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MG MGB Technical - Clunking nightmare!

I've got a '78 MGBGT and it driving me mad at the moment...

I've recently fitted uprated front and rear lever arm shock absorbers. After about a weeks use i started to get loud knocking everythie i went of over a bump from the right hand side rear - so i investigated it further to find the shock absorber i had just fitted was leaking oil badly.

So i contacted my supplier and got another sent out which i then fitted - but my 'clunking' still there!!!

It only happen when i hit a harsh bump in the road if i go over gradual bumps like speed bumps it does not make a noise.

So today i emptied the back of the car in case it was something bouncing around the back of the car is now very stiff - this made no difference.

So i then thought it might be the exhaust hitting the petrol tank as it quite close but is very solid - so i tied it back slightly further away from the tank and it made no difference.

Then i thought it may be the wooden boot cover bouncing around but again i though this was unlikely and it held down securely but i still managed to convince my dad to get in the boot and lie on this whislt i drove round the block!

Photo evidence!

But despite that effort it still clunked!

So at the moment i am completely bamboozled as to what it is, the shock absorbers can't be clunking surely?

Forgot to mention i have also made sure everything is nice and tight underneath...

Any suggestions would be great!
Gavin J

You seem to have covered most things, the only thing I can suggest is go back under and tighten the mounting bolts till your eyes pop out and check the bushes on the drop link.
R. Algie

Yes, unfortunately, the shock could still be bad. Disconnect the link and push the arm through the motions to feel for a spot with less resistance. That would be a problem. Recheck the fluid level in it also.
The differential also could make a similar clunk, as could a problem with the brakes. Are your lug nuts tight? Are the end links on your anti-roll bar good? Jump up and down in the boot and shake the tar out of the rear end. Maybe you can find it that way?

Jeff Schlemmer

You've got a great Dad to do that. I remember doing the same for my Dad when I crawled into the trunk to listen for a squeak.

BTW, could it be your front end instead? Sway bar?

Mike MaGee

Jeff - could you explain more about the diff making a similar clunk? the only readon i ask is because the diff is put through its paces on track days so i may have damaged something?

I'm just off outside now to give it a good clean and polish and i will get it up on the ramps again tomorrow for another look round!

Cheers for the suggestions so far.

Gavin J

Forgot to apologise for my poor english in the first post! did it in a rush just before i went out...
Gavin J

My first guess was a lose shock mount at the wheelwell, but you covered that. I've experienced similar noises in the past. Most times, it was a lose shock mount. Once, however, it was a bouncing battery and it took me a week to find it.
Steve Buchina

Damn, loose not lose.
Steve Buchina

Gavin. Great photo. As Mike mentions, the more fortunate of us have memories of doing things like this with our Dads.

The possible rattle points would be the attachment of the shock (dampener) body to the frame. The attachment of the drop link to the shock arm and springs. The attachment of the anit-sway bar (if so equipped) to the body and to the rear axle. The attachment of the rear axle to the spring. The attachment of the wheel to the rear axle. I may have missed one, but, it so, someone else will mention it.

Check all of these for movement and tighten as necessary.

Les Bengtson

I'd look closely at the shock link where it bolts to
the leaf spring shock plate.

Many times, the bolt there just rotates without
much torque and so it is easy to work it's way
Daniel Wong

Thanks guys, i've just done a checklist of things to check in the morning - will let you know how i get on.

I may end up taking a video clip so you guys can hear the noise and try and diagnose it!

Thanks again.
Gavin J

Gavin. Yes, check all of that, then, take your father with you for the test drive. While you may not realize it yet, since you and your father seem to be relatively young, these shared times are rather important. In later years, they will be a time for the two of you to laugh and joke about together. An indication that the "parent/child" relationship had evolved into something even more important, a "friend/friend" relationship. This is not something which always happens, but, when it does, it is a very special bond.

When I looked at the photo you, so proudly, posted of your father, it reminded me of my own father. He had taught me how to tune up my car and, while he was not happy that I did not drive Fords, as he did, kept my MGA for me while in Germany and my MGB for me while I was in Alaska. (I picked the MGB up when my wife flew in from Germany enroute to schooling in Denver, Colorado, where she drove it until her car came back to the US, then, picked it up and drove it back to Florida, then, to Austin, Texas, our next duty assignment.)

My last "photo" of my father and I together is on video tape. One I did not know was taken. I had, for the first time in ten years, shaved my beard and put on my Air Force officer's uniform. The Air Force Presidential Honor Guard had accompanied his body to his grave at Arlington National Cemetary. I put on my uniform, my wife put on hers and we stood beside my mother as the Airman delivered to her the flag which had drapped his coffin. As he saluted her, Adrienne and I returned his salute.

My brother had the funeral video taped. The final portion, unknown to me until I viewed it was when I, Captain Vernon L. Bengtson, Jr. rendered my last salute to my father, Major Vernon L. Bengtson, Sr. The first one I had ever given to him was when he commissioned me as an Air Force officer. He, later, came out to Arizona to re-commission my wife as an Air Force officer.

So, save the photo and take your father along for the test drive. You will appreciate this in late years.

Les Bengtson

Les, your right times like that should be and will be remembered.

Well i have checked the following this morning,

Shock absorbers are nice and tight with no movement.

Link arms are bolted on nice and tight and the bushes are ok as they are only 2 months old.

Anti roll bar is mounted securely both to the body and axle - bushes ok on both.

Exhaust is not knocking the petrol tank - I put some waxoil (rust prevention stuff) on the side of the tank and then took it for a drive over some bumps and there was no marks in the wax oil after.

All the bolts on the leaf springs are tight.

Nuts are tight on all the wheels. There is no play on the rear wheels so the bearings seem ok.

The battery was nice and solid, but i did go for a drive with the battery cover off and my dad put his hand on it whilst i was driving and it made no difference - so its not the battery bouncing about.

So the only thing i think it can be is the shock absorber on the p/s side is faulty.

The problem i have now is that i no longer have my old units as they were bought on an exchange basis - so i can't put my old one on and see if the clunking stops.

So tomorrows job (or todays if i get the time!) is to to get the link arm off and try moving the shock absorber by hand - is it possible for there to an air lock?

The only reason i ask is because when i got the shock absorber i was unable to move it by had at all - i even put it in a vice and still had not joy trying to move it - so i phoned my supplier who said that it will free up when I start using it and it appears to as it moves when you bounce the car.

Gavin J

That is a bad shocker, it will be stiff , but should move.
S Best

The shock should be much easier to move while bolted to the car, but it shouldn't be that tight.

The common differential clunk stems from worn thrust washers behind the spider gears. Essentially, there's just enough slop in the gears to clunk when you come on and off the throttle. I though that could be happening as you hit bumps in the road? If the noise occurs while coasting, that's probably not it. There'll be no damage done to drive with worn thrust washers.

Jeff Schlemmer

Gavin. Sounds like a bad shock to me also. I replaced the ones on my GT a couple of years ago with a good brand of rebuild (World Wide Auto Parts in Madison, Wisconson). All of the shocks could be moved through their full travel before being installed. It sounds like you got a bad shock and poor quality of technical advice.

Glad you and your Dad got some quality time together. My older daughter is coming up next weekend when we will spend some quality time together doing an oil change and front end lube on her B. Certainly makes my whole week brighter when this happens.

Les Bengtson


Have you fixed the upper mounting brackets on the wrong sides of the car. The brackets are no semetrical and if installed on the wrong side will shorten the active length of the shocks and may cause the shocks to bottom out before the bump stops hit.

Dave Merritt

This thread was discussed between 24/09/2005 and 26/09/2005

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