'My first': rear end refresh - on going questions

[Malicious]

Hi all,

Rather then starting multiple threads I thought I'd start one thread and dump my questions in it.

I'm just about to attempt to install an new wheel stud, thanks for everyone's help on that, I'll update that thread and this once I've got it in.

Here are another question. The slack in between turning the input flange (drive shaft connection) on the carrier and the ring gear moving, I've known it as pre-load but I'm probably wrong? How much slack should there be? And how do I measure it?

I feel like there is too much but I'm hoping to avoid getting it rebuilt. If it does need to be adjusted, is it easy for some one with little diff experience to adjust? I'm good at swinging a ratchet but have never dealt with the actual diff before.


Looks like my ring gear is stamped with a 4.1, from memory you can count the teeth to confirm. What number of teeth would be 4.1 or is there a list I could find some where?


Next question, stoked as to find I have an LSD diff but it doesn't seam to be a stock unit. Can someone help I identify it?


Thanks all!

 

[747mopar]

If your referring to the slop between the 2 gears that's called backlash, you measure it by putting a dial indicator on a tooth of the ring gear and while holding tension on the pinion (where the driveshaft goes) turn the ring gear back and forth while reading the dial indicator (I can't remember the specs). The adjustment is made by adjusting the 2 big nuts (the round things with all of the holes in it in your pic) on each side of the carrier. These nuts are used to move the ring gear closer to the pinion reducing the backlash but once you mess with them you have to be sure to keep the preload on the carrier bearings correct plus there's a gear contact pattern to check as well. Best thing to do is purchase a good manual on it and just dig in, they can be time consuming to get just right but it's not hard by any means. I've done a handful and learned from a manual. Good luck

 

[Malicious]

Thanks mate, backlash according to the FSM is .006-.008 (.15mm - .2mm). Feels more then that. I'm trying to get this rear end back together quickly so I might farm the work out. If it isn't as difficult as you say hopefully it won't cost much to adjust. I'll look at doing myself next time. Well, pending the cost estimate from the diff guy.

Side note, over sized studs failed. Gonna have to tack the stud in now instead.

 

[Cranky]

As thick as the ring gear looks, I would say it's more than a 4.10 gear. Divide pinion teeth into the ring gear for the ratio. Check back lash in at least 3 different places around the ring. Nothing is perfect on these and if you end up with it being tight in one area but good in another you stand the chance of running it hot. I also like to run on the loose side with deep gears.

 

[Malicious]

So I've cleaned, painted and rebuilt very thing else on the rear end except this back lash issue. I've had a read of the FSM and it seams relatively straight forward except for having a dial indicator. I do have a very accurate ruler and I figure worst case if I mark where I am now, I can alway put it back to where it was when I started and send it off to the diff guy.

Also worked out why that wheel stud hole was reamed so large. Once I cleaned off the grim the was evidence of grinding and welding. Not only on that hole but most of the others. Looks like the opposite thread studs got someone along the line pretty good! Sorted now though.

Cranky, should I use the .006-8 as a minimum reading then? Also a really dumb question, how does the thickness if the ring gear help you tell it's ratio? Does the thickness of the ring gear indicate the diameter pinion and there for ratio?

 

[mopar12372]

i wouldnt touch it sounds good to me

 

[Cranky]

If the ring has 41 teeth and the pinion has 10, it's a 4.10 ratio but if the ring has 41 teeth and the pinion has 9, it's a 4.56. The deeper the gears the thicker the ring. A 2.76 has a very thin ring and the large diameter pinion. If you reduce the diameter of the pinion, you have to thicken the ring so it'll make up with the pinion as the side adjusters can't make up that much of a difference. Ring and pinions are made in matched sets and can not be mixed with others. Btw, dial indicators are not that expensive especially at pawn shops. Just make sure the plunger moves smooth and freely. I usually go with .008 if the rear is going to be drag raced and .010 if it's going on a dirt track car.

 

[HT413]

Next question, stoked as to find I have an LSD diff but it doesn't seam to be a stock unit. Can someone help I identify it?
View attachment 213746View attachment 213747View attachment 213748

Thanks all!

Looks to me like its a cone- type unit. Also, what center section do you have? If it's a 489 case, it has a crush sleeve and you can't just 'tighten it up'.

 

[Malicious]

Yup she's a 489. I was actually going to ask if it used a crush sleeve for preload tension. I swapped over to a solid preload tension sleeve on the 2-way power locker diff I run in my other car.

It also made me think; when the back lash feels a lot tighter then the when I twist the pinion yoke. It's feels like there is a lot more lack. Similar to my old diff before the solid preload sleeve.

So I measured the backlash and it was roughly .5mm or .019". That's with out a dial indicator obviously. It could be slightly more it slightly less. So community census, is that good enough for a weekend warrior?

Happy to rebuild it tighter later, but that will be 1-2 years off.

- - - Updated - - -

Cranky; I actually called around all the car stores in my area this afternoon before I posted and none had one, it was Saturday arvo here. All of the serious auto stores close at 12 on Saturdays and no Sunday trading so I'm out until next week if I want to get one.

 

[747mopar]

Keep in mind there is a preload for both the ring and pinion, if your yoke nut (pinion nut) is loose your backlash reading will likely be false. I'd buy a dial indicator, they can be had cheaply if you don't want to spend the money (try Sears or a local auto store). Get a good understanding on the whole thing and go from there. It's allot like the tapered bearings of your front wheels, you have to set the bearing preload on both ring and pinion (too tight and you burn them up and too loose will cause all kinds of wear and noise). The ring gear is adjustable from both sides to allow you to move the carrier back and forth for proper backlash. I wouldn't run it with .019 if it's supposed to be .006-.008 (that's more than double), like Cranky said I'd shoot for .008. I have a set of gears I'm about to do and if your still playing with yours I can post the process if you like. Mine is also a 489 that has 3.23s and will be a simple readjustment so it might be helpful, I might even do it tonight.

