Differential swap / bought it, work and install now

[bucket]

If I'd of known a couple days ago I would have been all over that, and I agree all the camper specials I've been around had 4.10's. This differential is in pretty good shape it seems and I can always use the springs off of it. I don't remember where you are at I'll shoot you a quick PM and we will see how close we are. Do you know what you'd want for the rear end?

Right, and from what I have gathered from Nick, and my local tranny guy Dan, that's about right. The biggest thing that kills overdrive as far as towing is if there is enough load to cause it to slip.

However and I mean no offence to anyone but this in not flatlandia here. There and mountain passes and where there aren't mountain passes there are ridges and hills. One example I like to give is coming back from west of the tri-cities then just after Yakima there are three ridges that I have to pull the highest is Manastash ridge at a crest of 2,600 feet the grade is steeper then the actual mountain pass we'll get to in a moment. So there are three ridges and then before getting to Snoqualmie pass which is a longer but more gentle climb there's about 40 miles of relatively flat road and I might cautiously trust overdrive on that 40 miles. But that just gives a little bit of info about the land out here. It's just not very flat so overdrive while towing would be of very limited use I would think.

I'm not saying no to the use of overdrive I'm just doubtful there would be a lot of use for it out here.

Ok, I wasn't sure what your goal was with figuring the desired rpm in 3rd gear.

So let me ask you this, how often do you find yourself using overdrive currently? Do you think you will be able to use it more often with steeper gears?

What about gearing it really steep, like 4.88's or 5:13's and using overdrive as a "normal" selection?

 

[Ricko1966]

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

Stick with the 3.73s save the money to use towards a torquey 350 build which won't need as much gear. I know your engine is tired. You need an engine and if it's not enough then,a gear ratio change could be in the future.

 

[bucket]

Stick with the 3.73s save the money to use towards a torquey 350 build which won't need as much gear. I know your engine is tired.

False.

Gear it for power AND build a torquey engine too! Lol.

 

[bucket]

Oh yeah... and how insulting. His engine isn't "tired". It's simply "less new"

 

[Ricko1966]

False.

Gear it for power AND build a torquey engine too! Lol.

Dammit @bucket your always posting while I'm editing. I know Robyn's due for an engine,I figure it is the next logical step. If he was pulling everything okay with his tired 305 a good 350 will be a big change. IMHO

 

[Ricko1966]

Oh yeah... and how insulting. His engine isn't "tired". It's simply "less new"

You did it again!!! You type faster than me. No I know he was having problems oil fouling plugs. And another 75hp and 100ft lbs,sure couldn't hurt things.

 

[bucket]

You did it again!!! You type faster than me. No I know he was having problems oil fouling plugs. And another 75hp and 100ft lbs,sure couldn't hurt things.

Lol, I'm just a 1-finger-typer. Yeah I remembered the issue he had with the oil fouled plugs, but I couldn't resist the opportunity to tease you.

 

[SirRobyn0]

Ok, I wasn't sure what your goal was with figuring the desired rpm in 3rd gear.

So let me ask you this, how often do you find yourself using overdrive currently? Do you think you will be able to use it more often with steeper gears?

What about gearing it really steep, like 4.88's or 5:13's and using overdrive as a "normal" selection?

Right now overdrive is about useless unless I'm going 60 - 65 on the highway. I doubt I'd go really steep like that. Although it would be cool in a way and really give me a nice low first gear for pulling away I'd probably destroy highway fuel economy 4.88's or 5.13's

And swapping gears is going to be a learning curve for me. So if this goes well going to something more normal like 4.10's or 4.56's then if I want more I'll probably be less afraid of diving in if that makes sense.

Stick with the 3.73s save the money to use towards a torquey 350 build which won't need as much gear. I know your engine is tired. You need an engine and if it's not enough then,a gear ratio change could be in the future.

I'm only going to spend maybe around $400 to regear it, more if I do all the bearings obviously. I have thought about just leaving the 3.73, but it's just not enough change from the 3.41's. Yes my 305 is tired and I know a fresh 350 will really up the power.

False.

Gear it for power AND build a torquey engine too! Lol.

And blow up my 700R4 swap in an SM465, with a ranger too! Sounds like a lotta fun! Lol

Oh yeah... and how insulting. His engine isn't "tired". It's simply "less new"

Yea I feel real insulted Lol (I'm kidding of course) Seriously though that old 305 has served me well and it's been a few years since I said I was going to pull it. If there's any way I can afford it after the move she's getting a 350 this winter!

 

[SirRobyn0]

Lol, I'm just a 1-finger-typer. Yeah I remembered the issue he had with the oil fouled plugs, but I couldn't resist the opportunity to tease you.

Oh also I can type around 30 words pre-minute if I focus on it. More often than not I'm a lot slower because I get distracted or make to many mistakes.

 

[Ricko1966]

Lol, I'm just a 1-finger-typer. Yeah I remembered the issue he had with the oil fouled plugs, but I couldn't resist the opportunity to tease you.

Oh I deserve to be harassed occasionally.

 

[SirRobyn0]

Well this might all go in a direction I wasn't planning.
So I looked at prices and for me to just slam gears in it. With an assortment of shims, a crush sleeve eliminator, and a pinion seal I'm looking just over $400, with pinion bearings, which I think I'd be crazy not to do that much at least around $450, closer to $500 if I do carrier bearings. And that's using motive gears which is a cheaper brand.

I have not pulled the drums off so I have no idea if it's going to need shoes or seals.

