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MG Midget and Sprite Technical - Vibration at speeds over 45 mph

This is the next problem. Why is life so hard!!!

OK, I converted to wires so the following parts have been changed.
Axle including the Diff, Half Shafts and rear wire wheels it came with. The front hubs and front wire wheels all from the same donor. I replaced the rear bearings, shoes, cylinders, adjuster etc.

So, over 45 mph a vibration starts which gets steadily worse as speed increases. It's more of a buzz than a shudder and effects the whole car. At it's worst the rear view mirror vibrates so much you can't see what is behind you.

At first I thought it might be that the prop shaft/diff joint needs rotating so I did so and it made no difference.

The diff makes a noise on the over run but is otherwise quiet.

I'm going to swap the wires front to back and see if it follows the wires.

Could it be badly balanced wires as it seems not many garages are capable of doing it properly?

Rob
Rob aka MG Moneypit

Rob,

That would be my thought that the wires have been balanced without the use of the proper mounting cones. My neighbour had that problem on his Morgan and his centre now has a set of cones to borrow to take to the tyre fitting place, he said it reduced the large amount of balance weights on the wheels dramatically when the proper kit was used. He did take their dimensions so if you have access to a lathe you could make you own, I'd just have to ask for the drawing..
David Billington

Rob

It could be a balance issue. As you say, not many people can balance them properly, as they don't have the correct cones for mounting them.

There was a guy at Stoneleigh last year, selling plastic cones for wire wheel balancing. MGOC also sell them.

Paul Hunt also had some made...

http://www.mgb-stuff.org.uk/wheelstext.htm#centre
Dave O'Neill 2

If not the wire wheels look at where the prop shaft bolts to the diff... it has 2 choices

the correct way or the 2nd way 180 degrees out
Prop and the Blackhole Midget

Prop, tried that and no difference.

I won't be able to swap wheels today as we have been entertaining my grand daughters all afternoon. Maybe tomorrow.

I did take one of the balance weights off one rear wheel and it seemed to improve a little. The weight I took off was a big one, 45 grammes according to the stamp on it, which I thought may be an indication of bad balancing.

Rob
Rob aka MG Moneypit

Yeah... it sounds like wheels more and more
Prop and the Blackhole Midget

You may also want to check U-Joints as well. Wheels would give you feedback through the steering column if it is the fronts. The rears will obviously give you rear shake. If the entire car vibrates, I would suspect U-Joints.

Cheers

Gary
79MGB
gary hansen

Got time tonight to swap wheels front to back. It made no difference so it's not the wheels. Still buzz's over 45 and mirror shakes a lot. No apparent effect on the front wheels.

Next I will swap out the prop shaft. I have a couple or 3 spare in the garage and a new set of UJ's.


Rob
Rob aka MG Moneypit

Rob... before you do that... jack up the front end and grab the wheels for a good shake and see if you get any play

You had to change out the spindles to convert to wires maybe the spindles bushings are worn or the FWB are not seated properly or the rack ball and cap acorn nut needs a little tlc

prop
Prop and the Blackhole Midget

You didn't change the engine mountings as well, did you?
Dave O'Neill 2

Vibration and mirror shaking at 45-50 mph is classic prop UJ symptoms. If you can drive through it and it gets less at higher speed, that's another pointer to it being the prop shaft.
Bernie Higginson

Hi Rob,
Have eliminated the engine? Have you tried knocking it out of gear to make sure that it isn't an engine issue. I had lots of vibration at about 68mph - a bit faster than you, that made the mirror shake so badly that you could not use it. I am sure I fixed it by fitting a new harmonic balancer (I also had the engine rebuilt and balanced at the same time, so cannot be sure exactly what the problem was). Harmonic balancers are now well over 40 years old for most of our cars and the rubber perishes. You would not expect your tyres to perform as they were designed after 40 years. Why do we expect rubber in harmonic balancers to perform for so long?
If you have eliminated the engine, I would investigate the wheels. Make sure they are true and balanced correctly, not on the usual wheel balancing machines as these mount the wire wheel using the wrong surfaces and they are unlikely to be true on the machine giving a false balance. Also look for buckles.
Failing that, prop shafts are not particularly well balanced. Proper balancing could be well worth it. Reco Prop in Luton did a great job on mine, they fitted decent UJs at the same time. I am sure they will do a postal service.

How is the restoration of the Orange midget going on?

Dave


Dave Brown

Dave oneil

.. GREAT POINT on the engine mounts i had forgotten that issue conserning the newer mounts. Vs the older

definatly worth consideration

prop
Prop and the Blackhole Midget

I tried knocking it out of gear and the vibration continued so I'm sure it isn't the engine.

