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Old 04-19-2004, 08:06 AM   #1
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gear ratios

How can I tell what the gear ratio on a vehicle is? I'm shopping for a van with the 3.73 or 4.10 gear ratio that I see is recommended by many...but every time I ask a salesperson what the gear ratio is they give me a blank stare! Be specific, about all I know is where the engine is (sometimes). thanks
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Old 04-19-2004, 08:11 AM   #2
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RVnuttie,

If you ask them about their what size 'rear end' they have, and they look over their shoulder, you should walk out!
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Old 04-19-2004, 09:13 AM   #3
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Count turns

A 3.73 gear ratio, for example, means the driveshaft spins 3.73 times for every one turn of the rear wheels. Hopefully, someone will correct me if I am wrong, but I believe you can chock the front wheels, jack up one rear wheel, put the vehicle in neutral (motor is off), mark the suspended wheel, turn the driveshaft by hand one or more times, and count the number of revolutions the suspended wheel made. Then simply recall your high school algebra for the answer.

I would give more detail, but am dancing on the edge of my experience base as it is...
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Old 04-19-2004, 09:27 AM   #4
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Quote:
Originally Posted by RVNUTTY
How can I tell what the gear ratio on a vehicle is?
If its a new vehicle, I believe that information is printed on the "Monroni" sticker. (with all the options, equipment, and the MSRP"). It should also be printed on a tag somewhere on the vehicle. its usually stamped on a metal plate on the rear axle, but also printed on a tag under the hood.

sales people are so clueless.
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Old 04-19-2004, 09:42 AM   #5
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i have ask that question also. but my sales person said check inside the glove compartment and there is a list of options. three digit codes so you need a book or a cheat sheet to decode. the parts department can help in that effort they can translate. or if you looking for only one option ask an then look for it. for gm products don't know about brand x.
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Old 04-19-2004, 12:46 PM   #6
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I had to push on my dealer guy to find and look up the code for my 96 gmc. It's in the glove box and coded. It took him awhile to find the decoder. These sales guys only want to sell you what they have and most aren't at all into the mechanicals. Find a place that sells alot of trucks and talk to the truck guy or order a nice new one.
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Old 04-19-2004, 01:27 PM   #7
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Decoder's available online

Run a google search for the brand you are looking for, use the brand and the word "decoder". A lot of good information can be found that way. I always run the VIN's before I buy a used vehicle...it has kept me from getting burned more than once. BTW I would reccomend a 3.73 or a 4.10 limited slip rear end.

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Old 04-19-2004, 03:19 PM   #8
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Quote:
Originally Posted by tcwilliams
A 3.73 gear ratio, for example, means the driveshaft spins 3.73 times for every one turn of the rear wheels. Hopefully, someone will correct me if I am wrong, but I believe you can chock the front wheels, jack up one rear wheel, put the vehicle in neutral (motor is off), mark the suspended wheel, turn the driveshaft by hand one or more times, and count the number of revolutions the suspended wheel made. Then simply recall your high school algebra for the answer.

I would give more detail, but am dancing on the edge of my experience base as it is...
Yes thats the old school way of doing it. I have seen some that the ratio was stamped on the Differental cover. the a cretain number on the VIN is the ratio of the rear end. the dealer "should" be able to look that up on the ALLDATA or what ever program they use if you call a dealer with the vin. Some parts houses have this info also if you provide them with the VIN
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Old 04-19-2004, 06:23 PM   #9
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Thanks for the replies, I see now why they give me a blank stare. I did research the vin number...but apparently on a gmc 1986 van...it does not give that type of information. (ratios) Next I'll have to get the flashlight and a scraper and go look underneath layers of gunk. Thanks for trying though...I guess it's not so easy to figure out on an older vehicle after all.
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Old 04-19-2004, 09:11 PM   #10
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gear ratios

Greetings RVNUTTY!

Quote:
but apparently on a gmc 1986 van...it does not give that type of information. (ratios)
I haven't run across any direct links to information in the GM VIN to identify much more than series and original engine especially and the early to mid 80s models. On all three of my GMC/Chevrolet tow vehicles ('83 GMC G20 Vandura/'95 K1500 Z71 Pickup/'99 GMC K2500 Suburban) there was(is) a placard on the glovebox door listing all of the factory option codes including the codes for differential ratios. A knowledgeable GM service advisor should be able to decode this information for you - - I know that the service advisor at my local GM garage was able to provide the axle ratio from this information when I was considering a used GM vehicle earlier this year.

Good luck with your research!

Kevin
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Old 04-19-2004, 09:40 PM   #11
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Codes

For GM products look for the following RPO codes in the glovebox :
GU4 for 3.08 rear end
GU5 for 3.23
GU6 for 3.42
GT4 for 3.73
GT5 for 4.10
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Old 09-04-2004, 04:38 PM   #12
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Most older rear ends have a tag on the rear cover(under a bolt) that will tell you the ratio. Works unless: 1.tag removed, 2. gear change. You can figure it out by the "tire/drive shaft" as stated earler, or the other choice , pull rear cover, count teeth , and do the math . But that will cost you the price of a gasket and the grease.
On my 99' suburban ,the dealership was able to just run the Vin#.
Good luck. Toby
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