gearheadgene

I realize most of the subject regarding gear swaps is covered almost everywhere. But I have a question that nobody seems to have touched on.
Backlash is the measurement of play between the ring and the pinion gear. It occurs to me that the 2 carrier bearings and shims should create a snug/friction fit. This keeps the carrier locked in position with no left/right play. Then to adjust the backlash, you make one side a little smaller and the other a little larger until the correct backlash is achieved. At all times, the total thickness of shims (left + right) is always equal.

Is this correct?
If so, how snug should the carrier be?

This all came about because I am changing gears and carrier. The factory shims make the carriere VERY tight to install but I don't actually know the backlash *if* I could get the thing in there.

sofakingdom

iTrader: (1)

Your description of backlash, the effects of the shims, etc. is correct.

DO NOT try to re-use factory shims. They are cast-iron, not steel; and usually have considerable wear.

I usually try to get AT LEAST .010" of preload on carrier bearings; i.e. the carrier plus bearings plus shims is "nominally" .010" or more larger than the space they are to go into, when sitting out in free space. Used factory shims are hardly ever that tight. Since they're made of such an inferior material and wear so heavily they often give no preload at all, but instead, play.

gearheadgene

Thanks!

Actually, the factory setup was really tight, and very hard to pry out.

sofakingdom

iTrader: (1)

Actually, the factory setup was NOT tight; they never are. No matter how it felt to you removing it.

For a good install you need to put it back tighter than however it was. With better shims.

Rob 97 Z28

iTrader: (3)

Obviously I can't speak for every 7.5" owners experience but when I tore the one in my 3rd gen down in '17 I wound up using a combo of original GM shims & some from the Yukon pack I bought. Now granted this was my first ever full rebuild from a bare housing (all new gears, bearings, races etc etc). I reinstalled the 4th gen posi carrier, new gears, bearings & races, seals etc. With a fresh rebuild, reinstalling the TrickFlow diff cover mines been great. Really impressed, 16 passes (after the initial 500 mile easy cruise break-in) with a M/T 275 60 R15 on the back (w/a final best of 12.34 last October)....Don't get me wrong, with the new combo I putting together to go back in before the end of the year I'm expecting to be in the market for a complete rear-end up grade, I'm not naïve to the good fortune I've had thus far.

I think when dealing with the 7.5" the hardest part is getting the pinion depth set correctly. The T&D kit that supposedly does GM 7.5" does Not actually work for these rear ends (the aluminum pucks they provide aren't small enough to fit the carrier bearing saddles, galled up 2 of mine and had to order new ones). Ratech sells a funky little tool for these rear-ends that I wound up using and works but its still a tricky process.

GTA matt

iTrader: (1)

Though most times we install the carrier by feel, the technically correct way is to take the rotating torque of the entire assembly (minus axles), and subtract your pinion bearing preload from this, then multiply that value by your gear ratio. You want to shoot for roughly 20 inch pounds of rotating torque (with new bearings). There is some fudge factor built in, as gear mesh will take some torque to overcome, but its a great way to see if you are way loose or way tight. So for instance, if the rotating torque of your pinion and seal are 25 inch pounds, and fully assembled you are at 30, with a 4.10 gear set, your math would be 30-25=5. 5x4.10=20.5, basically spot on

Rob 97 Z28

iTrader: (3)

Yup! That's how I did mine. There actually is a spec for it too in the GM service manual. I remember checking it against AllData at the time just to confirm 😁👍

TransamGTA350

iTrader: (2)

Yes, this is the proper way to do it and really isn’t too hard since you should already have the inch pound torque wrench to set the pinion bearing preload. Techs who have done it many times usually have a good feel for how tight the carrier should go in and don’t usually measure, but for those of us who haven’t done enough to know the feel, this works great.

8Mike9

Before I change gears, or bearings, etc on a new to me rear, I check the contact pattern. I want to see what I’m working with. If pattern is decent, here’s what I do.

I have a piece of 3/8ths x 1.5 flat bar. I milled out slots on it ( visualize this please). The slots I milled out would be where you would bolt the carrier caps down, then in the center of those slots I drilled and tapped for 3/8ths all thread.

With me still?


okay, now take the all thread and round/ bevel the end

bolt down the slotted piece to opposite carrier cap hole. Line it up so you tapped hole is centered over the pinion gear.


screw your all thread in and use a jam nut, and take your feeler gauge and leave around .030 between the rounded/ beveled end of the all thread and pinion. Snug the jam nut down

remove the contraption and put in your new pinion, then put the contraption back on. Measure the difference of what you started with, to what you have now. Add/subtract shims as needed

then set backlash with the ring gear

then check pattern, should be pretty close to what you checked at the start, adjust as needed


Hope I made sense

GeneralDisorder

iTrader: (1)

Tapered roller bearings love to be pre-loaded - you *almost* can't get enough load on them when cold. That's why you can buy case spreaders to allows installation of more shims for more pre-load. Also why the pinion bearings need to be set till they actually have drag on them with a torque wrench (pre-load) and you have a crush sleeve that takes hundreds of ft/lbs to crush. Very difficult to damage a tapered roller setup with too much pre-load.

GD

8Mike9

I agree to a point, but it depends wether the bearing is packed in grease, or oil bathed


Too loose in oil - like a pinion, etc - and the bearing pushes the oil away from the surfaces, too tight - like a wheel bearing - and the grease will exit the cage and not return.

That’s why we set rears up with a load on the bearings, and no load on front wheel bearings


I just wanted to put it out there so folks wouldn’t be running a preload on their front ends

I might add, I set the pinion preload without the carrier in it, on a 9 inch I take the ring gear off.

I know there are different ways to accomplish the same thing, but I was raised with MoToRs manuals, lol