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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Rear Drivelines, Drive Axles and Gearing => Topic started by: Stewart G Griffin on September 29, 2006, 09:18:00 am
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Can we discuss axle codes?
14066261 This was on the driver's side tube.
83 C-10 2WD.
I just want to know what gear ratio i got.
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Best way is to pull the cover and divide the last two numbers into each other or count the teeth and divide them if no numbers on the ring gear. 83 C 10 most common were 3:08 or 3:42.
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I don't really want to pull the cover.
I'm thinking it's a 3:08 by feel; Truck has little to no bottom end pull.
And the same token, it's merely loafing at 55-65.
The pedal is barely being pressed at that speed.
Any other ways?
Charts?
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The only real way is to pull the cover like stated. Another backyard job is to mark the driveshaft and one tire. Block the other tire and count the # of shaft rotations to one tire roatation but if you're going to go through all of that crap just pull the cover it's the only real way to tell what's inside.
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Quote:
Did these trucks (83 C-10 2WD) ever come with 2.56 rears?
Because according to my observations (jacked one wheel up and the driveshaft turned about 2 1/2 times per exactly two tire rotations) this is what i got.
Yes they did.
And the spinning tire trick is only a guess. It could be 3.08 which is the most common. The only way to tell is to pull the cover, and with the truck being over 20 years old it wouldn't be a bad idea to put new oil in it... Edited by: roundedline at: 10/2/06 3:01 pm
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PT.2, CONTINUED ETC.
(i am slowly, but surely trying to get the truck back to normal---it runs ok, but there are little "issues" that need to be addressed. i am doing this while juggling 3 jobs and other responsibilities, hence the slow replies)
Let's say i do pull the cover;
1) Will i be able to see all the teeth on the ring and pinion or will i need to still rotate one (or both) of the tires?
2)i'm assuming there is a gasket involved? If so, where to get a new one?
3) Where to get gear oil. i want to keep things stock for now. Also, how to check the level?
4) What torque should the 10 bolts be torqued to? (it's a 10 bolt rear. That much i do know)
The reason why i have to do this is to determine the rear gear because my speedo is not reading correct. Plus, it would be nice to know what gear i have. Actually, isn't this printed on the build sheet?
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You can get gear oil at the local auto parts as well as the gasket. If the gasket is not available a tube of RTV will work fine. You will not be able to see all of the teeth at the same time. In a rear end shop they have a marking compound that is about the same as shoe polish, only white or yellow. Mark a tooth on the ring gear and spin one tire, write this number down. Mark a tooth on the pinion gear and spin the tire again. write this number down. Divide the smaller number into the bigger number, this will be your ratio.
Note: This has to be done with the transmission in neutral so the driveshaft can spin.
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1) So can i use shoe polish or white out?
2) Does it matter which wheel i jack up? (this is a non-posi unit as far as i know)
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If you pull the cover off and look at the side of the ring gear the # of teeth will be stamped on it. Example 41 : 11 = 41 ring gear 11 pinion. Driven over drive will give you your ratio.
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1) Will i be able to see all the teeth on the ring and pinion or will i need to still rotate one (or both) of the tires?
Can't see the pinion, only the ring gear... roll it over till you find the stamping (see Vile's post above)
2)i'm assuming there is a gasket involved? If so, where to get a new one?
Any parts store will have a gasket. Autozone, O'Rielly's, Napa....
3) Where to get gear oil. i want to keep things stock for now. Also, how to check the level?
Get the oil from the same place you got the gasket. Use 80-90wt gear oil. To check the level you need to pull the cover, get the numbers off, put the gasket back on and bolt on the cover. The pull the plug out of the side to fill it. Once it get level with the hole, it is full. Get 2 bottles as I think it holds a more than one.
4) What torque should the 10 bolts be torqued to? (it's a 10 bolt rear. That much i do know)
tight. I have never torqued them, I just get the good and snug.
Actually, isn't this printed on the build sheet?
If you have a standard ratio and 83 will have 2.56 gear most likely and it will just show standard on the build sheet.
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Soooo.........
i guess it does not matter which side wheel i jack up?
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jack up either side. 20 lb-ft on the meatball cover bolts.
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OK, just checking----when i see the #stamped on the side, that's good enough? Or do i also need to count the teeth on the pinion?
