What is the awful noise?

[Cooper]

Update 12/04/2017: Some duplicated info [summary] here but it may assist.

When I accelerate quite hard to heavy I get this repeated bad vibration / banging sound which seems to be where the auto transmission is. I can't seem to pinpoint which gear it is in or be consistent rev readings. Anyway, it goes thud thud thud very rapidly for less than one second then goes away quite early in the acceleration. At first I thought I ran over a piece of wood and it was tumbling under the car.

I just replaced the tail shaft carrier bearing with no change. [today]
The flex disc was replaced in January this year.
The rear subframe is in excellent condition.
The shocks seem to perfectly fine.
The wheels seem good.
The driver's side auto trans mount is a little bit squished [looks like it is leaning over a bit] but the mechanic said it is fine. There is almost no movement in the trans when pushed heavily on.
Engine mounts are good.
Diff mount and surrounding area is good.
the exhaust and mounting rubbers are like new.
there is no visual damage from any parts hitting anything that can be seen.

You can see, both me and the mechanic are at a loss. I am wondering if that slight deformation of the trans mount is the cause. Any suggestions people?
Can something be wrong within the trans?

Cheers, Graeme

 

[Dickymint]

Its going to be so hard to find the problem, could be the gearbox mounts as they could look ok when pushed from under the car but when its being driven it will be trying to twist, sorry can be more help
Just had a thought If you had a gopro camera like cyclists use and attach in different places under the car you would be able to see what was vibrating... just a thought

 

[Cooper]

Thanks @Dickymint . I have mounts in a bag at home. I tried to replace them today but one must remove the exhaust to get access to the mounts with an auto trans as there is stuff all room. Oh yeh, the bolts are 15mm and I didn't have the spanner! Ahhh.

I am at work atm and I just got a cam to work on the laptop. I will mount it under there tomorrow and take her for a spin. When I resolve this issue I will certainly post the results!

 

[Cooper]

I might have a second attempt at changing out the trans mounts tomorrow. Last time I tried it I could not get good enough access to the top nuts holding the mounts onto the auto box.

I was conversing with someone [but I can't find it] who said I can lower the auto trans a few inches to allow better access to the upper nuts on the trans mounts. I forgot to ask if this can be done without having to remove anything else such as the guibo/artic/flexi disk. They advised me to keep an eye on the radiator fan clearance because when you lower the trans the engine will pivot upwards and close up the gap.

Does anyone here know if I can lower the auto box a few inches and if this is going to suffice to get access to the top of the trans mounts?

BTW, since I released the pressure and re-seated the trans mounts from below there has been an improvement in this issue.

Cheers,

 

[NZ00Z3]

When lowering the transmission, also keep a very close eye on the heater control valve mounted on the fire wall. The back of the inlet manifold will make contact with it and break it if you are not careful. You then have a water leak and and an overheated engine if you run it. Most M52 and M54 engine die on the first major overheating, so the heater control valve is one item you don't want to break.

 

[Cooper]

Does anyone know the actual size and torque specs for the 6 bolts that go through the guibo/flex disc? I think it is a 58mm M12 rating 10 but can't confirm. TIS is confusing and I like to confirm what is on RealOem. I will need the lock nuts to be replaced on the 6 bolts - I will re-use the bolts. I am not so confident when it comes to this stuff and I have looked everywhere for this info. Off to the stealers to get the nuts once I get this confirmed.

I have booked the car in to the mechanics for the guibo / trans mounts swap as I don't feel like crawling under the car by myself for this job. All happens on the 20th.

cheers.

 

[Gundun]

 

[t-tony]

In all honesty a good mechanic won't torque these bolts but will just use experience and a couple of spanners, even if you give him the figure.

Tony.

 

[Cooper]

OK Guys, need some more advice and suggestions please!

Mechanic just replaced the trans mounts and installed new Flex Disc. There is no change to this issue. He is at a loss on what is causing this issue. To date:

1. Replaced flex disc
2. replaced trans mounts
3. replaced centre support bearing
4. inspected tail shaft and U joints - all good
5. inspected engine mounts
6. inspected dif bush
7. inspect all links and such
8. no obvious signs of damage in boot [welds] or anything strange under the car

The awful sound seems to be coming from under the passenger side somewhere near where the seat gets buckled but that is just an estimate. I can confirm that I can feel the vibration building up when accelerating momentarily then the rapid thump thump thump , then all is good for the rest of the journey. BTW I have been 170 KPH with no issues [at speed] just while accelerating.

He said maybe it has something to do with the sub frame but he can't see everywhere up there therefore he is not sure.

I am at a loss!

