Author Topic: Diff Identification  (Read 18252 times)

Offline Bitzer!

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Diff Identification
« on: June 14, 2008, 02:07:26 PM »
Hi guys - silly question time again!

I got some numbers off the diff casing and wondered if it tells me what diff it is!!

numbers are 3977323  and  259  and the letters CFD

any ideas?

cheers as always  :)
1979 GMC CrewCab  C20 1t
454 750 Holley,TH350, 14bolt diff fully floating
Why aren't there 8 days in a week!
A K5 rolling shell *new addition*

Offline Fordeatinz71

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Re: Diff Identification
« Reply #1 on: June 14, 2008, 03:23:32 PM »
i'm not sure about the numbers because i'm on a work computer but if it's in your crew cab i can just about promise you it's the good 'ol 14-bolt FF rear axle. 
1991 Chevy Silverado K1500 ECSB, 350, 700R4 w/shift kit, 3.42's, exhaust work...
1983 GMC Sierra K1500 SWB-sold :(

Offline bfofish

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Re: Diff Identification
« Reply #2 on: June 14, 2008, 06:27:17 PM »
Check out this link.             http://coloradok5.com/axleguide.shtml
1987 Stepside 2wd , 2003 Silverado 1500HD Crew Cab

Offline Bitzer!

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Re: Diff Identification
« Reply #3 on: June 14, 2008, 07:14:02 PM »


Cheers for the link - it sure does look like the heavier duty 14 bolt.

Now the next question!!   Is it a slip/lock diff and are they a standard gearing?

cheers again   :)
1979 GMC CrewCab  C20 1t
454 750 Holley,TH350, 14bolt diff fully floating
Why aren't there 8 days in a week!
A K5 rolling shell *new addition*

Offline Bitzer!

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Re: Diff Identification
« Reply #4 on: June 16, 2008, 07:34:53 AM »
Is it a slip/lock diff and are they a standard gearing?   HELP!!!
1979 GMC CrewCab  C20 1t
454 750 Holley,TH350, 14bolt diff fully floating
Why aren't there 8 days in a week!
A K5 rolling shell *new addition*

Offline werewolfx13

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Re: Diff Identification
« Reply #5 on: June 16, 2008, 07:43:42 AM »
Most accurate way to tell what the ratio is, is to pop the meatball cover off and check..it may be stamped on the gears, or you might have to count the teeth..which isn't exactly easy with it on the truck and in the housing..
Chris
'83 Chevy c10 Silverado SWB
'76 Chevy k20 LWB 6.5'x8' Flatbed
“I know that you believe you understand what you think I said, but I'm not sure you realize that what you heard is not what I meant.”

Offline Bitzer!

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Re: Diff Identification
« Reply #6 on: June 16, 2008, 11:04:30 AM »

 :( I guessed that was gonna be the case! here's hoping it stamped!
1979 GMC CrewCab  C20 1t
454 750 Holley,TH350, 14bolt diff fully floating
Why aren't there 8 days in a week!
A K5 rolling shell *new addition*

Offline SUX2BU99

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Re: Diff Identification
« Reply #7 on: June 16, 2008, 02:50:33 PM »
I was just doing this on the weekend. You can check to see if it's a limited slip by jacking up both rear tires and then turning one of them (put trans in neutral). If the other spins the same direction, it's a limited slip. If it turns the opposite direction, it's open. Or I suppose a really worn out limited slip.  To find out a ballpark gear ratio, put one tire on the ground and mark the driveshaft in 1 spot and the tire still in the air in one spot (reference points). Turn the driveshaft 1 revolution and count how many times the tire has turned. If it turned 3 3/4 times, you have a 3.73. If it turned a touch over 4 turns, it's a 4.10. Most 14 bolts were either one of those.

If you take the cover off, there should be some numbers stamped on the edge of the big ring gear. Mine said 10:34 amongst a few others. That meant 10 pinion teeth and 34 ring teeth = 3.40 ratio. I also found out it was a limited slip by turning the tires so the carrier (guts of the diff) turned and saw a bunch of gizmo stuff within the carrier. If it's just the small gears you see (spider gears) than it's open. If it's got a bunch of other metallic stuff in there with pins and what not, it's a limited slip.
85 Chevy Silverado C10 short, wide, yellow, 2wd. Lowered, 60-over 350 with Dart Iron Eagle heads and Comp Cams XE268 cam, TH350 w/ shift kit, 3.40 Gov-lok 12 bolt.

Offline Bitzer!

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Re: Diff Identification
« Reply #8 on: June 16, 2008, 03:41:59 PM »
Cheers Sux i'll try that this weekend - whats the better of the two for normal street use?
1979 GMC CrewCab  C20 1t
454 750 Holley,TH350, 14bolt diff fully floating
Why aren't there 8 days in a week!
A K5 rolling shell *new addition*

Offline ccz145a

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Re: Diff Identification
« Reply #9 on: June 16, 2008, 03:48:30 PM »
Depends... If it's noramlly wet. ;D
1975 C10 Silverado LWB, 454CID, TH400, 10bolt 3.42
11MPG Downhill w/tailwind (but there ain't no hills here)

Offline SUX2BU99

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Re: Diff Identification
« Reply #10 on: June 16, 2008, 04:01:39 PM »
Well I've always been one to feel that a limited slip rear is the best way to go and is a desireable option. In the wet of England (like the wet of Vancouver), a limited slip can do 1 of 2 things for you depending on the power and traction you have: 1) either get you going without the hassle of 1 tire spinning or 2) kicking the rear end out when you don't want it to when the tires break loose. Generally speaking, 2 shouldn't happen if you aren't heavy of foot during inclement weather.  Situation 2 can happen even with an open diff. I've been driving uphill on a rainy road and gave it some pedal in 2nd while doing about 40 mph and had both tires start to spin and kick the back end out.
85 Chevy Silverado C10 short, wide, yellow, 2wd. Lowered, 60-over 350 with Dart Iron Eagle heads and Comp Cams XE268 cam, TH350 w/ shift kit, 3.40 Gov-lok 12 bolt.

Offline Bitzer!

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Re: Diff Identification
« Reply #11 on: June 16, 2008, 04:20:11 PM »

Ummm I've not managed to drive my truck properly yet!! I got it as a rust case and its nearly there! I'm guessing it'll be used on dry days (when we get them!) and holidays  :D
1979 GMC CrewCab  C20 1t
454 750 Holley,TH350, 14bolt diff fully floating
Why aren't there 8 days in a week!
A K5 rolling shell *new addition*