1985 Honda 250ES Final Drive Unit

[Trey Clanton]

Hello All,

I am the proud recipient of a bunch of boxes full of parts that used to be a 1985 Honda 250ES. It was a rebuild effort that barely got through the tear down phase. I have managed to get it running well and mostly cleaned-up, painted and assembled. I am a bit hung up right now on the final rear assembly, though. I have ordered all new axle bearings for the rear axle and have already replaced the swing arm bearings. One big up-side to this acquisition is that I got a brand new final drive unit in the deal. The old one was absolutely full of mud and other unrecognizable stuff.

I tightened the odd threaded nut that holds the pinion shaft, gear, and bearing in place and installed the seal. I sealed and bolted the side plate (ring gear side) onto the final drive unit and then mounted it to the swing arm. I then assembled the rear axle tubes and painted the whole mess. I then installed the swing arm and added the oil to the final drive unit. For chuckles, I fired up the trike and put it in gear without the rear axle or bearings installed to see how the final drive unit sounded. The answer is it sounds Very Bad.

I have been using a Clymer manual and it gives absolutely no help on determining if the final drive is properly assemble and tightened other than to give an exploded view. One thing I forgot to check before asembly is whether the shims were in place. Since it is brand new, I figure they must be in place. My biggest concern at this point is how to determine the correct tightness of the odd nut that goes into the pinion gear end of the final drive unit. I used a small drift punch to tighten this nut.

If anyone out there has rebuilt one of these monsters, I could certainly use some good advise. Please feel free to tell me what I did wrong.

Thanks,
Trey Clanton

[likestrikes]

Ohhhh Boy....

Sounds like your gears don't have the right clearances. You said "new" drive so I assumed that meant "assembled" but I guess not.

There are dozens of shims Honda makes for the ring gear, I believe the pinion to ring gear setup distance wise is fixed. But I know that the ring gear can be shimmed either way and the opposite side gets a shim to take out the slack. Your gonna have to treat it just like a 3rd member and get some marking compound and see whats up. Hi pattern, low pattern etc etc but it has to be close or perfect. I'd get the member right and then assemble it to the housings and axle.

[FlyingW]

Trey,

To add to LT's post, I just got done doing just that to my SX. The ES and the SX have the same diff but geared slightly different. The concept to understand here is that when the ring gear and pinion gear mesh farther in to each other the backlash becomes less and likewise when you pull them apart there will be alot of slop. The more slop, the worse the gear set will sound when it's rotated. The book sais to pull the fill plug and using a dial indicator measure the amount of slop in the ring gear when the pinion gear is locked. The backlash for mine is .08-.18 which is not much but if it put a backlash of .30 the final drive would be pretty noisy.

With all that said, I'd pull the fill plug, put your shifter in 5th gear to lock the pinion. Look in to the fill hole and move the rear axle. If there's alot of slop then you might as well pull the diff. You will need to find a dial indicator with a long stylus on it as well as a arm for holding the the dial indicator to measure the actual backlash. I know most people don't have these sort of measureing equipment laying around so you may have to do some calling around and find perhaps a machine shop who does.

If there is too much backlash then you'll need to determine which shims to use. Pull the existing shims and measure their thichness with some calipers. Look in the manual at the list of shim thicknesses and find yours. They may be slightly different then the list but find the one that is closest. For too much backlash, the gears will need to be moved closer together. For each shim thickness you go up or down will move the ring gear closer of farther to the pinion gear roughly .06-.08for every .04 change in shim thickness.

Now, if the diff is new as you were told then there should be .079 shims on the ring gear right now. .079 was the standard shim installed at the factory so I'm told..

The Honda rear diff is a very durable assembly but they aren't easy to adjust buy the average guy because of the special tools required to do it by the book. The locknut on the pinion gear is a perfect example of that. I had to do the same as you did in that I used a punch to remove and install it. The book sais to torque it to 2.2 in lb max. All this does is to preload the bearing. 2.2 isn't very much so just snug it and lock it down.

Get ahold of damnit and ask him for the link to his manual site and download the factory manual for your ES. The Clymer manuals are a bit vague sometimes. Let me know if you have any more questions. Good luck.

[ATCnut]

Here is a link to Dammit's site. Download the manual once and save it on your hard drive. Dammit pays himself for the bandwidth, and it costs every time it is accessed.

http://www.drivehq.com/file/ShowFolder.aspx?G=1&shareID=233462

[Trey Clanton]

Hello Again,

Ya'll are most awesome. I appreciate all of the information. I will start with the measurement technique and see where I am. I am really beginning to wonder whether this thing has any shims in it. While the unit is new, it wasn't bolted together, so it might not have shims in it. That will teach me not to check something so simple before I proceed. I also greatly appreciate the link to the manuals. I will have to PayPal a buck or two to Dammit for the bandwidth. I can appreciate the cost of bandwidth for such a large download.

If anyone else has any input, I will be listening. Thanks again and I will let you know how this goes. I am going to have to post some pictures when (and if) I get this thing finished up.

Thanks,
Trey

[FlyingW]

If it wasn't bolted together then I would bet one or both shims are missing. If they are missing, order the standard shims and start there but chances are if it new, you'll be ok.