakes you'll find on a typical 9" from a 57 - 72 truck are the same diameter as the stock 48-52 brakes, but 1/2" wider. You can use them without any real modification.

FWIW, the SROD is not without its problems from what I've heard. The TOD (top-rail OD) is similar but heavier-duty.

 

I'd put the nine inch in but look around for another set of gears. The 2:75 is too tall for the flathead....

 

Ok here we are again withthe weekly rear end gearing conversation. And once again noone is asking an all important question (unless I missed it above) - and that is what size back rims and tires do you have on the thing? Ross touched on it briefly.

I agree with Ross. I have a 2.79 (which is a 9 3/8 rear - "2.80" is the lowest I think the 9" goes but I could be wrong) and a C6 - doesn't matter unless you have overdrive - as all non overdrive transmissions are direct drive in top gear (1:1).

I was just thinking about putting a 20% reduction overdrive on my truck because it was freeway cruising at about 2600 rpm and was a little high for comfort - not bad, I just wanted to bring it down to about 2300.

So I went out and got two back tires the were 3" taller. And that did it and more. It actually added about 7 mph at a given rpm.

Your "short pole" is the 100 hp in the flat head. You will need a lower gear to take off especially if you tow or carry any weight.

If you have a 4 spd in the truck now, then the best combination would be to put in the 9" but chance the gearing to 3.25-3.50. That should be just about perfect if you still have the 16" wheels on the back. You will still have the granny - which now would act like a regular first gear, and 4th will give you a good freeway speed. If you are towing or driving with cargo - drive in 3rd. If you have a 3 speed then definately nothing higher than 3.50.

You can fine tune the rpm speed next time you buy tires.

 

yep, I forgot to add that info 235/75/15's for the tires, and I have a three on the tree.

The pumpkin I have is 16 over 44 = 2.75 28 spline. I know I can get a 3.50 or with a little more work a 3.25. but If I swap the rear I'd really like to not have to change the trans??

much of it comes down to keeping this flatty and the 100hp in the hilly area I live in. I know the more gears it has the better.

Sorry to beat a dead horse here, if it had the 3.90 , I'd just keep it that way for a while. Then decide what it needed. and it would most likely be a TOD or this SROD I have.

Just to many way's to skin this cat.

bob

 

Yours are the tires I'm switching to, I have the 3.92 and 3-sp. For 90% of my driving that will be OK, good up to about 50 without really winding out the engine. The 3.50 would allow me to take it out of town, which in the Albuquerque area means getting on roads that are 55 - 75 mph speed limit, and going a long ways before civilization. It also involves a fair amount of mountainous territory, which weighs for going the T5 route, but I'm just not ready to put the torch to my crossmember yet.

 

Just to keep this updated and we haven't had any drivetrain questions this week.

I picked up a 9inch rear at a good value the other day. unfortunately It came with 2.75 ratios. I also aqqired a 3.75 pumpkin. neither will work for me exactly.

My new options are the SROD 3.07, 1.72, 1.00, 0.70 w/3.75 gears (toploader)

or a T4 I found that has these ratios T-4 4.03 2.37 1.50 1.00 w/2.75 gears (t5 less OD)

I must admit, I'm having trouble finding a pre 90 T5 for an S10 reasonable price.

 

good luck with the s-10 trans . the ones i found around here were JUNK for a big price . seems everyone has figured out were wanting them for our old trucks i geuss . that and they are nowhere near as plentiful now . my original plans were to use an 8.8 i have and ready to drop in , with a 3.08 in mine in conjunction with the heavy four in it , but now i have an aod auto laying here from that 91 5.0 bird and they make a kit for my flatty , so ................................. here we go again !!!!!!!!!!

 

Bob, I can tell you're in that situation we all find ourselves in at one time or another. My advice is to pick a strategy and work towards it patiently. Don't buy what's available just because it's there in front of you! If you want to try a 3.50 9" , get one (the right one, a 57 - 72), even if it costs a few bucks more, or you have to wait a month or two for one to show up, because sure as hell if you settle for something else, the right one will pop up a week or two later for almost no money.

The whole thing with S-10 trannies started in about 2000, when the mid-80's S-10's were coming up on the end of their lives (usually failed engines) and they were cheap. The unfortunate fact is that not that many S-10's were bought with 5-sp's, only a narrow window of years are right for the conversion, and they were not a real HD tranny to begin with. They aren't easy to find at a cheap price, and are usually not a bargain when they are found -- worn out, busted, etc. We need a new alternative that is more plentiful and durable.

Considering how much more of a job it is to do a tranny swap of any kind on BB trucks, I'd stick with your plan to try the 9" first. There are millions of them out there, just be patient. A lot of them are junk too, so be picky!

 

Well. I own the 9" now it's from a 72 truck. even though it had the 2.75's I could'nt turn it down. It was already removed and complete except for the wheel studs. It will need a brake job, but for what I paid I expected so much.

Honestly I talked myself out of the 3.50/3.25. My first plan was to run that and the stock 3spd. But I know I would hate it in a hurry. I've had a non-syncro first 3 spd in the past and it was a real pain for the type of driving I do, just getting into my driveway got me killed a few times. (steeeep hill and a busy country road)

I grabbed the 3.75 pumpkin thinking , it's better than the 4.25 I have now and when I swap in the srod or t5 it would work well rpm/speed wise. After running the tire size and rpm range I was looking at I really didn't want to use the 3.50/3.25. I only just found out that the t4 was the same as the t5 in the S10. that brought me back to the 2.75 gears and the 4.03 2.37 1.50 1.00 that combo will give me a nice first and decent highway gears.

All the S10's I've been finding are either autos or 4 speeds. I think one is a t4 the others a integrated bell 4spd.

I'm mostly just hunting now. but when a deal shows up I want to jump. after watching an ebay auction on a t5 adapter it may be much cheaper for me to swap in the toploader with the speedway kit.

bob

 

Well, I agree with Ross. With those tall tires (which a have on my truck now) and a 2.75 rear (I have a 2.79) At 100 Horses your truck is going to GAG if you have to start out on a hill). The change in mine withthe taller tires is very noticable. Pulling onto the freeway mine definately takes a little bit to get up into a better HP powerband. And, I have a 390 FE with 395 HP!

I would not go above the 3.25/350 if it were me. And the 3.75 might work good for local driving if you have hills where you'll be starting and stopping.

Here's a pretty good RPM calculator if I didn't post it above!

Gear Ratio Calculator