70 CST/20 rear ratio - The 1947 - Present Chevrolet & GMC Truck Message Board Network

olyeller70 · 09-06-2009, 10:34 PM

I have a 1970 cst/20, I have looked all over this site and am at a loss as to what the rear end ratio is. I know the rear end is an Eaton and I am guessing 4:10 or 4:57. I there a way to detemine the ratio with pulling the cover? There is the ID tag on this thing maybe someone can help me decode it?

*2tons of fun* · 09-06-2009, 11:13 PM

search.

**mr48chev** · 09-06-2009, 11:17 PM

if no one has removed it there should be a tag under one of cover bolts. Otherwise it is probably most accurate to pull the cover and check the numbers on the ring gear or count the teeth on the ring gear and pinion.

**WorkinLonghorn** · 09-06-2009, 11:27 PM

Quote:

There is the ID tag on this thing maybe someone can help me decode it?

The thing to do would be to post what it says,then we can help with that.

**special-K** · 09-07-2009, 07:17 AM

The tag will state the ratio.If you pull the cover the tooth count is on the ring gear and you divide the smaller number into the bigger.

Green Machine · 09-07-2009, 07:54 AM

Assuming it is not posi, jack up one of the rear tires. Turn the tire exacty 2 turns while someone else counts how many times the driveshaft turns. If the driveshaft turns 4 and a hair more then you have a 4.10, if it turns about 4 and a half times, then it is a 4.56.

Hottrucks · 09-07-2009, 08:55 AM

does it say on the glove box door??

olyeller70 · 09-07-2009, 02:11 PM

I came here after a methodical search, the glove box door tag is gone, there is no tag on the rear end, I jacked up the truck today and the drive shaft turned 4.5 times so by that (per Green Machine) I am guessing a 4:56. I guess next weekend I will just pull the cover and confirm by counting teeth. Thank you to those that tried to help.

Green Machine · 09-07-2009, 03:45 PM

Just curious, does the truck have 16 inch split rims or 16.5 rims ? I'm wondering if the split rims were a little taller tire and maybe got the 4.57 while the shorter 16.5 got the 4.10 ???

olyeller70 · 09-07-2009, 09:30 PM

Green Machine:
I have 16" M/T wheels with 265/75/16 tires. The truck has the coils and the helper leafs. I can go put 2000#s in it and it doesn't even go down 2".

09-06-2009, 10:34 PM	#1
olyeller70 Registered User Join Date: Feb 2007 Location: Atlanta Posts: 51	70 CST/20 rear ratio I have a 1970 cst/20, I have looked all over this site and am at a loss as to what the rear end ratio is. I know the rear end is an Eaton and I am guessing 4:10 or 4:57. I there a way to detemine the ratio with pulling the cover? There is the ID tag on this thing maybe someone can help me decode it? __________________ Thanks, Mike

09-06-2009, 11:13 PM	#2
2tons of fun Account Suspended Join Date: Jan 2009 Location: galt ca, Posts: 749	Re: 70 CST/20 rear ratio search.

09-06-2009, 11:17 PM	#3
mr48chev Registered User Join Date: Jul 2007 Location: Toppenish, WA Posts: 15,708	Re: 70 CST/20 rear ratio if no one has removed it there should be a tag under one of cover bolts. Otherwise it is probably most accurate to pull the cover and check the numbers on the ring gear or count the teeth on the ring gear and pinion.

09-07-2009, 07:17 AM	#5
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,851	Re: 70 CST/20 rear ratio The tag will state the ratio.If you pull the cover the tooth count is on the ring gear and you divide the smaller number into the bigger. __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

09-07-2009, 07:54 AM	#6
Green Machine Senior Member Join Date: Jul 2004 Location: Estherville, Iowa Posts: 3,371	Re: 70 CST/20 rear ratio Assuming it is not posi, jack up one of the rear tires. Turn the tire exacty 2 turns while someone else counts how many times the driveshaft turns. If the driveshaft turns 4 and a hair more then you have a 4.10, if it turns about 4 and a half times, then it is a 4.56. __________________ 1968 C10 307 3spd Long Fleet ------ http://67-72chevytrucks.com/vboard/s...d.php?t=201103 1970 C10 305 Super T10 Long Fleet --- http://67-72chevytrucks.com/vboard/s...d.php?t=202285 1971 C20 383 TH350 Dana Posi ----- http://67-72chevytrucks.com/vboard/s...d.php?t=206894 2001 GMC Sierra 1500 C3 6.0

09-07-2009, 08:55 AM	#7
Hottrucks Redefining LowBudget Join Date: Mar 2009 Location: lebanon Cow Hampshire Posts: 4,538	Re: 70 CST/20 rear ratio does it say on the glove box door?? __________________ 1970 C10 CST fleetside 472 ....big dreams little cash... http://67-72chevytrucks.com/vboard/s...d.php?t=335721 SunShine Syndicate.. Mikes Sandwich Fair Run OCT 8th 2011 http://www.thesandwichfair.com/html/...auto_show.html

09-07-2009, 02:11 PM	#8
olyeller70 Registered User Join Date: Feb 2007 Location: Atlanta Posts: 51	Re: 70 CST/20 rear ratio I came here after a methodical search, the glove box door tag is gone, there is no tag on the rear end, I jacked up the truck today and the drive shaft turned 4.5 times so by that (per Green Machine) I am guessing a 4:56. I guess next weekend I will just pull the cover and confirm by counting teeth. Thank you to those that tried to help. __________________ Thanks, Mike

09-07-2009, 03:45 PM	#9
Green Machine Senior Member Join Date: Jul 2004 Location: Estherville, Iowa Posts: 3,371	Re: 70 CST/20 rear ratio Just curious, does the truck have 16 inch split rims or 16.5 rims ? I'm wondering if the split rims were a little taller tire and maybe got the 4.57 while the shorter 16.5 got the 4.10 ??? __________________ 1968 C10 307 3spd Long Fleet ------ http://67-72chevytrucks.com/vboard/s...d.php?t=201103 1970 C10 305 Super T10 Long Fleet --- http://67-72chevytrucks.com/vboard/s...d.php?t=202285 1971 C20 383 TH350 Dana Posi ----- http://67-72chevytrucks.com/vboard/s...d.php?t=206894 2001 GMC Sierra 1500 C3 6.0

09-07-2009, 09:30 PM	#10
olyeller70 Registered User Join Date: Feb 2007 Location: Atlanta Posts: 51	Re: 70 CST/20 rear ratio Green Machine: I have 16" M/T wheels with 265/75/16 tires. The truck has the coils and the helper leafs. I can go put 2000#s in it and it doesn't even go down 2". __________________ Thanks, Mike

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