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Re: diff nose hights

Posted: Fri May 04, 2018 7:25 am
by Clifford Pope

Re: diff nose hights

Posted: Tue May 08, 2018 5:42 pm
by bigestate
Looking at the prop shaft angle video, and comparing it with mine, mine all sits remarkable in line from the centre of the gearbox mainshaft through to the pinion bearing on the nose cone. All the different props I have fitted all seem to give a slightly different vibe at slightly different speeds, which to me can only be one thing, the prop out of balance or iffy UJ's?

Re: diff nose hights

Posted: Tue May 15, 2018 4:14 pm
by johnnydog
Maybe nothing to do your issue, but I understand there are two types of prop shafts fitted. There is the solid type, and then what they call the damper type which I understand may have been used on PI's etc. The parts book makes reference to the two types.
I think the solid type is a constant diameter along its whole length; the damper type has what appears to be like a sleeve of a narrower diameter at one end.
I have looked at one fitted to my PI, and it looks like a rubber insert fitted between the outer part of the shaft, and the narrower section.
If this damper is partially parting company with the outer body of the propshaft, then it may be a cause of the vibration you describe.
Possibly clutching at straws, but as with modern cars so called dampers don't last...you only have to look at dual mass flywheels....!

Re: diff nose hights

Posted: Wed May 16, 2018 1:06 pm
by bigestate
That's a good point, the rubber is, what I think a seal to stop the grease spreading out, but if this spline is slightly worn it too can cause vibration as you say. More food for thought if I'm on the right track of what you say about the props.

Re: diff nose hights

Posted: Wed May 16, 2018 4:50 pm
by johnnydog
The gap between the main body of the prop shaft and the slightly narrower sleeved end on the damper type is only an 1/8" , making it a total of 1/4" narrower overall, and it only extends about 1 1/2" out of the main body of the prop shaft. I don't think it has any relationship to preventing grease loss, as the only grease points are the UJ's themselves! Prop shafts as you know are hollow inside - otherwise they would weigh a 'ton'!

Re: diff nose hights

Posted: Thu May 17, 2018 7:41 am
by Rally D
Charles H wrote:
Wed May 02, 2018 1:10 pm
All very familiar! The rally car also has this issue, and I suspect one of two things now having gone through similar swops and replacements. I even changed the gearbox, but used the same overdrive. So, overdrive unit? or engine balance, possibly the front pulley damper? Clutching at straws. I too have learnt to just live with it.
Yes my rally car is exactly the same and the vibration is worse overdrive engaged but you I can drive through it to starship speeds but it never completely goes away. Ive replaced everything as well all the shafts, diff, nose, wheels, tyres, angles etc etc.

So on Tuesday I went to Vibration Free near Bicester and the service was brilliant, really thorough and helpful and spent a lot of time with the car in the air and driving it up to 70s and 80s and everything in between, sensors placed on the front of engine/side and bell housing prop and driveshaft and wheels checked (also balanced front wheels on the car now perfect.

Anyway the conclusion was surprising. Its not the prop or angles or driveshafts etc. There is a spike of vibration/inbalance recorded where the gearbox attaches to the engine. This is a completely rebuilt, balanced engine with dowels where the gearbox locates. Something they see quite frequently. Only has to be out by a very small margin to cause a significant vibration. Or could be gearbox input or spigot etc. The box has to come out so I will investigate further.

Re: diff nose hights

Posted: Thu May 17, 2018 9:05 am
by Charles H
Very interesting. I look forward to hearing the outcome of this.

Re: diff nose hights

Posted: Wed May 23, 2018 11:54 am
by bigestate
Me too.
One other thing I forgot to say I don't get any vibration when my car is first used, it only starts to develop into its vibe frenzy when it warms up, usually after 5 minutes of driving :roll:

Re: diff nose hights

Posted: Thu May 24, 2018 4:16 pm
by Clifford Pope
bigestate wrote:
Wed May 23, 2018 11:54 am
Me too.
One other thing I forgot to say I don't get any vibration when my car is first used, it only starts to develop into its vibe frenzy when it warms up, usually after 5 minutes of driving :roll:
Could that be because the rubber mountings are better at absorbing vibration when cold, but allow more shake as they warm and soften?