Differential swap / going to look at a rear end

[SirRobyn0]

Ok So I have another rear differential thread, but it's several years old so I'll give a quick recap and then tell ya what my plan is. So my truck is an 84' C20 14 bolt semi-float with 3.41 gears, 305 and rebuilt 700R4 with some beefing up. 3.41 gears with a 305 isn't the best at all and over drive use is limited to on the highway and flat ground. Towing my trailer (18 foot open trailer, occasional 6 - 7K load). I mean the truck will pull it even over the pass but it's not easy on the truck or me. So I'd like 4.10s or even 4.56's. I'd kind of like to go to the full floater, as well just because I do put weight in the bed from time to time and I'd prefer the heavy dutyness of it.

So there's a guy about an hour and a half north of me with a 14 bolt full floater out of a 78' C20. Other than the parking brake cable difference from the 70's models to the 80's models (I'll need to get new parking brake cables. It should be direct bolt in. That's a plus for me. Guy is selling it with the leaf springs $200. Rear diff is not locked up or anything like that, but he doesn't have a clue what the ratio is.

So my plan is at minimum to open the thing up find out what the ratio is and plan for it to need bearings and brakes. If it does not have a ratio that suits me, I'll do the gear change myself, but it will be out of the truck and I can take as much time as I need to fiddle with the thing and get it all set up correctly. If I'm lucky it'll have a ratio that will be good for me and I won't have to mess with that part of it. Which leads me to my question. What do ya'll think would be the most common ratios for a 78 C20? I haven't a clue about engine or transmission on the truck it's coming out of but my stab is it'll either have 4.10's or 3.73's.

I can't get up to see it until next weekend so I'll let ya'll know if I bring it home, but honestly at that price even if it needs to be fully gone though it's a deal at least for around here.

 

[bucket]

Yes, 3.73 and 4:10 seem to be the most common by far.

Iirc, '83/'84 is the year split between parking brake cable setups. You missed it by just one year, lol.

 

[PrairieDrifter]

Aren't the 3.73 and 4.10 carriers different? Or was 3.73 the cutoff?

Under 3.73 is a different carrier than 4.10's and up. Can't remember if 3.73 was the split though.

 

[Frankenchevy]

I thought it was 4.10 and down were the same.

 

[Craig Nedrow]

my 86 is 4:10

 

[SirRobyn0]

Ok thanks guys. I think this differential might work out well for me.

Also @bucket No worries about the parking brake thing. My cables are bad anyway and I've held off a few years not knowing if or when or what year differential I'd end up swaping in. So ultimately I'd just end up swapping to the older style cable setup.

 

[bucket]

I thought it was 4.10 and down were the same.

Yep. I haven't looked into it in several years, but I believe you can get the commonly used gear sets for either carrier.

 

[SirRobyn0]

Ok well I'm going to go look at the differential tomorrow at 11am. So I know how to get a rough calculation of ratio by turning the pinion and counting, but and I'm not sure if I will get to pop the cover before I buy it, I'd like to but we'll just see how it goes. Is the ratio commonly printed on the ring gear somewhere I might be able to see it?

 

[Ricko1966]

Ok well I'm going to go look at the differential tomorrow at 11am. So I know how to get a rough calculation of ratio by turning the pinion and counting, but and I'm not sure if I will get to pop the cover before I buy it, I'd like to but we'll just see how it goes. Is the ratio commonly printed on the ring gear somewhere I might be able to see it?

There will be a code stamped on the axle tube. The ring and pinion will have markings on it,not usually the ratio though. Normally the part number,a matching number so the ring and pinion stay as a set,like if one says 263 the other will be 263 so you know they are a set. And sometimes a date code. And 4 more numbers you will use for division to get your ratio. 41÷10=4.10 manufactured 03of70