1983 XJ750 rear end problem...

I have a 1983 Maxim 750. when i leave from a stop i have what can only be described as a "clunk" in the rear. my first thought was that the bar that runs from the frame to the brake was loose - but i dont feel the clunk when i hit the brakes slowing down. i checked it and its tight.

it's only when the bike starts moving forward, and as i let out the clutch.
it seams to happen even if i slip the clutch and let it get a rolling start. i have a feeling its something in the shaft drive....

anyone have dealings with this? any clues will help.

Thanks in advance,
Bruce

 

You can try removing the rear wheel and see if the rubber damper is shot and making too much free play in the drivetrain maybe?
Or check the U-joints on the driveshaft. They might be headed south too. Let us know what you find, it may be some thing we can address on our bikes before it's too late. Thanks!

 

If you haven't done already, check the rear brake shoes for delamination,
and DON'T RIDE until this clunk is fixed ! (test rides allowed, of course)

 

i have the same thing with my maxim, only mine is a sometimes deal
i can't make it clunk it only does it when it wants to
everythings tight, new brakes, no excess play in the drive line, no chunks in the differential oil, no shakes or vibrations at any speed, swing arm's tight, no strange noise
must be inside the differential is all i can think
i just know it's there and if it gets worse i'll look into it farther
it hasn't changer in two years

 

Would the final drive hypoid oil being old cause such a noise? Like if it's broken down chemically or something?

Definitely check those rear brake pads tho, could be something simple like the rear brakes needing some lube (it's sticking somehow).

Edit: I mean lube the pivot points not the shoes themselves or anything

 

i changed my oil 3 times in 2 years so thats not it, changed the brakes and did all that good stuff in there, no change
my theory is the ring and pinion need set and i ain't going there it's to easy to find one on ebay

 

There is so little play in the differential gears that it's hard to believe you could actually hear it. I do feel just a slight movement whenI let off the throttle and give it gas again, but it's not much.
If you add up the slop in the differential, the play in the rubber damper on the wheel and maybe a loose U-joint, then you may hear a clunk.

 

Yes mine has made this noise for the last 5,000 miles. i got the bike with 25,000+ on it and now it has over 30,000. it's always made "the clunk" Nope, it's not the rear differential oil - i changed mine, not to fix the clunk, but because i had no idea how old it was. i plan to keep ridding the bike, and someday i'll find the cause of that noise.

 

Just like with a car or truck, i'm sure you can tell when the rear diff has slop in it as you drive along. there is a point where the gears "float" and "sing". if ya jack up the back wheel you can get an idea if it has play.
And as far as i know these bikes don't have rubber dampers like a chain bike does.

 

Nope, not the gear oil. that's new (well, it was when i freshened up this bike) nope, not the brake pads - I adjusted them.

i thought maybe something in the swingarm or the shock mounts, but it does the clunk on hard acceleration from 1st to 2nd, and 2nd to 3rd - but there is no clunk if you baby it off the line (well sometimes it does, but not consistantly)

 

Painter, this ain't a hear it it's a feel it
kind of hard to describe, maybe like someone kicked the tire
it happens before the tire makes 1/4 revolution
that sound right Brewster ?

 

wow i never felt anything other than just starting out at
40 or 50 i might have to think a little harder on it

 

yea, mine is when the bike rolls off from the light, about 15 feet out... thump! almost like something is loose. and yes, kinda hard to describe. kinda feels a little like a "nuetral drop" but not with a big car, more like with a small light weight car.
i've looked - can't seam to see anything loose. ???

 

Yes, I guess there isn't a rubber damper in the rear wheel. I guess I was picturing the rear wheel setup on my Honda Shadow I just had apart last week (stupid me)
This ones got me stumped. Let us know what you find then. This could get interesting.

 

Well, i wish it had a rubber damper!! that would be the first place i would look!! I have it on the centerstand right now, and im futzing a bit with it - but im not going to start pulling stuff apart. i need it for this weekend. i have a Haynes manual and that lists the word "Clunk" and its associated with driveline components. if that's what it turns out to be, i'll just ride it till it falls apart.

 

OK, here is a question (i looked in my book, but find nothing about this):
with the bike on the centerstand and in 1st gear, i can get the wheel to rotate almost 4 inches before it tries to move the engine. not sure it this play is normal or too much, not sure if maybe some or all of this play is inside the transmission??

