7 replies to this topic

[malcolmspeirs]

Hi,

I'm Malcolm and needing a bit of advice.  I prepared my Nov 1959 mini for classic rallying and have entered it on a few one-day events, including the recent cancelled vale of Clwyd rally.  For the last three events there has been a persistent knocking from the n/s front suspension on rough test sections.  The knocking sounds metallic and occurs when the suspension is working very hard.  It doesn't occur on the roads, unless you go over a severe pothole.  

Before the latest rally I removed and replaced the n/s top arm as I had seen evidence that the ball of the knuckle joint had in the past evidently broken through the plastic retainer so that the recess was no longer conical - there was impact damage from the knuckle ball..  I also replaced the bottom arm bushes as well as the tie-rod bushes, although these weren't noticeably worn.  None of this had any effect, and the knocking on a rough section in this rally seemed to have worsened.

I'm now considering two possibilities.  The first is that I fitted "Hi-lo" suspension to the car and I've noticed that the fit of the knuckle-joint inside the Hi-lo strut is loose (although both were new). Is it possible that under very rapid movement the knuckle comes loose, then bangs tight again?  I can't see why this should happen, as the joint should always be under high compression, but it might be possible.

The second possibility (which I'm dreading) is that the knocking indicates that there is severe corrosion at the top of the subframe tower where the rubber do-nut fits.  I will admit that this car has a very early subframe, but it appeared to be in very order when I re-built the car.  I can't see any evidence of corrosion, but of course there is a very restricted view of the top of the n/s subframe tower, blocked by the rad housing.  I'm obviously dreading this conclusion as it would involve a full front-end rebuild!

Any help and advice will  be much appreciated.

Malcolm

[imack]

A piece if packing under the rebound buffer should stop the cone/hill dislodging, think I've got a 3mm packer under mine.
Other thoughts are is the damper bottoming out? Steering rack bush worn? Tie bar bushes? Tie bar mounting on subframe bent and washers hitting it under large suspension travel?

[GraemeC]

What dampers do you run? I find some can't handle sudden, big changes in extension/compression - especially the KYB Gas-a-just ones.

What rubber cones do you have and how old are they?
(I'm presuming you've spanned checked all fixings).

[minisi35]

What mounts are you running with? Solid , poly or original ?
Has the car got bump stops? (Ones that stop the top arm bottoming out)
Just as a quick check have you swapped the shock absorbers as graham has also said. I have had ones in the past that when they get warm under rough use that they used to knock.(the piston rod moved around ).
Simon

[Cooperman]

Check the top arm bearings. I had this with a Clubman GT rally car and we searched and searched until we finally discovered a top arm bearing was 'shot'.

Other than that, check the steering rack outer bush, the steering rack U-bolts, the damper bushes, the front tie-bar bushes and the lower suspension arm bushes.

it is unlikely to be the sub-frame tower or anything to do with the knuckle joint as these are permanently under compression. You could check the small rubber down-stop between the sub-frame and top arm, but I doubt it is that.

It could be a damper as these have been known to 'knock' even when still operating correctly.

One other possibility is loose bolts on the upper damper mounting bracket. There are 4 off 1/4" UNF bolts holding the bracket on. Another thing to check is that the inner wing is not corroded where the damper bracket bolts on - unlikely, but just possible.

 

Edited to add, if you suspect a damper, find a piece of road where the knock occurs and not the speed at which it knocks. Remove the damper and drive that road at the same speed to see if the knock is still present with the damper not fitted.

Edited by Cooperman, 23 September 2018 - 12:45 PM.

[rally1380]

I've had similar problems in the past and somewhere in my build thread is a bit about it I think.

Essentially if it's the same as what I experienced, it could be your shock absorbers are too long and they are bottoming out.

Easy way to check this is to adjust the hi-lo's a bit longer and see if the problem persists.

What shockers have you got? Mine are GAZ standard length and if I'm running the car at anything near standard height they do knock. A couple turns up to 'rally height' and they are smooth and silent. On one really rough night rally (before I realised the issue) the rears bottomed out so bad they split the top mount area away from the rear arches!

I'd have to hear the noise to say what it is exactly but my money is on the shockers.

[malcolmspeirs]

Hi folks,  Many thanks for all your suggestions.  At least you all reckon that it's unlikely to be the subframe tower and there seems to be a consensus that the shockers could be the cause.  I'm running with Gaz adjustable shockers, with negative camber lower arms and adjustable tie bars, all new.  New do-nuts and Hi los were added when I built the car for rallying.  The top arm and its bearing are new, and so are bottom arm and tie-bar bushes - all rubber. I hadn't even looked at the suspension since the last rally on Sep 1st.  I now find that a lot happened on that rally!  The drive-shaft cv joint has almost certainly gone (there is about 5 degrees of play from the brake-drum to the drive-shaft!  Also the gaiter around the inner sliding joint has drastically failed - presumably because of excessive rapid length changes of the drive-shaft.  And yes, I can now detect a distinct clonk in the steering rack on that side.

 

So I've got plenty of items to correct.  But before starting the work, I will as suggested try finding a pothole which gets the noise to occur and then try removing the shocker to see the effect.  I will keep you posted once I've finally sorted it!

 

Again many thanks.

Malcolm

[rally1380]

Hi folks,  Many thanks for all your suggestions.  At least you all reckon that it's unlikely to be the subframe tower and there seems to be a consensus that the shockers could be the cause.  I'm running with Gaz adjustable shockers, with negative camber lower arms and adjustable tie bars, all new.  New do-nuts and Hi los were added when I built the car for rallying.  The top arm and its bearing are new, and so are bottom arm and tie-bar bushes - all rubber. I hadn't even looked at the suspension since the last rally on Sep 1st.  I now find that a lot happened on that rally!  The drive-shaft cv joint has almost certainly gone (there is about 5 degrees of play from the brake-drum to the drive-shaft!  Also the gaiter around the inner sliding joint has drastically failed - presumably because of excessive rapid length changes of the drive-shaft.  And yes, I can now detect a distinct clonk in the steering rack on that side.

 

So I've got plenty of items to correct.  But before starting the work, I will as suggested try finding a pothole which gets the noise to occur and then try removing the shocker to see the effect.  I will keep you posted once I've finally sorted it!

 

Again many thanks.

Malcolm

 

One cheap way to see if it is indeed the shockers being too long that is causing the noise would be to buy a pair of something like minispares C-AJJ3359 as that moves the top mounting pin upwards thus giving the shocker more room to do it's full stroke.  Certainly cheaper than a new set of shock absorbers.

 

Obviously I can't guarantee that will fix the issue, but i'd be optimistic as what you describe is exactly what I experience if I run my car lower than my 'rally height'.

 

Best of luck.