**Help**Having trouble figuring out how to change rear Differential

[Lionc68c10]

I have a 1968 c10 that was once a police two truck. The rear end is at a extremely high gear. If I am driving down a hill and let go of the gas the truck slows down a lot. About three years ago I put a New 350 V8 four barrel engine and feel that I am not get the top performance from it due to the rear end. I just added disc brakes so I am looking for a cheap way to fix this...Any Ideas from the great minds?

[breeh]

Cheapest route would be to find a complete rear axle from a donor truck that has a numerically lower gear set.

[Lionc68c10]

Originally Posted by breeh

Cheapest route would be to find a complete rear axle from a donor truck that has a numerically lower gear set.

Could I look for a rear end from a new chevy truck or would I need to stay in the 68-72 years? thanks

[breeh]

If you don't want to have to change your wheels then you will need to find a 67-70 axle. You should have a 6 lug rear. In 71 the General went to 5 lugs on the 1/2 tons.

[Lionc68c10]

Originally Posted by breeh

If you don't want to have to change your wheels then you will need to find a 67-70 axle. You should have a 6 lug rear. In 71 the General went to 5 lugs on the 1/2 tons.

Great thanks for your help

[breeh]

If you were closer, I would give you one...

[C20_Paul]

I was able to pick up a used third member from my local 67-72 wrecking yard. It only cost my $150 and installed in about an hour. Although that thing is a heavy pumpkin.

I'm not sure if all the axles came with a removable third member though. Mine is a 1967 C-20. But if you have bolts on the driveshaft side of your rear axle you might consider this option.

[shortbed70]

If you were closer again I have a 3.73 I want to get rid off for something taller...

[Lionc68c10]

Originally Posted by shortbed70

If you were closer again I have a 3.73 I want to get rid off for something taller...

Dang...that stinks

[Lionc68c10]

Originally Posted by C20_Paul

I was able to pick up a used third member from my local 67-72 wrecking yard. It only cost my $150 and installed in about an hour. Although that thing is a heavy pumpkin.

I'm not sure if all the axles came with a removable third member though. Mine is a 1967 C-20. But if you have bolts on the driveshaft side of your rear axle you might consider this option.

That is a good idea, I will have to look into the third member option and get some more info on it, thanks

[Longhorn Man]

Lionc68c10... do you have a C/10, or C/20? You say tow truck, I am assuming it is a 20 or even a 30 series truck.
This can chainge things a LOT.

[Lionc68c10]

Originally Posted by Longhorn Man

Lionc68c10... do you have a C/10, or C/20? You say tow truck, I am assuming it is a 20 or even a 30 series truck.
This can chainge things a LOT.

It is a c10, I thought that same thing. But the original owner advised me that it was still used as a tow truck.

[Lionc68c10]

Also, I have heard stories of people using parts from Cj jeeps on the old chevy trucks. The reason I ask is bc i found a dana35 rear axle from 95 wrangler with 3.73 gears. Is this possible?

[Myself]

If you are going down hill and the truck slows down when you let off the gas, you already have 3:73 or lower. I think you are wanting higher gears like 3:50 or 3:08.

[Lionc68c10]

Originally Posted by Myself

If you are going down hill and the truck slows down when you let off the gas, you already have 3:73 or lower. I think you are wanting higher gears like 3:50 or 3:08.

I believe you are right, because I just got off the phone with a guy that recommended I get a 3.41 or higher.

[project 67 sub]

sorry had to do it. but

[Jtrux]

You don't have a drop out third member. You need either a whole rear axle or regear it.

3.42 is a good choice, I'd probably go with a 3.07 but that's just me. I would bet that you have a 3.90 or so right now.

A dana 35 out of a Jeep is very weak and very narrow ( about 60 inches wide) so would not be a good candidate for a heavy truck with V8 power.

BTW, if you still plan on using it for towing the 3.42 is probably a better choice than the 3.07's I said earlier but I think the 3.07's would be great for a non OD cruiser with V8.

[lts70]

Jtrux, I have a 3.07 posi rearend in my 70 chevy. I put an NV3500 tranny in her and It makes my OD kind of worthless unless I am doing 85mph or more. In your post you said regearing was an option. Have you done it? Is it hard? I was going to swap out for a 71-72 with a lower gear but couldn't find any in my area. I would like to keep my posi and I already have 5lug hardened axles that make my rearend basicaly a 71-72 5lug posi 3.07. So I like every thing about my set up, it works great I just wish I had more grunt in lower gears and the OD was more usable. Any advice would be great.

[Jtrux]

Originally Posted by lts70

Jtrux, I have a 3.07 posi rearend in my 70 chevy. I put an NV3500 tranny in her and It makes my OD kind of worthless unless I am doing 85mph or more. In your post you said regearing was an option. Have you done it? Is it hard? I was going to swap out for a 71-72 with a lower gear but couldn't find any in my area. I would like to keep my posi and I already have 5lug hardened axles that make my rearend basicaly a 71-72 5lug posi 3.07. So I like every thing about my set up, it works great I just wish I had more grunt in lower gears and the OD was more usable. Any advice would be great.

