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I'm trying to get better freeway speeds with less RPM. This is a stock 235 (maybe a 261 at some point), 4-speed Saginaw with 3.11 1st, 3.55 rear gears, 27" tires.
How high can I go with the rear gears without turning it into a dog in town?

[ 01-22-2002: Message edited by: DennisM ]

Patrick's Has 3.55 Gears that should work good for you.

J.Keith, I already have 3.55 gears. I'm wondering how much higher I can go. By the way, the rear is a 9".

DennisM, seems You have a winner combo, I would not use much taller tires than You're using now, I'd say that the limit is 31", more is going to kill all the get up and go of the truck.
Are You going to swap the 235 for a 261? ever considered hopping the 261 a li'l?? I see them as a really cool engine, but a li'l work would wake them up.

Do you guys think a 3.00 rear gears would do the trick or is that too high?

Alexandre, I think about a 261 from time to time but nothing in the near future. Unless one comes my way or if the 235 goes sour. So far it is running just fine. I'm just looking for lower cruising rpm's now. I communite about 70 miles a day. It seems most comfortable at about 55 so that's the rpm I want.

WOW I must need glasses or something
I dont think i would go to 3.00
I've got 3.08's in my '74 with a 300hp 350ci and a turbo 400 and it does real good on the interstate but not very good pulling a trailer or on the take off. But it get's about 16-17 mpg on the highway. So the 3.00's would be a little to high for that truck. Just my $0.02

Dennis,

My neighbor across the street has a early 50 truck, stock 235 and about a 3.00 rear end. He complains that he has to slip the clutch to get up the driveway. I'm running a car with stock 235, original wheels and tires, 3.73 rear and T5. With the .72 overdrive it really rolls down the road for cruising at 60 to 70, at 50 to 55 you really have to down shift to pull much of a grade.

I have to agree, the 3.55 is a good choice. With the 27" tires you could go to something in the 3.40 range, but it would only gain you 120 rpm at 65, not enough to be worth the swap.

I run a 3.90 in the 39GMC with a 25% OVERDRIVE The 37 Packard 6 runs a 4.09 with a
33 1/3% O-D and 650x16s Both run along at around 2000rpm @ freeway speeds!
It all works out to about 3.00 they accelerate fine.....go down the road OK
Even the 228 with an 18% was good with the 3.90 gears

DennisM, I'm using a 3.73/1 rear end in my truck, with 31" tires it makes 2000 rpms at around 50mph. Now You have 3,55/1 rear and 27" tires. Changing to 3.00/1 wolud be almost the same as putting the 31" tires. Don't You have a friend or someone elso that You may borrow 2 tires and put them in truck just to see how it goes, would be the same as swapping the rear, just easier and faster. If You like the results, them just return to the 27" and swap the rear or keep the rear and swap the 27" for 31".

Okay, you are cruising at 55 mph, because that's what rpm you like (I think that is what you are saying). That's about 2400 rpm with your setup, if you drop to 3.00 gears, you'll be doing about 65 at the same rpm.

The other thing I mention, since you say you are commuting, if your gonna be driving this thing like Phat at 70+ miles per hour in traffic, if you haven't already you should update your front brakes. Those brakes were not meant for repeated stops from 55+ mph.

With the 3.11 first, you should take off fine with a 3.00 rear end. I don't know how much those gears are gonna cost you. For the amount of money, you are gonna have to spend on some gears, you might get an overdrive tranny instead.

I drive 25 miles each way to work in my 52 coupe daily driver with a 235 and a 4.11 rear, only one short stretch where I get above 50, though, and I run about 3000 rpm at 65. I still get 15 mpg or so. I'm swapping to a T5 one of these days, I've got the tranny and a 3.38 rear, just can't bear to work on it on these nice sunny days.

