Unequal rear ride hieght

[minorjohn]

I have only just joined, and since buying my 66 convertible I wanted to correct the unequal rear ride height, the offside side sat 3/4 inch lower than the near. So I got a pair of springs, which although not new, had literally only done a few hundred miles, and set to work. Thought I knew all about car leaf springs until I discovered the unique front pin attachment !! Thanks to the various MMOC forums for guiding me through that. Actually I managed to drive one of the pins out intact, which I gather is pretty rare ?
Anyway, all carefully assembled with new bushes and rubber plates top and bottom. Lowered the car down to find NO change to the ride height ! Surely not a weak new spring ?
So next day, I bit the bullet, and swapped the springs over, still no change !!! And yes I did leave all the nuts a bit loose, and drove a few 100 yds to settle the bushes in before tightening.
I have measured everything as best I can, and the geometry all seems identical on each side. Shackles are identical, as are the springs with identical parts numbers on them.
I just can't see how it is possible, so have any of you Moggie experts got any bright ideas please ?

[bmcecosse]

If the underside has had some welding done - and perhaps new front spring location brackets , or rear hanger mounts - they may not be positioned correctly at one side... You could compare sides with a tape measure. Does the axle appear square to the car? If you take a length of nice straight timber (probably need to fix spacer blocks to it first) and hold it tight against the rear tyres (on the hub centre-line) in turn - held horizontally and pointing forward - does it look the same on each side? Other possibility of course is that the front suspension on the offside needs to be raised one spline on the torsion bar -if it's low - it could well be dragging the rear down. Over the years Minors do tend to settle lower on the driver side - since there is always a driver on board, but not necessarily a passenger to balance the car ! The other possibility is that the rear wing on the offside is fitted wrongly - giving the impression that the car is sitting low. Are the gaps between bump stop and chassis plate showing the 'lowness' - or are they the same ? One solution is to make and fit longer hangers on the low side - if you make them 1" longer between centres it raises the car by 1/2".

[beero]

To see if the front suspension is affecting the rear you can jack the front up in the centre so the tyres are just clear and then measure the rear heights. If they are equal you know the front suspension is affecting it.

[minorjohn]

Having been on the website numerous times before joining, I rather expected bmsecosse to reply, and thank you. I'll now spend the day checking all the suggestions you have both made.

[rayofleamington]

beero - great advice.
More than 90% of rear height imbalance issues I've come across were related to the front suspension.

If you imagine the car as a 4 legged stool - if you shorten or lenghten one leg without adjusting the opposite corner, then one leg is always in the air. The same goes with cars - assuming the shell is straight & none of the wheels are in the air (!) so if one corner is low, the opposite corner would be high. either corner could be the cause, but front suspension is the most likely cause on a Minor.

A Minor saloon shell doesn't twist that much (well, ok it shouldn't!).
Moving the front spring shackle doesn't have a massive effect to ride height* as the length of the spring is set by the load and the rear shackle adjusts to whatever length the spring wants to be.
If the car is lower on one spring - that spring should (in theory) be longer - that doesn't mean that the spring or the mountings are the issue.

Unfortunately with a convertible, there is some risk that the car has distorted if some of the structure rotted and wasn't put back square. and with any car there's risk that it was distorted during a crash.

* front shackle out of position will mess up the alignment e.g can cause crabbing,

[bmcecosse]

The 'timber' test will check for crabbing.

[minorjohn]

Right, are we sitting comfortably, then I'll begin ! Lovely sunny day here in Sumerzet so started following the advice. Using careful measurements, as far as I can see, everything is equal on both sides. The axle is square and the front to rear wheel distance is the same. If you measure from immediately below the shackle to the ground, there is 1/2" difference.
So, before I started, the measurements were nearside height 24'', offside 23 3/8''. Jacked up front, and now they were 23 3/8 and 23, so it looks like the front is affecting the rear as advised. As a temporary measure I experimented with various lengths of shackles, until it became ridiculous. So I've ended up with 1 3/4 longer between centres to achieve 25 1/4 and 25.
However, I'm not happy with this solution, the side ways loading on such a long shackle must be excessive ?
Looking at the manual, adjusting the torsion bar/ moving a spline is quite involved, but I'm very happy to do it. So any advice on how many holes / splines to correct this situation would be very much appreciated. At present both torsion bar bolts are in the lowest outside hole of the plate.
I might add, all this will not put me off as I just get so much enjoyment from driving the car !

[beero]

Now jack up under the centre of the rear axle and measure the front heights so you will know which side to raise or which to lower. BMCecosse will know how much height per spline I'm sure.

[bmcecosse]

Ohhhh - I wouldn't go beyond 1" longer shackle. You could brace the two shackle legs with a centre bolt and a spacer tube - but I don't see it as a good idea. Moving one spline is about 1 1/4" height difference at the front - and is not difficult at all. Yes - you can first try moving the rear adjustment plate to see if that makes enough difference for you. Ideally end up with the car slightly high on driver side - so it sits level with driver on board. But before moving anything - check the clearance from bump stop to chassis at the rear - and bump stop to inner wing at the front. This is the best way to determine any height differences.

