Noise rear axle when deceleration Yamaha xj 750 maxim 82

Hello ,

Everything is put together.
I got my license plate today and wanted to drive but i remarked a strange noise when standing on my main stand. It only happens when i throttle and let go of the throttle. ( when engine braking )
Idle is no problem.

When motor isn't running and in gear it only goes 10° or something. So the joints are connected good.

Sound it like something inside is lagging.

 

Welcome to the forum. It is not the rear axle on your bike. I believe the knocking noise you are hearing is parts 4 and 5 coming together in the middle drive gear damper inside the crankcase, see schematic. I thought there was something wrong with my bike when l heard that at first. It is normal on the XJ shaft driven machines. My 900f does the exact same when l blip the throttle when the machine is on the centre stand.

https://images.cmsnl.com/img/partsl...-usa-middle-drive-gear_bigyau0852c-7_911e.gif

 

Hmm thanks for the reply.
Well its not really a knocking noise, i made a movie and will upload it in a bit. Its rather a vibrational tone with a constant frequency .
It feels like the driveshaft is connected good when taking speed.
And then when the tension is gone ( because throttle is gone) -> that there is a lag or that it has room and not 'connected' as firmly as before.

When i go quickly to 70km/h , start breaking and then let go my throttle the sound is not there. But thats also because the tension stays.

Well thats what i feel and think though, but i have whatsoever no background in engines . This is my first diy project


I think the sound comes from the driveshaft , but it's really difficult to locate .. Could aswell be something else.
Is it normal that the driveshaft becomes a bit warmer while driving ? (not hot but a bit warmer then my rear shocks for example)

 

Before you work on the machine do you have a Haynes manual? Have you worked on any vehicles before? Have you checked the oil level in the driveshaft? You should put the machine on the centre stand and keep the rear brake on. Then rev the engine in neutral and let us know what happens. Is there any vibration or noise as you described? If you get the noise and the rear brake is on it cannot be the driveshaft that is making the noise.

Switch the engine off. With the bike on the centre stand grip the rear wheel at the top and bottom and try to move it back and forth. Is there any movement you can detect?

 

It can also be a stiff U-joint. It would vibrate and increase rotating force if it makes the drive shaft wobble around.

 

Let’s wait til the video…__

 

Sadly enough the video doesn't say alot. You only hear the wheel spinning loudly.( that also gives a bit a strange noise but i guess thats normal)
I know sounds can come from everything because alot of things are spinning with a specific frequency etc. But i really have the feeling what i'm hearing while driving isn't normal.
That's why i didn't drove further than one street to prevent damage.
Maybe i can ask that someone makes a video while i'm driving.


Yes i have a manual, that thing helped me so much.
I didn't worked on vehicles before.
Bought this bike 4-5 months ago in pieces. Only the engine and some other parts were together.

I've put new oil in the engine & driveshaft.
The rev thing with rear brake in neutral doesn't make a noise. Its only in gear.

I'll detect if there is any movement possible when i'm done working but i don't think so.




i've found this online but is about cars :
"You may also trace this noise to a loose pinion-bearing preload. It’s likely the case when you only hear the noise when decelerating."

 

Are all your exhaust header pipes secure? The pipes to the head and silencer joints. Anything loose in the silencer. Sounds like something is vibrating when you rev the engine. Not sure it is the final drive.

 

I agree it sounds like metal vibrating, but if it is the exhaust, then the sound should expectedly be the same whether in gear or not. But what about the shield fitted to the wheel, could that me loose? You can use a stethoscope to better pinpoint the source of the sound, just make sure you do not get caught by the spinning wheel.

 

There is one pin in my cilinderhead that broke off. (was like this when i bought it)
A friend will try to fix it in the future.
It has some backfiring because of it.
The others parts are tight and double checked.

I don't think this could be the cause as the sound is related to the decelleration.


Anyway i'm almost done working and when home i'll try to make a better movie while driving
Because when looking again to the video it doesn't give the right sound.

