D20 Jumping out of 2H

[EBGeek]

Count me in as one of the few who've apparently experienced this odd phenomenon, as the archives don't have a lot of material on the subject. My twin sticked D20 just has random bouts of neutral-fits, where it decides it wants to jump out of 2H at highway speed. I can't find a pattern, it seems to just pick totally random times to do it (typically at speed, under some load, never when I accelerate or decelerate). Sometimes it'll do it often, other times it'll go for an hour or more with no issues.

I've done a fair amount of searching on this topic, and had come to the conclusion that based on what others had said, that I had excess play in my output shaft. Well, I pulled my driveshaft and although I didn't have an impact handy, I tried for all my might to tighten my yoke with a breaker bar, no luck.

I then put it in gear and wanted to make sure it wasn't sloppy (no dial gauge). It had absolutely no play up/down, and very little from gear lash.

I say all this to say...does anyone have any other ideas to investigate before I go buying dial gauges and disassembling my output shaft?

 

[Lawndart]

Happened to me a few times when I first got my Bronco. Twin stick as well. Turned out the hole cut for the twin sticks by the PO was not quite large enough and in H, the stick would lightly rest on the back of the cut-out. I figured flex and drivetrain movement over time was pushing the stick gradually towards neutral until it finally popped. Trimmed the hole a bit more and it has not happened since.

 

[EBGeek]

Hmmmm, I like the idea of trying that before I start ripping my driveline apart. Thanks for the tip, I'll take my boot off and check clearance.

 

[Dlish]

Hmmmm, I like the idea of trying that before I start ripping my driveline apart. Thanks for the tip, I'll take my boot off and check clearance.

How stiff is the boot? Could the rubber boot be providing some push as well?

 

[englewoodcowboy]

I helped another bronco with the same problem by replacing the detent spring caps with a set screw and jam nut similar to the adjustable detent keepers you can get from Jeff's. We bought the stuff at a local ace and increased the detent spring pressure. I am certain that the springs get weaker with age etc. On my bronco I opted for new springs and the adjustable keepers from the get go. It solved the other broncos issue.

 

[JB Fab]

I would also check your driveline for any slop, imbalance or anything that could cause harmonics.

 

[EBGeek]

Well, digging up an old thread with an update and a question. I verified I have little to no 'lash' in my output shaft, absolutely no 'up/down' play in my output shaft, have installed a brand new driveshaft, and have installed new detent springs/balls, yet it continues occasionally jumping out of 2H (although less now it seems).

Now my question - if I remove my rear output assembly from my TC, how do I go about measuring end play on the rear output shaft? I'm assuming it has to be removed to measure that, but at this point, I don't have many other options.

 

[xcntrk]

What kind of case, T or J?

Did you modify the rails as part the twinstick? It's possible your rear rail is worn and the hump between HIGH and NEUTRAL has rounded off and is allowing the detent to pop out. Easiest/cheapest fix might be the adjustable detent springs available from JB. Then crank them down for more tension on the rear rail.
http://jb-custom-fabrication.myshopify.com/products/adjustable-detent-kit-for-early-bronco-d20

 

[EBGeek]

Thanks xcntrk, looks like that's my next step. I should've bought those instead of the stock set I got, but at least they're not expensive. Looks like one more attempt before I start ripping it apart...

 

[Viperwolf1]

Well, digging up an old thread with an update and a question. I verified I have little to no 'lash' in my output shaft, absolutely no 'up/down' play in my output shaft, have installed a brand new driveshaft, and have installed new detent springs/balls, yet it continues occasionally jumping out of 2H (although less now it seems).

Now my question - if I remove my rear output assembly from my TC, how do I go about measuring end play on the rear output shaft? I'm assuming it has to be removed to measure that, but at this point, I don't have many other options.

If there's no up/down movement there won't be any endplay.

There could be other problems inside the tcase like loose shift forks or a worn input gear. The thing I would try first is to use an adjustable detent plug like this from JBG, http://shop.broncograveyard.com/Adjustable-Detent-Balls-and-Springs/productinfo/11674A/

I've made those before using a 7/16"-20 bolt and nylock nut.

 

[Rustytruck]

I would also check the u-bolts on the axle. Make sure they are tight. I would also pull the drive shaft and lube it well. check that the u-joints are in phase and the slip shaft splines are still moving and not wobbly. Cant balance the shaft yourself so you would be stuck sending that out. But that's the last thing I would do.

 

[RPM289]

I would also check the u-bolts on the axle. Make sure they are tight. I would also pull the drive shaft and lube it well. check that the u-joints are in phase and the slip shaft splines are still moving and not wobbly. Cant balance the shaft yourself so you would be stuck sending that out. But that's the last thing I would do.

Trick to balancing the drive shaft is to take a hose clamp and place it mid way on the shaft snug it just enough to keep it from moving freely then drive it and then tighten it up where it centers up at. Centrifugal force will put it where it needs to be. I did this on a bent driveshaft in my mustang and drove it 980 miles home at 70mph no vibration at all. Before it would shake at 40mph.