Help in choosing rear end

[Bigdog44]

I'm putting a 700r4 tranny in my 65 chevyC10 long bed. What rear rand can I swamp out that will give my right gear ratios and disc brakes? Need help ASAP? Anyone?
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[DouglasRaymond]

Hi, what engine do you have? What type of driving do you anticipate? There are threads and a search engine here for your questions.

[tincan1966]

What rear gear ratio do you have now?
You might find that after the 700R install, you do not need to change.

Rear disc brakes can be done on these trucks pretty cheaply.
I bought a set of brackets off ebay for $70, then local parts store for 1980 Cadillac El Dorado calipers ($30 ea w/pads)also got the Eldorado rear brake hoses ($20 ea) and '88-'98 Chevy K1500 front rotors $ 35 ea)

If you want E-Brake use the El Dorado rear calipers and buy 2 right side cables and they'll be long enough to adapt to the trucks' cables.
If you do not want e-brake, just get front calipers for the ElDorado

[Bigdog44]

That's issue, I'm not sure what gear ratio would be best? I'm asking what best all around solutions. I don't want to buy something, then end up changing months later.

I have a 350 engine.
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[1963c-10]

You will need to use on of the online programs where you punch in engine/trans info, tire size and rear ratios until you find what gear you want. Easiest way I know.

[Bigdog44]

Do you have that link?
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[1963c-10]

hmmm...let me see if I can find it. There is also a member here who can email you the software. His name and user id are keith

[tincan1966]

To avoid buying something you may not need, you got to know what you have now....
that is why I asked.

[1963c-10]

Tincan is correct....you need to pop off the rear cover and start counting teeth to see what you have 1st. Helps to establish a baseline and will give you a good inspection as to condition off what you have.

[Lugnutz65]

Originally Posted by 1963c-10

Tincan is correct....you need to pop off the rear cover and start counting teeth to see what you have 1st. Helps to establish a baseline and will give you a good inspection as to condition off what you have.

As stated by others, you need to know what you have before going further.

I use this web site to calculate RPMs at different speeds. LINK Go to the bottom section and enter the rear diff ratio (3.73 or 3.42 or whatever you have), then the tire height, the MPH (I used 70 mph), and your final tranny gear (which is 1.00 for the 3 speed factory tranny). If your tranny has OD, then you will need to figure that out. A TH700R4 final gear is 0.70 LINK )

What engine you have is not a factor except for what torque it can produce at certain RPMs.

In the example above, a TH700R4 with a 0.70 OD gear and a 3.73 rear end and 29" tires will have your engine doing 2118 RPMs at 70MPH. That's a great number. If you went to a 3.42 rear diff (That's what my 66 parts truck had), then the engine drops down to 1942 RPMs.

I have a 0.63 OD on my manual tranny, so the 3.42 rear end I have will not work well for my setup.

If I had stayed with my factory 3 speed which has a final gear of 1.00, then the 3.42 would be a tempting swap. It would give me lower RPMs at highway speeds but at the sacrifice of less power in 1st gear.

You can calculate the rear diff ratio without removing the rear cover.
1. Chock the front tires and put the tranny in neutral.
2. Jack up the rear axle so both rear wheels are off the ground.
3. Mark the DS tire at the 12 o'clock position.
4. Mark the drive shaft so you can count revolutions.
5. Slowly rotate the driver's side tire and count the total tire revolutions while a helper counts exactly 20 driveshaft revolutions. (or any multiple of 10 - the more the better).
6. You should see that the driver's side tire spins and the PS stays still.
7. The tire will spin twice as many times as it normally would since both tires are off the ground.
8. The math is easy. Divide the number of shaft turns by the number of tire revolutions and then multiply by 2.
Example: 20 shaft revolutions divided by 11.75 tire revolutions = 1.70213 times 2 = 3.404. Those were the numbers I just got 2 weeks ago when I calculated mine. So it means the rear was a 3.42 rear.

Another way is to roll the truck in neutral and count the revolutions (but you don't multiply by 2 at the end). This method is kinda tough because it's harder to count shaft revolutions on a moving truck.

Anyway, I hope all this makes sense and is helpful.

[Bigdog44]

The gear ratio is 283. I'm looking to up grade to disc brakes to save money. Looking for a turn key rear end to bolt on and save money.
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[tincan1966]

never heard of a 283 gear ratio. How many teeth on the ring gear? On the pinion?

Unless you have a GMC w/ leaf springs, you will not find a late model axle assy that will bolt in.
You will have to convert yours or another rear end to get disc brakes.
As several have stated- you can do rear discs for around $200-300- which is pretty cheap. How cheap are you thinking you can do it? You still have to change master cylinder, and convert front and run new brake lines up front and add a proportioning valve.
About the cheapest I've seen 4 wheel disc brakes done is still going to be in the $600-700 range- and that's doing the work yourself for free.

[tincan1966]

let me clarify something-
When I stated no other rear ends will be a bolt in - I meant a direct bolt in without fabrication of some sort.

Feasibly any rear axle assy can be made to work, just depends on how much fab work you want to do...

[MARTYZ]

Have to agree, never heard of a 283 ratio, I am running 327with 700r4 and 373 rear gear and works great

[jesseo]

Originally Posted by MARTYZ

Have to agree, never heard of a 283 ratio, I am running 327with 700r4 and 373 rear gear and works great

What kinda of frwy mileage are you getting with that set up? I am looking to do similar and with my 283. Plan is to get 20+ mpg and able to tow (on occasion) a small travel trailer.

[Bigdog44]

Originally Posted by jesseo

What kinda of frwy mileage are you getting with that set up? I am looking to do similar and with my 283. Plan is to get 20+ mpg and able to tow (on occasion) a small travel trailer.

I'm not worried about mpg. But want to be able to cruise freeway at 85+.
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[tincan1966]

If you truly have 283 rear gears now, then freeway cruising should be no problem at all.

Disc brake conversion would be cheap.