Propshaft went "BANG" at 150+mph.......

[Max HEADVROOM]

140mph then with about 150mph showing i eased off the loud pedal at which point there was a "BANG!" followed by a strange sound and vibration from the propshaft area just underneath the centre console.

Fearing the worst, my mate dived underneath to see if he could see the source of the noise/vibration.


jesus christ.... your mate must be a fast runner !

[Laird Scooby]

He's about 8'5" so he can move quite quick!

[AndysR]

Sounds like you've been having some good progress despite the scare, good work. What was the engine revving at when the speedo was at the 150 ish mark btw..?

[AndysR]

Originally Posted by 760Simon

Dave,

I saw that two so trying to sort out getting over there before they close as I haven't yet sorted the panels

Depending on which panels you're after they have a blue 760 saloon and estate in for breaking ATM, same colour combo as mine

[Laird Scooby]

Originally Posted by AndysR

Sounds like you've been having some good progress despite the scare, good work. What was the engine revving at when the speedo was at the 150 ish mark btw..?

Thanks Andy - i have indeed! Finally got the last of the new tyres fitted today, the 4th one going on made all the difference!

It was feeling better but not quite right until then and it goes to show having the same brand all round really makes the car feel "right", even though they're only budget radials.

Where was the rev counter at 150 ish? It was somewhere near the 6k mark, can't quite remember but it works out about right for 25mph/1000rpm in top.

Talking of the speedo, i'm hoping the new tyres will help correct the speedo error which i worked out to be about 7-8% on the old tyres. Besides the fact they were down to about 3mm of tread, they were also 195/60 and i've fitted 195/65/15 for two reasons, slightly softer ride and hopefully correct the speedo.
Even if it only reduces the error to 3-4% that will be a vast improvement!

Originally Posted by AndysR

Depending on which panels you're after they have a blue 760 saloon and estate in for breaking ATM, same colour combo as mine

Best get yourself there pronto Simon! If you're lucky you'll get away without having to paint anything!

[TonyS9]

You need a bit of overboost to do 150mph but its (top speed) not recommended on the standard turbo, mine cracked at 140, still drove it like that for a year or 2 though.

[Laird Scooby]

Originally Posted by TonyS9

You need a bit of overboost to do 150mph but its (top speed) not recommended on the standard turbo, mine cracked at 140, still drove it like that for a year or 2 though.

Was that on a V6 (B280E) Tony?

[ie940]

Running it up to 150mph on axle stands is insane and mildly stupid.

Therefore I'm impressed. Excellent work.

[Rversteeg]

I understand it all started with a hunt for prop shaft vibrations, I guess after changing the prop shaft bearing. Did you find anything?

[Laird Scooby]

Yes and no - after changing the prop centre bearing there was still a lot of vibration and noise which was traced to the gearbox output shaft bearing/bushing and seal.

These components were renewed and then the high speed run on axle stands was conducted.

You see, the first time after renewing the prop centre bearing, there was a lot of strange vibration that was simply down to the prop centre bearing being slightly out of line on its mounting plate. The bolts were slackened and the car driven slowly round the block and the bolts tightened again, problem solved, except for the noise/vibration from the gearbox output shaft.

Once the extension housing/tailshaft/output shaft bush and seal were renewed it ran successfully at low speed on the stands so i brought the speed up. The only slight vibration and bit of noise is now coming from a slightly worn differential but it has done 220,000 miles so it's allowed to be a bit worn/noisy.

I may see if i can find a younger diff or back axle to fit instead but for the time being, i may try one of the additives that are designed for noisy diffs.

I'm not a big fan of additives in general but they have their place sometimes, usually when they alleviate symptoms that that are annoying rather than dangerous and would take a lot of work to sort out for what would be very little gain.

Meanwhile the diff oil is clean and looks reasonably young, no obvious trace of swarf or similar and is only a mild whine so easy to live with. Overall the car is now very quiet with wind noise being the biggest intrusion.