Prop shaft noise

inovermyhead

inovermyhead

Well-Known Member
Messages
516
Reaction score
166
Location
Sydney
Recently completed 3.5ltr and 5 speed transplant on my coupe and it looks like I have an issue with the prop shaft. When accelerating in first at anything more than gently then prop will thump onto the transmission tunnel and this is more pronounced with spirited acceleration, ie 3500 revs and up. Got a chance to look underneath the car yesterday to check that the new centre bearing was still in good shape and all appeared to be good, although it had a lot more flex than a X5 that was on another hoist. Tried to load up some torque with the hand break pulled on whilst in 1st gear and failed to recreate the thumping issue but the prop ran straight and true. I dought its a balance issue as that would appear in all gears at all speeds and the car has no issues once moving, able to pull hard in all gears. All parts in the drive line were replaced with new when the swap was done.
Thoughts, comments and suggestions would be appreciated

John
 
Is it aimed the right direction?
Pre-loaded?
A Febi brand?
 
Not sure of the brand but came from W&N
I looked at the posts on the board re preloading but failed to understand the concept/ technique, also my frendly wrench poo pooed the idea so no not pre loaded.
I was not aware the bearing was directional so there is a 50/50 chance that it may be backwards.

The sound of the thumping is behind the handbrake and it's not a gentle sound but a Bang,Bang,bang enough that you back off straight away.

John
 

Attachments

  • image.jpg
    image.jpg
    91.6 KB · Views: 188
Pre-loading is easy/simple.
Note that the bolts to the center bearing are in slotted channels.
Push the bearing forward a 1/4" from its natural position just as you tighten the bolts.
Done.
 
Propshaft...

Is the shaft straight. If not that is the reason. I would bet the rear of the gearbox is too low as a 5 speed always needs a bulge in the tunnel to get it high enough for the prop to be straight.
You can check it with a plank of wood with a cut out half way along to clear the centre bearing. Hold it onto the bottom of the rear half of the prop & see if the front half follows the same line.
 
Propshaft

Thanks everyone for the replies and tips, I will get onto them soonest as I am keen to be able to give the new engine more than the current slowly does it approach. I was quite shocked by the amount of lateral movement in the bearing and am concerned that the said bearing may not up to it although it looks fine..
Also as it may have been mounted the wrong way would I be best advised to replace? Thanks SF Don for the link, way cheaper than here or even Europe.

Re gearbox angle, when the box was fitted the GB mount, sent as part of a kit from Carl Nelson, I think it was from a E12 early 5 series, the mount looked so flimsly attached that we fabricated a new one and spent some time lining it all up but I wil check out the plank method now everything has had time to settle.

Donut looks brand new so that's fine, new bolts everything ??

It is a two piece prop and when it was shortened I don't know if it was taken apart and then rejoined and balanced ??

Thanks again for the tips I will get on with these and let you know

Cheers. John
 
Put the "flimsy" tranny support right back where it belongs!
They hardly ever go bad and will insure your
Angles are correct.
If you want I can order you a new center
Bearing with my next order and send via USPS.
 
It could also be an improperly mounted exhaust or center resonator (if you still have one), or one that is mounted too close to the body.

Another thought is to verify that the motor mounts are correctly fitted and torqued.
 
Thanks Don that would be great if you could order a new bearing for me, not sure how we go with the practicalities of this. I am happy to put my email up on this board or do I use private messages? I also have a pay pal account if that works for you.

Re the custom tranny support, It wasn't the support that looked flimsy it was the way that the support was mounted. The only way it fitted was at an angle across the tunnel because when lined up the support lined up perfectly with the cut outs in the rails making a perpendicular arrangement not possible. This ment that the support would only line up when set up at an angle of 20/30 degrees and also it ment that we had to rely on two bolts to support it. It just looked a bit suspect so a replacement was made up with 5 mm flat plate that allowed both perpendicular placement and extra security with a four bolt attachment. I still have the original support and will re look at it as we have to pull the gearbox out for an overhaul anyway.
My mechanic has built three of these mounts for the historic race cars that he has been building up. No problems with them only mine??. You may want to check out a You Tube video of a one off E9/E3 hybrid doing an engine test run,
Look for BMW M30 CSS Special 330 hp run. This car started life as a four door!!

Cheers. John
 
Sop is to mount at an angle or slot the bracket.
I'm ordering in the am- I ll get you a center bearing if
You need. Do you have a pic of one installed?
 
Are those historic race cars running solid engine and gearbox mounts? The reason I ask, is that I have had a very similar problem to you recently, and despite checking and replacing everything discussed in the thread previously nothing changed. It was only solved by reducing the flex in the engine mounts (which were new oem). I used vibra technics ones as my specialist uses them extensively in other cars. They appear an excellent solution, no change in vibration or noise but they certainly limit engine twist and movement under acceleration. Just to clarify- my car was already running new diff, gearbox, rebalanced prop shaft and all new bearings/ bushes that we aligned with a replica tool to the one BMW used back in the day.

It may be something to consider if nothing previously suggested works and your pulling your hair out like I was!
 
Propshfts woes

Not sure what mounts the race cars are running for the engine, but the gearbox supports are the same as mine with a poly bushing and 4 bolt support. It could possibly be that the new oem engine mounts are to soft as under heavy breaking sometimes the fan will rub slightly on the radiator!! If it turns out that is the case can you point me in the right direction for the uprated mounts?

Cheers. John
 
Thanks for the link to the mounts, I'll keep going to find the solution but stronger mounts would stop the Rad/Fan issue under braking as well This e30 mount is what you run in your road car?
 
No problem. Yes they are in my road car - they were designed as a solution for road cars needing to solve this issue. My specialist has used them extensively in road cars from multiple manufacturers and swears by them. They do of course do race versions as well.
 
You must log in or register to reply here.
Back
Top