350i gearbox rebuild - vibration sorted after 3 months!

[sprevett]

for those of you old enough to remember my previous posts you will recall that after my gearbox was rebuilt/replaced following its self destruction on the M40 one summer's day...the car had a bad vibration in 5th gear. In fact when I got the car back from the 'largest TVR dealer' it was undrivable. Heath and the boys at the factory have since done a great job of sorting it - and had to completely re-do the gearbox installation and get the prop re-balanced. the dealer had apparently re-fitted the prop without taking care over the spline positions, drive train alignment etc. and hadn't even fitted a new clutch despite being instructed to do so! So, if you have to get the 'box out - be careful with the prop/spline positions and avoid main dealers! yours, happy again etc ..

[campbell]

I would have never thought about the spline position, but im glad your back on the black stuff.
If I had to get this done I would be doing this my self so it a good note to take in

Cheers

Cambelt

[honourablepickle]

how does the spline position make a difference ?
just a balence thing ?

[eMog]

honourablepickle said:

how does the spline position make a difference ? just a balance thing ?

It makes a difference. This is a very common mistake made by home mechanics. It seems like a minor thing, by the effect is not. It is easily addressed.

Propshaft shafts use a universal or Hookes joints to carry drive from one shaft to another where the two shafts are not perfectly in line and particularly where they can move relative to each other.

These joints consists of a cross or spider which carries needle roller bearings at the four extremities. The bearing cups are fitted into yokes, two on the input shaft and two on the output shaft. The arrangement allows the drive to be taken through an angle, particularly where that angle can change (as it does in a propshaft due to suspension movements).

The universal joint is not a constant velocity joint: If there is a non-zero angle of deflection between the input and output shafts and if the input shaft is driven at a constant rate then the output shaft will accelerate and decelerate twice per revolution. This effect can be negligible for small angles of deflection but it increases with larger angles and can cause vibration.

The rotational speed of a universal joint varies or cycles as it turns through 360 degrees. Since universal joints are almost always installed in pairs, they are normally "phased" so this difference is eliminated. being cancelled out by the two joints. (As one joint speeds the rotation up, the other slows it down so the rotational speed of the output is fairly constant.)

If a harsh vibration at high speeds is keeping you off the road or worried, check your U-joints for proper alignment..especially after any work has been done that would remove one end of the other. A visual check will tell you if your U-joints are lined up correctly. Simply compare each end of the driveshaft to see if the yokes on each end (the parts welded to the driveshaft tube itself) lie in the same plane. If they do not line up, or are at right angles to each other, it is usually a simple matter to unbolt the driveshaft and re-orient the splines of the two pieces to bring the universal joints into proper phasing.

That will stop the vibration.

[leorest]

eMog said:

Stuff

Now this is good information and it makes perfect sense. A prop-shaft containing two UJs will be constant velocity if they are phased correctly. If there is a splined joint between the ujs it is possible to adjust (or more importantly mis-adjust) the phasing. With the "almost" zero angle difference between the sections of the prop-shaft as installed on a Wedge I am surprised it makes a difference, so I can only assume the angles are significantly off of "zero"... you learn something new every day!

[MJG280]

It also applies to the 2 joints in the steering column. There wont be a vibration but there will be binding which appears negligible but will wear out the joints faster

[rev-erend]

Hence why you often see a hack saw mark across both surfaces - where a careful mechanic has noted the position..