pcsguy88

I have had my Bulldog full metal tank for 2 weeks and have chewed thru 2 gearboxes in the exact same place. The first metal gearbox had a motor with 1 screw broken, so I thought it was to blame when it shredded. When the 2nd box failed yesterday, I inspected both very closely. It is the box with the bottom mounted motor and it is the inside facing bushing on the 3rd gear from the front. The bushing is wearing an oval pattern, causing the gears to strip enough that replacing the bushing does not correct the issue. The worse part is that it doesn't make a grinding sound until it is too late. The first box was standard and had been broken in with laping paste until it spun freely. The 2nd box came to me in perfect condition and spun for 2 seconds without break-in. I ran 1 battery on the 2nd with stock motors, 1 battery with Graupner 7.2v Spd 400's. I noticed a pile of brass on the floor of the tank when I made the motor swap, but figured it was just breaking in. The Graupners finished the job. Both gearboxes lasted 2 3650mh charges. Any suggestions to avoid destroying a 3rd box in 4hrs? Can I find stronger bushings? Are there any affordable alternatives to HL gearboxes? I can't afford $26 for every 4hrs I drive the Bulldog.

RCCOMMAND

Can you post some pictures of the damaged gearboxes? Have you noticed the bushings slipping/turning during your break-in? If so, try using a bit of CA or epoxy to secure the bushings in place, of course being careful not to touch the gear shafts. We have some gearboxes on the way with steel gears but you'll still need to ensure bushings are either tightly pressed or 'fixed' in place.

Bill

971wright

Hi Pcsguy88 have you any photos of the broken gearboxes or are you changing the gears and using the same gearbox I have had gears strip in the past it was down to worn bushes /shafts that let the gears jump then the first time they hit heavy load grind and bang no drive ,now cheack all gearboxes for to much play and side movement if nessasary I strip them done and shim them and replace any bad bushes before running them when I run my gearboxes in i make sure no abrasive gets to the bushes and causes premiture wear to them .


regards pete

RCCOMMAND

Pete brings up a very good point. Make sure you're not allowing any of the lapping powder/paste to reach the bushings!

Bill

pcsguy88

Crappy cellphone pic, it's the bushing in the strip of light. Funny how the camera colored all the metal golden. This gearbox was dropped straight in without any break-in or grease because it spun for over 2sec when you turned the axle. The brass is so soft, a pair of crappy needlenose pliers could easily deform the outside edge during removal. All bushings were tight on this box, the first one I had to CA half of them. It almost looks like it would function better if it did spin.

RCCOMMAND, I would be very interested in those stronger bushings, please let me know when you will get them. If the wait is too long, I'll be ordering a new set of the normal metal boxes. I am so glad I built up a VsTank collection prior to owning a HL otherwise I would have nothing to drive while waiting for the next package of spares parts. I do love working on this beast, it is 60% of the fun.

Thanks for you replies,
Ron

pcsguy88

The gears are not reusable by the time I pull the boxes. It's always where the large drive gear meets the tiny gear in the middle of the box that strip enough to spin freely.

971wright

Hi Pcsguy88 wish you had a picture of the gears in place some times ive bought gearboxes from ebay and they were real noisey and didnt last long bought some from a good dealer they were quiet and didnt require running in when you look down at the gearbox if the gears are inline and square to each other is usualy good sign that they will be ok turnning them over slowly and see if they run true then check for side play if all these are good the gearbox should be ok .Have you check the track to see if it is tight to turn over they should feel the same and make sure the motor is engaged corretly not to much backlash dont use the recoil this put to much strain on gearbox this is about all I can say if all these points are good you shouldnt blow any more gears .


regards pete

bubbajoexx

the problem with the metal gear boxes is the shaft end are not clean cut you need to remove all the gears and place each gear in a drill and round the ends of the shafts spinning them in the drill and using a good file then smoth out the ends with 300 grit paper after that the gear shafts will not wear the bushings out next you will need to square up the metal sides when they are made they are badly out of square some carfull bending will eleveate this and they will run as smooth as a clock I just did my new pz3 boxes and the do not need lapping or any breakin as the spin so freely the need no extra work

philipat

Steel gears? Are these the standard HL metal boxes or a different make? Details, please!

I'd like to move my Bulldog to metal gears with the sp400s, too.

