Noise Under Armrest???

[7thDimension]

Hello, I have a knocking/thumping noise under the armrest during heavy acceleration while turning, and sometimes just under heavy acceleration. It feels/sounds like somebody is knocking on the underside of the armrest, the noise doesn't occur when accelerating slowly. The car has 270k miles, I'm going to drop the tranny to replace the tc soon. What should I change while I'm in there to get rid of the noise? CSB maybe? The noise just started recently. I'd rather not replace the whole driveshaft... Please help.

[740il97g]

replace the whole drive shaft. Its most likely out of balance. If you just replace the center support. 2 months tops before it goes bad again. I got rebuilt one with a warranty from Bavarian for under 200 2yrs ago still good.

[dazednkenfused]

Mine just started too...no vibrations yet, but I feel the "knock" during heavy bumps and etc. :mad

[TxDarth]

replace the whole drive shaft. Its most likely out of balance. If you just replace the center support. 2 months tops before it goes bad again. I got rebuilt one with a warranty from Bavarian for under 200 2yrs ago still good.

I disagree completely.....when the center bearing support goes this is exactly what happens. Replace the bearing or drive shaft components only if they are bad when you get there....but I doubt it. Bearing and support at most I will bet on it.

[7thDimension]

So I'll just replace the center bearing. It also makes a ping noise when I shift from drive to reverse...

[TxDarth]

So I'll just replace the center bearing. It also makes a ping noise when I shift from drive to reverse...

That's not so good - now replace the drive shaft! You prolly have a bad "U joint" as well

[7thDimension]

Can I replace just the u joints?

[bobzdar]

Can I replace just the u joints?

I think you can replace the center u-joint, but it's likely that it's the CV joint at the rear that's bad which can't be replaced.

[TxDarth]

I think you can replace the center u-joint, but it's likely that it's the CV joint at the rear that's bad which can't be replaced.

That and I have never found a source for the U joint - BMW will not or did not offer it last I checked. I had one go bad on my old '86 L7 and could not find I went with the shop listed in back of the Roundel mag. I believe it was around 500.00 with life time warranty. The new one had a grease fitting but you would play hell getting to it on out cars......

[7thDimension]

So it's not the center bearing making the noise? Could I check if it's bad without going under the car

[TxDarth]

So it's not the center bearing making the noise? Could I check if it's bad without going under the car

You are giving two symptoms - first the rumble noise under the armrest is more than likely the center bearing. The noise when changing direction would be either the center U joint or the rear CV joint a the rear of the shaft at the rear end.

[740il97g]

I'm going off experience. I had the same knocking under acceleration. The center barring was torn. Replaced it. Two month's later. Knocking again.

[7thDimension]

It almost sounds like there is something rolling around under the armrest. The noise came about within the last 50 miles/a few days ago. The noise only occurs if I am turning left and accelerating hard, or sometimes if I punch it from a stop... It only occurs for about 1/2 a second. It's like clunk clunk, then it stops. It has always made the pinging sound from the rear when shifting from D to R...

[TxDarth]

It almost sounds like there is something rolling around under the armrest. The noise came about within the last 50 miles/a few days ago. The noise only occurs if I am turning left and accelerating hard, or sometimes if I punch it from a stop... It only occurs for about 1/2 a second. It's like clunk clunk, then it stops. It has always made the pinging sound from the rear when shifting from D to R...

Quit talking about it you have a drive shaft problem - face it!

[7thDimension]

So I have to replace the whole drive shaft?... Dammit...

[Podmore]

Long shot, but check to make sure you haven't just picked up a rock which is rattling around on the transmission support cross-member. I had an annoying rattle that only occurred on left hand bends, and only under some circumstances - found a rock the size of a golf ball had managed to bounce up and lodge on the cross-member.

Diagnose, don't guess! If it was the csb, it would rattle/thump under load whether turning left or right. And driveshafts don't 'go out of balance' unless they have had an impact.

[7thDimension]

Long shot, but check to make sure you haven't just picked up a rock which is rattling around on the transmission support cross-member. I had an annoying rattle that only occurred on left hand bends, and only under some circumstances - found a rock the size of a golf ball had managed to bounce up and lodge on the cross-member.

