Lowering a Rubber Bumper B

Work Safe!  Securely support the vehicle on axle stands when undertaking these jobs!

If in doubt seek professional help. 

On this page:

• Front & Rear Anti-roll Bars
• Lowering the Front
• Lowering the Rear

A good time to consider lowering a rubber bumper B is probably when doing a suspension overhaul.  Unless you are keen to get the most out of the driving experience, then it is a cost that becomes additional rather than a routine maintenance cost.  However if you are reconditioning the suspension then the lowering will not cost much more, in fact very little.

Springs would be replaced anyway, so a lowering set will cost the same as an original set.  Perhaps if you are seeking a more drastic lowering stance then you may need to add in the lowering block kit at £30-40, but even that could be less if you approach it in other ways.

Of course, if you are modifying the r/b bodywork to go for the chrome bumper conversion or Sebring or semi-Sebring look, then lowering the car is a must to complete the look.  

But first, how low do you want to go?  How low is necessary?  In today's speed-hump society, too low can be a bad thing for the exhaust, and if you still have a centre box then you should look into replacing it with a straight through pipe or at least a bomb, otherwise you will repeatedly hear the graunching of steel on tarmac or concrete.

Certainly, lowering the car can only benefit the roll centre, and thus improve cornering.  For many the lowering is simply part of an aesthetic appeal, whilst for others it is part of the continual improvement process of driving the car.  

The Roadster above belongs to Vince Badminton and has been lowered at the rear using blocks.

Front & Rear Anti-roll Bars

Lowering in itself will not necessarily benefit the handling so we need to look at a package of options here that complement the lowering. As I have done on mine and recently on Stephen's later r/b BGTs, this also includes issues such as removing the rear anti-roll bar which, if left in place, has a negative impact on the balance when the centre of gravity is lowered.  When considering the B's handling, the perceived wisdom is that the car should be stiff at the front and flexible at the rear.  This was also something that was noticeable with my car initially.  I had lowered the rear by almost 2", but I noticed that the rear had a tendency to snap out at the slightest provocation on roundabouts, which whilst fun, could be dangerous on a bend at speed.  Mind you, it did focus my mind into driving more sensibly.  At this stage, a colleague following me mentioned that he thought the car cornered too flat, and did not appear to tuck in at the rear as he felt it should for better handling (this is a gentleman that used to be a pit mechanic for Tiff Needel so I took his advice seriously, along with that of several other respected MGOC members).  Just prior to this the MOT inspection highlighted a failed bush in the o/s of the rear anti-roll bar which had been exhibiting itself regularly in the form of an annoying clunk from the underneath of the car.  So on these two counts, I decided to try removing the anti-roll bar.  It took some effort as it hadn't seen a spanner since new, so there was a bit of grinding to free the nuts.  On first trying the car, it felt a bit "squirmy" at the rear as if the car had lost some rigidity (something that Stephen also noted), however it soon became apparent that the car then had a tendency towards understeer rather than snap oversteer.  Disappointing as this is, it is safer in my opinion, and I have found the car can be better held if the rear does start to go.

The two photos below show the points on the n/s where the rear anti-roll bar is connected and where you will need to do your spannering to remove it.

However, the front anti-roll bar remains a crucial piece of kit, and in this case the stiffer the front anti-roll bar is, the more the tendency to understeer.  For improvements, consensus of opinion appears to be to use the 3/4" anti-roll bar.  Fitting it is fairly straight forward as it merely replaces the existing bar, and of course, it will mean new bushes.  Most bush kits include for the standard 5/8" bar, so unfortunately, you will find these surplus to requirements, and will need to add 3/4" bushes to the shopping list.  In addition, and here there is some discussion as to the need, but you will notice that the existing front anti-roll bar has locating brackets next to each bush, presumably to stop the bar sliding sideways.  However, these brackets will not fit the 3/4" anti-roll bar.  3/4" versions are available from the likes of Brown & Gammons, but it would seem that most people leave them off.  I have not fitted any and to be honest I am not sure I would notice whether they were fitted or not, but that is no recommendation!  It would not be difficult to machine or fabricate a set if you felt that they should be used.

The picture below shows the two points on the o/s where the anti-roll bar is connected, the right one being where the bush is located to the chassis rail, and which will need replacing if going to a stiffer unit.

A final point, bearing in mind that any lowering may have induced slight negative camber, is that the steering alignment should be checked after this work.  The figure, which many tyre centres will not have is between 1.5mm and 2.5mm toe-in.  Please note it is a toe-in, not toe-out, as the MGB is RWD.  It is amazing what a correctly set toe-in will do for a smooth ride!

Lowering at the front

Firstly, forget cutting the coil springs to reduce their free length, or heating the lower coils as the hot-rodders do.  The former approach does not spread the load correctly in the spring pan, and the latter can result in changes to the spring structure resulting in snapping.  For the price of a set of front springs, (~ £30) it is better to change them out completely.  

We have to first look at the front cross-member and examine the differences between this and the earlier cross-members.  The essential difference is that the car sits higher on the r/b cross-member, but it is not simply a case of fitting a c/b cross-member as this puts the steering rack at the wrong angle.  On r/b cars the steering rack passes through the engine mount, and the lower column is longer than the c/b cars.  it is possible to remount the steering rack further forward to accommodate the longer column and redress teh angle issue, but this then affects the steering geometry.

The picture below shows a r/b member at the top and you can clearly see the longer steering rack supports.