Prop makes a good point, but there is no discernable play in the front wheel bearings, although when I swapped the front and back wheels I did notice the steering wheel looks like it is one spline out of alignment. I didn't notice it before and can't really explain it except perhaps the front tyres have a slightly out of square wear pattern.

Dave, not well. Soon after I bought it I got the remains of an Austin Sprite. I hummed and harred for a few weeks and set to to restore the Orange one. I had almost got it fully striped and had decided to convert it to SWA, to re-build the Sprite, but luckily I found an ex-heritage SWA shell. So, I've been doing that and the Orange one has gone to the back of the queue.

I was going to use the wire wheels for the Sprite but decided to keep it original with steels which I didn't have - but my other Midget had steels - so I put the wires on that midget etc. etc. I'm easily distracted and as I found out it leads to all sorts of trouble.

The Midget was quite happy on steels but this seems to have opened a whole can of worms!!!!

Rob

Rob aka MG Moneypit

Rob,
you mention wear pattern on tyres, how old are your tyres?

See 'dot codes' just down from the top of this page for how to find the manufacture date of those tyres - http://www.carbibles.com/tyre_bible.html

And/or the wear pattern may be an indication of wear/misalignment elsewhere in the steering/suspension.
Nigel Atkins

Rob
try this
Jack the car up and sit the back axle on some blocks/stands ,remove the back wheels and give her a buz up like that and see if the vib. is still there If it is it has to be tailshaft speed related
There wouldn't happen to be a heap of movement in the pinion ?? seeing as you mentioned diff noise
Also while it's jacked up and idling in gear just have a look to make sure the tailshaft's not a banana
willy
William Revit

I drove my new Triumph 2500S from Adelaide to Melbourne when I bought it. 900 kms of teeth rattling, mirror shaking torture. The culprit was the Prop shaft unis front and rear. Now rebuilt and balanced professionally - smooth as silk.
IMHO its the Uni's, But get the whole thing balanced.
Cheers
rod
R W Bowers

Hi Rob,
If you are using the wire wheels from the Orange car, they are all fairly new and all balanced properly, two by Brown and Gammons and two by MGOC. As long as they all still have all of the balance weights, they should be fine. Tyres are not that old either.

Good luck

Dave
Dave Brown

Thanks top everyone with suggestions. The latest to be replaced was the UJ's on the prop shaft.

You know when half way through the day you realise you should have stayed in bed? Well changing those UJ's felt just like that.

The gearbox end went ok, no problems, about an hour to change it.

Then onto the diff end. All the circlips were seized. Two broke trying to unseize them, one had both ends broken off, the other only one end of the circlip broke.

So, several hours later after much aggro, I had the second one changed. I had these UJ's in stock, I must have bought them for the Frogeye because they had grease nipples. So, after triumphantly inspecting my hard work, a quick check over before refitting and.... The diff end only moves 3 ways and not 4. Close examination showed I had fitted this end with the grease nipple in the wrong position? The UJ should have been fitted with the grease nipple toward the propshaft, not the diff. The UJ has quite a big casting where the grease nipple fits and fouls on the casting of the diff yoke.

Never heard of this before, I always assumed they could be fitted any way around?

To get the UJ out again would have effectively destroyed it so I tried another approach. I drilled holes in the diff end to make more clearance. After another hour I had enough movement in all 4 directions but now it was too dark to continue.

The saga continues Sunday. I managed to get the gearbox end in first time, then time to connect to the diff. All the bolts but one were fitted but where the grease nipple was there was not enough room. So, out with the other bolts, remove grease nipple fit and tighten 4 bolts. Screw grease nipple back in, nip up with a spanner and... the nipple sheared leaving the end inside the UJ.

A few expletives later I found a flat needle file which just fitted inside the broken nipple and I was able to remove it. Rummaged around in the garage and found a spare propshaft with extended grease nipples. Removed one, compared the threads and they look the same. Under the car and screw it in, but no matter how I tried it wouldn't engage with the thread in the UJ. So, out with my micrometer gauge and measure the diameter. Spare nipple 6mm, broken nipple 5.85mm. WTF?

Last resort was searching through my collection of spare machine screwed bolts measuring the diameter of each. Eureka, found one! Grip with my bench vice, cut the head off and slot the cut end. Offered up to the UJ and it went in ok. Phew!!!!

So grab car keys and go for a test drive. Result... no difference. Still a bad vibration at 50mph.

So the only things left to try are the diff and both half shafts.

The saga continues......