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You only want to find the numbers stamped on the ring gear, it tells you the numbers on the ring gear and pinion. You can't see the pinion well enough to count the teeth...
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Alright, it turns out that i do have the 2.56 gear and, also, there is a blue and white decal on the driver's side inner fenderwell entitled SERVICE PARTS IDENTIFICATION and on this decal there is an RPO code GQ 1----Rear axle standard.
Also on the decal, it lists 195/75R 15's as the standard tire, although i have 235/75R 15's on the truck now. But that's close enough? (about 28 inches diameter)
1) My speedometer reads about 10mph less than actual speed----it takes 55 seconds to do a mile(so 65mph) with the speedo at 55mph measured by mile markers. With the speedo at 45mph, it's a little closer---48 miles per hour taking 73 seconds to do it.
So, offhand, does anyone know which speedo gear combinations----drive gear off the output shaft of the transmission and driven gear (driven by the drive gear) are correct considering i've got the 2.56 rear gear and 28 inch tires? Also, the trans is a TH-350C.
2) i will still do research ,including the inevitable taking the output shaft cone off the transmission to see exactly what i got, but i wanted to check if anyone knew first.
My theory is that the transmission in the truck got replaced somewhere along the line with one that came out of another truck or car with lower rear diff gears----this is why my speedo is reading lower than actual speed.
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PT.3 Continued:
Well, it's seems inevitable that i would have take the tailhousing extension cone off so i could see exactly what speedo gears i got so i would have some sort of reference.
But i can't get the driveshaft out:
(http://i223.photobucket.com/albums/dd31/sencraig/IMG_0241.jpg)
i tried tapping the ear things on the driveshaft (figure a's) with a 5 lb hammer to try to move the shaft foward, but to no avail. The wheels are chocked, the trans is in neutral, and, as you can see, the two u-joint retaining straps are off. This is an 8.5 inch 10 bolt differential if it matters. i've removed the shafts on a monte carlo and malibu (very similar to the truck) with no problems.
Any suggestions?
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I don't understand why you are taking the tailshaft off to check your speedo gear? Just remove the clamp and pop it out. To get the u-joint seperated from the yoke just pry against the pinion nut with a prybar or large screwdriver against the trunion.
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...... don't understand why you are taking the tailshaft off to check your speedo gear?
i need to find out what speedo drive gear as well as driven gear i got. i suspect that the trans was replaced with another one out of a car or truck with lower diff gears which is why my speedometer reads slower than actual speed. The previous owner didn't want to mess with it (figure out the correct speedo gears). i can sort of understand why.
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All you need to know is the driven gear just pull it out and see what you have. Check these links out
http://www.bgsoflex.com/speedo1.html
http://www.transmissioncenter.net/speedometer_calibration_______va.htm
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Yeah............i'm still not quite sure i'm following you; First, i thought that TH-350's came with different speedo drive gears---the one on the output shaft. So, that means if i do plug in what i know about my setup----tire size, rear diff gear and speedo driven gear, into those calculator links, this might not mean i will know what drive gear i got? And, i thought you need to know that one to get your speedometer reading correctly.
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I'm not getting what you're asking. The drive gear should be standard. The driven gear will have a different # of teeth to match the pitch of the drive gear based on rear axle ratio. If you know your axle ratio and tire size most dealers can tell you which driven gear you need without pulling anything apart.
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Ok, are you basically stating that all TH-350C's installed in 1/2 ton pickups came from the factory with the same speedometer drive gear? And, they (the factory), only changed the speedometer driven gear dependant on which rear differential gear came with the truck (i.e., 2.73, 3.08, 3.73 etc.) in order to get the speedometer to read correct?
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No but if IIRC there were 3 sizes per pitch. It's been a while since I had to recalibrate one but regardless you don't need to pull the tailshaft housing off. All you need to do is see which driven gear you have and call a competent dealer to help you find which setup you need or use the link I posted above. There's no point in pulling it apart if you know you need to change it anyway.
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Ok, i think i will try that. Much less work anyways.
