prop/problems

hi all   i have had this vibration now for about 8 months i have replaced ever bush on the car ill start again all that has not been replaced is the prop and half shafts the vibration starts at 70mph and has gone at 85mph and is back at 100mph on wards, it feel like it comes from midd of car or poss from rear bmw have had the car twice and can find no fault, a specialist as been over it once recognises there is a prob but does not no what ,my local garage has had the car all day and has now told me he thinks its the roach joint on the prop therefore needing a new propshaft, i have spent 100s and 100s of pounds trying to sort this problem out all to no avail if some body can help me on this i will be very grateful other wise i will have to sale the car....what with the money im throwing at it and the serious grief im getting of the wife to get shot     

Edited by b8alk

hi miles yes i have tryed wheels and tyres/brakes/hubs/bearings/so on and so i have just been told by wife that cost so far is£1347.89p you can feel it though all seats. Im not happy selling my car full stop..... but what else can i do but run it in for a part x

im going to try fab

have just picked up car from workshop they have fitted new complete prop and have told me every thing on my car is spot on there is nothing at fault SO WHY HAVE I STILL GOT THIS ******* VIBRATION

I had a similar thing after fitting s/h wheels (17"x8" style 36 I think) a few weeks ago although they were the same style as my old wheels, they had a 98 stamp (obviously not E34) and 74mm spigot bores my old wheels had a 93 stamp and 72.5mm spigot bores.  I machined some spacer rings tonight for the front and it cured the problem I didn't have to do the rears as I recently found a pair of brand new 9" rears stamped 93.

Warren

p.s. you must remove the wheel and mesure the bore from the back where fits the hub spigot!

have you tried gearbox or engine mounts?

I know its not the cheapest place to take your car but has a main dealer ever investigated the problem for you ?

Oooops just read your original post again and you say that it has been to a BMW dealer twice, i wonder if there are any other main dealers local to you ?


Miles

Edited by e34m5

Andy

Was reading a technical book at the weekend and I think I may have some different causes to your prop shaft woes.....which won't be cured by ploping on a new prop shaft.  Seeing as how you have tried everything you have nothing to loose......

One cause of prop shaft vibration is due to the fact that the angles that are made at each universal joint MUST be the same otherwise, Hooke's law comes into effect or out of effect, sorry can't remember which.  For example if the angle at the gearbox end is 5 deg then the angle at the diff must be also 5 deg.  If there is a variaion in the angles then the rotational speed of parts of the universal joint will be different. 

As the joint rotates the spider moves on its axis, as it moves on its axis it changes the radius of the spider, thus if the radius changes the rotational speed must change and its this change that causes the vibration as there are two different speeds.  BUT this is cancelled out when there are two universal joints in a shaft provided they are both at the SAME angle.  This is why shafts have two universal joints.

Basically check that your diff is mounted correctly in the suspension system and also that the tail end of the gearbox is correctly located on its mount.  Doing this will make sure that you have the right angles for the drive line.

If your diff and gearbox are out of alignment i.e. you can't get matching angles at your prop shaft universals, no new prop shaft will cure it as your are bolting it on to something that is not in the right positions to start with.

Also make sure that the mating faces of the prop shaft joints are perfectly clean with no crap or rust on the faces.  The joints do not rely on the shear capacity of the bolts to transmit the load but the friction grip between the flanges of the joint.  The joint is clamped by the bolts which generate the friction to keep the two flanges together.  If one of your flanges on your gearbox or diff isn't perfectly flat then it won't mate properly with the prop shaft flange which will upset the angle of the joint as described before.

Hope I haven't confused anyone with some complicated physics!

Andrew

 

This is probably way off beam, but I wondered if you have had a
full 4 - wheel alignment recently? If the car has nudgd a kerb or
gone over a few holes the thrust axis may be out, which a proper 4 -
wheel alignment will fix at no great expense.   Just get a good
mechanic to do the job!      Sorry you're having so much trouble.

Hi,

in all this, have you checked the ride height at the back of the car?

Ian.