By using shorter free length front springs this will lower the front, and most lowering kits include this for the front.  These are usually the c/b front springs. However, there is more to it that that.  A couple of issues arise, notably bump-steer and bump-stops.

In an ideal set-up, the steering arms should be horizontal to the rack, however, lowering the springs results in a slight upward angle from the rack.  Thus, in a bump situation, the steering arm can be pulled resulting in a wrench at the wheel for the unsuspecting.  In reality on both mine and Stephen's I have not encountered this to any noticeable degree, but in serious lowering terms, it is possibly a point of concern that would have to be addressed by raising the steering rack.

With regard to the bump-stops, the spring pan is sitting that much closer to the lower bump-stop, and consequently in a heavy shock loading, the spring pan is more likely to hit the bump-stop with a noticeable jarring through the body.  Again, this is not something I noticed on mine, although I have experienced it on Phil's c/b BGT.  However, there is a simple modification to address this and to minimise the risk.  Spacer tubes can be fitted on the top side of the bump-stop.  In the photo below, this is shown, we removed the alloy spacer block from the lower side, and used the longer bolts on the top incorporating spacer tubes from thick-wall s/s pipe.  Fitting it is not quite so straight forward as the geometry of the bump-stop changes, and so a hefty lever is required to bend the bump-stop to fit correctly.

Initially I fitted c/b front springs with a free length of 8.5", whereas the standard r/b front spring has a free length of a little over 10", but then I decided to try out the 550lbs rated front springs (TT40701) which according to the Moss catalogue should have given me a lower ride height than the standard 480lbs rated units.  I was a little disappointed to note the free length was similar to what I already had although they were definitely harder.  However, 6 months later I have noticed not so much a visual drop but more a slight loss of distance on the headlights which would suggest the nose has settled.

But in both Stephen's and mine, the drop resulting has been no more than about 1", despite the 1.5" suggested by the difference in free length which may be down to differences in stiffness.  I have a serious set of 600lbs springs to try out, though, with a shorter free length of 7.5", so I hope to gain another 0.5" drop and will report on this later.  However, the idea here is to reduce the spring travel to sharpen up the turn-in.  I have no doubt there will be a trade-off in the ride comfort I currently enjoy.

Lowering at the rear

Compared to the front this is probably of a similar cost (if not actually changing the rear springs) and also the easier job, in my opinion.  On Stephen's and mine, the job was completed in under 2 hours.  It may take a little longer if you are also replacing worn dampers or converting at the same time to telescopic dampers.  In my case, I was satisfied that the rear springs were ok (I was contemplating a longer term plan to fit parabolics), and so for the short term, I purchased a lowering block kit (~£30).  However, Stephen decided upon new rear springs as per the c/b Roadster.  The rear springs used on a BGT are generally stiffer than those on the Roadster owing to the extra body work at the rear, so the purchase of Roadster springs does make some sense. 

However, in to my mind, the fitting of c/b rear springs alone does not achieve much as the spring hangers were again modified on the r/b cars.  It may result in some drop owing to the lack of stiffness, and a different arch.

But to get a comparable ride height to a c/b car (which I have achieved in comparison with Phil's) then a little more effort is required.

Lowering Block Kits - The first, and easiest, but not cheapest, is the lowering block kit shown as fitted below.  The kit contains the block and shackles with new Nyloc nuts.  Fitting requires the body to be supported on axle stands, with the trolley jack to support the axle, preferably with another set of axle stands.  I found it easier to use the grinder to remove my shackle bolts, but as Stephen's had been rebuilt in the last 4 or 5 years, his shackle nuts were easy enough to undo.  

In my case, whilst fitting the blocks, I also managed to move the lower two spring leaves (just visible at the base of the spring) up to the top.  These leaves are not strapped as the others are so it was a matter of undoing the central bolt and refitting.  As you can see in the photo, the bump-stop plate has rusted away, and if you doing this conversion I would recommend fitting new bump-stop-plates while the shackles are out.  We did afterwards!

However, as you can imagine the axle has been moved further away from the spring, and whilst this is probably not an issue on tuned B Series powered cars, V8 conversions would no doubt encounter spring wind up where the leaf spring takes the shape of an S profile, which can be countered to a degree with anti-tramp bars.

Parabolics - Although the benefits of using these will be discussed elsewhere, the units also come in a lowered format although this is not common knowledge amongst the suppliers according to those that have fitted them.  Again, though, the units come with spacers to allow the ride height to be adjusted (see photo from Jim McGlynn's website below).  In this case, though, fitting parabolics also requires the use of telescopic dampers according to the suppliers, so would need to be factored into the job.

Spring Hangers - As you can see in the photo below, the spring hanger has quite a depth to it, sufficient at least to allow re-drilling of the holes at least 1" higher up.  This has been used by others in the past and is something I might contemplate in the future, the real difficulty being getting a drill in position and ensuring the holes match across.  This may be something worth contemplating when welding new spring hangers in.

Bump-stops and Check-straps - As with the front, any lowering will bring the axle closer to the bump-stop.  Although I have never experienced any contact between the axle and bump-stop on mine, any serious lowering should include removing some material from the bump-stop to increase the distance again.  Like wise, the check-straps should be replaced with c/b versions to prevent the spring dropping too far.  Although good luck to you on undoing the nuts on the check-strap mounts on the axle.

A final note - don't forget to inform your insurers of your changes!

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