 

The other pin on your exhaust is more likely to break if you keep using the bike. Get something to protect your hand and push the pipe against the cylinder head while the engine is being revved. I don't think it is your driveshaft, do you know how many miles or kilometers the machine had done? The transmission is bulletproof on these machines and it is unlikely that is the cause of your problem unless the machine has covered a lot of miles. Or the previous owner has stripped the rear hub or split the cases and not rebuilt it properly. Don't strip the final drive down you need to know how to set the gear backlash etc if you do that.

 

I have just listened to your engine through my computer speakers was the phone before, clearer now. Put the bike in first gear with the engine not running. How far can you turn the rear wheel?

 

Part 42. Did you remove the rear wheel to fit a new tyre? If so are any parts not replaced. There is also a big washer on the opposite side of the rear hub that must be fitted between the swing arm and spacer.

https://images.cmsnl.com/img/partsl...1982-c-usa-drive-shaft_bigyau0790d-6_0eb8.gif

 

Rear wheel spindle and spacers, 900f your bike should be the same. XJ 750 in the left picture. It does sound like something is grinding when the engine revs are increased.

 

Good suggestion! If a spacer is missing, things can bind or touch that should not.

 

I think he should spin the rear wheel without the engine running to see if the noise is there. If it is it hopefully rules out a problem with the transmission.

 

Check your engine oil level too and make sure there is no fuel in it. Engine and transmission share the oil.

 

Do you have a washer like this and spacer? Is the 750 the same?

 

Apologies for the late reply.
Had a super busy weekend and wasn't home. ( wedding and family etc)

Anyway, when i came home friday i tested it again.
I drove and the sound was gone, don't know why or what happened. But thats why i didn't posted a new video.
First it was on it head stand and i kicked it off it very hard, so rear wheel bounced very hard on the ground and maybe that putted something more in place.

I have the spacer on the rear wheel, made sure everything is on it a while ago because it looked a bit 'funky' to me.
When i had the sound i rechecked all the spacers again and it was all good. I know that spacer.

But but but , i did something before that also:
I've put more tension on my clutch cable, i thought it maybe wasn't enough because somethimes the first isn't taken properly.(looked the clutch wasn't 'on' enough)

And when riding i had something else that was strange :
When decelerating again it always pushed a bit further to then slow down.
It seemed that the engine still wanted to run for one milisecond before engine breaking.


When driving for a bit my throttle did also some strange things. ( i could give throttle by doing the normal throttle movement but also by doing it oposite )

So today i checked my cable and i saw it was screwed up. While putting it off my steer the cable snapped.

So i think that caused the 'engine still wanted to run'

Now i first have to fix the cable ( i have the old one laying around) , before i can check the sound again.


Then i also have a question about my fuel tank.
Probably i will switch it out later in the winter.
But now my 'tap' is very closely to my engine, that means my fuel 'pipe' hose is touching the engine. -> is this dangerous ?
Its a fuel hose with a thick layer on it , not only rubber.
But i can imagine if it melts everything gets on fire.
-> ( so if i get my new fuel tank i also should give the tap a better place )
My vacuum hose snapped because of this. ( still need to replace it but it seem to drive fine also without it) , but probably not 'optimal'


Also rechecked my engine oil and it still has the same amount in it that it had when i renewed the oil some months ago. I measured the cc's then so it should be fine.

 

Can you post a picture of your fuel pipe and tap. It cannot be routed correctly if the pipe is touching the engine. Try and re route it if possible. Yes your inner throttle cable has been sticking keeping the throttle valves open hence the lack of response when closing the throttle. You should lubricate the throttle and clutch cables to make sure they run freely.

 

If your vacuum line is not connected to the petcock you MUST block it off at the carb boot or stop up the line.

 

Was sick for some days so made no real progress.

Today i levelled the fuel tank because i didn't trust it.(see picture)

I drove a bit and it all seemed fine.. No real noise anymore coming from the rear.

Then i connected my vacuüm José to the petcock. Putted the stand on 'ON'
But IT seems that its hesitating while doing high revs in Gear. Its start sprutteling and engine dies after a while. So probably have a vacuüm leak somewhere.

