Rear diff rebuild - The 1947 - Present Chevrolet & GMC Truck Message Board Network

realsteelGM · 04-03-2014, 12:01 PM

Anyone out there know about the 283 stock rearend gear ratios? I have built up a 1958 corvette 283 semi-performance. The truck has a existing 3:54 posi dana 44 in it. The diff is growling and I picked up a 12 bolt diff from a 79 blazer with 3:08 gearing, rebuilt it and wondering if that is going to be too high gearing for the application.

Shaky · 04-05-2014, 05:36 AM

What transmission?

**Captainfab** · 04-05-2014, 11:48 PM

The 283's don't produce good low end torque, so the 3.08's may be too high. Of course this depends on the tire size as well as the trans as Shaky said.

realsteelGM · 04-08-2014, 12:00 PM

Quote:

Originally Posted by shaky

what transmission?

sm-420

realsteelGM · 04-08-2014, 12:02 PM

Quote:

Originally Posted by realsteelGM

sm-420

With the 3:54's I'm shifting into 4th gear around 35 miles an hour. With the standard trans SM-420 find myself chasing gears all the time.

Shaky · 04-08-2014, 04:40 PM

Quote:

Originally Posted by realsteelGM

sm-420

I think you're gonna need all the gear you can find to make up those big rpm drops on the SM420.

realsteelGM · 04-09-2014, 12:12 AM

Are you saying the 3:08 gears are going to be to high for the existing set-up?

Shaky · 04-09-2014, 05:08 AM

Quote:

Originally Posted by realsteelGM

Are you saying the 3:08 gears are going to be to high for the existing set-up?

In reality, 3.54 to 3.08 isn't that big of a change. However, The SM420 has a big drop between gears. So, you will have to wind out 2nd a little more and then when you hit 3rd, you'll be further down on rpm. So, you'll have to wait longer for the engine to "recover" and get back up to where it makes decent power.

It all depends on whether this matters to you or not.

Ultimately, I plan on either a Ranger or Gearvendors overdrive to make my SM420 into an 8-speed.

realsteelGM · 04-09-2014, 11:29 AM

The main thing is I'm chasing gears right now with the 3:54's but I believe this was

a stock set up with the original trans and full set-up from factory with the stock 283. My concern is will I be lugging with in town driving with the 3:08's. The 3:54 is a dana 44 posi, the 3:08 is a gm 12 bolt no posi. I have rebuilt the 12 bolt diff bearing shims etc. Before bolting this in I just want to be sure.

04-03-2014, 12:01 PM	#1
realsteelGM Registered User Join Date: Jan 2007 Location: Whitehorse, Yukon, Canada Posts: 169	Rear diff rebuild Anyone out there know about the 283 stock rearend gear ratios? I have built up a 1958 corvette 283 semi-performance. The truck has a existing 3:54 posi dana 44 in it. The diff is growling and I picked up a 12 bolt diff from a 79 blazer with 3:08 gearing, rebuilt it and wondering if that is going to be too high gearing for the application. __________________ "gotta love something that works without a computer"

04-05-2014, 05:36 AM	#2
Shaky Six in a row makes it go... Join Date: Mar 2009 Location: Vacationland: Maine Posts: 1,346	Re: Rear diff rebuild What transmission? __________________ 67 C20 long step resto: http://67-72chevytrucks.com/vboard/s...d.php?t=342086 66 C10 long step build: http://67-72chevytrucks.com/vboard/s...=1#post3814790 CT to Alaska in a 67 C10: http://67-72chevytrucks.com/vboard/s...d.php?t=399224 “The height of sophistication is simplicity." - Clare Boothe Luce

04-05-2014, 11:48 PM	#3
Captainfab 60-66 Nut Join Date: Mar 2007 Location: Coeur d'Alene, Idaho Posts: 23,252	Re: Rear diff rebuild The 283's don't produce good low end torque, so the 3.08's may be too high. Of course this depends on the tire size as well as the trans as Shaky said. __________________ Power Steering Box Adapter Plates For Sale HERE Power Brake Booster Adapter Brackets For Sale '63-'66 HERE and '67-'72 HERE and '60-'62 HERE and "60-'62 with clutch HERE Rear Disc Brake Brackets For Sale. Impala SS calipers HERE Camaro Calipers HERE D52 Calipers HERE 6 Lug HERE Hydroboost Mounting Plates HERE

04-09-2014, 12:12 AM	#7
realsteelGM Registered User Join Date: Jan 2007 Location: Whitehorse, Yukon, Canada Posts: 169	Re: Rear diff rebuild Are you saying the 3:08 gears are going to be to high for the existing set-up? __________________ "gotta love something that works without a computer"

04-09-2014, 11:29 AM	#9
realsteelGM Registered User Join Date: Jan 2007 Location: Whitehorse, Yukon, Canada Posts: 169	Re: Rear diff rebuild The main thing is I'm chasing gears right now with the 3:54's but I believe this was a stock set up with the original trans and full set-up from factory with the stock 283. My concern is will I be lugging with in town driving with the 3:08's. The 3:54 is a dana 44 posi, the 3:08 is a gm 12 bolt no posi. I have rebuilt the 12 bolt diff bearing shims etc. Before bolting this in I just want to be sure. __________________ "gotta love something that works without a computer"



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