Underdrive for the R1... Finally

[Calderwood]

Originally Posted by joneail

Is the underdrive really needed


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Obviously its not needed since no crawler comes stock that way.

It is however VERY beneficial.

[BadWagon]

This is f'n awesome. Great work bud.

[G-FORCE]

Excellent solution! I'm all over it!

[Captainkickass]

Sweet mod man. My only concern would be the tiny 2.5mm bearings (or bushings if u switched) in the portals would be stressed even more by the difference in drive ratios causing more frequent bearing/bushing failure and gear grinding. It probably wouldnt be too bad depending on how u drive but just something to consider. Not dissing the mod i know how beneficial OD/UD can be just my 2 cents.

[vtlandcruiser]

Nothing all that great to add aside from a bump to the top & a thank you to Super for taking the time and effort to find a way.

Would be pretty cool if we could drag the section outta the graveyard too...

an easy way to give the whole front/rear under-drive/over-drive thing a try would be to simply have two different sized tires front/rear.

Would accomplish the same effect as doing it in the diffs.
Might look odd granted but it'd give ya an idea of how the set up handles and if you'd like it or not.

[krwlr]

Just did this to my R1 last week. It's like night and day difference in the rocks.

[krwlr]

[bill mossor]

thanks for your post it was very informative . I'm getting a sawback. Do you think it will work to put the R! gears in the sawback to give it over or under drive ?

[spoo76]

Originally Posted by bill mossor

thanks for your post it was very informative . I'm getting a sawback. Do you think it will work to put the R! gears in the sawback to give it over or under drive ?

You would likely have to do the opposite. Possibly shave the hub & shim the pinion

[bill mossor]

Originally Posted by spoo76

You would likely have to do the opposite. Possibly shave the hub & shim the pinion

Thank you for responding.

[Fivos Rock City]

Wouldn't it work if you kept the original ring gear of the r1 and just use the filed down pinion? It would save some time having to adjust the ring gear with the shims etc.

[Jeepiac]

Originally Posted by Fivos Rock City

Wouldn't it work if you kept the original ring gear of the r1 and just use the filed down pinion? It would save some time having to adjust the ring gear with the shims etc.

Nope. Tried it and it just wouldn't work as well as it needs to. I did mine a little differently, but same results. Very noticeable difference and well worth the time. Now to put the R1 gears in the front of my Sawback

[Fivos Rock City]

Just figured it would because the ring gears are same tooth count. I don't own an r1, just guessing lol
got both OD/UD in the front/rear respectively on my wraith though and it really made a difference so I think there should be something similar for the r1 which is a nice kit imo. Maybe junfac will make some gears?

[Jeepiac]

I'm sure that they will come out with under/over drive gears now that mine are all done.

[bilinvic]

I just finished this underdrive mod. Thanxs very much supermoturd for the idea & explanations. The mesh in the rear axle is absolutely perfect.

[Natedog]

Originally Posted by supermoturd

Don't know why I even post on this forum anymore. Aside from Dravpnir's Wrapter thread (which is awesome), this forum is as quiet as the grave. Kind of makes you wonder if anyone is buying/building/driving Gmades anymore.

Even after everyone pooped on the idea of using the ring and pinion (differential bevel gears) from the Sawback to affect an underdrive in the rear of the R1, I just could not give it up. The Sawback bevel gears (GM52106) are only about $8 a set so I took a chance and ordered them.

Installing the Sawback ring and pinion in the rear differential of the R1 turned out to be a lot more work than I expected. However, it was not an unreasonable amount of work, and the amazing results made it worth while.

As you can see, the Sawback pinion is much thicker than the R1 pinion and the ring hub on the Sawback ring gear is shorter than that of the R1 ring gear.

I had to file the Sawback pinion down to the same thickness as the R1 pinion to get it to fit and mesh properly with the ring.

As for the rings, both the Sawback and the R1 rings are the same diameter and have the same number of teeth (32). However, the hub on the Sawback ring is shorter than that of the R1 ring. This turned out to be advantageous since it gives you some play with which to adjust the position of the ring and ensure proper mesh with the pinion. I used washers at each end of the ring hub to shim and position the ring.

The shorter hub on the Sawback ring allows the axle shafts to be inserted further with the undesirable result that the outer ends of the shafts (especially the left shaft) don't quite reach the outer support bearings in the portal housing. To fix this, I had to drill and tap (M3) a hole through the center of the ring hub and install a set screw that could be adjusted to prevent the shaft from being inserted all the way. You can see the set screw in this picture. (Edit: A better solution would be to use cytogen's HD locker solution Poor Man's HD locker. This will remove slop from the drivetrain and will provide you with the ability to precisely adjust the locations the diff output shafts relative to the ring carrier.)

And here is an image and explanation of the adjustment.

With the pinion filed and the ring adjusted, the mesh is perfect.

Test drive revealed a marked improvement in turning radius and lowered and stretched suspension as expected. I can't wait to test on the rocks. My calculations indicate that for each turn of the transmission output the front wheels travel 0.5 inches (~12mm) further than the rear wheels. There is no discernible spinning of the front wheels or dragging of the rear wheels except in sharp turns. The drive ratio front-to-rear is a little greater than that for an Axial Wraith with underdrive. However, it is less than that for a Wraith with both overdrive and underdrive installed.

Awesome job, enginuity and thanks for documenting well with pics and posting up for everybody!

[FVIcySwan]

I know this is an older thread, but the information and photos remain helpful. I have been looking at an R1 at my local hobby store. It is put together but without electronics. I have been hesitant to jump in for several reasons, including chatter about underdrive. This thread lays that to rest and I will take another hard look at that rig. Thanks, OP, for great information.

Mike

[Muddy Udders]

I will chime in with my thanks also.
I just ordered my R1 kit and will be doing this mod straight outta the box!!

[supermoturd]

It has been a while since I got on the forum. It just got so quiet around here that I quit visiting. But I'm glad to see that so many of you guys have found my Under-Drive mod useful. It takes a bit of work, but it is well worth it. The R1 is pretty lousy in stock form, but with work, it can be transformed into a formidable crawler. And that is what makes it so much fun.

[Captainkickass]

How does this mod affect the longevity of the bearings (or bushings in my case) located in the outer axle portals?


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