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250 V8 20 MPH vibration

DickSpeedy
Posts: 46
Joined: Sun Mar 20, 2016 2:07 pm

250 V8 20 MPH vibration

Post by DickSpeedy »

I have completely rebuild my 250 V8 from the ground up. I am struggling to rectify a vibration that comes in at 20 MPH.
All the engine & auto gearbox rubbers are new, the prop shaft has new universals and has been balanced.

I have set up the alignment as per the service manual ensuring that the rear engine mount was disengaged whilst aligning the prop shaft.

The Auto gearbox and torque converter was rebuilt by specialists. The engine runs smoothly.

Can anyone help with suggestions as to a remedy. I have been through all the past postings and found nothing to guide me.
Richard

Christopher Storey
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Posts: 404
Joined: Wed Mar 16, 2016 6:40 pm
Location: Cheshire

Re: 250 V8 20 MPH vibration

Post by Christopher Storey »

Does this vary with drive/overrun or with load and which gear is selected ? Is it BW35 or BW DG ? Have you tried selecting N and seeing whether it persists or varies if engine is allowed to idle or for that matter runup to significant rpm in N? This will give you some guide as to whether it is an engine/transmission vibration, or whether it is chassis orientated i.e ? wheel balance or, at this low speed, more likely to be a defective wheel or tyre e.g. excessive run out/bent wheel or the like, or , perish the thought a bulge in a tyre tread

PS Have you checked that the propshaft u'j s are correctly assembled with all the yokes in the same plane - failure to do this can lead to this sort of problem because these are not constant velocity joints

tjt77
Wise Man
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Posts: 525
Joined: Wed Mar 23, 2016 7:01 pm

Re: 250 V8 20 MPH vibration

Post by tjt77 »

difficult to diagnose without actually looking at the car.. cause and effect :- did it have this vibration BEFORE the engine and box rebuild ?? if not its likely related.. investigating the first question posed by Christopher should shed some light on the 'problem'.. is the vibration consistent and always @ 20 mph ? does it vary with engine speed and load ? consistent vibrations tend to be in the cars chassis components.. variations with engine speed and load are generally down to issues with engine/gearbox and possibly prop shaft .. Its certainly NOT at all unusual to have balance issues in the torque converter.. this will set up vibration that is more enhanced at certain engine speeds.. is it vibration free above 20 mph ?

DickSpeedy
Posts: 46
Joined: Sun Mar 20, 2016 2:07 pm

Re: 250 V8 20 MPH vibration

Post by DickSpeedy »

Thanks for the feed back guys. The vibration only comes in when under load or when the car is held at a constant 20 MPH.
The car was scrap when I bought it and had not run for 30 years so I don't know if the problem was there before the rebuild. Wire wheels are brand new as are the tyres.
I'm going to put the car on a lift today to check out the alignment of the U.J's.

classiclife
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Location: Ridgewood - East Sussex
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Re: 250 V8 20 MPH vibration

Post by classiclife »

Hello Richard,

Is the vibration localised or does it transmit through the entire car - thus making it difficult to locate the source ??

Not knowing what type of ramp you have is it possible to lift the car just off the ground so the wheels can run in D and R ?? That may help to narrow the area.

I do know of a case similar to this where the problem was eventually identified to one rogue wheel (also wire) it was determined by swapping the wheels back to front and vice-versa; the vibration disappeared. All wheels were then checked by a fitter of which one of the wires was found to be slightly out of "true"; I think it eventually necessitated the tyres being removed and checking the wire bare. Replacement made and the issue was solved no matter which wheel was placed where.

On a personal note I had a minor vibration on my Alpine, of slightly higher speed 35-40, many years ago which lasted over that 5mph band. Eventually identified it as the exhaust being a about 5mm (!!) too close to the chassis. When I first checked the gapping it looked fine, but minor movement / vibration of the car was just enough to make the slightest of contacts thus causing a very short term vibration. For all intents and purpose the exhaust looked spot-on and was well supported; it just needed adjusting slightly to allow for that 5mm movement.

