OK guys and gals, this is something I know very little about so I ask of your assistance.

With my new van, I've been going over and updating a bunch of little odds and end things but I'm looking bigger now.

I'm thinking about changing my gear ratio and adding a posi rear to boot.

Two questions I have that maybe you can help with is which brand of posi should I go with. I see SummitRacing has two, Eaton and Strange. They both are simarly priced but and I see no major difference from their descriptions.

Also which gear ratio to go with. People are telling me 3.42's are a good all around gearing but I prefer the number of 3.73 in my head.

I'm not too concerned about gas mileage, more about giving the van some snot off the line. The motor is a tuned 305 with nothing crazy special but a couple of nice pieces to give it its extra get up and go... now I gotta get that power to the wheels.

Another thing I see is Clutch Operated and Cone Style... I'm assuming Cone is sronger but noisy??? I'm not looking to do massive burnouts but I would like something that is strong versus just an OE replacement.

Any help is appreciated... thanks

Both brands are very good. I've always used strange, mainly because back when I bought this type of thing they were the best. I believe Eaton product are just as good now tho.

The 3:42 gears would be a better choice if you plan on going to truckins (I hope so). The 3:73 will give you a bit more umph off the line, but will buzz the motor more on the highway. The height of the rear tires will make a difference as well. The taller the tire, the less the ratio will be. Also with a taller gear 3:73's you need to make sure you have enough rubber on the pavement as to not sit-n-spin.

As far as the clutch or cone settup. I'm assuming the cone is more of a "lockup" type unit. The clutch is like a limited slip posi. The new ones are both quiet. The biggest thing to remember is to use the right gear oil. I prefer the lock up type, but it will wear your rear tires faster than a limited slip type.

Thanks for the Info Ken, shoulda IMed you directly like the norm.

And yes I do plan to come this year with my new ride that I'm planning out now. Thats part of the reason, I'd like to keep up in the runs, the gearing I have now is for the birds. Its great on gas but living where I live the hills are killing me.

I guess its going to be the 3:42's then, I just dont want them to be wimpy on me.

Now looking on Summits site, its seems I can piece together a Posi unit from either make and get the Gears seperately. Both say they'll fit my Application. Is this true though? I know I can get a whole new rear end complete from the wrecker but I'd prefer new if the cost doesnt kill me. Ideally I'd like to keep what I have and just plug in the new parts in the existing pumpkin. Do I need new axles and bearings as well. I dont know what the gear spline they're referring two when looking at the Posi. They say 28/30, is this what I have already or anyone know how I can find out.

I exhaust myself too... sorry bout that. ;)

First it is best to find out what you have. There is no sense in ordering gears if they are the same as what you have. Like I said above, your tire height will make a difference too.

To find out what you have, if the previous owners can't tell you is to pull the rear cover. Spint the rear till you find the numbers stamped on the ring gear. This will tell you all you need to know. If you can't find the numbers, count the number of teeth on the ring gear and we can come close to what ratio they are. The 28/30 is the number of teeth (spline) on the axles. Sorry, not a Chevy Guy, but I'm assuming the 28/30 means you can have 28 spline or 30 spline.


Again best to find out what you already have first.

If your using a OD trans 700R4 or a 4L60 your rpm with 373's at 70 MPH will be about 2300 thats not to bad I say about because tire diameter comes into play.

There are a lot of RPM calculators online I had one but didn't keep it in the favorites. I think the final gear ratio of the OD box is .076

As far as my wheels go they should be stock rolling diameter or close to it. I'm a big fan of running that way, I know anything can be adjusted but still. I'll be running 17's when i get my summer wheels but overall they'll be the same diameter as the 15's I run now with their stock tires.

I havent a clue what kind of tranny i'm running though I believe it doesnt have an OD.

We already have the backlash tool and according to my friend anything else we'd need. Seemingly I'm at the point that I can go ahead an order other than not knowing the spline size whether 28 or 30. I wanted to know that before I ordered to keep the rig on the road as long as possible with as little down time as possible but that might be unavoidable.

aS LONG AS IT WAS NEVER messed with. I would still recommend pulling the cover. You can do it in less than an hour. Will save agrivation in the long run. If you order the wrong one you will have to send it back and wait for the new one. If you clean the housing well, you can save the old gear oil to put back in till you do the swap and you can just use some silicoln on the cover for a week or so without any leaks.

