Johnny_Cracker

iTrader: (1)

Do you guys think the above looks to be excessive backlash as measured at the rear diff input flange?

The FSM specs "backlash of ring gear and pinion" measured at the ring gear(ie 3rd member pulled from axle) as .0035-.0043 inches. Is it legit for me to just multiply .0035 and .0043" x the -SE pinion ratio of 4.076 to get backlash at the pinion flange? I don't wanna yank the axles and pull the diff just yet if this is a normal amount of play.

If my math assumption is okay then I would should expect to see between .0143-.0175" backlash at the flange. I'm just not sure where I'd set the dial indicator on the pinion flange for a proper measure.

..Even without measuring, it visually looks like there's way too much backlash.

I'm considering just pulling it and using some gear paint to get some real answers.

Any ideas???

Carl

iTrader: (2)

To take the measurement you need to remove the third member and set up a dial indicator on the teeth of the ring gear and measure how far it moves back and forth before engaging the pinion. Not really very hard to do, but still a pain to pull and set-up. Also you need a dial indicator with magnetic base.

Having said that though, the movement you are seeing is probably a little loose, but not too bad.

Johnny_Cracker

iTrader: (1)

Thanks Carl.. knowing that it's not an excessive amount is some relief.

I need to do the rear wheel bearings, so I suppose I'll pull the 3rd member while the axles are out and give it a stare..

Carl

iTrader: (2)

Here is a picture of how you set up the dial indicator to measure the backlash.

DreamInRotary

iTrader: (49)

Thanks for the info Carl, I'll be using it when I pull mine in a few weeks!

Glazedham42

iTrader: (4)

I agree this looks like a lot to me. There's really no way to be sure without actually measuring. I just finished rebuilding a GSL differential and didn't have near this much movement when I was done setting up the backlash to factory specs. You should be able to hear it when you rock the pinion back and forth but the Mazda specs are so tight by most standards that you shouldn't see a whole lot of movement. Most diffs are about twice as much backlash as ours. At least the big 4WD stuff is.

DivinDriver

iTrader: (15)

Jamie, Is there an "easy" way to adjust that backlash out... or is this where you need to pull the pinion and use new crush collar? Or is it simply the ring and pinion worn past use?

I've never done a diff set-up; I replaced mine entirely when it got too bad, but that's not as much of an option these days as good parts get scarce.

Carl

iTrader: (2)

Basically you adjust the ring back and forth using the ~3" diameter threaded adjusting thingamajigs on either side. Loosen one and tighten the other the ring. Look in the manual. It explains it pretty well. Not that difficult.

Glazedham42

iTrader: (4)

I would guess that most of the slop in his setup is from one of two things.

1) Someone loosened the pinion nut without realizing that they had just opened pandora's box. Once you loosen that nut you basically have to setup the entire diff again, which requires pulling the axles, and the whole 9 yards. They then re-tightened it and threw everything out of whack, and moved on.
2) The bearings are so worn out that they are allowing this much slop to be present. Looks like to much slop for it to be bearings to me though.

Either way you have to do just about as much work to put everything back the way it is supposed to be. Assuming that #1 is in fact the problem, then theoretically you could re-use the crush sleeve. The FSM gives allowable limits for re-using a used crush sleeve, but it is possible that you will fully crush it down and never obtain the necessary pinion bearing preload. I say it's ALWAYS better to just use a new one. They are pretty darn cheap, and you've probably done 2-3 hours work minimum to get everything apart. Just replace it. Assuming that you successfully re-use the old crush sleeve, and set the pinion bearing preload successfully you would then move on to adjusting the backlash. The backlash of the gears is set by using the threaded adjusters to either increase or decrease the distance between the teeth on the pinion and the teeth on the ring gear. Crank them closer together and they tighten up, giving you less backlash. Crank them farther apart and they loosen, giving more backlash between the gear teeth. The trick that I learned the hard way is to set the torque on the adjuster caps incrementally. I think they are spec'd at about 30 ft-lbs. My problem was that I would get the backlash dialed in to the FSM specs, and then when I torqued the bolts down on the caps everything went out of whack again. If you do this tighten the bolts to about 10 ft-lbs. Set the backlash. Then tighten them down to about 20 ft-lbs. Check the backlash again and adjust slightly if needed. Finally, torque them down to the full 30 ft-lbs and verify one more time. I learned this the hard way, but after much trial and error I figured out that this is the best way to do it. I ended up with a unit that is pretty much dead on the factory specs all the way around. Be sure to check the backlash at about 6 points around the ring gear. Each combination of teeth is different, so you are really shooting for an average. You won't get the same backlash on every tooth. The world is too imperfect a place for that to ever happen.

So back to our other scenario of #2. If the bearings are worn out then you basically strip the diff down completely and pound/press/pull all the bearings and races out of the housing. Then press the bearings off of the pinion. Press the new bearings on, along with a new crush tube. Everything from there on out is the same as #1 above. So you can see why in my opinion you should just go ahead and do it the right way. Replacing all of the bearings and races only adds about 30 minutes to the whole job if you have the right tools. Might as well do it.

Hope this helps,
Jamie

Johnny_Cracker

iTrader: (1)

Thanks guys, good stuff...

I'll likely pull it and adjust the backlash using the carrier bearing adjusters then paint them to check the pattern.

If pinion depth is okay then I might not screw with pulling it assuming axial play and preload are fine. If it feels smooth I'll leave it as the bearings have only 52k on them.

I'm hopeful all I'll need adjust is backlash at the ring.

So it looks like I have something to do after I finish the Al flywheel and ST1 Exedy clutch upgrade underway.