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There are only 3 drive gears available, 15 = gray, 17 = red and 18 = blue. If you pull the driven gear out you should be able to tell what color it is. then you can use this to calculate which new driven gear you need...
http://73-87.com/7387garage/drivetrain/speedo.htm
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Ok, something "interesting" happened today; A) i went to the dealer to try to determine what speedometer gears are stock for my application so i could get a baseline. It is beginning to appear that i do, in fact, have the right drive and driven speedometer gears. So, if anyone is interested, for an 83 truck with 2.56 rear and 195/75 15's the driven gear is the blue 20 tooth #3987920 and the drive gear is the purple, 10 tooth #6261785.
B) the other thing i discovered is that on TH-350 long tailshafts, you can actually see the drive gear after you pull the driven gear out----with a flashlight. These aren't the best pictures, but you can just see the "purplish" (hopefully) drive gear in there:
(http://i223.photobucket.com/albums/dd31/sencraig/IMG_0242.jpg)
(http://i223.photobucket.com/albums/dd31/sencraig/IMG_0241-1.jpg)
C) But what i discovered is that since i do not have the stock size tires (P195/75 15's), i have 235/75 15's, perhaps this is what is causing the speedo to read slow. Originally i did not think there was much a difference between the two since it was only 40 millimeters. But that is over 2 inches.
So, in your opinion, do you feel that 2 inches difference between tires could throw the speedo off by 10 mph slower reading?
P.S. Capt., i think you are getting the 700's drive gears confused with the 350's. i appreciate the help though.
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Why did your truck have 195s? The stock tires were 225/75R15 or 235/75R15.
What's printed on the placard?
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Yes, believe it or not, the stock tires for an 83 1/2 ton custom deluxe are 195/75 15's. The decal on the driver's side front inner fender well says so. (i will try to find the RPO code) Also, i confirmed it at the dealer. As if the 235/75 15's that i have on there now don't already look lost in there---imagine how the 195's would look like? But that's another thing i like about these trucks---plenty of space for huge tires.
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Are you sure that's not just listing the spare?
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Yes, i'm 99.8% sure these are the baseline stock tires for this truck because:
1) The dealer had a listing in their speedo gear chart that lists this tire as the base tires.
2) The spec decal on the left front innerfenderwell lists these as the "standard tires."
3) The owners manual lists these as the base tire (which by the way, apparently 1/2 ton trucks also use passenger car tires?)
i think the prev owner upgraded to 235/75's but didn't switch speedo gears.
P.S. this is not a silverado, it is a very spartan (but loveable) custom deluxe.
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Everything that I have for listings on stock tire size for 81-87's state the stock tires is 215/75/15.
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A difference in tire size that much will surely throw the speed off. Mine seems to be off by 20%, reading low.
That's all great info about changing the diff oil. I just bought a new cover and was going to do that myself. Then the parts guy asked me if I had the bed off, which I don't so he tried to sell me a small transfer pump to get the mollasses-like oil into the diff. He said it's a huge pain to fill it by squeezing the bottle. That true?
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I never had a problem filling them with a tube. If you have a problem, just slip a hose over the end.
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2) The spec decal on the left front innerfenderwell lists these as the "standard tires."
It physically says on the sticker 195/75R15 ?
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OK, first off, i was shocked as well, but here's the pudding:
(http://i223.photobucket.com/albums/dd31/sencraig/100_0373.jpg)
(http://i223.photobucket.com/albums/dd31/sencraig/100_0372.jpg)
Again, we have to remember that this is a bone stock, spartan custom deluxe, not a silverado. i have a rubber mat for a carpet and absolutely no headliner.
So, it seems with my truck and many others we basically have a truck with a car drivetrain and i kind of like it that way.
2) About filling the rear diff, if you could give me a few hours/days to get my other pictures up that relate to this topic, i have a few more "interesting" twists.
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Interesting. the first letter X = Front tire and Y = rear tire, so it did come with those on all 4 corners.
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Yes, occasionally you'll see a pickup with really tiny looking tires with those step-van hubcaps that don't cover the whole wheel---that's what i got.
It would not suprise me if some of these 70's models came with 14's
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That I know didn't happen, they were 15's the whole time.
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Ok, well it sure looks that way---the tires seem so lost in that big fenderwell.
