Changing Rear End Gears

[Bluevee33]

I've got a 4.10 Rear with posi!! I wanna change it to the 3.73? gears.. Is it just a gear?? What all do i need to buy and change out!!
Robert

[sixnickel]

To change gears you have to change the ring and pinion gears. If it's 4WD you have to do it twice. You have to know what you are doing to do this job right and if you have to pay to have some one do it, parts and labor can get costly $$$$$ I am guessing that you have a 3500 if you have 4.10s. IF you don't tow or load the truck I would go to 3.42s to go from 4.10s to3.73s for what you will gain in milage is not worth the cost. I have a K3500SRW with 4.10s that I want to slow the engine down also, but when I do it will be with a Gear Vender's O/D unit that will give me a final drive of 3.30s and I will have the best of both worlds. My K1500 Burb has 3.42s and with the HP upgrades it is no slouch, it goes!! And gets 20/21 MPG.

[Bluevee33]

It's only a 2wd and i do a lot of towing.. and my fiance is thinking about gettin a bigger trailer too.. (we have horses) I tow a trailer when loaded 2 horses is about 4500 lbs. I have a thing about driving right around 65-69 mph. I just drove a trip (towing) of 700 miles 2 weeks ago and got 15 MPG with my wastegate solenoid gone bad, so i had no turbo the whole way to Seattle and back!! I would like a little better mileage.. That OD kit you where talking about whats that?? Any other ideas on getting better mileage! When I tow it's not just across town! It's hundreds of miles at a time!! My girl has a thing for horse shows!!! Thanks all
Robert

[Garth J]

www.gearvendors.com
best invention ever I had one on my 85 6.2 with the 3 speed automatic it gave me 5 useable gears. I put a 2 speed axel shift button on the shift leaver and that was it.
The electronics in it wernt working so the button did the trick just wired it to the solenoid and a pilot light to let me know when I was in O/D

[njdevi11]

(1). remove axle shafts, If they are full floater this is really easy.
(2). remove diff cover
(3). remove 4 bolts holding the carrier in place
(4). remove carrier and shims, remember which side the shims came from.
(5). swap rings on the carriers
(6). reverse steps 4 through 1

After the carrier is installed it's a good idea to check for the proper alignment of the gears using gear marking compound, it should be meshing right in the middle of the gears. If you put the shims back in the same place it should be good enough. Remember to fill the diff back up with gear lube with posi additive. If you feel like going all out go to sears and get a dial indicator to measure the run out.

**note**
It might be a very tight fit to get the carrier in and out, so much so that using a soft mallet may be necessary.

[sixnickel]

Hey Robert Here are some numbers to think about. With 245/75-16 tires. 4L80E transmission and 4.10s at 65MPH 2205RPM 70 MPH 23754 RPM with 3.73s at 65 MPH 2006 RPM at 70 MPH 2160 RPM. Thats only about 200 RPM difference. I don't think it's worth the gear change for 200 RPM. Also unless your pulling in the flat lands all the time your are better off with the 4.10s. With the Gear Venders unit you will be turning about 1850/1900 RPM in double O/D for the flat land and back to 2200/2300 RPM for the hills. That's my 6 and a half cents worth, something to think about!!

[njdevi11]

I thought you were saying you wanted to swap an open carrier for a posi. But now I see you mean you just want to change the gear ratio, if you want to swap 4.10 gears for 3.73 don't waste your time. Go 3.55 or lower or don't swap at all.

When you said you had a rear with a posi, I thought you had another axle with the posi in it that you wanted to put in your rig...

[MBBOB]

I thought I read on another thread that the 4:10 and 3:73 are the only two gears that interchange on the heavy carrier. If you go with a 3:42 it involves a thicker ring gear or somthing?

I have drooled over the Gear Vender OD for some time, but the price tag Ouch!

Is there any way to verify the accuracy of the tach? I have read those MPH/RPM figures a couple of times and my rig has the same tires, 4:10 and trans but comes closer to 2500 at 70 MPH. I would guess the tach is off because it appears to be off at idle also by a couple hundred RPM.

