What gear ratio do I have? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

wyoman64 · 02-25-2004, 01:55 PM

Can anyone tell me an easy way to determine what gears I have short of popping off the covers and counting teeth.
'69 K20, no tach, but it's definately "screamin" at more that 60mph. Do I have 4.56's? If so, anyone with 3.73's want to trade axles? LOL Speed limit on I-90 here is 75mph and I just about get rear ended by 18 wheelers . . . Is it easier and cheaper to change the ring and pinion gears, or to just swap out the whole axle for ones with taller gears?

wyoman64 · 02-25-2004, 02:11 PM

P.S. I'd Like to do a disk brake conversion also, would I be wise to convert my current axle, or just look for a set of axles with the taller gears AND disk brakes off of a '71 or later and kill two birds with one stone?

2wdBlazer · 02-25-2004, 03:00 PM

Too bad your in SD. I'd love to trade my 3:73 for a 4:56.

**JIMs70GMC** · 02-25-2004, 04:04 PM

it's either 4.10s are 4.56s. What size tires are you running. I have 4.10s w/33" tires and turn about 2850RPM @ 65mph. What rear axle do you have? You could be limited in what ratios are available. Big round cover = no better than 4.10s stock. dana60s came w/3.54 gears I believe. You could try and find a leaf sprung truck w/ a dana 60 and the higher gears. Don't forget to change the front to match.

drink2mny · 02-25-2004, 04:31 PM

As for rear disc conversion option you can check out our site to see if we have a kit for you..
This is just an option, there are other companies out there.
So take a look around and get prices.

We are over in Spokane Wa

Blackbird's Custom Trucks

We also have an axle ID page

1969 GMC · 02-25-2004, 11:23 PM

best bet would be to find a 73 up 3/4 ton 4x4 and take the axles. you would get disc front brakes from the dana 44, the dana 44 is larger diameter on 73 up trucks also, you get the really strong 14 bolt axle, and i believe you could get factory 3.73 gears, perhaps even higher.

72-396 · 02-27-2004, 01:13 AM

I have a formula you can use. take your (rpm) x (tire diameter) and devide that # by your (MPH) x (336) and you will have your answer

*60apache4* · 02-29-2004, 02:23 AM

There is an easy way to figure your gear ratio without having to remove the differential cover. Block the front tires, jack the rear end up (both sides) and put the truck in neutral. While rotating the tire one complete turn, count the number of turns on the driveshaft, then just multiply by two. Also, if the tire on the other side turns the opposite direction you have an open differential; if it turns the same way it has a locker of some sort.

A factory 69 K20 with a 4-spd should have a 4.56 and with an auto 4.10.

The whining you are hearing at highway speeds though is probably the transfer case and not the gears. That is normal for this type of transfer case.

02-25-2004, 01:55 PM	#1
wyoman64 Registered User Join Date: Feb 2004 Location: Northern Black Hills, SD Posts: 38	What gear ratio do I have? Can anyone tell me an easy way to determine what gears I have short of popping off the covers and counting teeth. '69 K20, no tach, but it's definately "screamin" at more that 60mph. Do I have 4.56's? If so, anyone with 3.73's want to trade axles? LOL Speed limit on I-90 here is 75mph and I just about get rear ended by 18 wheelers . . . Is it easier and cheaper to change the ring and pinion gears, or to just swap out the whole axle for ones with taller gears?

02-25-2004, 02:11 PM	#2
wyoman64 Registered User Join Date: Feb 2004 Location: Northern Black Hills, SD Posts: 38	P.S. I'd Like to do a disk brake conversion also, would I be wise to convert my current axle, or just look for a set of axles with the taller gears AND disk brakes off of a '71 or later and kill two birds with one stone? __________________ 1969 Chevy K20 Fleetside 1979 Chevy K10 "ROBAHOR" (Rusted Out Beyond All Hope Of Repair)

02-25-2004, 03:00 PM	#3
2wdBlazer The Blazer King Join Date: Sep 2000 Location: Valrico, Fl (Tampa) Posts: 1,213	Too bad your in SD. I'd love to trade my 3:73 for a 4:56. __________________ 72 2wd Blazer. Its the superbichinest, megacoolinest, superflowinest.

02-25-2004, 04:04 PM	#4
JIMs70GMC user # 2756 Join Date: Jun 2001 Location: Chesapeake, Virginia Posts: 4,612	it's either 4.10s are 4.56s. What size tires are you running. I have 4.10s w/33" tires and turn about 2850RPM @ 65mph. What rear axle do you have? You could be limited in what ratios are available. Big round cover = no better than 4.10s stock. dana60s came w/3.54 gears I believe. You could try and find a leaf sprung truck w/ a dana 60 and the higher gears. Don't forget to change the front to match. __________________ 1970 K25, 8' stepside bed 350/465/205 44 up front, 60 in the rear 4.10s rolling on 33" Dunlop MTs 1986 K5, 350/465/208 Dana 60/14 bolt from a cucv 36" Super Swampers TSL/SX 1983 K20 w/ CUCV axles, 350/700R4/208 sitting on 37" Goodyears 1986 M1031 6.2 diesel, TH400/NP205 locker in the rear and a LS in the front, all stock for now..... 1986 K30, 350/400/205 dana 60 and 14 bolt. I kept the drivetrain. Body/bad and chassis are gone. 1981 K30, 350/465/205 dana 60 and dually 14 bolt. Has a G80, and a flat bed. Going to replace the flat bed. 1985 K20, 350/400/208 10 bolt and SF 14 bolt. I wonder where I can find some 1 tons. Hmmmmm

02-25-2004, 04:31 PM	#5
drink2mny Registered User Join Date: Jun 2003 Location: spokane wa Posts: 2,189	As for rear disc conversion option you can check out our site to see if we have a kit for you.. This is just an option, there are other companies out there. So take a look around and get prices. We are over in Spokane Wa Blackbird's Custom Trucks We also have an axle ID page __________________ Support The Board

02-25-2004, 11:23 PM	#6
1969 GMC Registered User Join Date: Feb 2003 Location: The Rubber City Posts: 5,498	best bet would be to find a 73 up 3/4 ton 4x4 and take the axles. you would get disc front brakes from the dana 44, the dana 44 is larger diameter on 73 up trucks also, you get the really strong 14 bolt axle, and i believe you could get factory 3.73 gears, perhaps even higher. __________________ 1969 GMC K2500 1996 Honda Accord 2007 Kawasaki KLR 650

02-27-2004, 01:13 AM	#7
72-396 Registered User Join Date: Nov 2003 Location: tulsa ok Posts: 55	I have a formula you can use. take your (rpm) x (tire diameter) and devide that # by your (MPH) x (336) and you will have your answer __________________ 1972 K20 custom camper 4x4 LWB 396 700r4 1965 chevy II 420 hp s/b 4 speed

02-29-2004, 02:23 AM	#8
60apache4 Account Suspended Join Date: Nov 2001 Location: Oregon Posts: 147	There is an easy way to figure your gear ratio without having to remove the differential cover. Block the front tires, jack the rear end up (both sides) and put the truck in neutral. While rotating the tire one complete turn, count the number of turns on the driveshaft, then just multiply by two. Also, if the tire on the other side turns the opposite direction you have an open differential; if it turns the same way it has a locker of some sort. A factory 69 K20 with a 4-spd should have a 4.56 and with an auto 4.10. The whining you are hearing at highway speeds though is probably the transfer case and not the gears. That is normal for this type of transfer case.



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