 

[Cranky]

Yup, it's a cone type SureGrip and .019 is too much. And I forgot to mention the marks on the carrier that shows where the pinion got into it and the marks look fresh. That happens when the crush sleeve gives up the ghost and you end up with a loose pinion. I also file the crush sleeve into the trash bin whenever I build up an 89 unit and use a solid spacer in it.

 

[Malicious]

Yeah ok so this is starting to get expensive.

Two questions: can I just adjust every thing reuse the current, most like, worn out crush sleeve? I realise it's not ideal, just seeing how bad it would be.

2: can you buy replacement sleeves, either crush or solid? My last was custom made ($$), I'm assuming though that they have to be machined into spect to suit the preload you need though. Is that correct or can I use an off the shelf unit?

747: thanks for the offer, if you could do that walk through that would be amazing. No stress if you can't.

Going to chase up some leads on a dial indicator today and see what I can find.

 

[Malicious]

Doctor diff to the rescue! http://www.doctordiff.com/8-3-4-minimum-installation-kit.html

I'll order this in next month and start studying the FSM.

 

[HT413]

Awesome. Cass (dr diff) also sells new clutch-type sure grips for a nice price. But beware, members here have said he's out of stock.

 

[Cranky]

When you use a solid spacer, you set up the bearing preload using shims. There are shims for setting the pinion depth and more for setting bearing preload. Like I said before I get rid of them and go solid and once they are used, they are usually not good to be reused. They can also crush more under severe use and that's what it looks like might have happened with yours.

 

[smb03]

geeze that ring gear looks to weigh 30lbs lol, talk about un-wanted centrifical weight

 

[747mopar]

O.K here's what I did with my 489 case. After everything was cleaned up it all checked out good so I only bought a new crush sleeve, seal and gasket for the job.

In this pic you can see how the ring gear is moved side to side to adjust the backlash and for setting bearing preload.



Since I'm putting the same gears back in I didn't mess with any of the pinion shims and just used a new crush sleeve. The book calls for 0 lbs of turning force (spinning the pinion) with used bearing so I just used a dial indicator to check end play. Crushing the sleeve is a choir (I used a BIG pipe wrench on a junk yoke and a cheater pipe on the wrench to crush the sleeve with it sitting on the floor), once I started getting close I took it a 1/4 turn at a time checking the end play every time and stopping once all end play was removed.



Your carrier will be different from this (this is the earlier clutch type). I'm thinking (hoping) the blue around where the shafts go is from heat treating???



Here is something you don't want to forget to do if opening up the posi unit, there are 2 sets of splines that have to line up before torqueing it down. Luckily I had an old set of axles laying around to do this. As you start tightening the bolts keep working the axles in and out to be sure they go in easy otherwise getting your axles in will be impossible (allot like using a clutch alignment tool).




Next I adjusted the endplay out of the carrier, again using the dial indicator. This can be a little tricky because you want the backlash close at the same time your adjusting the endplay so you have to keep checking the backlash as you go to be sure to tighten the right side. The book wants you to end up with .0005-.0015 backlash once you get all of the endplay out of the carrier and then adjust the nut on the tooth side (pushing the ring gear away from the pinion) to get the .006-.008 backlash "preloading the bearings in the process". Since I'm reusing my old bearings I thought that was a bit much preload and set mine up a little looser.



This is how you want to check the backlash.



I checked the wear pattern and it all looks good, this isn't the typical pattern you will see illustrated because these gears have already lapped in together making the pattern really even. If installing new gears this will look different.








- - - Updated - - -

Forgot to mention the book calls for torqueing 1 cap bolt on each cap and leaving the other finger tight while making the carrier bearing adjustments.

 

[Malicious]

Wow thanks for that 747. Seams pretty straight forward then?

A couple of questions, I have a small amount of forward and aft (end?) play in the yoke. Does that indicate the need for a new bearing?

Also the side bearings; if I'm going to go to this much trouble, whats involved in replacing them? they look like you could just pop them out easy in your pic, is that the case? or would I need a 'tool'?

Shot an email off to doctor diff to see what I'm up for.

On a side note, a local diff builder quoted me $930 to change the bearings, seals, solid sleeve and set it. So yeah I'm gonna go balls deep and try and do it my self.

 

[HT413]

Wow thanks for that 747. Seams pretty straight forward then?

A couple of questions, I have a small amount of forward and aft (end?) play in the yoke. Does that indicate the need for a new bearing?

Also the side bearings; if I'm going to go to this much trouble, whats involved in replacing them? they look like you could just pop them out easy in your pic, is that the case? or would I need a 'tool'?

Shot an email off to doctor diff to see what I'm up for.

On a side note, a local diff builder quoted me $930 to change the bearings, seals, solid sleeve and set it. So yeah I'm gonna go balls deep and try and do it my self.

Wow, the install kit including bearings is, what, $150? So the rest is labor???? I spent less than that including new gears, sure grip, bearings, solid spacer and seals, etc.

 

[Malicious]

Yup, welcome to Australian pricing! $750 for the rebuild, $180 for the solid sleeve. I might have considered it if I had a new crown & pinion and center but I'm reusing all that so if there are any issues with the center later on or I ant to change the ratio, I'm going to have to do this all over again. So may as well learn it now.