Stealth Trans w/Gear Diff

[XLR8]

The right case has been updated. I've added a counter-bored screw hole inside next to the diff gear. This will align with the existing bottom hole in the motor plate eliminating the need to modify that part. The original screw hole remains but has been resized to allow the case halves to be screwed together. Many thanks to Jeff for this feature.

[XLR8]

The main drilling template is finished and has been used to make a set of test plates.

Hole locations and gear mesh is good.
On to the prototype gear cases for running tests.

[XLR8]

With most of the machine work completed on the prototype cases, I thought I’d pause here for an update and step you the machining process.
As many of you who have ever made anything on a lathe or milling machine already know, most of the time is spent on equipment setup so, rather than making only one part, you might as well make multiples while the machines are setup. As it happened, four case halves fit nicely on my blank so I’ll be making four complete cases. This also works to my benefit because I usually make mistakes and some of these will likely end up in the trash. I just need one good pair to perform the running tests.
Here, I’ve drawing outlines from the template so I can stay oriented and I’ve drilled the alignment pen holes, followed by the screw holes and finally the bearing counter bores.

Next, I'll need to make room for the gears. I didn’t have the correct size cutter to make the large clearance hole for the diff gear so I’ve started with a smaller cutter to remove most of the material then…

I’ve setup the drill press like a milling machine to cut a larger hole. Here I have the cutter positioned slightly off center of the drill press table, then by loosening the table’s center post clamp slightly, I’m able to carefully rotate the table and enlarge the hole. It takes some patience to get it right but it works pretty well. The aluminum plates are just clamps to hold the work piece tightly to the table (they’re bolted to the table from underneath).

Here I’ve planed the material to the correct thickness, cut each part to rough size using a band saw, then I’ve used a flush-trim router bit combined with the aluminum drilling template (shown in the first photo) to trim the parts to their final size. The design calls for the right case half to be 0.625” thick and the left 0.500” thick. I got lazy and made both case halves 0.625”. The added material on the left case will only add strength and won’t in any way affect fit or function.

As it happened, I’ve used a tool path diameter on the “milling machine” that was larger than was necessary to provide clearance for the diff gear and this has led to some breakout on the bottom of the cases. This won’t happen with the 3d printed cases. I’ll cover the hole with a piece of packing tape to keep dirt out of the case. The important thing to note here is that the diff gear doesn’t protrude from the bottom of the case.
At this point, I couldn’t wait to perform a test assembly. With the thicker cases comes the need for longer screws which I don’t have so I’ve improvised by using some threaded rod and nuts.

So, the final step is to drill the screw holes for mounting the case to the chassis and the top brace plate and its spacer.
I’ll create templates for these holes so that I don’t make any mistakes.
As I’m writing this, Hurricane Sally (or what’s left of her) has moved out of the state headed toward the Carolina’s and the weather here today is absolutely outstanding. It’s looking like I’ll be able to get some test runs in over the coming weekend.

[GoMachV]

Glad to hear Sally is leaving. We are still deep in smoke here, enough that i am not working in the shop at all.

That case is looking great! Really nicely done!

So, the final step is to drill the screw holes for mounting the case to the chassis and the top brace plate and its spacer.

This is where I ran into the most trouble- that massive diff gear is right where my screws want to be. Well, couple that with the fact I really wanted to have both sets of holes in case an A stamp was being used, or a C stamp that lacked the countersinking on the 6 gear holes.

[radioactivity]

Doug

Very nice.
Really setting the bar high for innovation and creativity.
Just love it!

Chuck

[jwscab]

What material is the white plastic?

[XLR8]

Glad to hear Sally is leaving. We are still deep in smoke here, enough that i am not working in the shop at all.

That case is looking great! Really nicely done!

So, the final step is to drill the screw holes for mounting the case to the chassis and the top brace plate and its spacer.

This is where I ran into the most trouble- that massive diff gear is right where my screws want to be. Well, couple that with the fact I really wanted to have both sets of holes in case an A stamp was being used, or a C stamp that lacked the countersinking on the 6 gear holes.

Thanks Jeff.

Given a choice, I'd rather have a hurricane than those wild fires. We're in north Alabama and far enough from the coast that hurricanes typically don't create much trouble for us; just rain and a little wind.

So, yeah keeping the screws from crashing into the diff gear is tricky. The key is that the front screws are spaced farther apart than the rear ones.

For instance, when viewed from this angle, it appears there is interference with the front screws...

...but they are actually spaced farther apart than the width of the gear at this location so there is ample clearance.

Also, screw length cannot exceed 3/8" or there could be a problem.

[XLR8]

What material is the white plastic?

Hi Joe.

"I can machine these cases in the shop from some blocks of PVC that I have lying around. I’ve used this material for a variety of projects including a transfer case for one of the crawlers and it seems to be holding up fine so far."

I'd much rather use Delrin because it's stronger and yet it machines beautifully but I'm using what I have on hand.

