Suspension - lowering the standard dry set-up
Possibly one of the most asked questions by new Mini owners since not only does lowering the car improve it aesthetically - giving that 'mean low' look - it also further improves the Mini's already phenomenal road holding. Lowering the car reduces its centre of gravity, which helps to reduce body roll. However, just how low you can go needs to be sensibly considered to avoid a number of problems, and trying to advise just what height to run any particular car at for any particular instance is really impossible. There are too many factors to consider. Here we will look at lowering the 'dry' suspended Mini - that is the type with rubber springs as opposed to the hydrolastic displacered 'wet' types.
For a race car the general rule is take it as low as you can without actually running on the bump-stops all the time - say about 1/8" clear. For a road or rally car where rougher terrain than smooth tarmac is to be encountered, going this low will cause the ride to be excessively harsh and soon remove most of the parts hanging lower and less solidly fixed to the rest of the car than the floor pan! Particularly if heavier loads than just the driver are to be carried - four passengers, increased car weight as for a reinforced rally car, and so on. Dirt racers, such as rallycross and grasstrack cars, can be run lower than standard ride height as they are only likely to be hitting dirt clumps instead of rocks, kerbs or 'sleeping policemen' (speed control humps).
Then there are the various effects lowering the car has on suspension geometry. There are two to bring to your attention in this initial, basic project. The most immediate geometry-related positive effect as far as increased road holding goes is the reduction of the factory set positive camber base settings on the front of the car. Positive camber on the front causes excessive under-steer where cornering grip is concerned. This, therefore, is a good thing and needs nothing doing about it. The other thing is front track settings. Lowering the car will cause the track to change - generally going toe-out. This must be re-set once the car has been lowered to the required track setting for the type of wheel/tyre combination used. For more detailed explanations on effects on geometry, see the various other articles on suspension I have done on this site. Here we are merely concerned with how it is done and points that need immediate attention.
At the rear there is really only one point to watch out for when severely lowering the car - brake pipe location. On the dry suspended cars the brake pipe is located on top of the radius arm. Lowering the car a lot can cause the pipe to become squashed between the radius arm and floor pan (underside of boot floor). Obviously dangerous since damaging the pipe will cause loss of brakes! If in any doubt as to whether there will be sufficient clearance, chisel off the rivets that hold the pipe-retaining bracket to the arm, or cut through the bracket with a hacksaw blade. Re-site the pipe underneath the arm, and retain it in place by using either a couple of strong tie-wraps ('zippy clips') or hose clamps ('jubilee clips'). Since the radius arms operate at 90-degrees to the car centerline, lowering the car at the rear has no effect on the suspension geometry.
And the last main effect is on the dampers. Lowering the car by more than 3/4" really needs a suitable damper fitted since the standard length ones are likely to run out of stroke, smashing the internal valving into the bottom of the damper tube. The only other thing to watch for at this point is the tyre fouling the wheel arches. So the goal should be to lower the car as much as you can without running into any problems that you can't deal with - so common sense must prevail here!
Lowering a dry suspended Mini is pretty straightforward; no different to altering the spring platform height on a coil-over suspended car. In the Mini's case, the spring platforms are the four ally 'trumpets' at each corner sited between the rubber spring and the knuckle assembly that connects it to the top suspension arm at the front and radius arm at the rear. To alter the ride height, you need to alter the length of these trumpets; to lower the car they need to be shortened (to raise the car, if required, is simply the opposite, and generally has the direct opposite effects on suspension geometry that lowering it has). Before starting out with the mechanicals - measure the cars existing ride height before you jack it up to give you base data to work to when assessing how much you want to lower it by.
Lowering the front
To enable this to be done, you will need the special tool manufactured for compressing the rubber springs. Without this you will not get the ally trumpets out since the rubber spring is applying considerable pre-load force on the trumpet and knuckle assembly. They are readily available and are not expensive. Every long-term Mini owner should have one anyway! It is possible in certain areas to rent one if buying one is out of the question. Perhaps a local Mini owner or club would be willing to share theirs.
1. Slacken off the wheel nuts, jack the car up, and lower onto axle stands positioned underneath the front subframe. I usually site them directly under the inner bottom-arm pin. Make sure the car is secure and stable then remove the wheels.
2. Remove the bonnet (hood). On post 1976 (rubber mounted front subframe cars) remove the 1-5/16"AF-headed bulkhead to subframe tower bolt. I strongly advise doing one side at a time, although hopefully the car won't go anywhere if securely positioned on the axle stands!
3. Use the spring compressor as described in the literature supplied with it. If none is available - the Mini Spares-sourced type is a two-piece tool - a threaded rod with large cast T-handle screwed onto the top and a T-bar at the very end, and a long metal tube with a plate at one end. The metal tube is placed with the plate against the bulkhead. The 'pointy end' of the threaded rod placed down inside this, and screwed into the spring. The T-handle is then screwed down to compress the rubber spring. CAUTION; there are two types of threads used in the rubber springs. Pre 1976 had a fine, 1/2"UNF imperial thread and post 1976 ones had a coarser, 14mm metric thread. Don't wind one into the other - cross-threading the rubber spring will be a nightmare of epic proportions! Smear a blob of grease onto the thread on the rod, and take your time to carefully screw the rod into the spring. If you are getting a great deal of resistance - you may be using the wrong thread type. Once happy you've got the right thread match, wind the rod in at least nine or ten full turns to ensure complete thread engagement in the springs threaded section. Use the cast handle to compress the spring. This will take some doing as the force that spring is applying is in the thousands of pounds area. Compress it about 1/2".
4. Remove the bump-stop fixed to the subframe tower elbow to give maximum working room - two nuts on inner side of tower for early non-rubber mounted subframes, one nut for rubber mounted types.