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When growing up living at home I remember the neighbor across the street bought a plain brown truck with the tiny stock tires/wheels with the hubcaps. I thought it odd to look at with the painted white front bumper, no rear bumper and a real ugly aluminum cap. My 85 C-20 shows 2 different tires on my truck. D rated on front and E rated on back. The 195's back then paired up with the 2.56 was probably borderline anyway.
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........That's all great info about changing the diff oil.................. huge pain to fill it by squeezing the bottle. That true? etc.
Ok, i got my pictures up. While we're on the subject of rear diffs and changing gear oil and all that, the only thing i could find that resembles a plug to check and fill oil appears to be this pipe-plug thing; Is this the drain/fill plug? (fig. a?) It's a 10 bolt, not a 12 bolt rear if that makes a difference.
(http://i223.photobucket.com/albums/dd31/sencraig/IMG_0256.jpg)
Also, what is this tube thing comming out of the rear? (fig. b?) There is a plastic plug at the end of it.
(http://i223.photobucket.com/albums/dd31/sencraig/IMG_0251.jpg)
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that is the fill plug, and the tube is the vent tube to vent the diff.
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Similar deal here. On my 1987 R-10, the axle comes back reading, "standard ratio". The other options are 2.56, 3.08, 3.42, and 4.10. I am assuming I probably have the 2.73 as it is the only one not listed and I run 1450rpm at 72mph in OD.
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87 it means 2.56
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Thanks for the fast reply. I have an 87 shop manual and it could not tell me. Will 3.42 gears fit on that 2.56 carrier or does it need a different one? I have the tools and what not to regear one, and I like the overdrive, just like the engine to do more than idle down the interstate.
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AFAIK the 2.56's are on a 3 series carrier, if so it will work.
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UPDATE:
Alright, basically what is happening now is i'm close, but not close enough; When i used driven gear #3987918--18 tooth "brown" gear, i was actually doing 63 with the needle at 60 and the odometer reads 1/10 more than one mile. i then tried #3987917--the 17 tooth "purple" gear and i'm doing basically 58mph with the needle at 60 and the odometer is still about 1/10 over one mile.
Normally, either of the above would be good enough for me. But i'm trying to figure out my gas mileage so i need something precise and since i really don't have time to further mess with it, i think i'm going to go with one of those electronic speedometers---either from autometer or cyberdyne. These can be calibrated exactly.
The #3987918 is the stock driven gear for 235/75 15's and 2.56 rear according to the dealer. But i think what's happening is my tires are off brand and thus are different from everyone elses 235/75 in size. Either that or my speedo is slightly out of whack.
So, in case anyone is interested, the stock speedo gears for a TH-350 and 2.56 rear equipped GM vehicle are:
a)With 195/75 15's
drive gear (on output shaft)----#6261785 "purple" 10 tooth
driven gear -------------------# 3987920 "blue" 20 tooth
b) With 235/75 15's
drive gear---------------------#6261785 "purple" 10 tooth
driven gear--------------------#3987918 "brown" 18 tooth
These are the stock gears as they came from the factory. Again, it's not working for me because i suspect that my tires are "funny."
So what did i/we learn?
1)The GM dealer is an excellent resource for not only knowledge of the different part combinations, but the actual parts and prices; If you've switched to a different size tire and/or rear gear that was available on one of these cars, the dealer knows exactly which gears are the right ones. Also, they were cheap--about $5 per gear. Try buying one from summit or tci etc. You'll probably pay at least $20 after all is said and done.
2) Don't get into a rush and get all hasty. Think about what needs to be done and ask a lot of questions; i was getting ready to take the driveshaft out and the tailhousing off and Mr. Vile stepped in and questioned the situation. On top of that, i still have no idea how i would get the drive gear off the output shaft if it had gone that far.
3) Custom Deluxes (as opposed to Silverados) apparently did come with "small" car tires. i think the silverados had 215/75 15's as standard. But the deluxes were an entry-level 1/2 ton pickup with fullsize car drivetrain. We have to remember that the S-10 had only been out for a year and until those sales picked up, the custom deluxe was still filling the role of the light 1/2 ton pickup? i guess?
Actually, one of the members had a setup that illustrates these smaller tires. i think it looked rather nice actually:
http://forum.73-87chevytrucks.com/smforum/index.php?topic=7156.0
i think i may start another thread strictly on speedo calibration, because we we're getting slightly off the original topic.