C2-3 differential backlash

[Timothy B.]

This question may have been asked before but how do you check backlash on the differential pinion (spider) gear.

I know the dial indicator is set on the gear tooth and it measures the play between the differential side gear and differential pinion gear, correct??. Or does it measure the distance the differential pinion gear moves back and forth??

My question is about the procedure, do you just rock the gear or???

Is this same procedure used for a open differential? I have open diff and the side yoke end play is approx .016 on one side and .006 on the other. I understand the backlash is the important measurement as this will reduce end play.. When you shim the side gear do you do one side at a time then remove side gear to do the other side gear?

Last, Please explain the same procedure for the ring gear backlash check. Do you check the R&P tooth pattern first just in case pinion depth is not correct then set backlash or does backlash help determine the tooth pattern??

I re read the article from Duke and Bill Bradley but had a few questions.

Thanks for the help, Tim

[Gary R.]

Re: C2-3 differential backlash

To check the spider BL you need to lock the side gear with a screwdriver wedged in between the cross shaft and side gear, indicator on a pinion tooth. If you're going to do this I suggest you tune the posi without the springs. Done correctly it will out perform and last longer then the stock spring setup.
The BL in the ring & pinion is set by shimming the case. With a 63-68 carrier then the shims are thin and do not come in the kits, I grind shims to size when rebuilding this type, it's the only way to dial in the BL that is correct and not just close enough.

[Timothy B.]

Re: C2-3 differential backlash

Thanks Gary,

To expand on this, are you saying backlash is the movement back and forth of the differential pinion/side gear meshing? Is this checked on each side so shims are different for each differential side gear? Does the side gear need to be removed after checking so it does not interfere with the other side gear checking/setting?

What do you mean by tune the posi, are you after even brake away torque with the clutches?

Thanks for the help, I want to understand this better.

[Gary R.]

Re: C2-3 differential backlash

yes check each side the shims will be different most likely. Tuning is the process of setting the gears up to run less the springs, I usually end up grinding shims to size to setup. It's time consuming to do but works better then the spring setup.

Here is a 12bolt vette diff I just built,notice the 12 bolt tuned posi case,steel cap,ARP's.

[Duke W.]

Re: C2-3 differential backlash

This question may have been asked before but how do you check backlash on the differential pinion (spider) gear.

I know the dial indicator is set on the gear tooth and it measures the play between the differential side gear and differential pinion gear, correct??. Or does it measure the distance the differential pinion gear moves back and forth??

My question is about the procedure, do you just rock the gear or???

Is this same procedure used for a open differential? I have open diff and the side yoke end play is approx .016 on one side and .006 on the other. I understand the backlash is the important measurement as this will reduce end play.. When you shim the side gear do you do one side at a time then remove side gear to do the other side gear?

Last, Please explain the same procedure for the ring gear backlash check. Do you check the R&P tooth pattern first just in case pinion depth is not correct then set backlash or does backlash help determine the tooth pattern??

I re read the article from Duke and Bill Bradley but had a few questions.

Thanks for the help, Tim

Don't confuse the differential side shims with case shims. Case shims are used on Positraction axles to control differential (not ring and drive pinion) backlash, which effects side yoke end play. They are installed between the inside of the case and the first disk of the clutch pack. There were three sizes available through service parts, but I doubt if they are still available.

As mentioned in the article there is a spec for differential gear backlash, but none for side yoke end play, however, if diff. gear backlash is in spec, yoke end play should be no more than about .010" or the yokes are probably not in spec.

The case shims are only applicable to Postraction axles. AFAIK there is no shim adjustment for open diffs. If all parts are machined to spec the diff. gear backlash should be in spec, but there is no way to adjust it on open differentials other than trying different parts - case, side and differential pinon gears, and pinion thrust washers.

You might get a little better (more equal) measurements on the yoke end play by swapping the side gears side to side, but it could also get worse. Measure the widths of the side gears, and with a little math you can probably determine if swapping them will improve the situation.

Duke

[Gary R.]

Re: C2-3 differential backlash

Duke is correct,to be clear the shims for the posi,pinion,and case are all different diameters.