[njdevi11]

The Dana 44/60 model axles have different carriers, the corp. 14bolt has one carrier for all ratios.

I don't see a problem with running a really high gear in the diff. I've got 4:09's in my rig which would be about right if I was only going to keep it on the highway. I'm on 36's, I'll get my gear reduction through the trans 6.6:1 in first gear and the range box 2:1. My final drive ratio is 50:1

[Husker 6.5]

The Dana 44/60 model axles have different carriers, the corp. 14bolt has one carrier for all ratios.

I don't see a problem with running a really high gear in the diff. I've got 4:09's in my rig which would be about right if I was only going to keep it on the highway. I'm on 36's, I'll get my gear reduction through the trans 6.6:1 in first gear and the range box 2:1. My final drive ratio is 50:1

Be careful, there are two different corporate 14 bolts used in the C/K Series, a 9 1/2" and a 10 1/2" ring gear. Make sure if you're going to swap from a used rearend, or buying new gears, that you're using the right ones.

Husker 6.5

[sixnickel]

I thought I read on another thread that the 4:10 and 3:73 are the only two gears that interchange on the heavy carrier. If you go with a 3:42 it involves a thicker ring gear or somthing?

I have drooled over the Gear Vender OD for some time, but the price tag Ouch!

Is there any way to verify the accuracy of the tach? I have read those MPH/RPM figures a couple of times and my rig has the same tires, 4:10 and trans but comes closer to 2500 at 70 MPH. I would guess the tach is off because it appears to be off at idle also by a couple hundred RPM.

MBBOB
To get a true tach reading you need a scanner plugged in under the dash (Snap-On, OTC, Tech 2 etc) They get the tach signal off the crankshaft position sensor through the ECM. The dash tach gets the signal of the alternator. Most aftermarket alternators have smaller pulleys to turn them faster for a higher output. I think the only way to get a accurate tach is to use a AC Delco reman.

[Chevylover]

Or do a drive with a portable navigation system. The most will show your speed, calculated through the GPS Signal. It is not the 100 % method, but it is okay to check if your speedo is out of range for 10 mph or only for 1 or 2 mph.

Cu,
Sven

[MBBOB]

The spedo seems to be off 5-6 mph high based upon my wife following in a stock vehicle, and the flashing radar signs at construction sites.

The odo seems to be right on checked against five consecutive miles of markers.

I have a 94 with OBD I, will the scanner read the rpm?

[Chevylover]

The spedo seems to be off 5-6 mph high based upon my wife following in a stock vehicle, and the flashing radar signs at construction sites.

The odo seems to be right on checked against five consecutive miles of markers.

I have a 94 with OBD I, will the scanner read the rpm?


Does the Speedp shows more than you drive in real or is it lower than reality ? It is normal that a speedo shows a bit more than real, but should never lower than reality.

Mine is ahead with 245/75/16
Speedo shows 100 Km/h and reality is 96 Km/h

Accurate with 265/75/16
Speedo shows 100 Km/h and reality is 100 Km/h

and lower with 285/75/16
Speedo shows 100 Km/h and reality ist 107 Km/h


Cu,
Sven

[MBBOB]

The tires are 245/75/16 with a diameter of 30.5 inches which is factory size. The odometer reads miles within a foot, but the speedometer reads 75 at an actual 70mph. The tach is 2500 exactly, at 70 indicated.

[Chevylover]

The tires are 245/75/16 with a diameter of 30.5 inches which is factory size. The odometer reads miles within a foot, but the speedometer reads 75 at an actual 70mph. The tach is 2500 exactly, at 70 indicated.

That seems absolutly normal for me. In every car the speedo should go ahead a bit from the real speed, because of tolerance by the manufactor.
In germany every speedo is allowed to go about 7% ahead from the last value of the speedo, but it is forbidden to show a lower speed than the real.

The most speedos in cars here go about 5-10 Km/h ahead.

If your odometer and your tach is right, than the speedo is as it should be from the manufactor. If you on 265/75/16 wheels on it will read nearly the exact value. That is, because GM doesn'z build different speedo if the truck is equipped with other optional wheels, that could be ordered as an option.

Cu,
Sven