Strange drivetrain judder- whaddya think?

[Luxobarges_Are_Us]

This morning I was heading down the A61 which has a nice stretch of decent quality tarmac where one could contemplate driving one's Scorpio near the national speed limit. After getting up to 4000rpm in fifth (the reader is to assume that the speedo had stopped working for a few minutes ), I eased the pressure on the gas, and the car started juddering quite a bit. The lightest nudge on the gas pedal would return things to normal, as would (obviously) getting out of gear, but I thought I'd try to observe it more systematically. The judder would disappear on its own accord after the revs dropped to about 2500. I then tried easing the gas from 4000rpm in 4th (the speedo was still broken!) and 3rd, and the car was super smooth as always.

 

I'm obviously not particularly bothered about the situation, but does anyone have any possible explanation to suggest?

[KruJoe]

Propshaft out of balance? Prop bearing mount?

[Luxobarges_Are_Us]

my understanding of physics is nearly non-existent, so do forgive me if I'm talking bollocks, but wouldn't an out-of-balance propshaft do the same dance coming down from 4000rpm irrespective of which gear you're in?

[KruJoe]

No.

Prop speed is directly proportional to road speed, not engine speed.

Remember, there's a gearbox between the engine and prop.

[Luxobarges_Are_Us]

ah, I knew I was talking bollocks!

 

I'll try redlining it in 3rd and see whether it does it then. Stay tuned for a spectacular engine failure report!

[meggersdog]

Does it shudder on both lpg and petrol.If it's only on lpg you need hotter spec sparkplugs.

[Guest Len H]

My Scorpio TD had a bit of a drivetrain shudder, I thought it was the propshaft but didn't investigate as it wasn't too alarming.

 

Probably the central bearing.

 

http://www.fordscorpio.co.uk/propshaft.htm

[504GL]

We had a similar thing on the Subaru and it was an inner joint on one of the front driveshafts.

[Pete-M]

I think you're ragging it too much, and it's probably either the centre bearing or one of the cv joints in knackered.

[Luxobarges_Are_Us]

Right, I've tested it in both 3rd and 4th at speeds where it would judder in 5th, and it's perfectly fine...Confusing stuff!

 

Pete, I don't normally rag my cars, au contraire I usually drive in a very sedate/lazy way. I just do the Italian tune-up every now and again because I want to know that the power is available in case I need it as well as get an idea about any potential faults in good time.

[Pete-M]

4000 in fifth? I'm no saint when it comes to speed limits, but that's a very broken speedo

[Luxobarges_Are_Us]

well, it's only a 2.3...

[Luxobarges_Are_Us]

Does it shudder on both lpg and petrol.If it's only on lpg you need hotter spec sparkplugs.

 

Good point! I 'll also give it a whirl on petrol but, as it doesn't seem to have the problem in lower gears, I can't see it making any difference.