What gears do I have?
 

Looking over my SPID, I see the code GQ1 Rear Axle-Standard. What gears does the standard axle have? The engine is a 350, and the transmission is a TH400
84 Sierra Heavy Duty Chassis(C6P)

Re: What gears do I have?
 

The c6p trucks often came with 3.42 gears. The only way to know for sure, is to actually check them.

This process is easier with a second person, and takes about 5 minutes.
Place a jack under one side of the rear axle.
Leave the other wheel on the ground.
Put the vehicle in neutral.
Place a chalk mark at the 12-o'clock position on the tire.
Place another chalk mark on the driveshaft.
Have a buddy turn the wheel EXACTLY 20 revolutions.
Count the driveshaft revolutions, to the nearest 1/4 of a turn.
Divide your result by 10. This is your ratio.
Compare this number with the known possible ratios, and pick the one that's the closest(3.08, 3.42, 3.73, 4.11, etc). If you counted accurately, it should be obvious.

For example, if you saw 34 and a quarter revolutions, your ratio would be 3.42

The 20:10 difference is compensating for the differential action. If you have a limited slip, this method won't work, since you won't be able to turn just one wheel. In that case, jack up the entire axle, and turn the whole axle 10 revolutions instead of 20.

Re: What gears do I have?
 

Never saw/heard of a GQ1 code

GU1 is a 2.41
GU2 is 2.73

Those were very popular for the 80's trucks, supposedly for better fuel economy. I beikive 2.73 was considered the standard ratio in 81 to about 87 in the 1/2 ton models

Re: What gears do I have?
 

I'll try to post a picture of my SPID later. I peeled it off my inner left wheel well. Seems like a strange place to put it, since most were in the glove box.

Re: What gears do I have?
 

never seen one on a fenderwell

Re: What gears do I have?
 

GQ1 simply means its the standard gear ratio available for that particular model, in this case C20903 or K20903. But since you have C6P- you have either a C20 or K20, so GQ1 is either 3.73 or 4.10. This then depended on the transmission- MX1 is 3 speed auto and MX0 is 4 speed auto.
Since yours is TH400= MX1 so then you got 4.10
https://www.gmheritagecenter.com/doc...olet-Truck.pdf

*I see from some of your other posts you have a C2500.

Re: What gears do I have?
 

It's a C2500, and the Trans code says MX1, 3-Speed Automatic Trans. Codes must have changed from year to year? I'm going to get the original build sheet etc from the GM Heritage center for it, and will see how correct the SPID is.

Re: What gears do I have?
 

I haven't either. I was thinking maybe someone had pasted one there just to have it, but it was hard to get off, without destroying it. It's the correct one going by the VIN on it.

Re: What gears do I have?
 

I went back and double checked the RPO- MX1 is 3 speed auto and also updated my post, you have 4.10 gears. The link I included will take you to the info kit for 1984 trucks.

Re: What gears do I have?
 

Thanks. I was reading on a few other forums, the MX1 may have been used for the TH400, although it was for the TH350. Anyways, the links you're referring to, are those the 2 at the bottom?

Re: What gears do I have?
 

I found the link. Thanks

Re: What gears do I have?
 

and all that could mean nothing if someone changed the rearend at some point in time
they are 30ish yrs old..
pull the diff cover and count the teeth is the sure fire best way..probably time for a fluid change anyway

Re: What gears do I have?
 

The SPID sticker could be either on the glovebox door or the driver's side inner fender. Generally the older trucks put the sticker on the inner fender, but there seems to be no specific reason for either location.

Re: What gears do I have?
 

My 84 K1500 GMC has it on the drivers side fender well

Re: What gears do I have?
 

Thats where mine was.

Re: What gears do I have?
 

Heres my SPID

Re: What gears do I have?
 

https://www.gmtruckclub.com/threads/...3%3A23%20ratio.

Re: What gears do I have?
 

Just based on your SPID, it should have come with 4.10's from the factory. You can confirm by pulling the cover and checking the numbers stamped in the ring gear but the SPID is all we have to work off of.

Re: What gears do I have?
 

I am with Kipps. Although two turns of the tire is all I’ve ever done. Just have to approximate. There are only so many options. Way easier, faster and cleaner that popping the diff cover just to check ratio.