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to grind shift rails or not

Big Slim

Jr. Member
Joined
Dec 11, 2007
Messages
315
i am resealing my transfer case and since i have it apart i have the opportunity to grind the shift rails. im leaning towards not since i dont think this will see much off road. and probably never extreme off-roading / rock crawling. but the other side would be if i ever needed to do a front wheel low only i would have that option.
 

Yeller

Contributor
Bronco Guru
Joined
Mar 27, 2012
Messages
6,653
Loc.
Rogers County Oklahoma
I use front wheel low all the time, handy for tight maneuvering, helps keep body panels away from things they shouldn't be near. Although, I don't use it near as much as rear wheel drive low, I use that all the time we're traveling off pavement under 20-25 and traction needs don't dictate 4x4. Keeps a very happy transmission, even a good step to prevent overheating the engine, nothing has to work hard.
 

papy

Contributor
Sr. Member
Joined
Jun 13, 2012
Messages
822
never heard of this grinding of the shift rails. does this only apply if you don't have twin sticks or?
 

papy

Contributor
Sr. Member
Joined
Jun 13, 2012
Messages
822
I did the twin stick set up on my T shift case when I rebuild it, but I don't remember any grinding. Is that just a terminology that we use for the T shift case when going twin stick set up?
 

jamesroney

Sr. Member
Joined
Sep 11, 2007
Messages
1,913
Loc.
Fremont, CA
Do they mean grinding the detent slots deeper or changing their shape so the sticks don’t pop out of gear easily?

Here it is. To prevent cross shifting.
https://classicbroncos.com/forums/threads/grind-shift-rails-or-remove-pills-poll.208917/
Not exactly. The point of the interlock pills is to prevent cross shifting AND to prevent the transfer case from violating the shifting logic.

There are only 9 possible transfer case options:

1. Rear H, Front N
2. Rear H, Front H
3. Rear H, Front L
4. Rear N, Front N
5. Rear N, Front H
6. Rear N, Front L
7. Rear L, Front N
8. Rear L, Front H
9. Rear L, Front L

Of these, there are two that are not Logical, and are the cross shifting situation. These must be avoided at all times to prevent internal damage, and / or immobilization of the Bronco.
3. Rear H, Front L
8. Rear L, Front H

The interlock pills and rails are designed to prevent / avoid 3,5,6,7 &8. Leaving 1,2,4 &9 Which are the one's you know and love:
1. Rear H, Front N = 2Hi
2. Rear H, Front H = 4Hi
4. Rear N, Front N = N
9. Rear L, Front L = 4Lo

Lastly, there are three that are defeated via the design logic.
5. Rear N, Front H - This is called a High range front Dig.
6. Rear N, Front L - This is called a Low range front Dig.
7. Rear L, Front N - This is 2WD Low range.

So the debate distills down to the cost / benefit analysis to enable the 3 remaining modes that are not currently available.
5. Rear N, Front H - High Range front Dig. Also known as Front Wheel Drive. Who wants a front wheel drive Bronco? With single cardan axle shaft joints, and V8 power, they are unruly to drive aggressively on the road, with a lot of torque steer, and prone to self destruct. You can get some fairly dramatic front wheel drive burnouts, but pulling on the coast side of the ring gear is not optimal, and things break pretty fast. High speed driving with a limited slip and low traction is even more hairy. (but can be fun!) So I'm going to say "useless." If you really need it, you can always remove the rear driveshaft and yield the same result.
6. Rear N, Front L - Low range front Dig. This is kinda cool, and I've seen some interesting use cases from skilled operators in low speed maneuvers around obstacles. @Yeller makes a compelling case.
7. Rear L, Front N - 2WD Low Range. -2Lo. Also useful, and sometimes cool...but easily achieved by simply shifting to 4hi, and unlocking a front hub. So while the use case is compelling, it is easily achieved in other ways. If you are running front drive slugs, then I can see where you might want to enable this feature in the transfer case shift logic.