Also I found a lot of the kits on the market are missing some parts, some are less the correct yoke bearings, some use cheap seals and import bearings, most I see do not have the correct case shims for a 63-68 carrier and don't bother to mention this fact to customers. These use thin single shims, best if ground to size. Not sure if GM still offers the posi shims, they were over $7 each the last I looked and were limited in size. I start with shims in 005 increments and fine tune them.

[Timothy B.]

Re: C2-3 differential backlash

Gary and Duke, Thanks for helping me understand this better.

I don't know what the differential side gear looks like on a open rear and why it will not accept a shim to close backlash. I am going to remove a side gear and have a look.

Gary, when you tune a posi I assume you shim each side gear to where the breakaway spec 50-70 ft.lbs is reached without springs. What happens when the clutch pack wears, there is no tension to take the slack and maintain a preload..

[Duke W.]

Re: C2-3 differential backlash

Also try swapping the yokes side to side to see if the yoke end plays are more equal on both sides. If not, swap the gears and then try the yokes both ways.

The total end play is .022" and one of the four combinations might yield both sides closer to .011/.011" with the same diff. gear backlash.

The open axle case assembly is what's called a net build component. If everything is machined to spec, the final specified diff. gear backlash should be within the spec range, and yoke end play should not be more than about .010". No shims. No select fit parts.

With the multiple clutch disks of the Positraction clutch pack there is more variance in final diff. gear backlash, which is why shims are used.

As the Positraction clutch pack wears, both diff. gear backlash and yoke end play increase, which is why Positraction axles tend to develop "clunks" when they get old.

In normal service an open differential will not wear significantly inside, so diff. gear backlash does not change, and any increase in yoke end play is due to yoke wear.

Also understand that there are TWO backlash specs in the axle - differential gear, and drive pinion/ring gear.

The differential gear backlash can be checked and adjusted (on Positraction axles) before the case is installed in the carrier. Then a check of yoke end play after the axle is completely assembled will tell you if you have to go back in, pull the case, remove the clutch pack and install different shims. Getting a Positraction axle to achieve both minimum diff. gear backlash and minimum yoke end play equal on both sides may require multiple assemblies/disassemblies with different clutch pack shims to optimize all measurments.

Note that in the article I was careful to define terms. There are two "pinions" inside the axle, the differential pinions and DRIVE pinion that mates with the ring gear.

Guys throw these terms around indiscriminantly and constantly confuse "case" and "carrier", which is why very few people actually understand how a differential axle works or how to put one together to very tight tolerances!

Duke

[Gary V.]

Re: C2-3 differential backlash

Just wondering which artical by Duke and Bill Bradley you are talking about?

[Duke W.]

Re: C2-3 differential backlash

Just wondering which artical by Duke and Bill Bradley you are talking about?

It was published in The Corvette Restorer about 3 years ago. Sorry, I don't recall the exact issue, but given your NCRS number, you should have received it.

Which reminds me to those in charge or influential - it would be a great idea to have an online index page to The Corvette Restorer as part of the NCRS Web site.

Duke

[Terry M.]

Re: C2-3 differential backlash

Which reminds me to those in charge or influential - it would be a great idea to have an online index page to The Corvette Restorer as part of the NCRS Web site.

Duke

Work on that is underway Duke. In the mean time:

Part I of your tire story is in Volume 29 Number4, Page 16-19
Part II is in Volume 30 Number 1, Page 18-20
Both of those issues are in 2003 according to the information I have.

[Duke W.]

Re: C2-3 differential backlash

Terry, have another glass of wine. (I know I will!)

He was referring to the axle overhaul article that I co-wrote with Bill Bradley. IIRC it was circa 2006.

Duke

[Timothy B.]

Re: C2-3 differential backlash

The article is published in the Restorer Magazine volume 31 #3, (winter 2005) and volume 31 #4, (spring 2005).

Tempus fugit!!!

[Terry M.]

Re: C2-3 differential backlash

Way past my bedtime.

[Timothy B.]

Re: C2-3 differential backlash

Merry Christmas everyone..

I have another question about the checking procedure for pinion tooth pattern.

Is there a problem with preloading the pinion bearings without crush sleeve just to check backlash and tooth pattern? In my thinking the bearings should seat and allow preload for this check. In the event the pinion depth should have to be changed the crush sleeve is saved until final tightening of the pinion bolt..

Is the tool that's used for pinion depth still available for the GM ring and pinion gears?