Rear end help. - The 1947 - Present Chevrolet & GMC Truck Message Board Network

GobbleStalker · 09-18-2010, 10:50 PM

I just found out my truck is not posi and has 3.07 gears. I want ot make it a posi and am pretty sure I will want to change the gears to 3.55 ot 3.73's. What is the spline on these trucks. Can I put a 12 bolt camero gears and posi in or will they not match up?
Thanks
Kev

raycow · 09-19-2010, 02:33 AM

The 12 bolt car R&P can not be used in the truck rear. You will need gears made specifically for the truck. The truck shafts (65-up) have 30 splines.
http://tomsdifferentials.com/catalog.asp?pg=10

Ray

Shaky · 09-19-2010, 06:32 AM

Have you ever set-up a rear before? Setting the pinion depth usually requires special tools...

cdowns · 09-19-2010, 08:49 AM

if you buy the parts//posi,gears,bearings shims seals etc it's right around the $800mark

to me investing that much money it's worth the extra to have it installed by a pro for the few extra hundred

another option is to look for a 40year old junkyard piece and take your chances with a well worn $300-$400 piece

LONGHAIR · 09-19-2010, 09:35 AM

Once again, cdowns is on it. "Pay a Professional"

Setting up a rear end is a very precise thing. It has to be done exactly right or it will fail quickly.

GobbleStalker · 09-19-2010, 03:21 PM

I would not be doing htis myself. Beyond my capabilities. Thanks
Kev

Shaky · 09-19-2010, 03:30 PM

Quote:

Originally Posted by GobbleStalker

I would not be doing htis myself. Beyond my capabilities. Thanks
Kev

Well then - raycow is right, you can't use car parts in the truck rears. There's plenty of truck 12-bolt gears and posi carriers available.

GobbleStalker · 09-19-2010, 06:13 PM

So now the question. I am building the 350 to be between 300 and 350 hp. Have a 350Turbo trans. Should I stay with the 3.07 gears and just put a posi in or change the gears. I am afraid if I go to 3.73 I will rev around 4000rpm on the highway. Anyone have experience with this set up? I don't want the truck to be a dog of the line either.

Kevin

LONGHAIR · 09-19-2010, 08:19 PM

It depends upon what you consider "highway speed" to be, and how much of the time you are driving that speed.

GobbleStalker · 09-19-2010, 08:23 PM

Quote:

Originally Posted by LONGHAIR

It depends upon what you consider "highway speed" to be, and how much of the time you are driving that speed.

Highway speed here is 100km so 65mph.

Kevin

Sammy · 09-19-2010, 10:24 PM

I'm going to make a wild guess...350 turbo..307 rear..60-62 MPH Maybe some where around 5500-5900 rpm?

mixermike · 09-19-2010, 10:39 PM

my truck 350 motor,turbo 350,3.07 gears at 60mph = 2000 rpm. i had a 66 chevelle 396,4speed,373 gears at 60mph =3000 rpm.

MudBug · 09-20-2010, 12:49 AM

If your gong with all new stuff, go with a 3.42 gear set and good differential.
Also like it has been previously said, let a pro put the rear end together.You will save money in the long run.

**El Jay** · 09-20-2010, 02:18 AM

Quote:

Originally Posted by GobbleStalker

Highway speed here is 100km so 65mph.

Kevin

I have 2 trucks, both with 4.10:1 rear gears.
Both turn about 3000-3100 RPM at 65 MPH.

FLEET72 · 09-20-2010, 02:29 AM

I have 3.07s with 29.5" tall tires ~2400 @ 65mph

http://www.ringpinion.com/Calc_RPM.aspx

68Stepbed · 09-20-2010, 08:30 AM

My 350/TH350/3.73 combo with 28" tires runs about 3300 at 65. 3.07 gears are more highway friendly. I say go with the 3.42 gear and have a compromise of 3.73 and 3.07 gears.

Shaky · 09-20-2010, 03:49 PM

Quote:

Originally Posted by MudBug

If your gong with all new stuff, go with a 3.42 gear set and good differential.
Also like it has been previously said, let a pro put the rear end together.You will save money in the long run.

I like this compromise if you're gonna go with the TH350.

