I have finally got my car running well enough to get back on the road. I ran it up and down the road a bit today, and I see that the speedometer is off a bit. I don't know how much yet, but it read 60MPH and a Prius was pulling away from me on a stretch of open road. The prev. owner put new wheels and tires on it, and I think they may be a different size than the old ones.
I think I need to replace the speedometer gear in the transmission. And I think in order to determine what gear I need, I need to know the rear end gear ratio.
So, I put the car up and started looking for the 2 letter stamping that should be on the left axle, but I can't find any. I looked high and low on that left axle, but no letters or numbers or anything. I checked the right (passenger's) side, and on the forward side there was a stamping that read "PW 12210". I couldn't find much on the differential case itself...but I haven't looked much there yet. I was hoping to get some direction on where to look before I covered myself in crud.
Anyone know what kind of rear end this is? Ultimately, my goal is just to get the speedometer to be accurate, but I think I need to know the gear ratio on the rear end to do that.
Looks like you have a 10 bolt chevy rear. To check what ratio you have there are 2 ways. If it has a posi you can just mark a tire or brake drum and turn the pinion by hand untill you get a full rotation at the tire/drum and count how many turns you had to turn the pinion. For a open rear you have to hold one of the tires from spinning and mark the other tire/drum and turn the pinion by hand counting the rotations of the pinion to get a full rotation at the tire/drum take that number and multiply by 2. This is to take in account of the gear reduction in the spider and side gears. OR you can just pull the cover and there should be a stamping on the ring gear. If not you can just count the teeth on the pinion and then on the ring gear and just do the math.
Yeah, that eye lid on the diff cover is a dead give away that you have a chevy rear end and likely the stupid c clips that hold the axles in. I've seen a few of the c clips let go at the strip and then the axle walks out. Not good.
The Pontiac rear ends are much superior. The chevy drag racers use a c clip elimination kit which makes them just like a stock pontiac rear with press on bearings. Pontiac had it right all along. LOL !!!
I know what you mean. I have looked all over my rear axle housing and can't find any stamp marks at all. I saw a whole row of rears on the ground at a guys house so I know where they are supposed to be.
OK. Looks like I need to try the "counting revolutions" method of the tire and driveshaft. I think I understand how I'm supposed to do it. I determined that I have an open rear end because as I turn one tire, the other turns in the opposite direction. So I need to block one tire, mark the other relative to a stationary reference point on the car, and also mark the driveshaft relative to the diff housing. Then count the number of driveshaft and tire turns it takes for the marks to line up again. Then (driveshaft/Tire)x2 is the ratio:1. Right?
I have a list of the common Pontiac ratios. Does anyone know of if the chevy ratios are the same?
From there, I think there's more math to figure out the speedo gear I need.
Here are the gear ratios and tooth counts. Would be best to pull the cover and change the fluid anyway, you dont know how long its been in there.Then you could just see what gears are in there. 2.56:1 41,16 2.73:1 41,15 3.07:1 43,14 3.08:1 40,13 3.08:1 37,12 3.31:1 43,13 3.36:1 37,11 3.42:1 41,12 3.55:1 39,11 3.73:1 41,11 4.10:1 41,10 4.11:1 37,9
I probably should change that fluid out. It about the only thing on the car that isn't leaking, or hasn't leaked in the past few weeks...so given my luck that probably means it's dry!
I marked the wheel and driveshaft, and blocked one wheel and counted the revolutions to get my markes re-alinged. It took 41 revs on the driveshaft and 30 revs on the wheel. So, if I understand the math right, that's (41/30)*2=2.73...so 2.73:1 right?
Is that differential cover gasket fairly standard? If I went to NAPA for a 10 bolt chevy rear end cover gasket, would it probably fit OK? Or are there a million different covers to try to match to.