I think I'm going to hold off ordering gears until this weekend. I'll pull the axles out, get the drums off and see what's going on in there.

With me moving into a new house being just a little more than a month away this might not be there best time for me to blow an extra $500 to do a minimalistic gear swap leaving old bearing still in service.

So I think I'm going to see how things look with the brakes and take it from there. As much as I really don't want to, I may end up simply installing this rear end with the 3.73's and change the gears later. The semi-float that's in the truck now, had a slightly bent LR axle when I bought it and I've never replaced it. There isn't much lining left on the shoes. Plus I'll get the larger brakes with the full float. And any money I invest into the brake on the FF I get to keep unlike if I do brakes in the SF.

So that's my current train of thought anyway. Well see what happens this weekend and go from there. But this might come down to not wanting to spend the money before moving date.

 

[HotRodPC]

I know that everyone says not to pull in OD. But I've always been of the opinion that if it's not hunting for gears and the converter is staying locked, just run it in OD. The steeper the gearing is, the easier it is to achieve that scenario.

If the converter is locked, it's not hunting between gears and the fluid isn't getting hot, how could it possibly hurt anything?

Exactly right. I've towed in OD many many times. As you said, if not hunting, and not locking unlocking, and engine doesn't seem to be srained, run it in OD. Only time I've even pulled it into D was climbing a grade it was wanting to upshft and then immediately back down, again known as hunting. It wanted 4th, but needed 3rd, so I just left in 3rd, and then the converter was able to lock up and stay locked up since it was 3rd and 4th capable of lock up.

 

[ali_c20]

Well this might all go in a direction I wasn't planning.
So I looked at prices and for me to just slam gears in it. With an assortment of shims, a crush sleeve eliminator, and a pinion seal I'm looking just over $400, with pinion bearings, which I think I'd be crazy not to do that much at least around $450, closer to $500 if I do carrier bearings. And that's using motive gears which is a cheaper brand.

I have not pulled the drums off so I have no idea if it's going to need shoes or seals.

I think I'm going to hold off ordering gears until this weekend. I'll pull the axles out, get the drums off and see what's going on in there.

With me moving into a new house being just a little more than a month away this might not be there best time for me to blow an extra $500 to do a minimalistic gear swap leaving old bearing still in service.

So I think I'm going to see how things look with the brakes and take it from there. As much as I really don't want to, I may end up simply installing this rear end with the 3.73's and change the gears later. The semi-float that's in the truck now, had a slightly bent LR axle when I bought it and I've never replaced it. There isn't much lining left on the shoes. Plus I'll get the larger brakes with the full float. And any money I invest into the brake on the FF I get to keep unlike if I do brakes in the SF.

So that's my current train of thought anyway. Well see what happens this weekend and go from there. But this might come down to not wanting to spend the money before moving date.

Regarding the brakes: On the old FF axles you have to remove the hub to access the brake shoes cause the wheel studs are pressed in thru the drum and then the hub. Rebuild the brakes and replace all seals in the hubs when you have them off. The hubs with slip on drum and press on drum are not interchangeable.

 

[Grit dog]

I know that everyone says not to pull in OD. But I've always been of the opinion that if it's not hunting for gears and the converter is staying locked, just run it in OD. The steeper the gearing is, the easier it is to achieve that scenario.

If the converter is locked, it's not hunting between gears and the fluid isn't getting hot, how could it possibly hurt anything?

You’re correct.
Don’t tow in OD is just part of a towing for dummies tutuorial. Or more accurately the “safe” way to go when explaining towing to someone who is mechanically challenged or doesn’t speak car.
Speaking of towing and OD….i cannot wait to go test drive the new Chummins with the 8 speed……finally!
4.71 first gear. Not a horrible split to second, especially if the computer knows what it’s doing and from there. Arguably just as good of gear splits as the other guys’s 10 speeds. Fckin Ram has had this in the works since like 2017. Bout time.

 

[Grit dog]

If I'd of known a couple days ago I would have been all over that, and I agree all the camper specials I've been around had 4.10's. This differential is in pretty good shape it seems and I can always use the springs off of it. I don't remember where you are at I'll shoot you a quick PM and we will see how close we are. Do you know what you'd want for the rear end?

Right, and from what I have gathered from Nick, and my local tranny guy Dan, that's about right. The biggest thing that kills overdrive as far as towing is if there is enough load to cause it to slip.

However and I mean no offence to anyone but this in not flatlandia here. There and mountain passes and where there aren't mountain passes there are ridges and hills. One example I like to give is coming back from west of the tri-cities then just after Yakima there are three ridges that I have to pull the highest is Manastash ridge at a crest of 2,600 feet the grade is steeper then the actual mountain pass we'll get to in a moment. So there are three ridges and then before getting to Snoqualmie pass which is a longer but more gentle climb there's about 40 miles of relatively flat road and I might cautiously trust overdrive on that 40 miles. But that just gives a little bit of info about the land out here. It's just not very flat so overdrive while towing would be of very limited use I would think.

I'm not saying no to the use of overdrive I'm just doubtful there would be a lot of use for it out here.

Like you said, present company excluded (the gear heads here in this thread), many do t understand the difference between towing across Kansas with a head wind or tail wind vs towing in the mountains. And we don’t even have the elevation factor here. Take your same rig and add another mile in elevation to Umtanun, Manastash and Snoqualmie, either direction, and you’d never even be tempted to try OD. Your be happy if it gets out of 2nd gear! Lol.
Sounds like you found a great deal on an axle. Should be a great start to that project!