Converting to Posi

[HYRDGOON]

Having second thought now about changing gear ratio and looking at cost effectiveness vs. changing my 3:23 open carrier to LSD vs. swapping in a 3:55 or 3:73.

I don't know much about Differentials so could you guys give me an idea of the cost difference between parts as well as the man-hour difference in swap... Those 2 combined would give me an idea of how much more economically feasible it would be

 

[67 B-body]

I think your lowest cost option would be to watch the for sale section, and simply purchase a center section complete with the desired ratio..

 

[BeastlyBirdie]

If you have it far enough open to put in a limited slip/locker, you still have to mount the gearset on the actual differential, and set run-out, etc. So, your real question should be, "do I like the look of the gearset I have?" You didn't say what you have, 8 3/4, Dana, etc.

 

[Grabinov911]

I bought a complete new center section from Dr. Diff with an Eaton True Trac 3.55 when switching from an open 3.23. The outcome is great - handling is awesome -but it WAS expensive. I think all in I spent about $1,300. One thing to watch out for is the change from tapered bearing to "green" type bearings. Many of the new differentials only work with the green bearings. There is a lot of debate about whether the green bearings are appropriate for "handling" cars (as opposed to straight line drag cars). Some say they don't hold up. I DID switch to green bearings and they seem to be fine, but with only low miles so far. Time will tell...

 

[HYRDGOON]

I bought a complete new center section from Dr. Diff with an Eaton True Trac 3.55 when switching from an open 3.23. The outcome is great - handling is awesome -but it WAS expensive. I think all in I spent about $1,300. One thing to watch out for is the change from tapered bearing to "green" type bearings. Many of the new differentials only work with the green bearings. There is a lot of debate about whether the green bearings are appropriate for "handling" cars (as opposed to straight line drag cars). Some say they don't hold up. I DID switch to green bearings and they seem to be fine, but with only low miles so far. Time will tell...

Thanks for letting me know. I do like the idea of a whole new section and while it is a bit expensive at least it's NEW and should be headache free.. Have you found it noisy at all? I'll watch for any updates on your green bearings as you get more miles on the car

If you have it far enough open to put in a limited slip/locker, you still have to mount the gearset on the actual differential, and set run-out, etc. So, your real question should be, "do I like the look of the gearset I have?" You didn't say what you have, 8 3/4, Dana, etc.

It's an 8 3/4 and I need to get a look at the gears before any decision is made for sure.

I think your lowest cost option would be to watch the for sale section, and simply purchase a center section complete with the desired ratio..

Agreed and that's something to keep in mind. Truth be told I don't even know what case mine is yet I haven't gotten that far I'm just forward thinking because Diff's are a mystery to me. Also considered I'm in Canada so I get murdered on the shipping cost with the weight of a used Diff it almost makes more sense to buy new

 

[67 coronet]

unless you know how to set up a rear diff then purchasing an assembly is the way to go.by the time you buy the posi unit,gears,bearings,and have someone build it,you are better off and cheeper buying a full unit.you should be able to find one for around $600 or so if you look carefully and watch for sales.green bearings work great.i use them on all the cars i build.drag,street,and auto cross.never had any problems.switch em over if you need to with the new rear section.

 

[Seax440Dodge]

First thing I thought when I saw this thread was "Ooo he said the P word!"


But yeah, cheapest way IMO is get one used in the gearset you desire,yes, shipping will be high, but, like the others said, you gotta figure the cost of the suregrip unit, then the gearset, then the install kit price, then maybe a set of green bearings, then having someone set the gears up (if you don't want to mess with it... from reading your post I'm going to assume that you fall into the camp that believes that the rear end is filled with voodoo and black magic and maybe a rabid hampster)

 

[bm02tj]

Google niagara falls border mailbox and it will give you options to save shipping and brokerage

I use package express in Sumas WA but just about every border town has them

to make life easier call your credit card company and have there zip code added to your card so purchases go better

the service is no cost to join and only a fee when you have a package and is billed by weight and size

Bruce

 

[HYRDGOON]

First thing I thought when I saw this thread was "Ooo he said the P word!"


But yeah, cheapest way IMO is get one used in the gearset you desire,yes, shipping will be high, but, like the others said, you gotta figure the cost of the suregrip unit, then the gearset, then the install kit price, then maybe a set of green bearings, then having someone set the gears up (if you don't want to mess with it... from reading your post I'm going to assume that you fall into the camp that believes that the rear end is filled with voodoo and black magic and maybe a rabid hampster)

Lol I did use the "P word"

I'll be honest I just finished reading a MOPAR magazine article TWICE about decoding differentials and between I get lost in True Trac, Sure Grip, LSD, Poly Dent etc... Differentials and Clutches are the 2 things that absolutely make my head spin. And you are correct in fear of getting bit by a rabid hamster the Diff will be handled by someone else.