Yeah with gears that high your OD is kinda useless. I've done it and I personally thought it was cake. Just take your time. I did it with the axle outside the truck but you can do it with it in the truck just as well. There's alot of info online and some really good info on those Horse Power tv shows as well.

[lts70]

sweet! Where did you get the gear? Can I get a gear out of a non posi used rearend? How much did it cost you if you don't mind? Did you have to buy any other parts besides the gear? What gear ratio would you recomend? Sorry about all of the questions.

[Lionc68c10]

Originally Posted by Jtrux

You don't have a drop out third member. You need either a whole rear axle or regear it.

3.42 is a good choice, I'd probably go with a 3.07 but that's just me. I would bet that you have a 3.90 or so right now.

A dana 35 out of a Jeep is very weak and very narrow ( about 60 inches wide) so would not be a good candidate for a heavy truck with V8 power.

BTW, if you still plan on using it for towing the 3.42 is probably a better choice than the 3.07's I said earlier but I think the 3.07's would be great for a non OD cruiser with V8.

This is great info....I am not going to be towing anything, I really just what to make it a fast hot rod so I think the 3.07 would be better, but would I still get off the line quick?

[kcjones]

Originally Posted by Lionc68c10

This is great info....I am not going to be towing anything, I really just what to make it a fast hot rod so I think the 3.07 would be better, but would I still get off the line quick?

If you wanna hot rod it, go lower [numerically higher]...getting a 4000 lb truck off the line like a hot rod with a 3.07 is gonna take a lot of grunt, like 502 cubes of grunt...If you're running a small block, and you wanna launch like a hot rod, run short/low/numerically high gears: 3.73 would probably be a reasonable start (good launch but 31-3200 rpm at 65 with a stock height tire and 1:1 tranny). Don't forget all the other hot rod stuff, though...big cams & heads usually like short/low/num. high gears, big stall converters, and tough trannies. But, they can be a pain in the a$$ to drive every day.

[kcjones]

First, so everyone is clear, when someone says "I have a high gear ratio, they mean numerically low (2.73 is a "high" rear gear ratio). "Low" gears are numerically high, i.e., 4.11.

Second, so everyone is straight, 67-72 C10s came with GM truck 12 bolts, which do not have a 3rd member. The ring, pinion, and diff carrier are removable of course, but the housing is all one piece. A 3rd member is a removable portion of the rear end housing that contains the ring/pinion/diff carrier (i.e., F*rd 9").

Third, If you're using near stock tire size (30" or so tall), and a 1:1 final gear tranny (th350/400), a 3.07 would give you good 60+ mph mileage but would not work well in towing heavy loads. A 4.11 (I just swapped mine out) would be fantastic for towing heavy loads, but puts you at about 3300 rpm at 65 with your 30" tires and 1:1 tranny.

A 3.42 is a great compromise. A beefy 200R4 or 700R4 and 4.11's is much better, though.

Fourthly (is that a word?), changing gears is easy but the backlash and spacing needs to be set by a professional before you drive it very far or you'll tear them up quickly.

Fifth, there are 2 diff carriers in 12 bolts, 1 for 3.73 and numerically higher gears, and 1 for 3.42 and numerically lower gears. If you have a 4.11 now, and you buy 3.07 ring and pinion, your diff carrier will not bolt up.

Eaton posi's for truck 12 bolt are about $450 new.

This is why what breech said is right on: changing housings with another 67-70 C10 housing would be easiest. If you go with a newer housing, as I did recently, you have to change wheels (5 lug axles), change leaf pads to coil pads (cutting, grinding, and welding required), and come up with a panhard bar solution. Leaf rear end housings do not have a provision for panhard.

Sorry for the long $.02. Maybe that was $.03?

[Jtrux]

I know the 12 bolt was common but wasn't there a different axle in the 67 and 68's. If i'm not mistaken wasn't there a Dana 44 rear axle in some of them???

Good info about the carriers, I didn't know that. I don't however think it takes a "professional" to set up gears. Everybody has to start some where.

[Senator350]

Originally Posted by Jtrux

I know the 12 bolt was common but wasn't there a different axle in the 67 and 68's. If i'm not mistaken wasn't there a Dana 44 rear axle in some of them???

Good info about the carriers, I didn't know that. I don't however think it takes a "professional" to set up gears. Everybody has to start some where.

My .02... It might not take a pro to put in new ring and pinion gears... but for the guy who doesn't know his way around a differential, it's probably not a good idea. Even with the really great help on the internet, I grenaded a 12 bolt under a '70. and if you are even THINKING about swapping gears while the axle is under the truck...

EASIEST OPTION... BAR NONE: buy 3.42 ring and pinion gears and the right sized carrier from Randy's ring and pinion or eBay. Bring the gears to a shop and have them install them.