Diagnose, don't guess! If it was the csb, it would rattle/thump under load whether turning left or right. And driveshafts don't 'go out of balance' unless they have had an impact.

Well, it occurs mostly when turning left under hard acceleration... I think I'll check if there is an object which could be rattling around. When I drop the tranny I'll replace the csb and add grease to the rear cv joint.

[Nyc Dito]

Hello, I have a knocking/thumping noise under the armrest during heavy acceleration while turning, and sometimes just under heavy acceleration. It feels/sounds like somebody is knocking on the underside of the armrest, the noise doesn't occur when accelerating slowly. The car has 270k miles, I'm going to drop the tranny to replace the tc soon. What should I change while I'm in there to get rid of the noise? CSB maybe? The noise just started recently. I'd rather not replace the whole driveshaft... Please help.

did your rattle go away?

[WarMachine7]

Hey so your gonna change your tranny oil at 270k? Have you done it before after 200k? How did it go for you because im at 207k and the mechs keep sayin to leave it alone but i have the tc shudder and i wanna get rid off it, also change my filter also. What do you guys think?

WAR MACHINE

[Mayorchuck]

Hey so your gonna change your tranny oil at 270k? Have you done it before after 200k? How did it go for you because im at 207k and the mechs keep sayin to leave it alone but i have the tc shudder and i wanna get rid off it, also change my filter also. What do you guys think?

WAR MACHINE

I think you need a new mechanic. Fluid/filter change and some Dr. Tranny Shudder Fix solved my problem at 210k.

[7thDimension]

did your rattle go away?

Yes the noise went away, I pulled the transmission when I replaced the tc, and I changed the guibo, and csb, I also re-greased the driveshaft cv joint, which fixed the pinging noise when going from drive to reverse.


Hey so your gonna change your tranny oil at 270k? Have you done it before after 200k? How did it go for you because im at 207k and the mechs keep sayin to leave it alone but i have the tc shudder and i wanna get rid off it, also change my filter also. What do you guys think?

WAR MACHINE

I changed the fluid and filter when I got the car at 269k, pretty easy job. Shifts much smoother now. I wouldn't recommend a flush, just have them change the filter and refill with fresh fluid.

[7partsonly]

Most people just change the center bearing but, they never take into account of why it broke.. Well after changing two I found that I needed the lower ball joints. Everytime I accelerated the rear wheels moved in and out, this in turn moved the rear end, tweaking the driveshaft......

[WarMachine7]

What is the fluid i need to use? Im pretty sure i cant just use any kind of tranny fluid?

WAR MACHINE

[7thDimension]

I use pentosin atf1, the fluid you use must be compatible with the spec.

[WarMachine7]

Well i drive a 95 740il, do anybody know which one i use?

WAR MACHINE

[7thDimension]

You can use the same fluid, pentosin atf1 is fine. 5hp30 and 5hp24 use the same fluid.

[WarMachine7]

And that is the bmw recommended fluid? I thought it would be mobil1 or castrol or something

WAR MACHINE

[7thDimension]

I don't think mobile1 or castrol makes a BMW compatible transmission fluid. Most auto parts stores can find you the correct fluid. I've had good luck with oriely's.

[jmarloltd1]

So if I'm getting the knocking under my armrest in my e38 then is it the center bearing or the whole drive shaft i see a lot of people saying either one just looking for some answers.

[Podmore]

So if I'm getting the knocking under my armrest in my e38 then is it the center bearing or the whole drive shaft i see a lot of people saying either one just looking for some answers.

Centre Support bearing (CSB) is a known failure point on the E38. The rubber diaphragm which centres the bearing in the bracket gets brittle with age and eventually tears, allowing the centre bearing to flail around under acceleration. On a 20 year old car, it's more than likely the problem. The drive shaft itself is a pretty solid unit and only needs replacing if the rear universal joint fails, as apparently that is not available as a replacement part. So if you haven't let the thing flog itself to death yet you should be OK just replacing the CSB. You will need to ensure that when it is installed there is no tension in the diaphragm (there is a small front-rear adjustment).