This is my attempt at trying to further understand my options and have a better clue what I'm speaking about.

So without making myself further look like a fool and dumbing this down for me (My car isn't even here for me to go look right now)

What I would need to know before even being able to order a new center section? What is there now (i.e. 742, 741?) which can be decoded off the centre section stamping as I understand....

 

[bm02tj]

If you buy new go with the Trutrac it does not need special oil and has no clutches unless you are drag racing then go with a locker

Bruce

 

[HYRDGOON]

If you buy new go with the Trutrac it does not need special oil and has no clutches unless you are drag racing then go with a locker

Bruce

Thanks, It's a driver

 

[HT413]

I've seen plenty of 3:55's go for like $500 to $600. 3.73's seem to be a bit more rare but are out there. Buying a new setup will cost $1200ish but you can recoup maybe $200-$300 by selling your open unit

As far as 741, 742, 489... look at the center section on the driver side right near the u joint. The casting number is pretty big and easy to read and ends in 741, 742 or 489. (there are a couple other lesser known ones but those 3 are 99% sure to be it.) Finding a nice 741 will save you a couple hundred $$ because people feel they're the weakest of the bunch but unless you race it with some big slicks, it don't matter at all.

 

[MoparBill]

I live in the Buffalo NY area; if it'll save you $$ you can ship it to my place. I can meet you on this side of the border near the peace bridge.

 

[BeastlyBirdie]

I would go true-Trac not a Detroit style locker, unless you have experienced a non-peg leg rear. Just my opinion, but having run lockers on the street, they can be ummm, interesting, lol. The true-Trac is reliable, quiet, and as good as a factory diff. Detroits and spools are fun, but much more race oriented.

 

[HYRDGOON]

I've seen plenty of 3:55's go for like $500 to $600. 3.73's seem to be a bit more rare but are out there. Buying a new setup will cost $1200ish but you can recoup maybe $200-$300 by selling your open unit

As far as 741, 742, 489... look at the center section on the driver side right near the u joint. The casting number is pretty big and easy to read and ends in 741, 742 or 489. (there are a couple other lesser known ones but those 3 are 99% sure to be it.) Finding a nice 741 will save you a couple hundred $$ because people feel they're the weakest of the bunch but unless you race it with some big slicks, it don't matter at all.

Thanks that helps a lot... and just so I'm clear if I have a 742 now I would order a new TrueTrac 742? I hear talk of spline counts etc... I guess what I'm asking is what information is necessary to know before being able to order a replacement?

I live in the Buffalo NY area; if it'll save you $$ you can ship it to my place. I can meet you on this side of the border near the peace bridge.

Thanks Bill, that's a generous offer! If I do take you up on that make sure we'd have enough time when I'm picking up to buy you dinner and have a couple beer!

Mike

 

[Cranky]

Of those 3 cases, the spline count on the axles are the same so the LSD unit as long as it's bought for the 8 3/4 will work.

 

[HYRDGOON]

Of those 3 cases, the spline count on the axles are the same so the LSD unit as long as it's bought for the 8 3/4 will work.

Thanks Cranky! I feel like I'm getting more better smarterer....errr...

 

[BeastlyBirdie]

742/741/489 all are for ring/pinion

 

[HT413]

I literally just brought my center section over to a local guy's house for him to swap out my gears. I have a 489 unit with the auburn cone type sure grip. I let him buy all the parts because I didn't want to bother with getting the wrong stuff and shipping it back/wasting time, etc. he's gonna machine the cone (it's an oem 40+ year old gear set) and it'll be good as new (better lol, since it'll have the crush sleeve eliminator and 4.10's instead of the 3.23's it has now).

Really, the only parts to buy are ring and pinion, sure grip carrier and an install kit. The clutch type sure grip is more popular and desirable because it is rebuildable. But the auburn cone type is just as good and is really rebuildable too, just only a couple times so I understand. But unless you're gonna race A LOT or put 100k miles on it, you'll never be rebuilding either unit. The clutch type will have a higher resale value but why would you sell it?

The sure grip unit is swappable to any 8 3/4 rear (741,742,489) but gears and rebuild kits are specific to the 741, 742, 489.

 

[HYRDGOON]

Now I feel like I'm getting somewhere

So just what I gather as an idea of cost wise from Dr. Diff site... Housing Gasket & Seal $25, Installation Kit $43, Ring & Pinion $185-200, and 8 3/4 clutch type sure-grip $375.... comes to about $730 plus taxes etc...

So vs. a new complete centre section for $1300 this seems more feasible... Unless the installation of the components vs. installing a new centre section would take more than 12 Hours @ $50/hr


Thanks everyone for your replies I actually have a better idea now of the breakdown of components and what goes with what


OOPS! I didn't compare dollars to doughnuts! add $200 to $730 to compare and Eaton True Trac to a complete centre section... so difference of $400