There is one clamp i didn't connected so maybe its sucking air at the place. Will try in a bit.



https://ibb.co/bX1JTMr

 

Why is that exactly?

 

Otherwise the cylinder will suck false air through the port, causing poor running.

 

Yes like a vacuum leak weakening the mixture.

 

Okay never thought about that because IT was running properly.

When i started thinking , i probably found some big leaks. 2 of my carb boots are old and have some cuts in Them. So i ordered new ones directly . And they also didn't have the metal o ring in Them for tensioning.

Bummer i have to wait a long time for Them to arrive. Probably Will be after my vacation to finally test it. Hopefully het drives better then.



My shock absorber Height extensioner came this week. 3cm. Ill give Them a try in a bit.
Just Worry about the strength as its alloy alluminium from AliExpress

 

I hope you didn't buy the cheap Chinese carb boots, they are not worth the money. They fail and you don't want anything from them getting sucked into the engine. Better getting the Yamaha ones and be careful removing the bolts because they can shear off in the head. Not being negative just seen this happen before. cmsnl in the Netherlands have them, pricey though. Don't know what they would cost from Chacal, you can contact him on info@xj4ever.com if you want. Or Fowlers Yamaha in the UK might have them or your local Yamaha dealer. With the clamps not there that secure the carburettor to the inlet boot vacuum leaks can happen, your boots might be fine, if the cracks do not go all the way through. Spray a little carb cleaner near them (with a cold engine just started) to see what happens to the revs. If is does not change you can fill the cracks with silicone RTV I think it is.

 

Shock absorber height extension. Be careful regarding the driveshaft angle. Someone will know what the limits are.

 

Ow crap ,i bought those chinese ones indeed -_-
Looked online for other ones from yamaha themself but couldn't find them rapidly so decided to go alieexpress.
Hard to say indeed if my boots are still fine or not , but i guess they are old and a bit 'rotten'. And there are alot of cracks ..
So i'll try with the chinese ones and if that indeed screws up i'll need to look further for the original ones !

Hmmm interesting what you say about the silicone.
I tried the spraying and it didn't really affect something. But i tried this with my fuel tank on prime. (not sure if thats a problem ?)
Or should i try it on the regular 'ON' mode.


Regarding the height extension, i would also like to know the limits. My plan was just try and see.
Tried to do alot of reseazrch on this subject but not easily to find usefull info ..

 

I bought cheap Chinese intake rubbers for my XVS650. Have no idea how they will hold up over time, but they still looked like new after a year, and were still flexible. Also bought a radiator for a Honda CB400SF once. With freight, it cost less than 10% of an OEM radiator. Yes, it was flimsy in comparison, but lasted a decade with no leaks.

 

It doesn't matter with carb spray if engine does not rev you haven't got a vacuum leak. @k-moe knows the limits for the driveshaft.

 

The OEM u-joint can't take more than 2" of lift or drop. Adjust the ride height more that and it will go beyond the range of motion while in use and be damaged very quickly.

 

Okay small update.
Yesterday i wanted to up the Idle because it was running poor. I accidentally screwed with the synchronisation . Wouldnt start anymore,but i found a YouTube video on doing the sync with water and it helped. Starts again and i upper the Idle so it runs a bit better.
Was driving 30mins and after 20min it started to die. I was able to drive home but without the real power. Sounded like it was going dead and turning off,but it didn't.

So what the case is atm :

I have no stock air filter. I have those aftermarket seperate ones.
I have a new tank( benelli Mojave) ,new petcock but without the vacuum lines.
So i capped off the vacuum lines between the carbs.
I checked my inlet boots again and i think they still are fine,cracks are only on the outside. (Alltough my new ones are ordered)
My Idle screw is fully open. But it still needs a bit throttle to not die in Idle.

My spark plug indicates a grey color.


And btw it runs heavenly good the first 20min. It was like a dream !! So nice.

Anyway i had this problem before. That day was alot hotter (+10degrees). So that why it started earlier then probably.

So it means its only when the engine gets hot.