prop donut

Thu Jan 11, 2007 11:17 pm

hey has anyone had a problem with there prop donuts breaking ive had 2 go before turboing my car and then when i fitted the turbo i put another new one and new bearings bolts etc in the prop that was 4 months ago and its broke again! anyone no whats going on? and if and where i can get uprated ones?
all help gretly accepted

Fri Jan 12, 2007 7:34 am

basil wrote:hey has anyone had a problem with there prop donuts breaking ive had 2 go before turboing my car and then when i fitted the turbo i put another new one and new bearings bolts etc in the prop that was 4 months ago and its broke again! anyone no whats going on? and if and where i can get uprated ones?
all help gretly accepted

These usually only fail due to not being aligned correctly. If you have any sort of angular deflection in this coupling, it will rip it's self apart.

You must have the front section of the propshaft in perfect alignment with the gearbox output flange. If you find you have to push the propshaft centre bearing up (or it's already tight against the floor and therefore being pulled down) to bolt it up, you are not in alignment.

Is the engine and gearbox standard (apart from turbo), or have you done some sort of transplant ?

Ian.

Fri Jan 12, 2007 4:26 pm

hey mate its all standard ive changed everything but the prop wich makes me think the prop may be bent or summit whats the best way about checking the allignment?

Fri Jan 12, 2007 9:15 pm

jack up the car (rear only), remove the heatshields (exhaust may have to be dropped / split), put it in neutral with the handbrake off (obviously with the front wheels chocked and on good axle stands), get a willing assistant to spin a rear wheel round and watch the prop revolve and look for any distortion / wobbling.

are you breaking just the donuts or the bolts? the bolts will break if they're not torqued up correctly and being under the car it's a real pain to get a swing on with a torque wrench. oh, make sure the prop bolts are good quality too, the cheapo halfords high tensile ones are poor and will break but bmw ones are only about 20p or something daft.

i've been through a few bolts too! no donuts though...

Fri Jan 12, 2007 9:28 pm

i had similar problems after my engine conversion,every hard launch would break the centre bearing,one lasted 10 minutes after changing it

turned out my custom prob hadnt been balanced properly by the 'specialist' since balancing ive not broke one yet.have you had the prop off and perhaps refitted the bearing the wrong way around as its off centre.ive also had problems with a car that had previously been crashed and the shaft in the gearbox had been bent causing vibraions to break the bearing

Sat Jan 13, 2007 2:36 am

Mine broke because the sliding join was to stiff. Did cause a vibration aswell though.

Sat Jan 13, 2007 9:06 am

if this joint is set too tight and the gearbox / diff length is changed (new engine mounts fitted badly?) then it will push on the prop and could provoke it into kinking. if this was the case, i suspect it would vibrate like a swine!

Sat Jan 13, 2007 10:22 am

ive been breaking bolts and props from both bmw and euro car parts, the last time i had it done i got it done by a garage just incase i was doing it wrong so they should have been torqued there i hope! thanks gareth il ave to get under it and check that out, if it is that i think it mite be a trip to reco prop to get the prop checked out.
thanks for your help guys