Rearend Swap for '55 1st Series

[tjf8801]

I'm new to this site and new to forums, so excuse me if I don't know the proper etiquette. There seems to be a lot of members with good knowledge, so I've got a question for you experts. I've got a 1955 Chevrolet 3100 (1st Series) that has the original rear differential. According to what I've read, it has a gear ratio of 3.9 to 1. This causes some issues on the highway, as my 350 V8 has to run at high RPM to stay up with traffic. What are some common rearend swaps that require only minor modification? I do not want to lower the vehicle or really make it ride better, I'd just like a lower gearing. I still use it to haul things, so it needs to have a pretty stiff suspension.

I guess another good question would be to ask what I need to look for in a prospective rear end that will make it fit correctly and function appropriately.

Thanks!

Ty

[IvanfromtheCrackie]

I pulled my rear end out of a 71 (V8) Camaro. Seems like a popular and sucessful swap.

I'm fourlinking mine so it's a little different considering I own't be running any leafs or anything like that.

I think that most all of the early 70's Camaros/Novas etc had rears that were pretty damn close to the same track width as your OE rear end.

Alot will do with what offset your running in your rear wheels too.

Do some research, find out what rears you can use (or at least what is close) and there are boatloads of good ones in the junkyards for under $100.

-Ivan

[mr48chev]

I think I now have about a 74 Nova rear end under the 48. I have to run reverse wheels with a pretty deep offset to clear the bed. The 15x8 wheels with 255 60 15 tires do fit well in the wheel wells though.
I have a 76 Cad Seville rear end out here that is supposed to be a little bit wider than the Nova rears but pretty much the same otherwise. It does haveme bigger brakes and the 79/80 or so (rear wheel drive square body Seville) had to disk brakes on the rear. I don't know what ratio the 76 rear has though.
you might also look at S-10 4x4 rear ends. as they are pretty close in width To the early trucks and you should be able to find a friendly gear ratio with a bit of hunting. I have one under an S-10 Blazer that I picked up to use in the 48 but haven't done any measuring yet,

[Houston54]

The 2nd generation F-body (camaro/Firebird) rear axle is what I am running in my 54 but your concern is minimal modifications. I would get a new set of highway friendly rear gears from Patricks and swap the original ring and pinion out. Might cost you some dollars but the end result will be much slicker.

The advantages of the F-body axle is a better ratio, better brakes and a lower stance if you flip the axle on top of the springs. You could leave it with the axle under the springs if you wanted though. The installation requires removing the original spring perches and welding on new ones. I assume you are retaining your original rear springs.

If you do use the F-body axle you will need to ensure the backspacing on the rims is no more than 4" and preferrably 3.75" or the tires will rub the bed on the inside.

[solidaxel]

Welcome from So. Arizona

There is some very good advise here so you can take your pick.
The operation is very simple and cost effective with the Camaro/Nove or others that are listed, you may also add a 70's Monte Carlo/Cutless to the list
Patrick's conversion is a BIT high after all is said and done with the set up, as compared with just a swap. You can get the exact emergency cables from Control Cables Inc for what ever rear end you chose those folks have seen them all.
Clean the donor rear end of spring attachments and pick up a pair of 3" saddles from a trailer supply co, center the new rear on your springs attach your fluid lines, drive shaft and enjoy.
....... Or you could change your transmission to a OverDrive 700R4 and enjoy stop light starts or freeway speeds and leave your existing 3:90-1!!!

Here is a Camaro in my 55 1st series with 3:73 and overdrive 29" tires 2200RPM 75 MPH

[tjf8801]

This is good information, fellas! I was told that replacing the pinion gear and ring gear was not going to be possible, so I haven't even checked out that route. The nice thing about that would be that I wouldn't need to get a new set of wheels, since I doubt I would be lucky enough to have the right amount of offset. I'll check into it. I'm grateful for the responses!

Ty

[solidaxel]

It is possible, but check the price for parts and labor to set up a ring and pinion profressionally unless you have ALL the tools

[primered 55]

I didn't see anyone mention bolt pattern; if you want to keep it 6 lug, a late 60's 2wd pickup rear is the perfect width. New spring perches and I was good to go. Only thing I don't like is that it has the track bar mount cast in to the top of the center section.

[BruceJr.]

Hi, tjf8801. I have a 55 1st, and I used the Patrick's ring and pinion conversion, which is a 3.38:1 ratio. It is the same rear end as the 2nd series, and that is the kit you use. The kit comes with very good instructions, clear and easy to follow. If you have good mechanical ability, you shouldn't have any trouble. Also the folks at Patrick's will go out of their way to answer your questions.

[wild one]

You can use a rear end out of a 1960 - 1970 chevy truck, they are the same width, same bolt pattern, and can be found with gear ratio's ranging from 3.07:1 to 4.10:1. If the rear is the same a 1957 truck, the only modifacation needed is to remove the trailing arm pads and weld on leaf spring pads - this was the only mod needed on a friends '57 truck - took us an afternoon to complete. We put a rear end out of a 1968 in, had 3.07:1 gears - he can now cruise the freeways at 75 mph in 5th gear (T5 tranny swap) at 1700 rpm with 29" tall tires.

