Differential swap / bought it, work and install now

[Camar068]

So this isn't really a question or a statement, it's more of a thought process. I've already thought it out and read it so I know at least part of the answer for me, but given that the 31" tall tire is factory, and even my tires which are a bit wider than factory and still the same height so perhaps this information will help someone else, or maybe you'll disagree with my thought process and share yours.

So this is a speed / RPM chart for the various common ratios, or at least the ones that concern me atm.
Current gears at 3.41's so I'll start with that one. Mainly we are concerned with direct drive but I have included 2nd gear to see the RPM change at speed for a downshift like getting slowed down climbing a hill. Anyhow.
3.41
65MPH - 3RD 2,400 RPM
60MPH - 3RD 2,200 RPM
55MPH - 3RD 2,000 RPM
60MPH - 2ND 3,600 RPM
55MPH - 2ND 3,300 RPM

3.73 (the ratio my differential has in it)
65MPH - 3RD 2,650RPM
60MPH - 3RD 2,450RPM
55MPH - 3RD 2,250RPM
55MPH - 2ND 3,600RPM

4.10
65MPH - 3RD 2,900RPM
60MPH - 3RD 2,650RPM
55MPH - 3RD 2,450RPM
50MPH - 3RD 2,200RPM
50MPH - 2ND 3,600RPM

4.56
65MPH - 3RD 3,200RPM
60MPH - 3RD 2,900RPM
55MPH - 3RD 2,700RPM
50MPH - 3RD 2,500RPM
45MPH - 3RD 2,250RPM
45MPH - 2ND 3,600RPM

Ok so it's easy for me to see from this chart that keeping the 3.73's are out. It's not enough. As ya'll already know no matter what I choose everything is a compromise. I kind of feel like the cruising RPM in third towing should be at bare minimum 2,500RPM. And not over 3K. Not saying that the engine wouldn't run along happily at 3,500 but I sort of feel like that's great for a hill climb but not really necessary at other times. 4,10's put me in this range for towing at around 60 - 65mph (speed limit for towing on the highways around here is 60mph or lower in some cases.) 4.56's are pretty much going to cap me at 60mph, though I could do 65, 4.10's would allow 70. It's all a compromise. With the hills around here 4.56's look real attractive for towing.
Now I'm going to throw in my second but not quite as big of a concern. Running empty in overdrive.
3.41
80MPH - OD 2,050RPM
75MPH - OD 1,900RPM
70MPH - OD 1,700RPM

3.73
80MPH - OD 2,250RPM
75MPH - OD 2,100RPM
70MPH - OD 1,950RPM

4.10
80MPH - OD 2,450RPM
75MPH - OD 2,300RPM
70MPH - OD 2,150RPM

4.56
80MPH - OD 2,750RPM
75MPH - OD 2,600RPM
70MPH - OD 2,400RPM

When running empty and looking at that it's no wonder why the engine likes to run at 80mph or higher on the highway! Even though I like to run at 75!

I can see why 4.10's are kind of considered the gold standard in these trucks. No not as good a towing gear as 4.56's but not as limiting in direct drive either. I honestly don't think 4.10s will hurt my empty freeway mileage much if at all, but 4.56's certainly will. If I still had the bird farm and was running all over the state for feed I'd go with the 4.56's, but now.... I just really don't know how much towing I'd do and if it would make the 4.56's worthwhile or if they'd just become a PIA. I think because of the 700R4's low first gear that I don't think I'd have to worry to much about it short shifting 1 - 2 even with 4.56's so there is that. Although delayed a couple years now I still plan to replace the 305 with a 350.

So I will probably order parts on Monday, that gives me until then to decide if I'm going to go with 4.10's or 4.56's. I think I'm leaning towards 4.10's

I've got 3.73's in mine and drive 10 miles interstate on the way to work. I start off in 3rd and shift into OD 75-80 MPH.....it'll hold it in that area provided no hills. Hit 85 in OD....she starts to sing with power regardless of hills. Really wish I had 4.10's

 

[SirRobyn0]

I've got 3.73's in mine and drive 10 miles interstate on the way to work. I start off in 3rd and shift into OD 75-80 MPH.....it'll hold it in that area provided no hills. Hit 85 in OD....she starts to sing with power regardless of hills. Really wish I had 4.10's

I'm coming from 3.41's so maybe I'll notice some improvement from where I was. And if it ain't enough for me when I'm settled in my new house I can always do the regear this winter. I'm also thinking that going from 3.41s to 3.73 I'll know what one "step" of change is like so to speak. So hopefully that will help me to decide if 4.10s are enough or if Ill wanna go to 4.56s. All I can say is we'll see how it feel about.

 

[Bloodhound1981]

I had 3.73's, 31 in tires (really 30.5 if you measure), and a 700R4. I just went to 4.10s during a rear end rebuild. It's perfect at highway speed in OD now.

