Last Special

My 1978 manual states 20-25 in-lbs for new pinion bearings, but other sources state 14-19 and 15-17. Which is correct? It is intended to be a moderate performance street daily driver. Also, my current out of the car differential 10 bolt clockwise (from the front) is 16-19 in-lbs, but counterclockwise is 22-24 in-lbs as measured with a new dial 6-30 in-lb torque wrench. I am using a shimmed solid spacer. Can I use it as is? All comments and suggestions are welcome.

dugsgms74

Are you sure is says new ring and pinion and not new bearings? Typically there will be two specs, one for old bearings and one for new bearings, the new bearing spec is naturally the higher of the two. Also, just in case you weren't aware, the measurement must be taken with the ring gear carrier(the actual diff portion) removed, you're trying to just read how hard it is the rotate the pinion only without the drag of the ring and pinion mesh and the carrier bearings.

That being said, if you are at 16-19 with new bearings Id call that a bit low. Would more than likely be fine but you're better off a little too tight than little too loose. Might want to think about removing the smallest shim(assuming you have one really thin shim) and re measuring.

Last Special

Good catch - Yes, I meant new bearings. The measurements were taken without the carrier installed. The torque is 22-24 in the normal engine clockwise rotation. It would only be 16-19 in reverse gear.

TimAT

Send a message to GTR1999.. He's the rear axle guru.

dugsgms74

Okay, if you have 22-24 in clockwise you should be good to go. Kinda odd that its lighter in counterclockwise but maybe thats just the torque wrench.

Last Special

Thanks for the OK. I was hoping for some support.

GTR1999

I just saw this and also responded on another forum.

If you are building a 78 vette diff the pinion only preload is 17-20 in/lb. You could go low to 15 but I keep it at 17-20. With the case installed you have to add the case bearing preload so add another 8-10 to the pinion total. ie, if the pinion is 17 then you want the total 25-27 in/lb.

There should be no change in drag cw or ccw. I suspect your new bearing is damaged.

You can bolt it together like that is you like but it's not right. If I was doing that build I would start with fresh pinion bearings and get them to a smooth 17-20 in both directions.

Solid spacers have to be machine fit, the shims in the kit are not going to get you close at all. Surface grinder is the preferred method since we are talking about a few tenths to get it correct.

Last Special

Thanks to all for your comments. I found out that I was using my new torque wrench wrong. Correctly used, the pinion bearing torque is 19-21 inch pounds both ways. Possibly, I can keep it there. I added a 0.004 inch carried bearing shim to each side resulting in 22-24 inch pounds total both ways. With a 3.73 ring gear, that amounts to a (24-21 = 3) x 3.73 = 11.2 inch pound carrier preload. Correct me if I'm wrong. The carrier felt tight before I added the 0.004 shims. The shims had to be carefully hammered in. Is my carrier bearing preload too low? Thanks for any comments.

GTR1999

I don't know where you got your calculations or advice but the ratio has nothing to do with preloading the bearings. I setup 273-456 gears all the same way, no reference to the ratio is applied. 19-21 is still moving too much for me but then I don't know how you are really checking them or what type of TW you are using. I use setup bearings to dial in a diff and after 10-12 diffs I can see the setup bearings jumping around like that, once I do the final install with new bearings the reading should be pretty much dead smooth, maybe 1/2 in/lb variance.

So lets say you are really at 20 in/lb, then the total needs to be 28-30 in/lb with the case in place and caps torqued. 22-24 is too light. Now there are plenty out there that would call that good, as I have repaired 100's of "rebuilt" diff's over the years and have seen cases so loose they would drop out. You do not need a case spreader to do a 63-79 vette diff but the shims will be a hammer fit that is why you do the final preload last, so you don't have to pry out the shims. What is your lash and are you using new gears? If new what brand? If GM keep the lash between 6-8 max, no less then 5. You should know your pattern before final setup, once the pattern is correct all future shimming should only change the preload and not the lash.

Now you said you're using a solid sleeve in place of the stock crush sleeve. Are you making your own or using the Ratech sleeve? Are you using it because your application is one that will see hard launches? Are you fitting a LH Steel cap as well? Do you have the bearing caps set to 001" rock- both L & R? All these parts and procedures work together, bypassing or missing part of the setup will affect the overall quality of the build.

Now with all that said I will step away from this thread and let you decide on what you will do. Good luck, if you do it right it will be stronger then any stock diff and depending on usage should last a very long time, if you don't it won't last 500 miles.

Last Special

After reading GTR1999's comments, I believe it is necessary to respond.

1. The ring and pinion ratio has nothing to do with measuring pinion bearing preload, but it has everything to do with measuring and calculating the carrier bearing preload. The reason why is that the ratio is the only factor that can compensate for the torque multiplication of the ring and pinion gears. In my 3.73 ratio case, when the pinion gear is rotated 3.73 times, the ring gear rotates 1.00 time. That fact represents the torque multiplication for that particular gear set. Knowledge of that ratio allows the calculation of carrier bearing preload after measuring pinion bearing preload and the combined pinion and carrier bearing preload. The correct formula to calculate only the carrier bearing preload is as follows:
Carrier Bearing Preload = (total preload - pinion bearing preload) x the differential ratio. I am currently measuring it to be (24 in-lbs - 21 in-lbs) x 3.73 = 11.2 inch-pounds.

2. My backlash is 0.009 inch to 0.010 inch using new Tom's US Gears, which recommends 0.010 for street applications.

3. I'm using a Ratech solid sleeve and stoned burred shims to avoid having to re-crush a new sleeve if it has to be changed.

4. I'm am using Tom's left and right bearing caps, both set to 0.001 inch rock following your well written method (thank you).

I, also will be stepping away unless someone else is interested in commenting.

Kasper Helset

looks like no one saw this, I was off here a week or so.

I never setup new pinion bearing over 20. I set mine to 17-20 add another 8-10 when in you install the case for total.

You should not have the variance in readings like you have could be a bad bearing or solid sleeve setup, Solid sleeves have to be machine fit using the shims that come in the kits will not get you close. 001= 4-5 in/lb drag. Doing this on a lathe can be done but a surface grinder is the way to do them.
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Link broken for review.

GTR1999

So what is the game here Kasper? Your response is a copy of my reply on Digital and on Digital you copied & pasted my response from this thread there. That is pretty odd.
Mods please check this person since they just joined and apparently have another motive then to resurrect a dead thread I replied to a year ago and do it on two different web sites.

vettebuyer6369

Closing thread for review.