[jwscab]

Nice. It looked to machine very smoothly so figured abs or pvc. Plenty strong enough for what you are doing.

[scr8p]

This is a cool project.

As someone who would have no problem cutting a square into a tub, have you though about making the case so the diff could sit down inside the chassis and make a separate "plate" that would go on the bottom of the case for those who just want to mount it on top? Especially with the rere cva's, they're already to short to be raising the outdrives, and I worry about the telescoping of the bones in the outdrives with the steeper angle (bones bottoming out).

Just some thoughts....

[XLR8]

This is a cool project.

As someone who would have no problem cutting a square into a tub, have you though about making the case so the diff could sit down inside the chassis and make a separate "plate" that would go on the bottom of the case for those who just want to mount it on top? Especially with the rere cva's, they're already to short to be raising the outdrives, and I worry about the telescoping of the bones in the outdrives with the steeper angle (bones bottoming out).

Just some thoughts....

Thanks.
The design I'm working from places the outdrives 0.086" higher than the original Stealth's (and 0.049" farther back) so CVA bone engagement could be a problem. I wasn't too concerned about it since I'm running CVA's with the longer 9911 bones in my primary runner car and standard dogbones and axles in everything else. Since AE's short bone CVA fiasco and subsequent discontinuation of the 9911's, I've basically given up on them all together and gone back to running standard old school axles with dogbones. Sadly, I no longer race. Instead, I just run on the backyard track and relive the glory days in my mind so running CVA's isn't important to me.

That said, I really appreciate your suggestion. I'm always looking for a new design challenge and I'd like to see what I can do with this.
From a design perspective, slotting the chassis to drop the diff won't be a problem. The chassis is about 0.063" thick so dropping the case flush with the chassis bottom still leaves the outdrives 0.023" higher than standard. Drop the gear any farther and the cases will be hanging below the chassis and prone to damage. I guess you could reduce suspension droop by 0.023" or add a horse shoe shaped shim under the bulkhead and suspension mounts - effectively lowering the chassis and transmission the additional 0.023". The horizontal screw holes into the sides of the chassis and bulkhead would need to be slotted but I think this is possible. This would restore horizontal alignment between the axles and outdrives.
I think simply reducing suspension droop by 0.023" is the better solution. Thoughts?

[GoMachV]

Easier to solve by creating new rear hub carriers that both fix the driveshaft angle and also correct the bone engagement. The ones I made adapt b6 cva’s over which also fixes the wheel offset problem by using modern wheels. That’s my .02 anyway

[matt1ptkn]

Wow! This is a very impressive undertaking with great looking results. I'm curious to hear about the performance. Keep up the good work!

[XLR8]

Thank you Matt. This has been an interesting project.

So, the mounting holes are in and the test trans is finished but before installing it in the car, I wanted to perform a trial fit with a re-re that was assembled with kit parts according to the manual to check bone engagement (kit shocks, CVA’s, etc. and at 1 degree camber and full suspension droop).

As you can see, engagement is terrible but not as bad as I had expected.

Of course, swapping the blue washer and the shims around greatly improves engagement.

Also, at full compression, the end of the bone does touch the o-ring bumper in the outdrive but it doesn’t limit compression. I could remove the o-ring or just leave it in.

I have the longer 9911 bones in my runner car so I’ll also want to check it at full compression – might want to remove the outdrive o-ring bumpers for that car.

One aspect of the original Stealth’s design that could present a problem is the placement of the top shaft’s bearings relative to the spur gear; the closest bearing on that shaft is nearly ½” from the spur gear. For the original 6-gear trans, the bearing is positioned immediately adjacent to the spur. Since the material I’m using is much softer than the Stealth’s nylon, my concern is that the top shaft could deflect under load at full throttle and cause the pinion gear to skip and ruin the spur.
The solution seems simple; fit an additional bearing to the shaft closer to the spur. Depending upon how the running tests go, I might add this feature to the 3d printed case.

I’ll swap this trans over to the runner car and get some track time in this afternoon or tomorrow at the latest.

[XLR8]

The weather here was great again today (low humidity, low temps and plenty of sunshine) and I've finally gotten in some track time.

I have four 10 minute runs on the car and apart from a broken rear camber link from a tumble, there were no problems to report. The car definitely sounds different - much more quiet than with the old Stealth trans.

Regarding overall performance, I really can't tell a difference between the ball and gear diff. I was able to setup for and power out of the turns just as before and the car always tracked straight under power just as before. I have literally thousands of laps on this car so I'm very pleased that I won't need to adjust my driving style or the car's setup to accommodate the gear diff. It fits me like an old pair of shoes.

The track was swept and watered for maximum traction and with the slipper clutch locked tight, it was nice to be able to pin the throttle in the hi-bite sections without worrying about the ball diff barking. I'll run the car again then pull the trans apart for close inspection but I really don't expect to find anything wrong.

I'm looking forward to phase two of this project - a 3d printed case that resembles a Stealth.