Upgrading rear end gear

[dragginass]

Well considering I have the factory 3-speed in my 71. And I have never used 1st cuz it is such a low gear. And that 3rd tops out at around 65. I was considering going to a much higher gear ratio in the rear end so that it would bring first into a range of use and would up my mph in 3rd for interstate travel.

So my question is....

1-Is this feasible to do? (Such as will it be worth the time and money?)
2-What is a good ratio to run with for my rear end as in how high can I go before it is a serious strain on the motor?
3-Will I need to change my chunk if I go with a ratio much higher than factory?

[Classic69]

I know the feeling...My '69 has a stock 4.56 geared rear end. With my TH350/327 combo, on the highway at 70 MPH I'm reving around 4000 RPM's!! But nothing my 1000W stereo can't muffle...lol...I'll bet it would be worth the time/$ to do, I'd suggest maybe a 3.73 gear. For sure no higher than a 3.08 though!

[dragginass]

Originally Posted by Classic69

I know the feeling...My '69 has a stock 4.56 geared rear end. With my TH350/327 combo, on the highway at 70 MPH I'm reving around 4000 RPM's!! But nothing my 1000W stereo can't muffle...lol...I'll bet it would be worth the time/$ to do, I'd suggest maybe a 3.73 gear. For sure no higher than a 3.08 though!

Yea I dunno what it takes or what I need so as soon as I can figure that out... Then I can figure out what its gonna cost... Then I can figure out if I can afford it. lol.

[whatnow123]

I agree with Classic 69, not sure how much freeway driving you do, but a 3.08 will run really well at freeway speeds, 3.42 a little less freeway friendly but will have more "get up" driving around.

Either way, if you buy a new gear set, it's going to be about 200 for that and figure another 250 or so to set it up. You can set the gears up yourself if you have the gauges along with plenty of time and patience as there is a lot of trial and error to get it right. I've done it but you have to remember that close enough doesn't work with gears.

[dragginass]

Originally Posted by whatnow123

I agree with Classic 69, not sure how much freeway driving you do, but a 3.08 will run really well at freeway speeds, 3.42 a little less freeway friendly but will have more "get up" driving around.

Either way, if you buy a new gear set, it's going to be about 200 for that and figure another 250 or so to set it up. You can set the gears up yourself if you have the gauges along with plenty of time and patience as there is a lot of trial and error to get it right. I've done it but you have to remember that close enough doesn't work with gears.

Thanks. A buddy of mine runs a diesel repair shop and I can get him to install and set it up for me for nothin. But hes leaving it up to me to find the parts and everything I'll need cuz he doesnt know a lick about old trucks.

What info do I need to know in order to order the ring and pinion set? And if I go with a 3.08 for instance will I need to change the chunk due to the decreased diameter of the ring?

[lowriden58]

if your rear is all factory, i would replace the posi/center with a upgrade, get all new bearings/seals when you do the gears. better to do it 1 time JMHO

[cdowns]

if you're going from something like a 4:11 or 4:56 up to a 3:08 highway gear there is no choice in the matter you must change the carrier or posi section out !!! like said you'd also be smart to change the bearings and the axel seals and plus the installition kit and the total parts bill will run in the $500-$750range with smart shopping to rebuild the rear

[WIDESIDE72]

My suggestion would be to find a factory 3.08 rear axle and swap it in. This is what I did for my dad's 71 GMC. (my avatar pic). We replaced the 3.73 rear with a 3.08 posi. With a 3.08 and the stock 250 I-6, it really slows the motor down on the highway. It would not be too good for towing, but the most he would ever pull anyway would be a 12 ft aluminum john boat. I am not sure on the exact break on your rear. What gear do you currently have? from your post, it sounds like a 3.73. I may be wrong, but I believe you could change the 3.73 to a 3.08 gear set without changing the carrier. However, you will soon find that even though you have a friend wiling to set up your new gears, by the time you buy all the parts, you are looking at big $$$. With my dad's, we tore the rear down and replaced the bearing seals and brakes. The ring gear and pinion were OK. I bought the axle for $100, and spent another $100 on parts, including cleaning supplies and paint. New gears alone are $200+

[Longhorn Man]

we'll have to assume you are talking about the 71 C/10 in the signiture?
We'll also assume that there is no optional gear listed on the SPID?
Assuming the 2 things mentioned, and again, assuming it has not been swapped out, you should have a 3.73 in there already.
If it "tops out at 65", you have other bigger issues to look at. You have a tach installed? You should be able to run over 100 MPH without topping out.

