20 Most Recent 1991 GMC C1500 - Page 9 Questions & Answers

The short answer is yes. Rear ends are made in a variety of gear rarios depending on what you want to do with the truck. If you want to haul heavy stuff around most of the time then you are loking for a gear ratio in the area of 4.10 to 1. If you occasionally put a load in it and do a lot of empty driving you would want a ratio about 3.00 to 1 or lower. They will all affect mileage.

To find out what your truck has there should be a tag on it but it's probably rusted off by now so jack up the rear end and remove the cover. Have a drain pan to catch oil. Use something like White Out to mark a tooth and count the teeth on the big (crown) gear and do the same with the small(pinion) gear that drives it from the driveshaft. Divide the small number into the big one and that is your gear ratio. If you are looking for better mileage go to a smaller ration. The closer you get to 1:1 the better mileage you will get but you will lose grunt on take off. If you want help moving a loaded truck go away from 1:1. Hope this helps.

Can test in THIS LINK: Enter a VIN Number to begin HERE.

Official GM car and truck VIN decoder cards: http://service.gm.com/dealerworld/vincards/

Get complete VIN info on your GM car or truck that looks like this:



Hope helps.

Hi.

Below you get all the parts breakdown for GMC Sierra 1500, including steering column assembly:

1500 SIERRA

Here diagrams for all 1989 GMC trucks.

If you need to take apart the steering column you will also need wiring. below the color codes and wiring tips:

GMC SIERRA 1988-2005 VEHICLE WIRING

Regards.

Ginko

Brake light switch. If I remember correctly, the third brake light works off a seperate circuit from the other brake lights so part of the switch could be bad.

Keep in mind, the spark plug wires can be placed in any position (depending on the spark plug wire length) in relation to where the number 1 spark plug terminal is located. In other words, once you assign a port on the cap to number 1 cylinder the rest will follow the 1-8-4-3-6-5-7-2 firing order.

The knocking is a motor and gears that move the fresh air/recycle flap - it is up behind the dashboard behind the glovebox
the problem is that the gears wear and become misaligned
the flap then can not open fully, its doesnt reach its end stop which switches the motor off
so the motor keeps going the and the gears keep clicking over.---------- Remove the dash assembly then the glove box and inspect the blower motor and its gears.This will point towards the problem causing this noise.The blend door actuator motor needs to be inspected.That is what makes a thumping noise when the key is on or off.------- This will help.Thanks.Helpmech.

rt side from under truck all 350 is same

Check the spark plugs, distributor and air flow meter (best to clean it thoroughly and grease it), don't forget to check the fuses.

sounds like someone put water in it!!! only fix is to drain tank and lines out.