Bolt-on differential locker?

So, one of the higher-cost items in my Challenge budget at the moment is the posi rear end (I started a thread a ways back debating whether it was worth the cost or if the money would be better put elsewhere). There were a number of things put forward, and I'm still seriously considering the more radical of them (an Explorer 8.8 posi rear end). However- once I got through with everything that would be necessary to make that work it would still be pushing 2/3 of the cost of my current bolt-on posi rear (albeit with better brakes and a more robust rear end overall), and I'm kind of scraping to try and build the engine up as best I can.

One of the suggestions made by one of my friends was to take the (cheaper since it's not posi...) other rear end that I have and weld up its diff, drive down on the open (with a more highway-friendly gear ratio) rear end, and swap the welded-up rear in for at least the drag day. This isn't a bad idea, but it would involve a solid bit of work in swapping the rear ends out, re-aligning everything, bleeding and checking out the brakes, etc.

So I got to thinking (which is rarely a good thing). Shouldn't there be a way to make a bolt-on setup to lock up the rear diff? Something along the lines of taking another couple of gears pulled from a diff and locking them into place so the rest of the gears can't rotate like they normally would? I'd think something like this could be fabbed up on the cheap and installed in fairly short order and then removed in even less time.

Thoughts? Has anyone here tried something like this before?

I think what you're looking for is called a "spool" and swapping it out is just as much work

Are you talking about installing a locker when you need it (like a detroit locker) and running an open diff the rest of the time?

I think that's very possible!

You'll have to pull the axles out a bit on either side to get the carrier out, but I think you could do it without having to re-bleed the brakes etc... May take some practice to become proficient though.

Ashyukun wrote: So I got to thinking (which is rarely a good thing). Shouldn't there be a way to make a bolt-on setup to lock up the rear diff? Something along the lines of taking another couple of gears pulled from a diff and locking them into place so the rest of the gears can't rotate like they normally would? I'd think something like this could be fabbed up on the cheap and installed in fairly short order and then removed in even less time. Thoughts? Has anyone here tried something like this before?

There is such a thing as electric lockers in the 4x4 world. no idea if they are budget friendly (might be if used!)

There are electric lockers, air lockers, and cable-actuated lockers. The air lockers sure as hell aren't budget-friendly, cable ones aren't a whole lot cheaper, and the electric ones are basically rare relics of the past because people got fed up with how E36 M3ty they were - not sure if it's a problem with the technology itself or a case of bad reputation ("American Diesel syndrome").

There are electric lockers, and air lockers. Rarely are they budget friendly. Toyota has some factory electronic lockers. Wonder if it would be easier to do the old off-roader trick of dragging the rear brake to equalize pressure on either side.

Diffs with the removeable center section (ford 8-9") - have 2 centers - one welded up/spool the other open. Welding wire is cheap - 8/9" spools are only about $25. Swap in when needed. Still a pain, but you wouldn't have to do brakes every time. On the spendy side - air or electric lockers - which now makes me wonder if you could patch up a broken air/electric locker on the cheap.

No, I'm aware of what a spool is, and I did consider it- though it would definitely require a good bit of work since from what I understand I'd need to transfer the ring gear too.

What I'm thinking of is something that would bolt (for lack of a better word- I'd figure bolts would be involved though) on to the open differential without removing it from the rear end and lock the gears from turning. Something like welding another of the gears to a steel plate that would bolt through to the other side of the carrier and prevent the gears that spin in the carrier from turning and functioning as a differential.

sachilles wrote: Wonder if it would be easier to do the old off-roader trick of dragging the rear brake to equalize pressure on either side.

For the record I have never even been able to budge a stuck 4x4 with this technique. For destructive last-ditch techniques, moderate clutch kicks are much more effective.

Didn't GM offer electric lockers as factory stock in some of their trucks? I think it was called the g80?

Would that be a junkyard option?