It is super easy to enable ALL of the modes by leaving the interlock pills out. But to SELECTIVELY enable and disable modes requires twin sticks, and interlock rail grinding. Which is where @JB Fab comes to the rescue. Because he has done all of the thinking to enable some modes and still prevent the evil ones.

Hope that helps.
 
Last edited:

rocknhorse76

Contributor
Bronco owner since 1993 💪🏻
Joined
Jun 7, 2014
Messages
426
Loc.
Central WA
I use front dig a lot. It works great on super tight trails to basically “pull” your rig around obstacles. I’ve also gotten myself out of hairy situations while snow wheeling on side hills. Keep in mind though, I also run an NP205 transfer case and a high pinion Dana 60 front axle. I did it once in awhile with the Dana 20 and stock Dana 44 axle, but I was always super careful to not hit the gas too hard.
 

Yeller

Contributor
Bronco Guru
Joined
Mar 27, 2012
Messages
6,653
Loc.
Rogers County Oklahoma
As a side note. I’ve not found the evil combinations of high range front or rear and low range front or rear to really not be detrimental, everyone told me the case would blow up. I found it to just spin or drag the rear tires depending on the combination with no I’ll effects other than stopping and rocking back and forth a little to unload the gears and correct the issue. I used to have a twin stick case with no pills and occasionally would get them out of sync shifting them quickly.
 

jamesroney

Sr. Member
Joined
Sep 11, 2007
Messages
1,913
Loc.
Fremont, CA
As a side note. I’ve not found the evil combinations of high range front or rear and low range front or rear to really not be detrimental, everyone told me the case would blow up. I found it to just spin or drag the rear tires depending on the combination with no I’ll effects other than stopping and rocking back and forth a little to unload the gears and correct the issue. I used to have a twin stick case with no pills and occasionally would get them out of sync shifting them quickly.
On another side note...there is this:

1. Find the narrowest, longest, most congested trail with no possible bypass. Get yourself about halfway up a giant rock. Apply brakes on the steep incline.
2. Frantically shift transfer case into both Low and High.
3. Release brakes and allow vehicle weight to load gears in the transfer case.
4. Apply engine power in forward, reverse, and sideways. Adjust, move, shift, bang, rev, slam, and rock all other controls with equal futility.
5. Exit the Vehicle and observe the situation that you have created. Ponder your next move carefully.
6. Allow additional traffic to accumulate behind your giant turd in the trail.
7. Explain in excruciating detail EXACTLY why you cannot move your rig, and no...you do not need a "tug"
8. Try to convince someone behind you to get in front of you, (because your group has left you behind.) ...because you are stopped for no reason on the "easy" part. If you do find someone...go to step 10.
9. Go to step 6.
10. Get the operator of vehicle 2 to apply tension on the winch to allow you to use your high lift jack to lift one wheel to relieve the torque on one wheel. This will invariable apply torque from your locker to the other wheel, as the vehicle strains to move either forward or reverse. Usually the lifting of the jack will allow one wheel to slip enough to allow the Bronco to fall off the jack. Repeat this process numerous times, until you have successfully "landed" your Bronco into a flat place. Keep in mind that you will probably have to lift all 4 corners one at a time until you have removed the load off the transfer case.
11. Reach inside and slip the transfer case out of gear.
12. Observe the persistent gallery of gawkers, and and do your best to find the guy that is complaining the most, laughing the loudest, and reveling in your discomfort. Provide him with a cold beer. Because it's probably me.

Now go re-Install your interlock pill. Because there is NEVER a reason why you want it in high and low at the same time.
 

Yeller

Contributor
Bronco Guru
Joined
Mar 27, 2012
Messages
6,653
Loc.
Rogers County Oklahoma
Wow that’s complicated. Never ran into that situation. You are right there is no need for high and low at the same time. The trails I run doing those maneuvers rarely has anyone behind me, the trails are dumb and no one should be putting rubber on them, there certainly isn’t anyone passing unless there is a crane handy. I will say that was a time before the fine parts that @JB Fab provides were available, just buy their shift rails and not worry about it. Once you’ve learned to use a twin stick, wheeling without it feels like abuse, and in some places (all of southern Utah) it is abuse of your drive train.
 
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