09-18-2010, 10:50 PM	#1
GobbleStalker GobbleStalker Calls Join Date: Aug 2010 Location: Port Hope, Ontario Posts: 653	Rear end help. I just found out my truck is not posi and has 3.07 gears. I want ot make it a posi and am pretty sure I will want to change the gears to 3.55 ot 3.73's. What is the spline on these trucks. Can I put a 12 bolt camero gears and posi in or will they not match up? Thanks Kev

09-19-2010, 02:33 AM	#2
raycow Registered User Join Date: Mar 2003 Location: San Francisco, CA USA Posts: 2,454	Re: Rear end help. The 12 bolt car R&P can not be used in the truck rear. You will need gears made specifically for the truck. The truck shafts (65-up) have 30 splines. http://tomsdifferentials.com/catalog.asp?pg=10 Ray

09-19-2010, 06:32 AM	#3
Shaky Six in a row makes it go... Join Date: Mar 2009 Location: Vacationland: Maine Posts: 1,346	Re: Rear end help. Have you ever set-up a rear before? Setting the pinion depth usually requires special tools... __________________ 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

09-19-2010, 08:49 AM	#4
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: Rear end help. if you buy the parts//posi,gears,bearings shims seals etc it's right around the $800mark to me investing that much money it's worth the extra to have it installed by a pro for the few extra hundred another option is to look for a 40year old junkyard piece and take your chances with a well worn $300-$400 piece __________________ 71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY

09-19-2010, 03:21 PM	#6
GobbleStalker GobbleStalker Calls Join Date: Aug 2010 Location: Port Hope, Ontario Posts: 653	Re: Rear end help. I would not be doing htis myself. Beyond my capabilities. Thanks Kev

09-19-2010, 06:13 PM	#8
GobbleStalker GobbleStalker Calls Join Date: Aug 2010 Location: Port Hope, Ontario Posts: 653	Re: Rear end help. So now the question. I am building the 350 to be between 300 and 350 hp. Have a 350Turbo trans. Should I stay with the 3.07 gears and just put a posi in or change the gears. I am afraid if I go to 3.73 I will rev around 4000rpm on the highway. Anyone have experience with this set up? I don't want the truck to be a dog of the line either. Kevin

09-19-2010, 10:24 PM	#11
Sammy Registered User Join Date: Apr 2000 Location: Bonne Terre, Mo Posts: 3,005	Re: Rear end help. I'm going to make a wild guess...350 turbo..307 rear..60-62 MPH Maybe some where around 5500-5900 rpm? __________________ '69 Chevy Long Fleet & '71 GMC Short Step & Project "ODD BALL" "You can wash a pig, soak it in most expensive perfume. In the end it is still just a pig." ODD BALL build thread http://67-72chevytrucks.com/vboard/s...d.php?t=478629"

09-19-2010, 10:39 PM	#12
mixermike Registered User Join Date: Jan 2008 Location: Post Falls, Idaho Posts: 606	Re: Rear end help. my truck 350 motor,turbo 350,3.07 gears at 60mph = 2000 rpm. i had a 66 chevelle 396,4speed,373 gears at 60mph =3000 rpm.

09-20-2010, 12:49 AM	#13
MudBug Registered User Join Date: Jan 2007 Location: tennessee Posts: 159	Re: Rear end help. If your gong with all new stuff, go with a 3.42 gear set and good differential. Also like it has been previously said, let a pro put the rear end together.You will save money in the long run.

09-20-2010, 02:29 AM	#15
FLEET72 Registered User Join Date: Jan 2007 Location: Sonoma, CA Posts: 521	Re: Rear end help. I have 3.07s with 29.5" tall tires ~2400 @ 65mph http://www.ringpinion.com/Calc_RPM.aspx __________________ Oscar '72 Shortbed Fleetside '95 Jimmy 4X4 '69 GMC Custom Camper

09-20-2010, 08:30 AM	#16
68Stepbed Registered User Join Date: Mar 2005 Location: 10-Uh-See Posts: 5,609	Re: Rear end help. My 350/TH350/3.73 combo with 28" tires runs about 3300 at 65. 3.07 gears are more highway friendly. I say go with the 3.42 gear and have a compromise of 3.73 and 3.07 gears. __________________ Matt 68 C10 stepside, LS1/700R4, TCI Engineering suspension system



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