 

[NZ00Z3]

Is it an out of balance drive shaft???

The drive shaft is a two piece item. If a previous owner had taken it out and separated it and put it back incorrectly, then you could have an out of balance drive shaft.

Just re-read your first post, you have an auto, when was the fuel and filter last changed? Don't believe the "sealed for life" BMW talk. Change the fluid and filter on a regular basis extends the life of the auto transmission.

 

[Cooper]

Is it an out of balance drive shaft???

The drive shaft is a two piece item. If a previous owner had taken it out and separated it and put it back incorrectly, then you could have an out of balance drive shaft. Just re-read your first post, you have an auto, when was the fuel and filter last changed? Don't believe the "sealed for life" BMW talk. Change the fluid and filter on a regular basis extends the life of the auto transmission.

Thanks. The auto has been serviced regularly by BMW in Victoria. Fuel filter was also changed. The engine purrs like a team of tigers, gear box change is good, no slack when it downshifts.

The tail shaft has been out twice by my mechanic now with me present for one of them. Perhaps there is a possibility that the tailshaft is at fault but I don't know how or why as the issue is only when I accelerate. I can literally go 100 MPH with no vibration at all. I am hoping to snag someone that will say aha! it is likely to be......

Cheers,

 

[Cooper]

After spending countless hours reading every post I can get on so many forums I am convinced that I need to have a reconditioned tail shaft. Not because the shaft tubing is at fault or it is a balancing issue but because the U joints will be binding under load. It is likely to be the part that attaches to the dif. One other guy made the observation that the threads go dead once people replaced the tail shaft, meaning it solved the issue cause the desperate cries for help are silenced! That sounds like proper logic to me.

I am now hunting around for a replacement.

 

[Cooper]

Update: With the wife handing me the tools on demand like a good nurse in the op theatre, I successfully removed the drive shaft and inspected. It's not an enjoyable job removing this stuff

The U joint near the dif:
No discernible play, smooth in all directions, flops slowly under its own weight, no oil fling

The U joint in the middle:
If I try hard I can get a little 'click' sound on one side, both sides smooth but one side is somewhat tight while the other seems quite loose, a little bit of grease fling in the tunnel but that could be due to the slip yoke.

So, its off to Hardy Spicer on Monday for refurbishment and hopefully this solves the issue. Reading up on drive shaft issues this can definitely cause my issues, but who knows at this point in time.

 

[t-tony]

Good luck mate, I hope it's needle you're trying to find in the haystack!

Tony.

 

[NZ00Z3]

Drive shafts are balanced as one complete unit. You need to mark it when you separate the two sections so they go back together correctly balance wise.It may pay to take both parts of the drive shaft with you. That way, it can be balanced and marked so you can put it all back together correctly.

 

[Cooper]

Thanks. I am taking the whole unit in. I also noticed that there are marks on the dif flange so I suppose I need to make sure it goes back in there properly. They will refurb the entire shaft.

 

[Cooper]

This is being documented in detail as so many people have similar experiences.

UPDATE: When I took the driveshaft in to Hardy Spicer the guy looked it over carefully and commented on how good it looks and the U joints feel good as well. My heart dropped. He said he will check it out on the machine anyway.

I went to pick it up Thursday and he advised me that they found fault with the centre joints and it would def give the bad symptoms I have been complaining about! YES! He also said there is a slight bit of movement in the rear joints so he wants to change them over as well. Unfortunately they did not have it ready for pick up today [being Friday] so I get it back Monday night.

I am feeling confident about this but the proof will be when I get her back together and give her a thrashing. More to come Tuesday

 

[t-tony]

This is being documented in detail as so many people have similar experiences.

UPDATE: When I took the driveshaft in to Hardy Spicer the guy looked it over carefully and commented on how good it looks and the U joints feel good as well. My heart dropped. He said he will check it out on the machine anyway.

I went to pick it up Thursday and he advised me that they found fault with the centre joints and it would def give the bad symptoms I have been complaining about! YES! He also said there is a slight bit of movement in the rear joints so he wants to change them over as well. Unfortunately they did not have it ready for pick up today [being Friday] so I get it back Monday night.

I am feeling confident about this but the proof will be when I get her back together and give her a thrashing. More to come Tuesday

Sounding like a positive result Coops, happy for you mate. Hope it's put it to bed.

Tony.

 

[Cooper]

The issue is now RESOLVED! Just got her back together a few moments ago and pressed her hard - no vibration and tunnel slap. It was definitely the U joints which looked and felt great, but had an issue when under extreme pressure. I hope this helps someone else down the track.

 

[t-tony]

That must've put a huge smile on your face mate.

Tony.