gxlbiscuit

i need to swap my diff out i dont have the gauges to check backlash. Any shadetree advice? frustrating stuff. from what im seeing looks like i shouldnt care people just swap it out and go on.. im using the original gears.....

gxlbiscuit

what the hell is backlash i keep looking at the manual and i know about setting the pinion depth and crap but i dont get this backlash thing.. the manuals says measure in three different spots that thrwos me off i dont know what the hell its all for.

BASTARD

iTrader: (4)

Are you removing the gears and bearing from the carrier? or just swaping a complete third member for another third member out of a different car. If your just swaping out the complete unit then don't worry about the backlash

When installing new bearings an/or ring and pinion gears you have to measure the amount of bearing free play from side to side but at the same time you need to make sure that the ring gear and the pinion gears are meshing correctly. most rear ends have either threaded collars or shims to set within spec

micah

As a disclaimer... people on RX-7 forums typically take their cars and pay way too much to have their gears swapped/installed. Most people don't know what backlash is, or that they can even install their gears themselves.... properly.

Its really not that hard. Go to harbor freight, pick up a 20 dollar dial indicator and a magnetic stand. Follow one of a million guides on the internet and 4x4 sites/forums... You'll probably have to buy a master gear install kit as well (not sure where to get one for an RX-7) or atleast a shim kit. You can probably get those from Mazda. They'll be cheap.

It isn't hard, and isn't expensive, it just takes freaking forever, and a lot of patience. First time you do it... post pics of your gear mesh pattern. Get some opinions. And do a write-up; since I don't think one exists for RX-7's yet.

FCKing1995

iTrader: (3)

+1, LOTS of patience. But certainly not out of anyones boundaries who can do most basic stuff. Its pretty straight forward once you see first hand what the manual is talking about

NZConvertible

If you don't have the tools and don't know how to do it then find someone who does or pay a professional to do it for you. Don't just bodge it.

And unless they're very lucky they'll have a noisy and fast-wearing diff as a result. Don't do that.

micah

bodge.... cool word. A note about paying somebody though.... if you DO pay somebody to do it, don't pay more than 300 bucks to have it installed... Any more than that, and they ARE ***-raping you. If you search, you can find local shops to do it for 150 bucks.

RotaryEvolution

iTrader: (30)

that depends if it includes removal and install of the diff. good luck finding someone competent for that price to do a full days work for $150.

gxlbiscuit

well i cant tell you how excited that i am to be getting intelligent responses and thanks. i am using the same ring gear from the previous diff. im even using the FDs bearings(go ahead make faces). i dont have money to pay someone to do it. i still dont understand what the backlash is (i dont have the diff apart yet to understand fully) it wants me to measure a solid thick metal ring gear to check for some kind of play that can be different in three spots of the ring gear.... odd. i have installed solid delrin diff mount i wont know if its good or not ive got it in my head it will whine:-)

FCKing1995

iTrader: (3)

Pretty much just think of play in place of the word backlash. Its sort of the same idea. But the backlash has to be in the right areas or all of your parts will be thrown off a bit

gxlbiscuit

so its basically checking to make sure it doesnt have "excess wigglage" i got the diff for 100 bucks shipped by the way. ill redo my s4 t2 diff later

micah

Yeah.. I figured that was obvious... Even with pretty simple tools you can remove the diff. If it saves a bunch of money, there should be no question. I've never driven a car to get my gears done... when I DID have them done.

I say do it yourself!

RotaryEvolution

iTrader: (30)

alright...

backlash comes in a combination of carrier bearing play and ring gear depth in combination with carrier housing seating. in other words if the ring gear is too deep then backlash will increase, if your carrier is preloaded to far to the left then it pulls the gears away from the pinion and backlash increases, if you preload the carrier too far to the right then backlash decreases or it can bind up completely.

so, you have 3 angles to work with: pinion depth and carrier preloading(assuming the torque on the carrier bearings is set properly..) which all affect the backlash and gear tooth patterns. each of these 3 angles can run the gears off the face of the ring gear and cause a whine from the diff meaning the gears are wearing and singing while they work.