P.S. look for a rear end out of a 1964 to 1970 Chevy or GMC, they have 30 spline axles which are stronger and bolt on backing plates compared to the 12spline axle and press on/weld on backing plates on the older rear ends.

Good Luck,
Pete

[see ten]

If you go with a car rearend the Novas and Camaros are different widths. The 68-76ish Nova is 60" from flange to flange as is the S10 4x4. The thing about the S10 4x4 is that most of them were setup for overdrive transmissions so they're going to be geared pretty low as well, which wouldn't help your situation. The 2nd gen Camaro rears are either 2" or 1 7/8" wider then the Nova axles (depending on whose website or tape measure that you're reading). I don't have any knowledge of how the later fullsize truck rears will work...but it sounds like these other guys do and it just might be what fits your needs.

[BIG CHEVY 3600]

You have a bunch of helpful information on gears but you didn't say what tranny you're running. Like Houston54 said the overdrive 700R4 would make as much difference as gears and tires. I have 3.73 gears and a 700R4. With that combo you should be able to cruise at about 70 mph and 2000 rpm.

[Gene Sharp]

I agree with the 700R-4 or If you like stick shift the NV 3500 or one of several other standards with over drive ,,,,,,fun to drive and not much more money than a rear end swap
I got my 700-R4 from Art Carr in Abaline Texas and it works great
I went with a pretty much stock converter for good street manners

Gene Sharp

[BIG CHEVY 3600]

I got my 700R-4 at Phoenix Transmissions over in Weatherford. They specialize in beefed up racing transmissions and their prices are reasonable.

http://www.phoenixtransmission.com/

[Lennart]

Besides the lack of parts (diff, locking diff...) is the 55 rear end strong enough to handle the power of a 400 rwhp engine?
I just bought a 55 1st and need to decide if I want to keep the rearend or swap it out for a 12-bolt.
Not shooting for 400 rwhp at this point but want some safety for future mods.

[BIG CHEVY 3600]

Originally Posted by Lennart

Besides the lack of parts (diff, locking diff...) is the 55 rear end strong enough to handle the power of a 400 rwhp engine?
I just bought a 55 1st and need to decide if I want to keep the rearend or swap it out for a 12-bolt.
Not shooting for 400 rwhp at this point but want some safety for future mods.

400 if you drive like my old aunt Sadie will not wear out the stock rear, however you would be smart to upgrade to something stronger. The Ford 9" would be the best choice but expensive unless you can find one at the salvage yard. A 12 bolt truck would be my second choice.

[dan42]

Just a thought - is the 55 1st series a closed drive line, or did it have u-joints? I can't remember the cutoff year.

[OrrieG]

Originally Posted by BIG CHEVY 3600

400 if you drive like my old aunt Sadie will not wear out the stock rear, however you would be smart to upgrade to something stronger. The Ford 9" would be the best choice but expensive unless you can find one at the salvage yard. A 12 bolt truck would be my second choice.

Even if you find a stock one, you will probably need to upgrade it. Reason they are popular is ability to change out the pumpkin to change ratios (drop in a 2.74 to the cross country trip, change to 4.11 when you get to the strip). From what I have read by the time you modify them, you can buy an after market one set up for the Ford pumpkin with brackets for your application. When I was young the hot upgrade was to a 57 Olds rearend, I had one in a 57 Chevy I hammered hard.

[primered 55]

Originally Posted by dan42

Just a thought - is the 55 1st series a closed drive line, or did it have u-joints? I can't remember the cutoff year.

Should be the first year of open drive line. My late 60's rear with new spring perches literally bolted in to my 55 1st series long bed GMC, no u joint change needed.

[Lennart]

I might have misunderstood, but are you saying that I could install the Ford pumpkin in my 55 GM axle?

Originally Posted by OrrieG

Even if you find a stock one, you will probably need to upgrade it. Reason they are popular is ability to change out the pumpkin to change ratios (drop in a 2.74 to the cross country trip, change to 4.11 when you get to the strip). From what I have read by the time you modify them, you can buy an after market one set up for the Ford pumpkin with brackets for your application. When I was young the hot upgrade was to a 57 Olds rearend, I had one in a 57 Chevy I hammered hard.

[BIG CHEVY 3600]

No that won't work. You can buy a new differential from someone like Currie below or find one at the salvage yard.

http://www.currieenterprises.com/ces...le_hotrod.aspx

[Harleydad]

I am also new to the site. My question and i am hopeful that someone can answer, is: i have a 55 3100 second series. I want to switch over to the 5x4 3/4 bolt pattern. This is mainly for wider selection of aftermarket wheels and brake setups. Which rear is a bolt in. NO welding required. If none exists is there a company that makes axles that can be swapped out. Thanks

[_Ogre]

you might get better results starting a new thread
rather than adding post #22 to a 5 year old thread