Hope the above may be of assistance ??

Good luck,

Richard.
1968 Daimler V8-250 Saloon
DLOC East Sussex Branch Secretary
DLOC 2.5L V8 & V8-250 Registrar - https://www.dloc.org.uk/v8-250
DLOC 2024 International Rally - https://www.dloc.org.uk/rally-2024

DickSpeedy
Posts: 46
Joined: Sun Mar 20, 2016 2:07 pm

Re: 250 V8 20 MPH vibration

Post by DickSpeedy »

I drove the car to a freind who has a ramp about 10 km away. The car now vibrates quite heavily at 10 MPH, 20 MPH and from about 40 MPH it is reduced but still there. It seems to come from the transmission tunnel right next to the driver which would indicate either the front prop shaft or the bearing housing where the two shafts join. I don't see or feel a problem there!

On inspection, we discovered that the lower spring rubber had dislodged, presumably when I refitted the carrier bracket. Otherwise the the two prop shafts are in alignment according the the marks placed by the repair specialists. They have also been balanced.

I have subsequently jacked the car up at home and removed both support brackets.

How important is it to have the rear engine mount totally disconnected ? I have loosened both the lock nut on top and the flange nut at the base giving about 15 mm play. Is that enough? How I test the center bearing which is new? There is no play in it.

Your input is really appreciated.
Richard

DickSpeedy
Posts: 46
Joined: Sun Mar 20, 2016 2:07 pm

Re: 250 V8 20 MPH vibration

Post by DickSpeedy »

It is BW 35 auto box. The vibration goes away when in neutral.

tjt77
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Posts: 525
Joined: Wed Mar 23, 2016 7:01 pm

Re: 250 V8 20 MPH vibration

Post by tjt77 »

evidence points to the most likely cause being the propshaft :- a universal joint could be the issue.. sometimes when they are dry after years of storage and/or corroded, they have tight spots which reveal themselves as a vibration at certain speeds and loads.... driving loosetens them up and the problem becomes more apparent.. another common propshaft issue is incorrect alignment on the splines of the sliding section.. ( check the workshop manual for info on this) originally there was an alignment 'arrow' stamped on both pieces (but the stamping is very light and almost impossible those if there is any dirt or thick paint) its its out of phase with rear UJ it will fight itself and eventually wear BOTH UJ's.. personally I take propshafts from cars with 'unknown history' to my local drive line specialist for rebuild and balancing.. rather then rebuilding them myself ( which I often do on cars that have 'known' history)

DickSpeedy
Posts: 46
Joined: Sun Mar 20, 2016 2:07 pm

Re: 250 V8 20 MPH vibration

Post by DickSpeedy »

As I noted earlier the prop shaft was rebuilt by a professional company so the UJ's etc are new. However on the center bearing mount I discovered this morning that the safety bolt passes through the bearing carrier and has a rubber grommet type which had been replaced with a solid rubber doing nothing. I have ordered the correct rubber from Manners and hopefully this will sort the problem out.

I will let you know the outcome next week.

DickSpeedy
Posts: 46
Joined: Sun Mar 20, 2016 2:07 pm

Re: 250 V8 20 MPH vibration

Post by DickSpeedy »

Hi Guys, after a week of frustration I completely removed the prop shaft and refitted with the necessary rubbers. Only one was incorrect and the was on the safety bolt on the center bearing carrier.

I also loosened the front engine mountings to ensure all was traveling in a straight line.

I adjusted the rear engine support according the manual. The auto box is not fouling on the body.

I changed the wire wheels front to back. (Wheels are brand new as are the hubs & bearings)

Still the vibration persists. It comes in at around 10 MPH and gets progressively worse and at 30 MPH is is quite bad.

I'm at my wits end, can anybody help with some new ideas.

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