Removing Bosch Drill Pins - Cause of Failure?


Last year we did not modify our bosch trannies from the way we received them. We used them in a four motor drive and never once did they fail. However, they would make aweful crunching noises every now and then, that I assume is the pins.

To make for a smoother driving experience (like running on only Chips), I was thinking we would remove the pins this year.

I read all the other posts and threads on this topic and have not found my exact question asked or answered before.

**Is there a direct correlation between removing the pins and drill tranny failure? **

I don’t think removing the pins would be the source of the transmission problems but perhaps taking the gearbox apart would cause it to go back together differently or looser. Is this true?

I want those pins gone but I never want to have to open or replace the transmission after that.

we removed the pins from our trannsmissions without ever experiencing a single problem after a regional, nats, and 3 off-season comps. I don’t know exactly how it was done, but that’s because we made sure that the guy who did it knew a lot more about subtly tweaking transmisions than the rest of us did.

in short, do it, it won’t hurt you as long as you make sure that you do it right and don’t damage other parts of the motor/transmision in the process.

At the bottom of the rule state below you find the following text i typed in italicsRule 5.8.4 The drills clutch housing contains 2 internal back drive preventer pins thats keep the motor shaft from being turned (back driven) by its ouput shaft. These pins may be removed allowing the motors to be back driven by the robots momentum in an un powered state. FIRST recommends that you remove these pins. Detalied instructions about doing so are available on our site.

Does this help???

If you apply enough force, you can cause those pins to fragment. When they do, you destroy the transmission. We have always removed them.


My team removed the drill pins last year, but an important thing to remember is to know how the drill motors go back together. We had some motor problems because of not putting it back together exactly as it was before. Just pay attention as you are taking it apart, and it will cause no problems.

From my experience, there is a correlation between not removing the pins and drill tranny failure. Removing the pins is very simple, you just turn the top 1/2 of the transmission and it comes apart one stage above the planetary gears. We destroyed a transmission last year by not removing our pins, and after that we removed every pin from the transmissions. Removing these pins help prevent transmission failure.


If you need to put something back together exactly as it came apart, take digital pictures, ALOT of digital pictures.

Also, the drill motors are not that hard to put back together…just set aside about 30 mins per motor and take your time. I had no trouble putting one back together after it rolled off the table once we took it out of our kit. Spur gears were everywhere! Just remember to take you time putting it back together, and test it OFF the robot! Try to backdrive the gearbox, on or off the motor, with the pins removed you should be able to backdrive the gearbox. Be careful the first time you test with power apply power gently. When you test, you wan to have it running at free load. Good luck, if you’re in the same neighborhood and need some help look us up, we would be happy to remove the pins and put it back together again.

Good luck

Many teams leave the pins in for one reason or another. In my experience more teams have been hurt by leaving the pins in place than not. Depending on many factors (like robot weight and speed and defensive strategies) when the locking pins click into place, all of the robot forces are now transferred to that one spot in the transmission. It is not designed to take that kind of force. The locking pins were designed into the drill/screwdriver to allow users to tighten/loosen screws without the need to pick up a different tool. When disassembling the transmission, go slow and watch how it comes apart. There was a complete instruction set with pictures on the CD site last year. I believe this is a Power point presentation on how to do the mod…
The locking pins are very obvious, they are about 3/16" in diameter and about 1/4" long and fit at the end of the “dog bone” in the assembly close to the output shaft. When you reassemble the transmission you need to rotate the output shaft a little to get all the parts to mesh. The case only goes back together one way so you may want to mark it before you disassemble. This is a very simple mod and can be performed in a very few minutes.

I have to add - GUARD your drill motor gear boxes from the general student population on your team

Several times I have watched a student pick one up, say “hey whats this thing?” handle it like any person would lookin at something new and strange

and within seconds, the transmission is open and the gears are all over the:

A. table
B. floor
C. student
D. all of the above

and they only go back together one way (not obvious)

denfinately let students look at them if they want to - but first make sure you know how to put one back together -second issue the warning “be carefull - it comes apart really easily!”

with our experience last year, after we took out the pins, our clutch started slipping and wouldnt stop. We tried changing the clutch setting but that wasn’t the problem. So we actually had to weld the clutch together to stop the slipping. The drill transmission kept falling apart after every match and we kept putting it back together. But after a while parts wore out on it and it just wouldn’t work. So we got two new drill transmissions and left them alone. We never had any problems after that.

if you need step by step directions i’ll ask my friend to see if he can post them

From what I have seen and heard, there is the opposite. Unless you want to stay put when power is cut(like on a ramp), there isn’t a reason to leave them in. So long as you put it back together properly, it should work just fine. If you havn’t done it before, take 20 minutes to do it so you will see how it fits together. Its easier that way then picking things off the floor and trying to figure out what goes in first.

And wear a shirt that you don’t mind if it becomes permanatly grease stained.


the clutch plate is in a completely different location from the pins (you don’t need to go to that bottom layer of planets where the cluch is so i can’t see any reason that THIS would have caused the problem. although it is possible that incorrect reassembling could have lead to the problem…for this reason i also recomend taking the gear boxes apart slowly and over a white piece of paper.

If you dissassembled the trans to take the pins out and the clutch wouldn’t lock, you had reinserted the clutch plate upside down when you put the trans back together. This is a common mistake.

Does anyone know where we can get some drawings for the output shaft and the other parts you have to make when you get rid of the the back drive pins??? Please share if you can…

We have some people to help the students machine these but maybe not design them.
Can you buy them???

Please help… :confused:


You don’t need to manufacture any new parts on account of taking out the pins from the drill trannys, they run beautifully unmodified after removing the pins.

Thats good news. The last slide in the powerpoint pres on the FIRST site said make a new shaft, etc.

Am I correct that there are only two pins?http://


yes, there are indeed 2 pins. Dr. Joe recommended a new shaft so that it wasnt threaded., making it easier to couple to another shaft, or mount a sprocket on.


That PowerPoint slide set was assembled based on the assumption that you wanted to replace a major portion of the standard Bosch gearbox (ie. with a modified “Dr. Joe’s Output Shaft” or similar device). If you are just removing the anti-backdrive pins, then you can stop after Slide #4.


We took ours out today. We were following the PowerPoint to the pixel and started to pull off other parts until we realized “hey, we already got the pins out, we’re done!” Hehe. Anyway, it is an extremely easy procedure if you are careful. I can’t wait to try them in the new “QuadraMax G2” :slight_smile: