50 mph + full throttle: grinding noise?
#1
Rennlist Member
Thread Starter
Problem solved: 50 mph + full throttle: grinding noise?
Just took a spin around the city which I enjoyed a lot, summer is here I think I have a new thing to work on on. When I floor it in any gear its smooth until about 50 MPH...if I floor it in any gear at 50+ MPH the car gives a grinding sound...
I think I noticed the sound also when driving over a big bridge...so It could just be related tot the engine load?
I am afraid it is the transaxle or does it sound familiar tot somebody and is it something else? Hopefully easier
Cheers
'79 euro stick shift 928
I think I noticed the sound also when driving over a big bridge...so It could just be related tot the engine load?
I am afraid it is the transaxle or does it sound familiar tot somebody and is it something else? Hopefully easier
Cheers
'79 euro stick shift 928
Last edited by wopfe; 09-30-2014 at 03:05 AM.
#2
Burning Brakes
Fan hitting the shroud? Had that happen on an old Corvette when the motor mounts were worn. Only did it under heavy load when the drivetrain would twist from torque.
#3
Rennlist Member
Torque tube bearings? Search here. Hard to diagnose as you can't just put it on a lift and listen to it. Need to eliminate those other things, like the fan shroud. I've heard it in another car and it is between "chatter" and grinding, at least that one sounded that way. And at initial stage, it is intermittent: a particular harmonic had to occur within the drive train or it wouldn't do it. Maybe yours is more advanced. How many miles on car?
#4
Rennlist Member
Thread Starter
It has at least 100.000 miles on it, nut probably more (previous owner was not sure about the history)...original fan is still there...
Any tips on how to find out if it is the fan shroud? Take of the belt and test it shortly? Other thoughts? Thx
Any tips on how to find out if it is the fan shroud? Take of the belt and test it shortly? Other thoughts? Thx
#5
Burning Brakes
If it was making contact, there should be obvious scrape marks on the shroud. A quick 10 second check before moving onto other things like the torque tube.
#7
Nordschleife Master
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#9
Nordschleife Master
If it isn't the fan, one more thing to consider before going to the big job of the TT.
How are your tires ?
I had a dramatic sound and vibration from 65 - 70 mph only. I had flat while in Canada and threw on a used 255 in the rear to get me home. A few days later I thought the worst. When my Potenzas came in the sound/vibration were gone.
Just something to consider.
How are your tires ?
I had a dramatic sound and vibration from 65 - 70 mph only. I had flat while in Canada and threw on a used 255 in the rear to get me home. A few days later I thought the worst. When my Potenzas came in the sound/vibration were gone.
Just something to consider.
#11
Burning Brakes
I think you found your problem.
There's not supposed to be any play and those appear to be scrape marks on the shroud.
I'm guessing you have collapsed motor mounts which caused all the above.
There's not supposed to be any play and those appear to be scrape marks on the shroud.
I'm guessing you have collapsed motor mounts which caused all the above.
#15
Rennlist Member
MM
I can't really tell from the video. If they are original, they can't be very good. If so, you might also want to replace pan gasket while the suspension is out of the way. Best indicator is, does the engine "rock" or pivot when you blip the throttle from idle? Another would be to measure another '79 with good mounts, the distance from a given engine part to the cross brace.