GameboyRMH wrote: For the record I have never even been able to budge a stuck 4x4 with this technique. For destructive last-ditch techniques, moderate clutch kicks are much more effective.

Then you need to practice more.......or fix your rear brakes.

Where have all the 7.5" lsd rear ends gone from the third gens and s10s......should be available cheap.

Don't take this the wrong way but you're over-complicating your build by a lot. Although a drop in locker would be cool you have to consider the cost to machine it, balance it, test it, and install it. (on your back, in a parking lot, no less) There is also a major safety concern for something that is enduring drag strip forces and spinning at 100 mph. (hopefully).

I said it before but... Cross reference all of the GM cars that used that 7.5" rear (F-Body comes to mind). Go to the junk yard or interwebs and buy a carrier with limited slip for cheap, like $50 max. With any luck it will have deeper gears already with it. Some S trucks had 3.73 or 4.10 gears stock. Get rid of the $300 rear end. That's WAY too much money to be spending on that.

The Explorer rear end is cool but you have to do a lot of fab work on it, not the least of which is drilling axles to fit your GM bolt pattern. The added strength probably won't come into play with an automatic trans equipped car.

My $.02

hrdlydangerous wrote: I said it before but... Cross reference all of the GM cars that used that 7.5" rear (F-Body comes to mind). Go to the junk yard or interwebs and buy a carrier with limited slip for cheap, like $50 max. With any luck it will have deeper gears already with it. Some S trucks had 3.73 or 4.10 gears stock. Get rid of the $300 rear end. That's WAY too much money to be spending on that.

The main problem with this is that the F-body and S-10 diffs would require my replacing the axles as well- IIRC all of those are 28-spline axles whereas the G-bodies used 26-spline axles. I believe that the S-10 & F-body rear ends are different widths than the G-bodies were too, so I'd either have to have the axles cut down or get custom rear axles (only G-body that used the 28-spline from my memory is the Grand National, and I've never seen one of those in a yard...) as well which would again be $$$. Making the F-body or S-10 rear end work would again require a good bit of fabrication since none of them have the same mount points.

Well that's just dumb on GM's part but you're right. 26 spline axles. That stinks.

In light of that, I'd leave the open diff in and buy a set of used slicks for the drags and possibly a set of deeper gears. That is still cheaper than using the $300 rear.

hrdlydangerous wrote: Well that's just dumb on GM's part but you're right. 26 spline axles. That stinks.

On this you'll get no disagreement from me. It would be MUCH easier had they just used the extra 2 splines on the G-bodies.

In light of that, I'd leave the open diff in and buy a set of used slicks for the drags and possibly a set of deeper gears. That is still cheaper than using the $300 rear.

I'll be running R-comps for the AutoX and had planned on using those on the drags as well. Slicks would be nice though if I could find a set. If I end up using the 700R4 and not the THM350 deeper gears might work- but this thing has to travel 700+ miles each way to and from Gainesville, so TOO deep of a gear and it will be horrible on the highway.

Yes, this thing has lots of compromises and limits. Which is why I'm trying to think outside the box a bit..

Thinking out load.....I wonder if thicker gear oil might do the trick for a one time use like the drag strip. Drain diff after autocross, refill with much heavier stuff.

I have seen "lincoln lockers" done in a less permanent way by filling in most of the gear teeth on the spider gears(leaving spots for the side gears to mesh), and reinstalling them. Depending on the rear end, you could swap spiders pretty fast.

what you are talking about is made by Powertrax.

they make a limited slip and locker that replaces the spider gears in your open diff, eliminating the need for setting up lash and whatnot, the carrier never leaves the case.

