Help! Is a 4.57 rear gear tolerable?

[oem4me]

Hey guys, Im seriously thinking of buying (real soon) a new to me C-20 truck equipped with the Detriot locker 4.57 rear end, and I want to do a fair amount of highway cruising pulling an old boat and/or trailer. Problem is, I once had a 4.56 rear in my current '62 C-20 and hated it. That gear was totally useless for me. Of course, that truck has a little 235 six and three speed trans. The new truck has the 327 V8 and turbo 400 trans.
The seller claims with 31" tall tires installed it's totally fine at 65mph. I have confidence that this is his honest opinion, but I want to hear from those who have this rear end or made do with their low gears. Also, anything else I need to know about detroit locker in particular? Thanks ahead of time for quick responses!

[contagious102]

Don't think you will be happy with that gear.3.73 would work fine with a 31" tire, 4.57 even with a tall tire is going to turn a lot of rpm.!!! go here and see.!!

http://www.wallaceracing.com/calc-rpm.php


I came up with 3200 rpm at 65.

[aerotruk63]

64 Gmc 6000 with 7.20 gears in the rear, 327, 5 speed Clarke with no overdrive. 55 mph max all day long. maybe 8 mpg. Joke was I had to pull over cause a Combine driver was trying to pass.

[markeb01]

My non-winter rear street tires are a little over 29" tall and I run a 4.10 gear with a manual 4 speed (no overdrive). 60 mph is somewhere in the vicinity of 3,000 rpms. Switching to my much shorter snow tires bumps the rear axle ratio closer to a 4.30 ratio. Driving the truck around town with the short tires is great fun as it accelerates very quickly, but my old tired 350 is not happy at freeway speeds with tires that small.

I would speculate a little 327 would be working pretty hard at 65 just powering a big heavy transmission like the TH 400, in a big heavy truck chassis. I can’t see the 31” tires being all that much help. They will certainly lower the rear axle rpms, but I don’t imagine the overall drivability would be any better than what I enjoy. And mine is so bad I basically don’t drive it on the freeway, it’s restricted to being a local fun car.

The other downside is the automatic transmission, or more specifically the torque converter. Generally a non-lock up torque converter will arguably add 500 rpms to the engine at cruise speed due to slippage. So if everything else was equal, your C-20 would still be turning 500 rpms more than a stick shift at speed.

I’ve never owned a locker, but I’ve known many that have. The two most significant features I’m aware of are they make a lot of noise ratcheting around corners, and can lock up violently on slippery pavement. This might be highly desirable at the drag strip, but on ice it can cause loss of vehicle control. Most of the guys I’ve spoken with prefer a limited slip or positraction axle instead, but they all owned street rods. On a big truck a locker might work just fine.

[theastronaut]

I think it just comes down to opinion. My daily driver is a mildly hopped up '64 VW bug with 4.37 R&P that turns 3000 rpm at 60 mph. I put 10-12K miles a year on it and wouldn't go to a numerically lower gear, I love it. 3000 rpm isn't hurting the engine, they were made to turn to atleast 4500 rpm or more I would guess. I think the biggest thing people complain about is the engine sounds like its "working harder" even though it isn't. It only takes a certain amount of HP to move a truck at 60 mph no matter what rpm it's at.

Our '97 S10 SS has a locking diff and it's either on or off- like having a spool when it's locked or an open diff when it isn't. I don't really care for it, a posi would be better.

If you take off the original fan and add an electric fan the engine would be quieter at speed. Or a T56 six speed from a LT1 Camaro will bolt right up... 75 mph at 2000 rpm and still have steep 1-4 gears for towing! You probably don't want to do any modifications though.

[joedoh]

Originally Posted by theastronaut

I think it just comes down to opinion. My daily driver is a mildly hopped up '64 VW bug with 4.37 R&P that turns 3000 rpm at 60 mph. I put 10-12K miles a year on it and wouldn't go to a numerically lower gear, I love it. 3000 rpm isn't hurting the engine, they were made to turn to atleast 4500 rpm or more I would guess. I think the biggest thing people complain about is the engine sounds like its "working harder" even though it isn't. It only takes a certain amount of HP to move a truck at 60 mph no matter what rpm it's at.