 

[SirRobyn0]

Ok thanks. But again for now I'm keeping the 3.73's for now because I'm moving into a new house in the middle of next month and don't want to spend the money right now. Maybe this winter we will see. A 350 might be more important though. Again we'll see.

No pictures from this morning because there's really nothing all that picture worthy, I took the passenger side drum off and the axle seal had seeped a tiny bit but just on the hub the shoes were dry but it so it was a much easier tear down and clean up. However the adjuster on this side was frozen. I managed to get it moving and apart with WD-40 I didn't have anything else to soak it in handy so I just let it sit in some WD-40, wire brushed it brake cleaned it off, treated it with anti-seize and it was working good again. New shoes, wheel cylinder and axle seal. It's all put back together. I just finished lunch and in a little bit I'm going to get the shoes adjusted up on both sides, I'll probably try to get the shocks off of it (I'm thinking of installing new rear shocks since I'll have it apart anyway. I'll have to see what a set of air shocks will cost, I've enjoyed having those on trucks before. Then it's just giving the housing a good cleaning and a paint job.

 

[SirRobyn0]

Ok the shoes are adjusted.
The housing has been cleaned as best I can under the conditions, which basically are no running water. So luckily it wasn't that gunky on the outside and the areas that were I wire brushed off the excess, hit it with engine degreaser, then brake clean. Let it dry and shot it with black spray paint. In all fairness it's not 100% done. I did the best I could to hit the underside of the differential, but when I get it to work and I get it up on the forklift I hit any areas that I might have missed.

While it might not be the gear ratio I was most hoping for this differential is definitely a lot less worn that my current one is. And when I decide to change the gears at least I'll know the brakes and hub bearings are all good.

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That will probably bit it for any real updates until I get to install it. Tentatively that will be next weekend at the shop.

 

[Ricko1966]

Ok the shoes are adjusted.
The housing has been cleaned as best I can under the conditions, which basically are no running water. So luckily it wasn't that gunky on the outside and the areas that were I wire brushed off the excess, hit it with engine degreaser, then brake clean. Let it dry and shot it with black spray paint. In all fairness it's not 100% done. I did the best I could to hit the underside of the differential, but when I get it to work and I get it up on the forklift I hit any areas that I might have missed.

While it might not be the gear ratio I was most hoping for this differential is definitely a lot less worn that my current one is. And when I decide to change the gears at least I'll know the brakes and hub bearings are all good.

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That will probably bit it for any real updates until I get to install it. Tentatively that will be next weekend at the shop.

No running water,use a concrete sprayer,or garden sprayer modified with a bigger feed tube. I have one of each,both with kitchen faucet sprayers and hoses on them. Started with the garden sprayer,ran across the concrete sprayer,at a garage sale. It was an upgrade because it holds more water.Its also black so I can leave it in the sun for hot water.

 

[SirRobyn0]

No running water,use a concrete sprayer,or garden sprayer modifies with a bigger feed tube. I have one of each,both with kitchen faucet sprayer and hoses on them. Started with the garden sprayer,ran across the concrete sprayer,at a garage sale. It was an upgrade because it holds more water.Its also black so I can leave it in the sun for hot water.

That's a good idea. But I'll be moving into my new place middle of next month so there won't likely be any or at least any regular working on vehicles in a field with no running water or power. I did drag out my generator so I could run my air compressor and use my air gun. I realize there are not that many bolts, but between the cover and axle bolts it seemed worthwhile to me.

 

[SirRobyn0]

I will have to figure out how to get it up and into the bed of my pickup. I'm sure that will be interesting. My plan is to tilt the dump bed and pull it up and into the bed of the truck.

 

[Ricko1966]

I will have to figure out how to get it up and into the bed of my pickup. I'm sure that will be interesting. My plan is to tilt the dump bed and pull it up and into the bed of the truck.

Tree limb and a couple of pulleys?

 

[SirRobyn0]

Tree limb and a couple of pulleys?

Open field unfortunately. The trees you Maybe able to see in the pictures are not on the property.

I have had pretty good luck dragging things into the bed by tilting the dump bed and working whatever it is up there. I might swing by harbor frieght and pick up two of their cheap furniture dollies. I bet the drums would sit right in those and I could just pull it up and on.

 

[ali_c20]

I use furniture dollies for moving axles around in my garage. I put my "shelved" transmission, engines, transfer cases and other heavy stuff on them so that I can easily move them around. No matter where I put them, there always comes a time when they get in my way.

 

[bucket]

I use furniture dollies for moving axles around in my garage. I put my "shelved" transmission, engines, transfer cases and other heavy stuff on them so that I can easily move them around. No matter where I put them, there always comes a time when they get in my way.

I've been doing the same. All my transmissions and transfer cases are pretty much all on furniture dollies now. There's a few engines that aren't on stands, but they haven't been in my way yet.

 

[SirRobyn0]

Thanks guys glad to know that will work. I think I've got a solid plan then to get it in my truck thanks!