I have had the Powertrax before on an S10. It was an early version without the soft locker option. It worked very well and held up to some abuse. They have been around for a long time and you could probably find a used one cheap. You could install it and drive the car to the challenge, my S10 was my daily driver and I put 50,000 miles on it with a powertrax equiped 10 bolt rear never had an issue, and I abused it.

you're making this too complicated.. find a good posi rear end out of an 87 or 88 Monte SS with the G80 posi option.. this will give you the slightly bigger 7.625" ring gear, 28 spline axles, 3.73 gears, and a posi . the Monte SS is not rare by any means, and most yards don't know or care that the rear ends in them are any different than any other G bodies, since they are just scrap to them.

What you are looking for is called a "mini spool". They replace the spider gears and lock the diff. Regular spider gears and mini spools swap out. A full spool won't swap out without pulling the diff apart, as noted prior.

Richmond Gear sells a Mini Spool for $90 but you may need C Clip Eliminators (not a bad idea anyway)

Mini spools are not for street driving or running with C clip axles but should hold up fine for a pass or 2 at the track as long as you are not on full on wrinkle walled slicks, launching a 3500lb, 750 horse car off the trans brake with a 150 shot to get it moving.

http://www.ebay.com/itm/7-5-GM-10-Bolt-Mini-Spool-26-Spline-Camaro-NEW-/370673176909?hash=item564dd7d14d&item=370673176909&pt=Motors_Car_Truck_Parts_Accessories&vxp=mtr Boom!

You could probably make one cheaper if you are a competent welder and have access to a lathe and a mill or big tight drill press and some reamers.

Basically take apart your rear end. Measure the distance between the faces of the side gears on the axles with the diff completely together (inside micrometer, needs to be precise) then pull out the spider gear pin that holds the smaller spider gears in place. Measure the inside width of the carrier and the diameter of the pin. Now make a piece up on your lathe that fits where the spider gears used to be and allows the pin to slide through (tightly, no slop). Now weld the extra set of side gears that go on the axle to the piece you made to take the place of the spider gears. Leave enough room to reinstall the C clips.

Now you can swap from a locker to an open rear end by just pulling the rear end cover and brake drums, push the axles in, pull the C clips, slide out the existing spider gears and pin and side gears, put in your home-made mini spool, reinstall the axles and C clips, put the drums back on, and put on the rear cover.

If you decide to go minispool on your car, do yourself a favor and bring a complete spare rear end carrier and gears. When it blows up at the track, you can at least swap the parts to limp it home or run it around the autocross course. Sure, you should set backlash, pinion depth, etc, but for running around the cones a few times or a one-time trip home, you can live with some gear whine.

Why not just weld the diff and then throw on some taller crappy tires for the drive down. There's no hit to the budget if you don't use the tall tires. They will drop your revs on the highway and if I scrubs a little in the turns, it doesn't really matter. I assume in your 700 mile trip, most will be on the highway where a welded diff won't really matter. And if you air up the tires enough, they should slip without too much stress going through the axles.

mw wrote: Why not just weld the diff and then throw on some taller crappy tires for the drive down. There's no hit to the budget if you don't use the tall tires. They will drop your revs on the highway and if I scrubs a little in the turns, it doesn't really matter. I assume in your 700 mile trip, most will be on the highway where a welded diff won't really matter. And if you air up the tires enough, they should slip without too much stress going through the axles.

I have customers who drive on the street with spools with no issue. One of them drives on 18" wide DOT slicks, roughly 5-6k per year. They drive perfectly fine.

Make like a FWD guy and don't back up and turn at the same time, and you won't break anything.

Hell, my VW has vacuum-operated locking diffs (a shift collar locks one output to the side of the case, it's pretty slick) and I drive with two out of three locked on the street. World has so far failed to end yet.

Hungary Bill wrote: Didn't GM offer electric lockers as factory stock in some of their trucks? I think it was called the g80? Would that be a junkyard option?

G80 is a generic locker code IIRC. Most of the ones in trucks are called a gov lock, its basically a REALLY stiff LSD that acts like an open diff unless a wheel starts spinning and kicks on a governor, they have a lot of lag and blow up when abused. Works great in a DD work truck though.