RCCOMMAND

Hey Philip,

Not standard but still from HL. They will cost about $7 more than the standard metal gearboxes.

Here's a shot of them...

Bill

philipat

Same gear ratios? Are they tighter and better made than the other metal gear boxes? I guess the better question is: other than being made from steel, how do they differ from the standard HL metal boxes?

RCCOMMAND

Same gear ratio. Waiting for our order to arrive and will report back.

Bill

j z

I would think that being made of steel they would have to be machined gears, not die cast like the present type gears. If thats the case,they will probably mesh a lot better and not have to be run in with any abrasive compound. Just my thoughts. Regards, JZ

philipat

That's my hope.

Sounds good, Bill. When do you expect them to arrive?

pcsguy88

971wright, both sets of gearboxes came from a quality source we all use here. Hopefully I will find the source of the problem before chewing up too many more gearboxes. I feel stronger bushings would minimalize the damage. BubbaJoe's approach sounds a bit extreme to me right now, but if I get a Dremel drill press for Christmas, I might be willing to try it.

Eagerly awaiting news on the upgraded gearboxes.

RCCOMMAND

Well, I was hoping our order was enroute but I was just told they expect to ship our order today. If that happens, we should receive them within the week.

Bill

swathdiver

You should run the gearbox outside the tank so you can see what's going on. Plop in your spare gears and bushings and let us know. What? No spares?

pcsguy88

It's hard to tell what is wrong because this is my first HL and really my first RC vehicle that required maintenance. Tearing apart VsTank gearboxes just isn't the same thing. It's obviously stress induced. I think the track is too tight on that side, but it could just be the way I run it. It gets jumped of a 2in concrete lip anytime it leaves the garage and it runs in thick, hilly grass 90% of the time. Maybe I just expect more than the Dog is capable of handling. Time to search for stronger gearboxes, then suspension, hull & wheels. The steel gears sound nice, but I noticed the bushings look like the old ones, making me think I would burn thru those with the current setup.

WhiteWolf McBride

My Feedback: (3)

Guys:

He's got a modded motor thread going too... same bulldog. Could altering the motors be contributing to this problem? It sure as heck isn't helping him any.

see: http://www.rcuniverse.com/forum/m_8100343/tm.htm

pcsguy88

Wolf, I made it very clear the exact sequence of events in the opening post.


And now for something I made while bored at work:

Matdragon

thats some nice work with photoshop! well done!! hehe dont think those tanks chew up their gearboxes that quickly lol

Matt

swathdiver

That's funny! And SCARY!!!

Back on topic: You don't run your Dog any harder then many of us do, so the problem is in the gearbox itself. It's unlikely to be motors either.

The problem could be a mis-aligned holes for the bushings, bad bushings or gears. With a supply of spare parts it'll be easy to make the necessary repairs and discover what went wrong. Like those T-72s the only thing that keeps them running is spare parts. Heng Long wanted you to get the full effect in realism with these babies!

philipat

Bill, sounds good.


That Photoshop work is too funny, but too real. [>:]

BIGMIG

Judging by who's in the picture,in a few months you may be out looking for work rather than having the problem of being bored at work.
BIGMIG [:-][:-]

pcsguy88

Update:

I completely disassembled 3 gearboxes to find the cause of the 2nd failure and think I found multiple answers. When my 2nd set of gearboxes arrived, I noticed the axle was bent, creating a significant wobble when turned. No big deal, I just swapped it out for one of my original axles. Well, i guess the bent axle box had been "tested" that way because I found the large bushing was completely destroyed on the inside. I feel this bushing caused the replacement axle to wobble, destroying the rest of the gears/bushings. Wish I would have noticed and replaced that bushing when I swapped the axles. Anyways, I mixed and matched the gears from the 3 boxes without much luck. Decided to inspect closer, so I scrubbed every gear clean and to my horror, found metal shavings jammed in many of the gear teeth. The good news is I managed to build a functional box and my Dog is running again. The bad news is every gear sustained some damage from the 2 previous failures and it is only a matter of time before they fail. You guys are right about the crappy frames, I took everything off of them and hammered them straight. Has anyone reproduced a frame with galvanized steel? Just trace, cut and drill? I might try it if I ever find the time.

Thanks for all of the info you guys provided me with!
Ron