Our '97 S10 SS has a locking diff and it's either on or off- like having a spool when it's locked or an open diff when it isn't. I don't really care for it, a posi would be better.

If you take off the original fan and add an electric fan the engine would be quieter at speed. Or a T56 six speed from a LT1 Camaro will bolt right up... 75 mph at 2000 rpm and still have steep 1-4 gears for towing! You probably don't want to do any modifications though.

well, you are somewhat right.

cruising rpm should be within 10% of the peak torque rpm of the motor. thats why v8 guys who buy 4 cylinders think they need an extra gear, because a v8 makes torque down low but 4 cylinder engines need more rpm. My 4 cyl 6 spd daily with 280lb ft cruises at 65 right at 3k, which is the tq peak for my car. So you should pick a cruising speed and work backwards from peak tq to get your gear ratios.

your air cooled engine especially needs the higher rpm to move air over the cylinders, overdrive would cook that motor. Even the porsche 5 spds around that era were all 1:1 5th, for more gear choices in the split between 1st and 5th.

Nothing will overcome air drag though, requiring exponentially more torque the faster you drive. I've seen guys take their rear end gear and tire size to figure out top speed, the truth is they will run out of torque usually WAY before running out of rpm, the wall of air just gets to hard to push.

The number one advice for people who want to save money on gas is to knock 10mph off their cruising speed. Try this once, start a timer and you and a friend start off for a destination 10 miles (mostly highway) away. you drive 75, he drives 65. Once you get off the highway it would be a miracle if he didnt catch you at the first stoplight. Worth the 50 cents to get there first?

In summary, its not always the lowest rpm that gives the best mileage, but this example is not the exception its the rule, 31s at 3000 rpm would get old quick. You will want a numerically lower rear end, absolutely, if you expect to drive on the highway a lot. if you mostly putt around town, you'll be all right.

[j.kirn]

putting around town

[Captainfab]

My DD for about 10 years was my '66 C20 with a 327, SM420 and a detroit locked, 4.57 geared HO52, and 9.50 x 16.5 tires. I believe the tires are about 30". I never did have a tach in the truck, but it was turning pretty good at highway speeds. The 327's do pretty good with the rpm's so I don't think that will be much of an issue. With those low gears, there isn't much trouble pulling a heavy trailer. The noise can get annoying though on extended highway trips. As already mentioned, the Detroit Locker is a bit noisey, and does jerk a little while ratcheting around corners. I drove mine year round and never had any problems in the snow and ice. In fact I rather liked it.

When the day comes to put that truck back on the road, it will have some higher gears in the Dana 60 that will replace the HO52.

[Born Lucky]

I am running a Eaton ho52 and hate the hi way . The rpm's are to high 3200 to 3500 at 65 70 mph. I am going to change over to a 3;08
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[63burban]

Remember, when these trucks were built they were designed to run 55mph at the most, C20 was a work truck, they are comfortable at 50mph with 4:57. The best ratio for all around is 3:42 or 3:55. Trust me I've had them all and currently run a 3:55 with a 700r4 in, my 63 2200rpm at 70mph. The 65 in my avitar has a 230 with 3 speed and runs 3200rpm at 65-70, she pushes oil into the air cleaner on long distances at those speeds.