Chris

2:73 with a t-5 and a warm 235 is on the edge.I never have to slip the clutch.(going across I-80 in PA i will have to drop to 4th every now and than if i am running 55-60) It probably gets only 1500 lbs at the most put in the bed. On the highway 70-80-90mph is were the motor is happy. The brakes .......well thats what bumpers are for. Seroiusly 3:00 would be fine 3:55 if you dont take it on trips.These little motors like to run 1500-2800 and will live a long time.Will it runn 4500 yep but you wont get 350,00 miles like my last one. I personally would not bother 3.11 to 3:55(what rear has a 3:11 anyway???)

This is all great advice, check out Joe's page @ http://50chevy.freeservers.com/Tire_Height_Changes.html to plug in your rear end (get it, lol) and tire size.

I spend a lot of time in western WA and am forced to use I-90, I-5 and I-405. You should get freeway brakes, steering and suspension in addition to the gears. Don't let your speed exceed what everything else can handle safely.

Wally,

I'm suprised that you can ride on an interstate. What is your rear ratio and tire diameter?

Larry Hayes
47 3/4 deluxe

I've got discs in front and late **** drums in the back already so I'm OK in the braking department. I have the beam in front so it still isn't what you would want for sudden major moves, but I don't plan on trying to outrun Phat. You have all given me a lot to think about. As usual I short on coin so I'll navel gaze this a bit more.

Inverse21, as far as cost of gears, this is a **** 9” so new gears are under $200. I've never changed ring & pinion so I might have to farm that out.

I like your idea Alexandre about running larger diameter tires to test the difference. That is a cheap test even if I have to get a couple from the wrecker.

Why not change the tranny Dennis? It'd certainly help you out, and you may not need to change the rear, cuz you're running 3.55 already, and with a T5 it'd work out ok. Yeah, try the tires, they certainly make a difference, just remember to check your speedo, otherwise you wont be getting the right mileage/gas/speed, if the truck doesn't know what size of tires you have on.

Nate

Just for you guys worried about a "beam"axle.That Peterbuilt or kenworth that went by you on the interstate runs a "beam" axle and does so well(sometimes over 85-90mph)Nothing wrong with a straight axle,the brakes are another thing.Disc's and a front sway bar are the best improvements you can make to your truck.Guys that have to go the "clip route" or stang II are looking for the ride. A properly setup straight axle well more than do on these old trucks at normal highway speeds(in my book thats 75-85 mph.) So......dont worry about your "beam axle" to much.Just get some good front disc's and your pretty good at highway speeds.If you maintain the front drums they also will stop repeatedly on the highway(54 drums maybe not the old style)however that means pulling the front drums every 10,000 miles and adjusting the brakes every 2000-3000.I will change to disc's this year cause if have done so many latly that now i relize how good front dis'c really are on a stocker.

Although we all hate SUV's all the past Jeep Grand Cherokees use a solid front drive axle.They ride and handle as as good as any IFS model.The nice part about disc's is the control you have when stopping hard.Drums are more prone to locking up, harder to control in a panic situation when there is no time fart around.The non power front discs on my 37 scrub off speed better than a newer truck.The drums on the 51 feel pretty good ,but there is absolutley no comparison , the discs are better.

Tony, We all hate SUV's, but don't You think that both the Sport, both the Grand Cherokee does not deserve the offense of being called such a thing, almost derogative comment like SUV. And when I see the straight axle up front, I want to buy one(but only the 5.9L - 360 V8). I see that it may be a good garage company to my 2500 RamV10!!

Larry (a few replies up), I don't drive the '48 in WA. I have driven my '48 3/4T with stock gears on our I-90. I hung a farmer's blaze orange triangle on the back, turned on my flashers and went my 40-45 MPH. It scared the ***** out of me. I spent all my time looking out the rear view mirror ready to hit the borrow pit. That was when Montana had no speed limit. I don't take it on the freeway anymore.

[ 01-25-2002: Message edited by: Wally / Montana ]

If you have a 9 inch, just go to the junkyard and pick out a couple of pumpkins from mid seventies wrecks. A lot of the sedans had high 2 series rear ends, you just have to look around. You can swap the gears in a matter of minutes. It's a lot cheaper/easier than a tranny swap.