Re-gear talk again 4.10 or 4.56

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SirRobyn0

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Some of you probably remember that I've been looking to re-gear or possibly swap to a lower geared full floater as I currently have the 14B semi-float. For those that missed the earlier conversations or want a refresher I'll go over that then give some numbers to think about.

The truck 1984 C-20, what was thought to be a 350 turns out to be a 305 after looking at the block numbers. Truck has the 700R4 with temp gauge and cooler and it is in good health, automatically locks converter in OD or has manual switch to engage lockup in 3rd. Current axle ratio is 3.41, stock 31" tires.

The trailer, 18' open car hauler type, but rarely used for cars. Most common loads are, my small tractor gross trailer weight about 5,000Lbs, or feed hauls where the trailer gross is around 6K.

Terrain, hills, lots of them when there isn't hills there's mountain passes that's just the way it is here. Some secondary roads, some freeway use.

Look I know a 305 isn't going to break any land speed records especially with the trailer loaded, but with the current 3.41 gears it will haul it, just not very well. I'm looking to go to either 4.10 or 4.56, I keep looking at the numbers but can't seem to decide so I'm hopeful that someone will look at the numbers or have some personal experience and say something that will get me to make a damn decision and move forward one way or another.

Numbers:
305 makes peak torque 245 @ 2,400RPM, peak horsepower 145 @ 3,800RPM so at the very least we want to keep the RPM within those ranges when towing, but also best if not right up against either end. I tend to like to keep it right around 60MPH on the highway with trailer, both because that's the law and where it feels comfortable, control wise.

current RPM with 3.41
65 MPH 3rd gear 2,400 (at peak torque, not ideal and above preferred cruse speed)
60 MPH 3rd gear 2,200 (below peak torque this is terrible, preferred cruse speed)
55 MPH 3rd gear 2,000 (below peak torque even worse)

If re-geared to 4.10
65 MPH 3rd gear 2,900 RPM (between peak torque and HP this is great)
60 MPH 3rd gear 2,650 RPM (great)
55 MPH 3rd gear 2,450 RPM (at peak torque not great) my biggest concern with this is for example I'm going up a hill or on the pass, I'm maintaining 60 MPH and have to slow down a bit for whatever reason to 55 or 50 I'm going to get under peak torque which may end in down shifting to 2nd and having to stay at or below 50 MPH for the duration of the hill.

If re-geared to 4.56
65 MPH 3,200 RPM (great within torque to horse power range, but my concern is a little high if for some reason I had to drive 65 for extended period.)
60 MPH 2,900 RPM (great within ranges)
55 MPH 2,700 RPM (great within ranges)
50 MPH 2,500 RPM (a little low but still with in ranges and now we are slow enough to reduce wind drag so if I'm pulling a hill at this speed I feel I'd be likely to be able to maintain it).

I understand it's 305 not a 454 and no I will not throw away a perfectly good 305, just because it is under powered, when the 305 is worn out I may consider BB or may go to 350, I'll cross that bridge when I get there, for now I want to get the most out of what I have. Will I modify the 305 slightly maybe, it's currently stock except for the carburetor, for right now I just need to make a gearing choice.

So with the 4.10 my main concern is if I'm on a hill and end up in the 50 -55 MPH range, I maybe forced to slow down more in order to downshift to 2nd and then would have to maintain a lower speed. End of the world no, concern yes.

4.56 would be better for maintaining various hill climbing speeds as outlined in my chart, and also for getting the load moving, my biggest concern with the 4.56: Towing in Washington the speed limit is 60MPH on freeways, while for cars it's 70, sometimes it is simply necessary to go a bit over 60 to keep up with traffic, at least for short periods, will I feel comfortable turning 3,200 RPM or possibly a little more for "a while" on the freeway if necessary? I know GM put 4.56's in 1 tons with 3 speed auto trannys and manuals, so that gives me some comfort but that was also in the day of 55 MPH speed limits for all.

With the 700R4 overdrive makes the high RPMs of the 4.56 a non-issue when I'm not hauling and running unloaded driving 70+ should not be a problem.