Rob

Rob aka MG Moneypit

Hi Rob, sorry it has been such an ordeal. Here are a few other items concerning changing u-joints (water over the dam for you but may save others in the future):
1. Before trying to remove the joints, tap the caps inward using a large drift - it sometimes helps to ease the pressure on the circlips
2. Grease nipples always aim toward the drive shaft.
3. Grease nipples should always be in compression as viewed by shaft rotation.
4. After the joints are assembled, slightly strike the shaft, yoke and differential flange with a soft faced / rubber mallet to seat the cups out into the circlips.
5. Grease the fittings before installation of the shaft.
6. When fitting the rear bolts, slide them all into the flange & then fit it to the rear. Slop in the drive shaft flange will allow the bolts to wiggle in since it is such a tight fit. If you try to do them one at a time, almost always, the last one will not want to insert thru the flange.

Been down this road a few times in my life.
s1

I had a similar issue with grease nipples on a 'B' propshaft recently. I made a blanking plug from a cut-down screw.
Dave O'Neill 2

Ive only done UJ once... and it was very much like your experiance

now i just pay a shop $50 per UJ and im done with it...its more art then science

But i hate to hear about your day... the good thing is the sun will someday rise in the west and all will be good a d forgotten

hang in there

prop
Prop and the Blackhole Midget

the drive shaft may still be out of balance despite the new uni's take it to the pros and have it checked and balanced
Cheers
Rod
R W Bowers

But it didn't have a problem until I put a new wire wheel axle on. With the old steel wheel axle it was perfect. How could just changing the axle upset the balance of a propshaft that is original to the car?

Rob
Rob aka MG Moneypit

I wonder if it could be bent axle casing. it may have suffered an accident in the past or the wheel wacked against a kerb at an acute angle. I had a problem with the hub bearing stub on a race car and took it mallock racing to get a new one welded on. before they started they checked the alignment on the axle tubes using a long straight steel rod which the same diameter as the hub tubes. When the rod was inserted it was amazing how out of line the other tube was. It was 'corrected' by using a press and a very large lump hammer! The car was certainly smoother on the track.

How you would test for a bent axle I don't know. Do the hubs rotate freely? Are all the u bolts up nice and tight?
Bob Beaumont

I suppose the diff pinion bearing could give similar symptoms to UJs.
Dave O'Neill 2

Diff and half shafts are next on the list. I have a known good 3.9 diff and a couple of spare wire wheel half shafts.

Rob
Rob aka MG Moneypit

""There wouldn't happen to be a heap of movement in the pinion ?? seeing as you mentioned diff noise""
William Revit

Have you actually measured the radial and lateral run out on the rim and tyre? I'd get a dial gauge and check out the values because wires - unlike steels or alloys are prone to a giant amount of run out even though they can be physically balanced up OK. I'd suggest any more than 3/16th on the tyres would give you a pitter patter vibration that builds with speed and could effect the whole car. Probably best if you can measure them on the hubs in situ.
Fergus

Willy, I'll be trying your suggestion but probably not till Friday. I should have done it last weekend but just completely forgot.

I could put it on axle stands and try it with and without rear wheels fitted, maybe check any runout at the same time.

The diff has a fair amount of backlast so I think it's the next most likely candidate.

Rob
Rob aka MG Moneypit

Rob I don't know but balancing the tailshaft will eliminate it as a cause.
Good luck
R W Bowers

Just thought I would report the latest findings on my problem. I got the afternoon free so went to work and put the car on axle stands and ran with and without wheels. Result, it's not the wheels, it still does it and it's a lot worse without the weight of the car damping everything.

So, having a spare diff, I set about changing the diff but retaining the half shafts. Result, no more vibration.

I examined the removed diff and for the life of me I cannot see anyhthing wrong. The diff seems really good. If I was buying it off someone else I would have handed over my money.

Any ideas what could be the cause?

How much can you do on a diff without having to replace the crushable spacer?

Rob
Rob aka MG Moneypit

Rob
Maybe the crownwheel carrier is flogged out letting the side gears slide around in there which lets the inside end of the drive shafts flop about--It would have to be fairly worn though to make it vibrate

With the crushable sleeve
Usually they are one go only but if you are stuck you can make a shim to pack it a tiddle and then recrush it a bit further----------
William Revit

Congratz rob

sounds like the diff housing maybe a bit bent/warped...considering the thickness of the halfshafts it probably wouldnt need to be bent more then 1/4 inch over the length of one side to make some vibrations

prop
Prop and the Blackhole Midget

This thread was discussed between 25/09/2016 and 31/10/2016

MG Midget and Sprite Technical index

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