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

[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.

[Senator350]

Originally Posted by Pont406

Why are you guys saying it's hard to swap gears? It's not that hard. First rear I had to do twice but after that it's not that hard. I changed gears in my c-10 without taking the rear out.

becuase, this guy has to do his FIRST! god forbid you don't do it right the first time (who does?!?!) because the u-joint at the tranfer case, for your rear driveshaft, might break its caps... and your rear driveshaft might become a giant pogo stick and vault your truck into the air at 20 mph.

or you could just be coming off the highway and hear a BANG, and have no more forward movement, and a differential full of metal chunks.


at least, have someone show you how to do it first. this is stuff that trained mechanics can do well, like tearing into a tranny...

[Pont406]

If you don't feel comfortible don't do it. It's almost sounds like my local drivetrain shop when they are trying to scare a customer into them doing the work. They wanted $450 to set up a 8.2 rear for me. Ever since I am doing my own.
You will know with in first 5-10 min during the break in if something is not right.

[kcjones]

Pont406: Can you post up instructions on how you did yours:

-Where you got the appropriate lash and spacing specs
-Anything unique about pressing on the new bearings
-HOW to set the gears

Maybe this is the wrong thread...sorry for hijacking!

[Lionc68c10]

Originally Posted by 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?

I wanted to provide an update and thank everyone for their help.

I found a 3.07 rear end and put it on my truck. The truck ride is great now and I can drive on the highway with out feeling like the engine is going to explode. Special thanks to board member Kayotic who find me on craigslist for the needed part.

[chevy_mike]

Awwww... can we feel the love.

Good job and hey... post some pics.

[Kayotic]

Damn bro, I was intregued about this thread because I recently sold a rear end out of a '68. I was just begining to wonder if I should have kept it... Then I continued reading and saw my name.

Does that make me a celebrity?

I am glad it has helped, and hope you get to beat the crap out of it for many years.

And yeah, Show us some pics of your ride when you get a chance, I know we spoke a about it when you drove it here, but it was too cold for too much chit chat. - even if it is chevy street trucks (being laid off made me soft).

[mr48chev]

Originally Posted by Pont406

Why are you guys saying it's hard to swap gears? It's not that hard. First rear I had to do twice but after that it's not that hard. I changed gears in my c-10 without taking the rear out.

A. We don't know his skill level. Although some of us have a lot of experience or are or were pro mechanics there are a lot of guys on here who are better off having someone else do the work.

B. On this style rear end, unless you have the proper tools (meaning measuring tools. There is a lot of chance of error. The pinion depth has to be set correctly and then the ring gear and carrier have to be shimmed properly to get the proper lash. If you don't have a shim assortment readily available you end up buying a shim pack to be able to do the adjustments.

c. If you change from a 4something ratio to a 3 something ratio you have to change carriers or buy one of the special ring and pinion sets that has a ring gear with the proper thickness to compensate.

I vote for going out and seeing if I can buy a complete rear end with the desired gear ratio. Around here most of them go for under 150 and often you can find a posi with the ratio you want for that. I just picked up a 3.55 Dana 60 with a posi for my 71 GMC 3/4 ton for 150.00 I'm getting away from the 4.11 set up that is in the truck now because most of mydriving is at highway speeds and I can still tow my boat with the 3.55.

The first thing I would do is get under the truck and check the tag and see what the current gear set is.
Then I would decide how I want the truck to perform. Do you want it to be quick off the line or do you look for good highway speed and easy cruising on the freeways?

[LONGHAIR]

Those weekend TV shows do a lot of people a dis-service by showing a very simplified version of gear swapping. It is not as easy as they make it look, but no instruction on TV ever is now is it?

My advice as always is to pay someone to do it. This is a job that most guys will only ever need one time. It is not worth the time, trouble, cost of tools, and frustration to get this done. Paying also gets you a warranty which you will never get doing the install yourself.

Originally Posted by kcjones

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.

Seriously? Don't even think about doing that...You have accomplished nothing but destroying the gears that someone would have to take back apart to set-up anyway. If you run them "wrong" no matter how far, they are junk.

Originally Posted by Pont406

Why are you guys saying it's hard to swap gears? It's not that hard. First rear I had to do twice but after that it's not that hard. I changed gears in my c-10 without taking the rear out.

That is fairly self-explanitory right there. Destroying a gear-set because of improper installation will generally throw all kinds of metal trash through the bearings, so it has cost you more than it would to just pay someone. Plus the cost of gears again.

Imho the pattern pic posted in this thread is not correct. Whatever was used far marking compound was applied too thick. It looks like lithium grease, which smears too much. The contact looks too long and too high on the teeth. The edges of the pattern should never be sharp.

This is a very exacting thing which is also somewhat "art" and interpretation. The set-up numbers should be on the packaging or engraved directly on the gears themselves. These come from the person that originally matched them at the factory. It is a hands-on process. The idea is that you are trying to get back to exactly where they had them.
It takes a lot of patience, an assortment of shims, a dial indictor, a torque wrench, marking compound, and synthetic lube at bare minimum....but guidence and/or experience are best.

[69gumby]

I was in the same boat. My truck had high gears. It was a kick off the line but I couldn't run down the freeway @ 70. I went out to the wrecking yard and picked up a rear end with 3:07s. I brought it home put it up on saw horses, cleaned and painted, new axle bearings and seals, new brakes and one day just made the swap. I cant tell you how much easier it was to do the work on saw horses rather then under the truck.

With the old rear end I will someday put it up on saw horses and do a total overhaul using a posi and all new parts but for now I'm crusing.

I use the freeway a lot so I think I'll stay with the 3:07s but I think gears in the 3:50 range would get you off the line and down the freeway. The 3:07s are no slouch though they will get you moving.

[Lionc68c10]

Originally Posted by Kayotic

Damn bro, I was intregued about this thread because I recently sold a rear end out of a '68. I was just begining to wonder if I should have kept it... Then I continued reading and saw my name.

Does that make me a celebrity?

I am glad it has helped, and hope you get to beat the crap out of it for many years.

And yeah, Show us some pics of your ride when you get a chance, I know we spoke a about it when you drove it here, but it was too cold for too much chit chat. - even if it is chevy street trucks (being laid off made me soft).

No worries, it was cold and I completely understand . I will post some pic's soon. I was just on the highway and man it felt like i was riding on Air...I may not get off the line as fast as I use to , but the ride is a lot more enjoyable in the long run...and I mean that in the total since

also, I find it really funny when I see people faces after I pass them on the highway, My truck is not painted yet and I know they are thinking "how is that guy passing me in that truck"....

[Lionc68c10]

Originally Posted by 69gumby

I was in the same boat. My truck had high gears. It was a kick off the line but I couldn't run down the freeway @ 70. I went out to the wrecking yard and picked up a rear end with 3:07s. I brought it home put it up on saw horses, cleaned and painted, new axle bearings and seals, new brakes and one day just made the swap. I cant tell you how much easier it was to do the work on saw horses rather then under the truck.

With the old rear end I will someday put it up on saw horses and do a total overhaul using a posi and all new parts but for now I'm crusing.

I use the freeway a lot so I think I'll stay with the 3:07s but I think gears in the 3:50 range would get you off the line and down the freeway. The 3:07s are no slouch though they will get you moving.

Quick question, In your pic of the rear end (which looks very nice) is the sway bar the long black bar thats screwed from the right side of the gear cover then goes to the left on to the frame?

[72freak]

"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."

I was waiting to see how long it would take for someone to come up with the IMPORTANT INFO!

[Senator350]

like pinion bearing pre-load, pattern maker brands, correct pattern pictures, or run out depth on a dial indicator?