Personally, I would locate another rear.
Going from a 3.73 to a 3.08 would drop the RPMs pretty much to the ideal cruising (freeway speed) RPMs.
However, you'll need to swap out carriers too. They aren't the same.
I say locate a whole rear from the wrecking yard, or scanning the calssified section on here, and crack it open and inspect it. (as a spare rear, your truck won't be out of service for this part) If it checks out OK (and probably will) then you spend a day swapping out the rear axle at the cost of a couple U-bolts.... 30 bucks or less.

[dragginass]

Originally Posted by Longhorn Man

we'll have to assume you are talking about the 71 C/10 in the signiture?
We'll also assume that there is no optional gear listed on the SPID?
Assuming the 2 things mentioned, and again, assuming it has not been swapped out, you should have a 3.73 in there already.
If it "tops out at 65", you have other bigger issues to look at. You have a tach installed? You should be able to run over 100 MPH without topping out.

Personally, I would locate another rear.
Going from a 3.73 to a 3.08 would drop the RPMs pretty much to the ideal cruising (freeway speed) RPMs.
However, you'll need to swap out carriers too. They aren't the same.
I say locate a whole rear from the wrecking yard, or scanning the calssified section on here, and crack it open and inspect it. (as a spare rear, your truck won't be out of service for this part) If it checks out OK (and probably will) then you spend a day swapping out the rear axle at the cost of a couple U-bolts.... 30 bucks or less.

Yes it is a 71. I posted that in the original post for this topic. And No I did not see any specific gear option on the SPID. As far as swapping the axel out.... Thats about out of the question at this point. Here is the trucks build thread....

http://67-72chevytrucks.com/vboard/s...d.php?t=302785

I am simply looking to upgrade the center section and go with a higher ratio. I would like it to have a limited slip anyhow so that is a good time to do soo. And of course I would do the bearings and seals while it was apart. So my question is now...

Where can I get the parts for my truck from at a reasonable price...?

[lowriden58]

Originally Posted by dragginass

Yes it is a 71. I posted that in the original post for this topic. And No I did not see any specific gear option on the SPID. As far as swapping the axel out.... Thats about out of the question at this point. Here is the trucks build thread....

http://67-72chevytrucks.com/vboard/s...d.php?t=302785

I am simply looking to upgrade the center section and go with a higher ratio. I would like it to have a limited slip anyhow so that is a good time to do soo. And of course I would do the bearings and seals while it was apart. So my question is now...

Where can I get the parts for my truck from at a reasonable price...?

Summitracing or Jegs i got both my gears and Eaton posi from them. i also got Moser axles at the same time for like 375. if you want nice axles i recommend Moser for them but you have to call moser directly for the axles, they are not available thru mailorder that i know of

[BradE]

I just purchased a 3.73 ring and pinion plus master installation kit from Randy's Ring and Pinion. Total cost out the door was about $380 inc. tax. These are some of the most knowledgable guys around in dealing with rearends. Google the name and you won't be disappointed in their knowledge or service.

BTW, if you do drop below 3.73, then you will have to replace the carrier. Probably better to go junkin at that point! I wanted to go to 3.42, but I'm opting for a 700R4 swap out from the TH350 and staying with 3.73. Good Luck!

[Longhorn Man]

You did say 71, but it would be a whole nother story if it was a C/20. So we need all the info before anyone can give good advice.
You should also probably make sure it is a 3.73 in there like it should be.

