Vibration - Any Thoughts On What's Growling

[andyparry]

Chaps

 

I've got a stainless 2B with wishbone front end, standard sierra back end, a honda blackbird under the bonnet, gaz adjustables allround with standard sierra brakes on the corners (discs and drums). Ever since I did the pinto swap a few years ago the car has been driving beautifully. Within the past six months, above 45mph, when going from driving the wheels with the engine to the wheels driving the engine, i.e. backing off the throttle, I get a horrible vibration and sounds. I suspected the diff and changed that for a spare that Bob Tucker had. Hasn't cured the problem. I sent the custom propshaft back to bailey morris to be rebalanced, and that was in spec, so still hasn't cure the problem. The problem only happens after about 3+ miles of driving suggesting to me that it is only after lubrication somewhere has warmed up. I thought is may be a knackered gear in the blackbird box, but the problem still occurs regardless of what gear I'm in or even when I depress the clutch in any gear about 45mph. It could always be the output shaft of the engine, but that feels tight as ducks back passage.

 

Any thoughts or suggestions on what to check would be greatly appreciated as I haven't got a clue what to look for next.

 

Andy

[Bob Tucker]

Hio Andy,

I can only think of rear wheel bearings?

Anyway if you need a hand, fetch the car up & we'll

eliminate everything one by one.

Bob

[Guest Tim Norman]

I have had excatly the same noise for years. I have replaced everything apart from the rear wheel bearings. Guess what's next!

[Guest Tim Norman]

Got the wheel bearings but I don't have socket "that" big. Anybody know what size socket I need to fit the rear drive hub nut?

[Guest Tim Norman]

Never mind found one, 41mm just in case anyone was wondering.

[Shaft]

Hi Tim,

 

Guess who's got a 42mm socket you can borrow?? lol.

 

oh, and a 3/4" drive breaker bar and extension.

 

Give us a call mate, borrow it whenever you like.

 

Nick.

[Guest Tim Norman]

Nick if I can't shift it on Saturday I will give you a bell.

 

Ta

[andyparry]

Just an update on the current vibration problem.

 

Bob Tucker came down about a month ago, I took him out for a drive and he thought the problem was coming from the back end as well. We took the car home, jacked up the back end and got about a 1/8 turn out of the drivers rear hub nut. After a test drive, it has made no difference. I've now also changed the rear bearings and still no difference. I've checked the diff fluid and that is good and 10mm below the hole. I've had the prop-shaft tested and it is well within balance spec.

 

Just to recap and also to be more specific, I get a horrible shaking / vibration coming through the drive train between 45 and 52mph only when the engine is not powering the wheels. Booting the car upto 80mph and then backing off, nothing until 52mph then 7mph of vibration then nothing again. Doesn't appear to make any difference what gear I'm in when it happens either. Also happens when the clutch is depressed. The problem only occurs after about 4 miles of driving, i.e. when rubber, grease, oil etc.. has warmed up.

 

I have had a suggestion of wheel balancing being an issue. This could be a possability has I have 17" low profiles on a very light car, so wheel balance could be more noticable. My next test will be to swop the front and back wheels over to see if that makes a difference. As I'm running a bike engine in the car, I'm wondering if it is clutch plate chatter or a knackered clutch cage. It's a fairly simple thing to dissasemble and check so that is on the list after balancing if balancing doesn't work! I don't know anything about bike engines to know if this is a likely cause or not, but the specific speed range suggests it is a natural frequency problem with a component in the final drive train, so the clutch may be an issue.

 

Any other thoughts? What should I try next?

 

Any ideas greatfully received.

 

Andy

[Al Milton]

Andy,

 

I'm no expert, but the easiest thing to look at is the wheel balancing.

 

You could have lost a weight or have a slightly buckled wheel.

 

I take it the driveshaft bolts are tight (from diff to hubs)?

 

About the limit of my knowledge i'm afraid

 

Cheers

Al

[Guest Noddy006]

Hi Andy

 

My first try would be tyres. Balance being out often causes vibration at certain speeds (45-60 being common) and with low profiles could be more sensitive to just minor wear. As you suggest swap wheels front to back and see what happens or if you have spare try replacing one wheel at a time and test etc. Best of Luck. Ian H

[richyb66]

Had a similar thing on my VW transporter, I checked all the usual suspects but found nothing and annoyingly it would do it for a few days or a week and then go quiet before returning weeks later.

 

I even pulled the boots of the cv joints to see it they were damaged but found nothing. In the end I suspected driveshafts but wasn't sure and couldn't tell which side so I swapped the both complete - about £100 a side exchange so not worth stripping down and fitting just joints.

 

Not had any bother with it since.

 

I'd suggest trying different rear wheels first to eliminate wheel balance issues. If it still persists, chock the car, jack up each rear wheel individually and drive the car through the gears allowing the raised wheel to spin (assuming no lsd), this should isolate which side is causing the issue. Make sure the jack is under the trailing arm, can't slip, go down or otherwise move or you'll be in big trouble. Get an assistant to observe the wheels turning and look out for vibration or run-out. That way you can concentrate on the driving bit.

[Guest peter2b2002]

had the same problem on a tin top , wheel balanced still there, took the car to a specialist

who balanced the wheels on the car problem solved

peter2b

[andyparry]

I've just changed the wheels over, front to back, taken out for a test drive and no change.

 

I'm now thinking along the lines of a CV joint on one of the shafts at the back. I think richyb66's idea of jacking up the back and spinning each wheel in turn is the next thing to try. For the vibration to occur only between 45 and 52 mph, surely it must be something in the final drive train that is either out of balance (so found a natural frequency) or something worn. As it only happens after a few miles driving, i.e. when lubrication has warmed up, maybe the biggest candidates are the four CV's. As I've changed the diff, rear bearings and had the prop checked, it's all that is left. Unless the diff I changed in is also knackered...??

 

Any other thoughts?

 

Andy

[Jamiep]

might be a daft idea but have you checked the rear drums, does sound like something is out of balance. Have you flat spotted a tyre? not normally noticable on tin tops but I felt it on my exmo after a "change the pants" moment.

[Bob Tucker]

As Andy says, this is not so much vibration as a really harsh mechanical misalignment. Imagine pinion teeth being out of mesh with the crown wheel...its far too harsh to be simply something out of balance. Maybe CVJs are the next thing to check...

Sorry Andy, Wont be coming down to help out any more, got my picture taken from a white unmarked van on the way home, happily trolling along down the main A20 London Dover road, through a wooded section, no sign of any residences, limits had been changing from 50 to 40 & back, I must have missed the 30 sign in all the foliage..got snapped at 39. Oh Poo...first transgression in 30 years...now signed up for a "speed awareness course" should be interesting.

Bob

PS Andy I have two push-in halfshafts that I use with my 3.62 diff if you'd like to borrow them they are the smaller shafts I can measure them once i get back from lemans if you like.