some people have thrown carriers in and had luck with them not failing, at least not within a short period of time. you can get a carrier in there and close and have it last a good while if the materials that the ring gear is made out of are durable to take the extra abuse it can last a while before destroying itself but the added material in the diff from the gears will be doing no favors to the bearings inside.

to properly set up a differential you do need the proper dial indicator and a torque wrench for measuring the pinion preload, there is no way around it and the only shadetree method results in a blown differential in several thousand miles.

only a very experienced builder can build a differential by feel with no gauges but even that is not a practical approach as it is very difficult to tell .0012" apart from .0020" which the latter can be devastating to the differential if that measurement is .0005" out of spec.

at the very least you need a 100ft/lb torque wrench and a dial indicator. the dial indicator is to measure backlash and the torque wrench is to torque the bearing caps and using feel for measuring the total preload of the differential. getting the backlash set properly is important to gear tooth contact patterns. you can use silver aluminum anti-sieze and paint it on the ring gear teeth to check the pattern but i make sure to completely clean it off prior to reassembly.

micah

Uhm... excess wigglage.... I guess that works. lol.. I would have used the term "gear slop" or something. but yeah, i think you have the right idea. Its just crucial to have the gears meshing correctly... too shallow or too deep and it'll wear wrong, heat up, move on accel/decel, etc... You'll know you have it right when you see it.

Out of curiosity, where are you getting your parts?

gxlbiscuit

ill go and get this damned gauge in the morning i was planning on at least torquing stuff to spec i may be silly but im not a complete idiot asking for trouble.. hmm you know leroy on 25th street he drive around in that ryder truck. i got the diff from him hes got a special on a t67s he "picked up" . but no really i got this diff off of the forum. i get my stuff wherever i can the diff was actually 75 bucks but i gave him 25 bucks more cuz im a coolguy....

NZConvertible

I wasn't talking about the R&R of the diff (that's easy), only the setting up of the centre in the housing.

That's exactly what I did.

Find out what it costs before making that assumption. The whole process takes less than half an hour, so if oyu take the housing in with the centre installed and ready to be set it should be cheap.

gxlbiscuit

i bought the dial set. i have taken the diff apart and alas now i understand how they set backlash you cant see it clearly in the FSM if you dont know what you are looking at.

micah

Yeah.. I know. I was talking about a full gear swap.. that includes re-shimming (centering).

NZConvertible

The FC diff doesn't actually need reshimming. The bearing caps are adjustable, so all it takes it a bit of patient fiddling with them. This is a Good Thing, and makes the job quick and easy. It should also make it cheap if you pay someone to do it also.

micah

All I've done is Jeeps.... adjustable bearing caps... thats bad ***.. Good to know! Thanks NZ.

EDIT: What about pinion depth?

gxlbiscuit

im doing it myself:-P ...or its doing me bymyself im trying to understand it all im picking up is that i can move the diff off center and i can tighten how hard the bearings are clamped in. clamped in. to adjust backlash it seems all i would be doing is moving the diff on center or off. ill be messing with this crap for a while ill let you know how it goes... up on top of omg wtf diff backlash mtn....

NZConvertible

That needs the right spacer selected, but it doesn't need to be done for a center swap like this.

RockLobster

iTrader: (7)

When we built diffs for toyotas and samurais we always laughed at the dana garbage. 3rd member style jap diffs and ford 9" are so much easier to work with.

Although you cant argue with the strength of the beefy dana 60.

RockLobster

iTrader: (7)

If you do a full gear swap you will need to set the pinion depth (reshim).

gxlbiscuit

omg wtf diff backlash mtn conquered had i not set the backlash i would have had nasty "excess wigglage." Basically all the setting of backlash is, is the fine setting or tuning of the distance of the ring gear and diff from the pinion worm gear. I marked the original settings for the adjustments with the old diff. It was not far off BUT made a difference in the backlash. the diff has already been centered to the pinioin so no reason to move it. oh and stock just from feel im pretty sure the backlash was excessive on the original. Anyways back to work. thanks for all the help. if this doesnt work you guys will know.