I have a 1987 formula, with the 3.42 (possibly 3.73) open rear end with drum brakes.

I know the factory rear ends went up to 3.73 posi. Trying to do some research for where to get a 4 series gear, either 4.11 or 4.10 (not sure which is the correct one), but i dont know where to look.

This is in preperation for a future T56 swap.

$$$ is always an issue, so i would like a good ratio of the least $$ for the best reliability. I want it to be a simple swap, ie: no cutting or hacking up of vehicle necessary, with 3rd gen back spacing of wheels. I already have 17" wheels that i bought for the car, so i cant go with a 4th gen rear.

Is this only an aftermarket option, or could i find something in a junkyard, or...?

Plz help.

 

For the 7.5" rear end there's only 2 series or 3 series.
2 series is the 2.73 and 3.08
3 series is 3.23 and up.

4.10's for this rear end.

Look for S-10 or Astrovans in the JY, the 4cyl variants sometimes had 4.10's. I couldn't find any though, so I went to 3.73's. But search for my thread on this topic, many people (mostly Fast355) posted axle codes so help find them.

 

Thx Sonix. CRAP i wish i knew this earlier, i just junked an Astro earlier this year. Will the rear end be a direct swap?

 

No; just the gears.

Or, you can just buy a new set, and be done with it. They're widely available. Moving around used gears with unknown miles on them and so forth, is somewhat risky. Gears are cheaper when you only buy them once.

http://www.drivetrainspecialists.com...5/randp-1.html

Plus, you'd need a "gear install kit", maybe $100 (which you'd need for used gears as well); and I'd stongly suggest a crush sleeve eliminator and a "girdle" type of cover.

http://www.drivetrainspecialists.com...ll-kits-1.html

http://www.drivetrainspecialists.com...duct-1781.html

http://www.drivetrainspecialists.com...-covers-1.html

 

Thanks for the info sofa, also, what if i wanted to go posi or locker? Obviously getting more expensive, but, what options would i have for that?

 

Here's what I have in mine.

http://store.summitracing.com/partde...%2D19599%2D010

http://store.summitracing.com/partde...SAG%2DEV10%2D4

Those will of course go into any year of housing, and will make it a 28-spline setup with FAR FAR better axles than stock 28-spline ones.

There are other choices; but I sure wouldn't go putting high-ratio gears into a weenie 26-spline setup, if you expect to have any traction (for example, a "locker" of any type in your existing carrier). If you "harden" the R&P against failure with the solid spacer and girdle cover, you'll soon identify the next weak point in the rear; which will be, you'll twist the axles off right where they slip into the carrier's side gears.

 

For another option, I am getting the Detroit tru-trac, $375. A similar design to the Torsion system in 4th gen cars. No cones to wear out, very strong helical gear setup.

 

Thanks for the info guys. Im gettin the idea of where to look.

Im not a cheap person, actually ive already spent way more than what i was going to in my car, just because i beleive when something is done, it should be done right. But budget is always and issue, and the least $ for best performance dont always go hand in hand.

Im liking sonix's sol'n but your sol'n also looks like a pretty good investment sofa.

I was looking at i think "strange" or possibly richmond, and i thought i saw a complete assembled ford 9" assembly for our cars for around 699 or so? But the setup your showing is easily more $ just for carrier and axles. Is it just higher quality? Or is it because its made to fit with the stock setup?

 

The "complete assembled Frod 9" assembly" at that price ISN'T a complete assmebled etc. for these cars. That looks like just the HOUSING.

Once you get that, then you add a center section, gears, carrier, bearings, axles, and brakes.

The full Frod 9" package for one of these cars is about $2200-2500 typically, depending on what size axles you go with, what pinion bearing support, etc.

A GM 12-bolt package that bolts into one of these cars is roughly the same price.

Both are very heavy-duty rears, that will stand up to about anything an even remotely nearly "streetable" car will hand it. The 12-bolt weighs less, takes less power to turn, and is overall a somewhat better fit to the chassis in several ways; but the 9" is MUCH faster to change the gears (you just have another gear set up on another carrier in another center section, and swap that; that's how the NASCAR guys swap a gear in 25 laps), and has better (wider) aftermarket support.

In both cases, just picking one up at the junkyard, leaves you A LONG WAY from having anything anywhere close to the Strange / Currie / Moser type of package. Needless to say, a great deal of fab work will have to be done to either to get it to fit into one of these cars; and a junk 9" isn't a whole awful lot "better" than the 10-bolt you've got now. The 9", as it comes from Frod, isn't what's so great; rather, it's all the AFTERMARKET SUPPORT for it as a PLATFORM that makes it so popular.