There has been alot of updates done to this van in the past so I have no confidence in what the tagging would say.

Sounds like we'll be pulling the cover, checking and counting.

I'm weighing my options to see Wrecker vs Rebuilt, Performance vs OEM etc.

Thanks everyone, I'll let you know how it works out. I'd like to do it all before the summer the only down side is my snowtires. I'd hate to eat them up laying rubber down at the traffic lights with all the little Civic kids. ;)

I called Summit and asked a few techs at work and they all say that a GM van is 28 spline no matter what. I told them they owe me cash if they're wrong.

Checking Summits site I cant find a 3:55 gear setup to fit my application. Only 3:73's and 42's. With no OD tranny again, I think 3:42's it is then.

Thanks for all the help, I'm hoping to have this all done in the next few months. I'll be taking massive pics since I dont know what the hell I'm doing it should be funny. ;)

I wrote a post about a month ago

http://www.vannin.com/threads/ubbthreads.php?ubb=showflat&Number=80410&page=1#Post80410

( See 407 stroker ) about chevy 10 bolt rears. Most drive line parts break on the launch. If your not going to put 12" slicks on the van and try to pull the front end off the ground it might hold up. Consider the fact that the its a van and 65% of the weight is in the front. Most of the time you will be spinning the tires. You won't be hitting the NOS until second gear. Before you spend the big bucks for a Detroit locker and a Ford 9 " carrier you will have to have shortened, have a look at this site. It has some good info on the 10 bolt.


http://www.chevyhiperformance.com/techarticles/48518_posi_10_bolt_upgrade_install/index.html

After I posted this, we have had some real nice weather here in the east so I took advantage of the sunshine and got a few things done to my heavy full size Beauville window van. Swapped out the TBI unit with a bored and polished throttle body. Fuel pressure adjustment via an adjustable regulator I added to the TBI unit. A fresh set of plugs. A fresh fuel pump. It was due to be changed out anyway had 115k on it. ( thanks for the help Josh ) Bumped the timing a few degrees. and so on. With the 8.5 10 bolt rear and the OEM governor style posi, it lock up and spin the tires when I nail it from a stop. I have some decent sized BFG's on there too. I don't expect to be doing that everyday and I certainly don't expect it to hold up if I was. I said before in a post. The factory Chevy governor posi is good set up not to be overlooked for a daily driver.

ps:

In case you havent seen one of these rears, the difference between a convential posi and a governor style carrier is that the governor via a centrifical arm moves out when you have a free wheeling side gear ( one wheel spinning when your in mud or snow ) and then engauges the posi clutches. All other times it operates as a regular open end rear. no noise on turns no posi clutch wear during daily driving. This is just my opinion. I hope you like the idea.

My previous, and possibly wifes new one if I get her to agree to trading our truck even, it has a 95 305 TBI, 400 turbo but a 3.07 gear ratio, I'll really be looking for a change, swap in a lower one from the junk yard. It felt so gutless being a conversion hightop, I'd look into upgrading to a 700R4 in the furure.

If you haven't swapped out your rear end gears yet, I can highly recommend the 3.73's with the overdrive trans. I ran up to LMDW a few weeks back and it was my first highway trip with the 3.73 gears in the truck. It ran great at 75 in OD with a light trailer. The van was begging to be let out but I have never seen so many cops on the Thruway. Here is the real kicker, the fuel mileage was the best I have ever had from any of my TBI motors.

I have 2:73's in my 1978 Chev with a 3 speed Auto...runs at 70 no prob, and about 14 mpg
In the Astro, when I blew the differential up, I went from 3:55's down to 3:23's ....lots better mileage.
In the Dodge, I have 3:90's 0-60 in 6 blocks, but runs all day at 70.00 with about 14.5 MPG
The Aerostar with a Flat Head, 8 inch posi with 2:90's so far

In my lawn tractor, I have 8.20's an it get terrible mileage in 3rd gear with the blades engaged. Eh