[j.kirn]

Originally Posted by 63burban

Remember, when these trucks were built they were designed to run 55mph at the most, C20 was a work truck, they are comfortable at 50mph with 4:57. The best ratio for all around is 3:42 or 3:55. Trust me I've had them all and currently run a 3:55 with a 700r4 in, my 63 2200rpm at 70mph. The 65 in my avitar has a 230 with 3 speed and runs 3200rpm at 65-70, she pushes oil into the air cleaner on long distances at those speeds.

you would be right anything over 50 is pushing them

[jocko]

I'm gonna call BS on the seller. You would be miserable at 65 mph. Is it doable? Sure. Would you be miserable, absolutely. Is it a highway-friendly gear - far from it. Here are the numbers (a few comparisons of different transmissions, TH400 included, vs. 4.57 and 3.73 (just for comparison) and you can be the judge. Considering that a comfortable cruising rpm on the highway is in the 1800-2400 range (BIG wag), I'm thinking 3220 rpm will make you want to pull your hair out). If you were to consider an o/d trans, it would ease the top end rpm, but make 1st gear miserable (much deeper 1st gear in 1st on the o/d transmissions vs. the TH400). So, I'm thinking a rear gear swap now to 3.73-ish would be nice. But lotsa work for a truck you might not have wanted to mess with the rear end on, but who knows. Ideally, a rear gear swap AND an eventual o/d trans swap would be the ticket, but $ in th elong run. If I had to choose between one way of skinning the cat vs. the other (different rear gear vs o/d trans) I'd probably get a higher rear end gear in order to avoid a humongously deep 1st final gear ratio that would be the result if you swapped to a 700R4, for example (i.e. 14:1 torque multiplication). I'm guessing you go about 10 feet before you needed to shift in 1st gear.

[LT1 Burb]

Holy crap, wear ear plugs and don't put a tach in it if you plan on driving at 65. On the bright side it would be perfect for a Shafiroff 427 ci small block.
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[awbrown]

I had a 72 chevy that I put a 350 with a th350 and that had 4.56 with a tall tire , but I dont remember going much over 60 mph and I was always checking to make sure it was in drive...

[capev86]

I swapped the H052 rear in my 72 Suburban C20 from the stock 4.57 to a 4.10 gears. rpm now is about 3k at 60mph. i stick to 50mph for long highway drives to keep the rev's down. the truck has the original 307 (327 w/ smaller bore) with a Q-jet swap and 3 on the tree. The efficiency/power combo of the carb plus the slightly better rear axle actually makes it better than original. i'm still planning an overdrive setup to get the best of both worlds...1966-69 Saginaw 3 speed with Borg Warner R10 unit. a 3.08 is too soft for anything less than a diesel or solo highway cruiser on flat land.

[padresag]

lot of it depends on what you grew up with and what your tolerances are. my 65 1ton with a 250 or maybe it ia a 230 goes just fine down the highway at 55 mph. must have 4;56 or whatever in it. mind you I don't seem to drive that much maybe a tank full a month at most. I just usually walk with the dog or I will ride my bike. if I was doing 200 mi. a day I would be looking at ways to change things. the duals on the back of the 1 ton are 33 1/2". I think that she may start to hum at 65. I drove my 64 4 x 4 for 18 years with that detroit in it . you can get adjusted to noise after a while. it used to be around 2200 at 60mph with the o/d , 3;73 and 33" tires. i did get her up to about 2800(gov at 2950) and it was starting to sing. you hear nothing else. it would run that way all day long and thrive on it. you could wear earplugs as you could never listen to the radio or a passenger.
ron

[capev86]

yeah, i'm kinda spoiled by modern vehicles with highway friendly gearing. i also like to keep wear and tear to a minimum and my truck has very little sound insulation so it's very loud going down the highway. with the mods i did, fuel mileage went from 10/11 to 14/15 in mixed driving. 10% reduction in gearing gave me a 30% improvement in economy. that's how ill suited deep gearing is for modern use and why trucks now employ overdrive transmissions. i don't plan to do any trips out of the new england area until i have my overdrive installed.