Yea, just checked. pulled the driveshaft boot back and that play is in the trans....

 

I had a pinion bearing go bad on a pick up I had. Is it possible that could happen on these bikes? The movement on my trucks was in and out on the rear end. Like if you push and/or pull on the driveshaft in a straight line front to back. Made kinda the sound you were describing,

 

i'll check. maybe there is a bearing holding the pinion in place that is sloppy.

 

does your book say anything about the middle gear and middle gear damper, thats about all thats left

 

I would look at the rear drive and (strange but true) the rear shocks. I used to get this weird clunk out of my rear end (ok, that is funny but I'm trying to make a point) and found it was the rear shocks. A lot of these rides (including mine) have cruddy stock shocks and they are notorious for being poor performers from the get-go. Now just add 25+ years and see how well they perform.

 

Mine does it too. I thought it was the clutch because when I felt,heard it it was just as the clutch plates about to lock up. Like it was loosing the last bit slip. Dissasembled the clutch and found the steels were all rusted up. Glass beaded them and got it back together. Haven't noticed it so far but I haven't gone for much of a ride. Also switched to motorcycle oil instead of car oil. Put new shocks on it too.I'll keep you posted.

 

That play is in the "dogs" that engage the gears and is normal.
The rest of the driveline "lash" is tiny by comparison.

 

I absolutely HATE the amount of slop in my drive line makes me sad, but that's one of the drawbacks to chain drive. I've learned to roll off and on the throttle carefully to minimize the jerkiness in town traffic.

 

Hey Brewster - have you checked your swingarm bearings?

My old Diversion had worn / dry bearings and it made the disconcerting noises you are describing. They are quite a small bearing for their application on the XJ's so they do tend to wear out quicker than conventional needle swingarm bearings.

 

I have thought about those shocks!! i think i may pull them off today and get them in a bench vice and see if i can tell if they are crappy. maybe the shock part with the oil damping is gone. cranking up the springs may make a difference.

 

I have looked at thoses swing arm bearings - they seam OK, but i haven't disassembled anything. just wedging a prybar up and down on them dosn't show any play - and the bike ride is good other than when i get on it. i'll look today and give them a shot of grease (I think there is a grease fitting??)

 

Hmmm i'll look into that middle gear damper. The book shows it, its a damper that would seam to make this kind of clunk if some higher (than what i normally apply) power were put into it. Also, the book makes a note of the fact that this middle gear runs in its own oil which while added by regular means through the main oil fill hole, to DRAIN that old oil there is a separate drain plug. I got this bike with 25,000 miles on it and no speedometer so im sure it's 25,000+. I have no idea if that oil was drained by the previous owner(s). I have drained that oil when i got the bike - but must confess that i have only drained it once in the 5,000 miles i have put on it. --- Sure sounds that this area of the driveline could be the "clunker"

 

I don't think there is a grease fitting - it's a take apart job on the shaft drive swingarms as there is no straight through pivot bolt, just tapered bearings on each side of the pivot point.

 

Brewster, don't mess with that middle drain plug, you could be heading for a world of hurt
Mr Time to Ride did a Mr Science on it not too long ago, there's not much in there and it seems those bolts like to strip
believe me that oil's not the problem

 

Not to bring up a dead thread, but did anyone have any luck figuring out what was going on? My '82 has been doing the same thing, but I can't recreate it with the bike on the stand. For me, it only happens when getting started rolling from a standstill, and not every time, either.

I have the normal (I think) amount of drivetrain play, but I don't think it's related. If it was, then it would be jerky every time I transitioned from decelerating to accelerating, wouldn't you think? This particular clunk only happens when it's under constant torque, after rolling about 5-10 feet, and only once. After that it won't happen again until I come to a complete stop, and then start up again.

I'll check the shocks, like Robert suggested, but I would think if they were the issue, I'd be feeling clunks all the time, not just under this one specific set of circumstances...

I've checked for play on everything I can see externally. I'm hoping someone else has already figured this one out, because I'm really not looking forward to opening up the drivetrain without even having a good idea what I need to do...

 

x2

 

I think I have the same noise in my new '82 Maxim. A little clunk when starting from a stop, even slipping the clutch and starting slowly, and doesn't happen all the time. When it does happen, it always feels like it's at about the same point as I release the clutch... when the handle is about 80% out.

 

Got anything in the trunk? I think my clunk comes from tools shifting in the tail section.