[cparman]

I drove my 69 550 miles home the day I bought it. I knew it was turning some RPM's, but HEY, I wanted to get home. My truck was a 3 on the tree, with a 3.73 ( I pulled the cover ) and IMO that is too much gear. I have since added p/s, pdb, and a 700r4. I love the tranny change, and I dropped about 1000 RPM in high gear. I am going to go to a 3.08, or a 3.42 gear. I am looking for quiet, and about 1500 rpm at 65-70 MPH. There several sites you can go to and plug in your data, and it will give you an idea what the engine would turn at a specific speed. My truck now turns about 1600 RPM at 45-50 in in 4th with the converter locked. I love my truck

[Longhorn Man]

a 3.07 gear with overdrive will more likely than not, kill your MPG. 3.73 to 3.42 is ideal (assuming a typical small block under the hood)

[KD70chev]

Staying on subject,I have a 70 C20 with the 456 gears.Coil springs and manual tranny.I can hardly run on the highway with it because I am afraid the 350 will blow apart if I go over 65 mph for too long.I would drive it more if it wasn't for that,what are my options in rear end swaps?

[Longhorn Man]

direct swap, you have two choices...
eaton 4.10. Came in small block trucks with an auto, and I think small block/4 speed trucks.
Dana 3.54 Came in big block/auto trucks.

[dragginass]

Well my truck is as original as they come for the most part. The old man I got it from had it for 28 years. And he was the 2nd owner. He said the only thing he ever did was convert it from a column shift to a floor shift cuz his wife had a hard time shifting it prior.

It has the original 307 in it and the first owner upgraded from the 2 barrel to a larger single barrel. There is no upgraded gearing on the SPID. The only thing it states aside from cosmetic appearence is a heavier rear spring. That is all. So I assume that it is the factory rear end with factory internals. I chiseled off over and inch of grim off of the housing so I assume it has been a few years to say the lease since anyone has even looked at it.

It is a C10. Not a 20. I do know that much soo... I guess I will just call a reproduction company and see what they say.

Thanks for the info from the ones who helped

[WIDESIDE72]

We have more than one member asking for rear gear advice, so things are getting muddled.

Draginass: (C10) I still say shop around the board or your local yards and find a 3.08, inspect the stock gears, refurb it with new seals and bearings, add a Lock Rite from Powertrax ( I have one and like it because I can swap it into another rear axle if Iever want to without having to reset the rear.) Summit or Jeg's will fix you up if you are convinced that buying a new ring and pinion for your existing rear. as far as what carrier you need for the 3.08 gears, I had a 7.5" 10 bolt in my 79 Malibu when I first got it. It had 2.29 gears (!). I swapped in a set of 3.42 Richmond gears, since I was going to have to run the TH350 for a while before going to a 200 4r overdrive. They were "THICK" gears designed to make up for it being a 2 series carrier. I have since upgraded to the 2004r and an 8.5" rear with 3.73 gears out of a late 80's 442. (I had to add a posi to it, though, strangely enough, they were optional in Oldsmobiles. I bguess the 307 didn't need posi HAHA.) the P.O. had bought a stock posi but never added it. Buick GN's had an 8.5" rear, all were posi, but had 3.42 gears stock. I am getting of topic into my other passion. SORRY

CPARMAN:How tall are the rear tires you are running? I would not advise going lower than a 3.42 rear gear with a 700r4 overdrive and 30" tires (taller tires would make it even worse). Changing from 3.73 to 3.43 is not worth the expense , IMO. Unless you have a Big Block with a lot of torque, You are also going to experience the trans shifting in and out of overdrive anytime you try to pull a slight grade. ANNOYING and it will eventually burn out your trans.!

[haysonj]

Originally Posted by KD70chev

Staying on subject,I have a 70 C20 with the 456 gears.Coil springs and manual tranny.I can hardly run on the highway with it because I am afraid the 350 will blow apart if I go over 65 mph for too long.I would drive it more if it wasn't for that,what are my options in rear end swaps?

You probably don't want to spend this much money but a Gear Vendors OD will give you a 22% reduction and can be shifted manual or automatic. I tow a 4000 lb boat and cruise at about 2000 rpm with a t400 and 4.09 gears. The OD makes the t400 a six speed when I hit a hill. Cost about $2500 if you install yourself. http://www.gearvendors.com/