[rtk434]

All depends on the person I guess. I daily drove a small block S10 with 4.10's and 28" tall tires for years. Took it on many 3 plus hour trips to the shore with it. Yes it's loud and uses gas but it never bothered me. I can't say I've ever owned anything with anything less than 3.73's. I'm a drag racer I like low gears.
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[gmcdeadhead]

i'm changing my locker rear out this spring for a 14 bolt with 3:73 gears . can't stand the 4:56

[maxwoof]

I have a 62 k20 with a 235 and 4.57 rears. I am running 7.50 16 tires, which are about 31". A few times a year, I take it on 100 mile highway trips. 55-60 is doable. It howls, but you get used to it after a while. Around town, where I do most driving it is fine. I don't know if I would want a lower gear ratio with the 235. The truck had 33" tires when I got it and it was sluggish. Much more peppy with the 31" tires.
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[capev86]

4.56 is a little too stout these days unless it is a farm vehicle or heavy tow vehicle. 3.73 / 4.11 range is a good general purpose range and is awesome when you combine it with an overdrive. a 4.11 with an overdrive is better on the highway than straight 3.08 gears.

even with 4.10 gears i usually shift it into 3rd gear by 20-25mph.

I don't know if I would want a lower gear ratio with the 235.

sounds like it's time for a 292 swap.

[Insideline]

I am the seller here, and so I assure all of you that there is no BS in my experience with driving this Custom Camper with the optional 17.5" 8R- Continental tires combined with the stock 327/turbo 400 3 speed trans. My '66 C10 250 6 with 3 speed is screaming very uncomfortably at 65mph, while I drive all over my state at 60-65mph in this '66 3/4 ton with much less noise and much less perceived engine strain from the 327/400 combination. Sure the 4:11 optional gears would make it better, and would not cost that much to change, yet this truck is more than comfortable noise wise and from a comfort point of view as is.
The only time the No-Spin rear locker makes "any" noise is when it is working to find traction in very icy and snowy conditions where it will click. I own a '66 Carryall with 3:73 Posi, and 10 out of 10 times I would take the No-Spin locker as it is a much more capable, durable and sophisticated design.

[padresag]

Originally Posted by Insideline

I am the seller here, and so I assure all of you that there is no BS in my experience with driving this Custom Camper with the optional 17.5" 8R- Continental tires combined with the stock 327/turbo 400 3 speed trans. My '66 C10 250 6 with 3 speed is screaming very uncomfortably at 65mph, while I drive all over my state at 60-65mph in this '66 3/4 ton with much less noise and much less perceived engine strain from the 327/400 combination. Sure the 4:11 optional gears would make it better, and would not cost that much to change, yet this truck is more than comfortable noise wise and from a comfort point of view as is.
The only time the No-Spin rear locker makes "any" noise is when it is working to find traction in very icy and snowy conditions where it will click. I own a '66 Carryall with 3:73 Posi, and 10 out of 10 times I would take the No-Spin locker as it is a much more capable, durable and sophisticated design.

those 17.5 tires do make it more desirable to drive as they are almost 34" new than a 29 or 30" tire and sbc don't tend to run out of rpm as a stock I6 does.
ron

[Insideline]

Actually the height of the 8R 17.5 tires is right at 31". What makes almost all the difference in this equation is Chev's 327 V8 engine architecture is designed to rev much more freely and has a much more free breathing crank case vent system along with a peak torque that is quite a bit higher. Whereas the 250 6 is a low revving engine with a 'tight' crank case vent system, and peak torque is much lower, so add all these things up and a 327 revving at 3200rpm is miles happier than a 250-6 at the same revs.
As a change up to this, I had Mike Sissell build me a custom lump port 292-6 with fully programable fuel injection built with light slipper pistons, lighter crank and rods, a full roller cam valve train with all of the reciprocating mass significantly reduced and that engine made 325 ft lbs of torque at 2200 rpm. I mated it to a GM factory close ratio 5 speed box, and that engine/trans is more efficient, more responsive and way more fun than a 327/350-700R combination. The only downside is it cost more than twice the V8 set up.
This stock GM 327/turbo 400/4:56 locker truly is a decent compromise between power, noise, torque and being quite drivable. As mentioned, putting the 4:11 gears into the locker assembly could make this set up ideal.

[hd74]

great for towing or drag raceing only will not work with hwy driveing, not even with over drive