[minorjohn]

Thank you all for the advice, and eyes down for todays results ! I re-installed the correct shackles and took the following measurements at the front with the car on the ground :- At the wing, nearside (NS) 25 1/2, offside (OS) 25, and at the bump stop, NS 2 1/8 and OS 1 5/8
Jacked up rear, under diff, and now at the front wing, NS 25 1/2, OS 24 7/8 and bump stop, NS 2 3/8 and OS 1 5/8. During this, I have also noticed that the NS rear wheel has always come off the ground well before the OS, if that helps ?
So I presume I'm right in saying that the OS front needs raising by possibly one spline, or does the NS need lowering ??
Sorry if this is starting to drag on a bit, with regards.

[bmcecosse]

Yes - the OS front needs raising one spline - but why?? Check the rear mount of the Torsion bar - has the crossmember started to crumble and the reaction arm working it's way up through the floor under the driver's seat ??

[minorjohn]

I looked again at the plate and cross member area and everything is rock solid, clean, and I believe as it should be. So as you say - WHY ? I have records back to 1985 when it was extensively restored, but of course it could have suffered accident damage prior to that. Short of putting her on a jig, perhaps a twisted body is the most plausible explanation, unfortunately !
Or, can you get one torsion bar weaker than another ? Anyway, I'll set to and adjust the front which will also allow to check the king pin parts over. I presume the tracking will need checking on completion ?
Thanks again, I'll keep you posted.

[bmcecosse]

Maybe had the suspension rebuilt between times - or maybe it's been like that for a long time. Who knows !! Just raise it the one spline and then let it settle again for a few days before measuring again. In theory yes the tracking should be checked..in practice the change will be tiny - I wouldn't bother!

[minorjohn]

I have now moved the spline up one and the job was very straight forward as you said. Everything dismantled very easily and were in good shape. However I did have to take the torsion off as the adjustment lever would not budge on the spline whilst on the car, again, so easy. Just one of many good reasons to run a Moggie !
I have to say it has not made a lot of difference, but I suspect for the following reason ? According to my Haynes manual, each hole in the plate represents 1/4 inch and mine was in the 2nd lowest hole. Having made the spline adjustment, I have put the bolt in the top, outside hole, which effectively means I've only raised the corner by 3/4 inch ? (That's plus 1 1/2 for the spline, minus 3 x 1/4 for the 3 holes I've moved on the plate = plus 3/4) OR have I got wrong !
So as you suggest, I'll run around for a few days and measure up again.
As ever, thank you for the help. With regards.

[bmcecosse]

You took the bar off?? It's much easier to just knock the front suspension arm back slightly and move it round one spline... If you moved the reaction arm one spline - I'm not sure what effect that has - it's a shorter arm and very probably not as many 'splines' - but that may add up to 1 1/2" just the same . You 'll just need to keep going till the bump stop to inner wing distance is same both sides. Then look to see what effect that has had on the rear bump stop/chassis clearances.

[rayofleamington]

as far as I remember - the splines at front and rear are the same, so it wouldn't matter which end you take off.
Now that you're good at it, moving a few more holes on the adjuster plate will be a fairly quick job.. (if needed)


What did make me a bit suspicious was that he rear axle (bump stop) clearance to body was still misaligned when you jacked
I know you mentioned replacing the rear springs already, so am a bit bemused as to why the rear clearance isn't equal when jacking up up in middle of axle

[katy]

I did have to take the torsion off

Did you mean tension?

[MarkyB]

torsion
ˈtɔːʃ(ə)n/
noun
noun: torsion

the action of twisting or the state of being twisted, especially of one end of an object relative to the other.

tension
ˈtɛnʃ(ə)n/
noun
noun: tension

1.
the state of being stretched tight.
"the parachute keeps the cable under tension as it drops"
synonyms: tightness, tautness, tenseness, rigidity;


Torsion seems like the right term though we all know what is meant.

[minorjohn]

Hi. Didn't realise that about the wishbone, I was following the instructions in the Haynes book which says to slide the Torsion bar lever forward, item 73 in their diagram, not the rear wishbone arm, but I imagine in your experience, it's better to move the latter ? Anyway, I shall play around with my new range of adjustment holes, shame you have to dismantle the wishbones each time !
The cannibalised SU pump seems fine, so the Hardi is in the boot.
Thanks again, John.

[bmcecosse]

Just slide the FRONT arm back and off the splines to adjust height - I used to do this at the roadside if I discovered that a rally route was including 'white roads' . It's very easy to do - very little dismantling involved. The little plate is easy to use if you have the bolt loose now, but it's range of adjustment is limited.