You can do EVERYTHING that can possibly be done to one of these 10-bolts for about $1000-1200. Sounds cheep; but in the end, it's still just a 7½" 10-bolt POS, a time bomb with an uncertain length of fuse. But at low power levels with not-so-great traction, it stands a good chance of lasting for a long time. But nothing about any of that is certain.... it's just a crap shoot.

There is no one universal "right" answer. Everything is a trade-off. Evaluate YOUR situation and needs carefully and honestly, and pick the option that suits YOU.

 

Ok thanks for pointing that out sofa. Upon closer inspection, yes its just the housing. The strange axles are $239/per and the summit link you showed me are only $209 or so.

With a total of above $2k (which is more than what i paid for my car), i dont think that is entirely worth it for me.

My situation is, i definately need a new transmission, and overdrive is a preference. So for a little more than it would cost to get a 700R4 prepped, i could spend it on a T56, to handle a roughly 400hp/tq motor.

Because the final gear is so low in those, i was seriously considering a 4 series gear. However, i definately dont want to spend more than about 600-700 on it.

My priorities for the rear end are,
1) posi
2) ease of swap
3) 4 series.

Perhaphs the used market, or even the 3 series posi is in store for me after all.

Thanks for all the info, i found search revealed alot of stuff about how to actually swap in the gears, or technical problems, but not enough info on where to shop.

 

In my opinion the best for the money is an open carrier with a powertrax or detriot ez locker. Open diffs are easy to find and super cheap. They are usually not beat to death. So you hit up eBay or the JY and find one for about $80 bucks. Get the install kit from summit $110 or so, then get a powertrax $350 bucks new or find a used one from a 4x4 site (they love them) then install (easier said then done). I like the fact you don't have a chance to burn out the clutches or cones and no spider gears which are the weak point.

And I think not suing a crush sleeve would make the install much harder. No fine tune adjustment. I guess that means you have to be good! lol!

 

Alright, seriously meow, what's a 4 series rear end?!? You're the only person i've ever heard make mention of that. Do you just mean 4.xx ratio? That's still 3 series AFAIK.
4.10, 4.56, etc, all 3 series.

I've put a good chunk of change into my 7.5" 10 bolt, summit girdle, detroit tru-trac posi, ratech solid pinion spacer, JY 3.73 gears (gears don't really wear out, it takes a while... as long as they aren't cracked or visibly worn, they should be ok to use...). I broke the stock posi, that's why I needed the tru-trac...

I think a beefed up 7.5" should satisfy your needs. Another option is modifying a GM 8.5" 10 bolt. If you can weld, that's a relatively easy JY swap. Right width, right bolt pattern, just needs brackets. There is an aftermarket following for the 8.5" 10 bolt, a bit more than what exists for our 7.5". These are the ones found in 2nd gen camaros.

EDIT - A solid pinion spacer (as opposed to a crush sleeve) comes with shims. Same install method.

 

hm... Well i THOUGHT i knew what i was referring to, but i guess not.

What i meant:
4-series: ----> Gear sets that have a ratio beginning with 4. ie: 4.11, 4.56, etc... (am i wrong?)

Rear end: A complete assembly, axle to axle. Preferably something in a housing. I dont really know how to do the swap for gears, but icould learn if necessary.

In any case, whats your cost so far into the rear end, just for parts?

 

Yes, you're wrong.

I mentioned above, 3.08 is still a 2 series, after that it's all 3 series.
Let see here....

True-trac (summit) - $375 (for 26 spline)
install kit (summit) - $90? (all bearings, seals, etc)
summit girdle - $230
JY gears - $35 (3.73, didn't bother searching for 4.10's)
Ratech solid pinion spacer - $75 (they sell it for $21, but since i'm in Canada I got RAPED by UPS on that one...)

I welded around the tubes to the center section as well. I also bought a carrier shim install tool ($40), and a 1 1/4" socket, etc. I don't really count tools though.
I think that's it. If I break the axles i'll get the superior ones off summit. If I break the gears, I can replace them myself with another JY set. Aftermarket ones aren't much stronger than the stock ones. If I really start shredding this rear then i'm going to fab up an 8.5". I just don't want to do that yet, I have dropped $800 or so on this rear, i'd rather not that be a waste....

 

There's not a "4 series" in this model of rear end. There is in some, but not these. They only come in 2 or 3 series.

The 4.xx gears are actually "3 series", as far as fitment is concerned. Just think of them as unusually large values of 3.

 

You can get 4.10 gears (or most other ratios for that matter) for both the 2-series and 3-series carriers. I had a set of 4.10s for a 2-series for awhile, but never got around to using them.

 

I bet THAT gearset weighs a ton.... the ring would have to be about 1½" thick!!!

 

It is, that ring gear is very.... robust

Doesn't look like it would ever break though (though thats not the 7.5"s weak spot, so its a moo-point)