4.10 or 4.56 your thoughts?
 

shiftpro

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4.56.
The 700 likes to be revved, they lubricate and cool better.
You can upgrade to a 350/383 and run a little taller tire with these gears.
 

Curt

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Looks like you did your homework.@shift pro is right with 4.56.You can go up tire size to offset if needed.Go with 4.10s and wish for more,then turn around and gear swap again...rather not.

If you are gonna change gear ratios,I absolutely think you should go with the full float.Beefy and easier for a gear setup.Easy conversion.67” wide rear out of a 1 ton van matched my front track with perfect.

Rear disks cheaper for the full float,much more aftermarket support.
 

Green79Scottsdale

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I agree with both of those guys. 4.56 should also take some strain off the 700, in addition to the pros shiftpro pointed out.
 

75gmck25

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If you want to change gears with a simple swap to a 14 bolt FF axle from the pick and pull, I think 4.10 is a much more common gearing, unless you find a 1 ton.

Bruce
 

SquareRoot

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4:56. Been there done that. The 4:10's were OK with the Th400 but then the NV4500 swap made it clear that 4:10's would have sucked with OD. That's not factoring in an anemic 305.
 

SirRobyn0

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You know I've been leaning in the direction of 4.56, with the one concern I previously mentioned. As I sat and typed out the chart last night it only pushed me towards the 4.56 more, seeing the numbers written down, and you all have just backed me up on that.

If I go to a full floater it would be out of a pickup, but one of the things that is hard here is there are virtually no junk yards left in the area, and in the few that are left finding a square is going to be a very rare thing. So that leaves craigslist, and probably a few hours drive to get the axle. Or ordering from a company like LKQ and having it delivered to the shop. The question is how much do I want to spend. I can do a gear swap for about $250, if I get an full floater I've got the purchase price, and then either gas or delivery, then fixing anything the new axle needs before install. Yes, I would love to go to the full floater, but this last year has been terrible at work so cash is short and regearing the existing axle maybe cheaper. I'll do a little looking around before deciding. 4.56's are out there in the full floater so I might get lucky enough to find one.

I have zero interest in a disk brake conversion, or taller tires. I've done enough disk brake conversions at the shop to know I'm not interested in that at all.

Thanks for all the thoughts so far guys!
 

SirRobyn0

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Last night I had to make run up north in the truck. This isn't a very far run and is only about 20 miles each way. The quickest time wise and shortest route in miles is a curvey road varying in speeds from 20 - 45 mph. As I was departing my destination I decided I'd take the long way home, the long way part of it is on a divided 2 lane highway with 55MPH speed limits and little traffic late in the evening. My purpose, to cruise at 3K+ to see if I'd be comfortable with that. Well now I see why no one ever complained about running those kind of RPMs in the old 1 tons, I ran it up to 3K felt comfortable so pushed it to 3,500RPM. Push it is a really silly thing to say because the truck had absolutely no issues with running those RPMs, and at 3,500, it was still more than willing to go higher, but I did not feel the urge. With the 3.41 rear end I currently have all of these test were carried out in 2nd gear, so of course I realize it will feel a little different in 3rd running those kind of RPMs when I'm towing, but this was certainly enough of a test to cement that running these RPMs will be ok. Of course it's not 90F out, and I'm not towing 3 tons of weight behind me, I think the worst thing I might find is that I need to have the radiator rodded out. On the flip side to that there should be less heat from the trans at the high RPMs as long as I can keep the TCC locked up, which I should so even that might be a non-issue.
 

Rusty Nail

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4.10 or 4.56 your thoughts?

Runnin 3.73s a guy would run out of second gear about 60 feet from the trap.
Blow damned near a whole quarter mile in second gear...

4.10 or 4.56?

Reckon if 4.10 sure you'd have to shift but then what? Then you are low in your range without much room left to run.

Reckon if 4.56 you end up in the meat of 3rd gear at the big end?

My opinion is that after all the work to change gears 4.10 leaves money on the table.

:flamingdevil:
 

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