5. Position the jack underneath the bottom swivel pin on the outer end of the bottom arm and jack the suspension up until the ally trumpet is just re-engaging the rubber spring. Now remove the rebound buffer under the top arm, fixed to the subframe by a Pozi-drive screw. You may need an impact driver since these can get corroded in. Doing this will maximise the 'droop' available on the top arm - again for maximum working room.
6. Undo the top and bottom damper fixings and remove the damper.
7. Lower the jack and allow the suspension to go to full droop.
8. Compress the spring far enough to remove the trumpet only. Fitting the trumpet back in will be easier because it will be shorter.
9. The existing knuckle may well be contained in the ally trumpet on removal. If so, use a suitably sized drift to knock it out. This is a good time to assess the condition of both the knuckle and the nylon cup it sits in. If either shows signs of wear, replace them. The whole knuckle assembly is very cheap. If they are serviceable, clean out any old crease and grit from the cup and re-grease before re-assembly. Getting the nylon cup out of its socket can be trying - the easiest method I have found is to use a butane gas torch to melt the thing. Alternatively a very sharp craft knife (Stanley knife) can be used to cut it to pieces. Both are far easier than trying to pull it out with grips of some sort. Clean any corrosion out of the nylon cup socket in the top arm, and grease lightly to abate further corrosion.
10. Now the nitty-gritty. The ratio for lowering the front has been distilled down to a widely acknowledged 3 to 1; i.e. to lower the car an inch and a half, half an inch needs removing from the knuckle joint end of the trumpet (3 x 1/2" = 1-1/2"). However, this ratio is not linear. The more you want to lower the car, the ratio decays slightly, so err on the lesser side of the required amount. If too much is taken off, you will have to strip the whole thing down again and put shim-washers in to get the height back up to where it is required. And incidentally - the 3 to 1 ratio is NOT the actual suspension leverage ratio.
11. Once the amount to remove has been decided, cut this off the end of the trumpet. This must be done as squarely as possible to avoid a tilting angle on the trumpet under suspension load. This can lead to collapse of the trumpet if the angle is excessive. If you can't cut straight/square to save your life (like me) get them turned down in a lathe.
12. Once trimmed, de-burr any sharp edges, use copper anti-seize grease on the knuckle pin, and re-assemble the whole lot in reverse order of removal then do the other side.
13. Refit the wheels, and lower the front onto the ground - it's time to attack the rear!
Lowering the rear
1. Slacken the wheel nuts, jack the car up and set it down onto axle stands, ensuring the car is stable then remove the wheels.
2. Position the jack underneath the drake drum on one side, and take the weight off the radius arm.
3. You need to disconnect the top damper fixing. I always find this a great deal easier if the boot (trunk) lid is removed first. Saves having to try and work at full stretch and awkward angles. Particularly as the fuel tank needs swinging in to the boot space to afford access to the left hand damper fixing. A little forethought here will see a bare minimum amount of fuel in the tank whilst this operation is being carried out to avoid the risk of spillage. To remove the tank, release the holding straps and filler cap. Ease the tank inwards to pull the filler neck back through the large body grommet. Once the filler neck is clear - re-fit the filler cap, and swing it into the boot space far enough to allow access to the top damper fixing.
4. Lower the jack and allow the radius arm to hang at full droop/rest on the floor. Slacken the lower damper to radius arm fixing, compress the damper and swing it back towards the rear of the car to maximise access to the rear suspension. If the dampers are to be changed, remove the lower fixing then the damper.
5. No spring compressor is needed to at the rear, as there is sufficient droop available to allow the trumpet and spring to be removed. The rear suspension is under less spring pressure so requires no pre-load to be used. However, if the assembly has been in situ for some time, the spring may be stuck to the trumpet by corrosion. This will mean some use of a hammer and possibly large chisel/pry bar to get them apart. Soaking the joint in WD40 pays dividends.
6. Once out, repeat the knuckle inspection/replacement as detailed in the front suspension operation.
7. Already mentioned is the fact that the rear suspension has no pre-load as it is under less pressure. This is because the rear of the car is far lighter than the front, so requires a 'softer' spring action. As a consequence the rear spring rides in a different part of it's operating 'envelope'. This causes the rear lowering ratio to be different too - 5 to 1. So to lower the rear by 1-1/2" only requires 0.300" to be removed from the knuckle end on the trumpet. However - all that applied to the front re non-linear behavior applies here too. As does getting that cut-off square!
8. Once the trumpet is shortened to your satisfaction, re-assembly is a simple matter of reversing dia-assembly. Clean any corrosion off of the spring seat on the trumpet and smear with copper anti-seize grease to prevent future corrosion.
If a change of dampers is decided on, and removal of the existing ones leaves the eye-bush inner metal sleeve stuck on the damper mounting pins (front and/or rear), use that butane torch to heat the sleeves up a bit and remove with Vise/Mole grips. Clean the pins up with abrasive tape and smear anti-seize grease all over them before fitting the new units.
Do not be at all surprised if the car still looks too high once you've set it back on the ground. You have disturbed the well-settled suspension components. Drive the car around for about a week, it'll settle down again hopefully to the pre-planned position. If not - you'll have to repeat all the aforementioned and make adjustments - chiv more off for lower, slip shim-washers in to raise it.
If you can't be bothered with all this messing about repeatedly to arrive at a suitable ride height, or you need to vary ride height now and again for occasional alternative usage, then you'll be wanting to fit Hi-Los. See separate article. Also see separate article re damper lengths and operating envelopes.
And for the record the front trumpet height as standard is 3.750" and the rear is 12.375" on the latest post 1979 cars and all vans/estates. The earlier ones were around 12.125". This is from the knuckle end to the spring platform face, both measured from where the spring butts up against it, NOT the over-all height.