Michael’s Blog

As the work on the conversion of AHX12’s rear suspension to coilovers proceeds I have been looking at other rear suspension systems for inspiration. One of the most interesting drawings that I have come across is that of the rear suspension used in the Lotus 33 F1 car of 1963.

This state of the art car used fully independent double wishbone suspension with the springs on an angle, similar to what I’m trying to do with AHX12. (I can assure you that the similarity ends right there).

The thing about this suspension type, which is used in many cars, and which has me most perplexed, is the angle of the springs. In the normal ride position the springs are inclined to the vertical and, as the suspension compresses this angle increases considerably.

At first glance this may seem a little unusual, but nothing to be particularly alarmed about. However, inclining the springs in this way, has a profound impact upon their effectiveness.

Let me explain. If the spring had a rate of 100 lbs/inch and was installed vertically such that its lower attachment point was the top of the wheel (ignoring for the moment of course the difficulty of actually achieving this) the spring rate would be equal to the wheel rate. i.e. if you pushed up on the wheel (the equivalent of adding weight to the car or going over a bump) with a force of 100 lbs the spring would compress one inch. Now lay that spring over at 45 degrees. In this case when you pushed up on the wheel with the same 100 lb force the wheel would move up 1.414 inches because the vertical force applied to the wheel by the spring is effectively decreased by the angle of the spring. Taken to the extreme if the spring was installed at right angles to the load it would have no effect at all.

Now let’s consider the Lotus 33. As far as I can determine the spring has an installed angle of something very close to 40 degrees in the normal ride position. This is in itself perhaps not to much of a problem however, when the suspension is fully compressed, the spring adopts an angle of something like 51 degrees. The results of this change of inclination, insofar as the effective spring force, is concerned is a decrease from .76 to .63.

The motion ratio of this suspension is about .66 , i.e. the spring is mounted to the lower wishbone 2/3rds of the way out. Presuming that the spring is a 100lb/in spring this means that the wheel rate is about .32 (.43 [motion ratio squared] times .76) at normal ride height and .27 at full bump. I trust you are keeping up here!!

The important point I’m trying to make here is that the wheel rate decreases by 15.5% from normal ride to full bump.

What I don’t understand is why they did this. It seems to me that a much more desirable condition would be an increasing spring rate as is provided by those wonky looking coil springs that you can buy with changing pitch, or arranging for the spring angle to decrease in bump!!

I can only presume that the decreasing rate was considered to be a reasonable trade off for simplicity and space savings.

All comments welcome (below).

5 Comments »

One of the problems I had with my MkIII (BJ8) was that the choke control kept coming loose in the dash. BJ8’s came through the shop on a fairly regular basis and at least half of those would arrive with the same problem. This fault did nothing to enhance the driver’s ability to adjust the engine’s fuel mixture requirements when the engine was cold and when they are correctly tuned BJ8s need a good choke to get them started in cold weather. Unfortunately this is not a repair to which the Workshop Manual devotes much space.

The choke control features a friction lock, the idea of which is that when a satisfactory setting is achieved the choke control can be held in position by merely rotating the handle a little to lock it. The locking mechanism, although very simple, is quite ingenious.
The choke control shaft has a groove along its length. The choke body has an axial hole up near the dashboard end and inside this hole resides a ball bearing. Over the outside of the hole and pressing the ball against the shaft of the control is a spring steel ring. The parts can be seen in this exploded view.

If the choke control is rotated relative to the body in either direction the ball rides out of the groove and is forced to move up the axial hole against the pressure of the spring ring.  This pressure creates friction between the shaft of the choke control and the body which locks the choke in position. Turn the control back so that the ball drops into the groove and the lock is released.
This is what the whole thing looks like when assembled.

Pretty tricky but, when used in a BJ8, there is a problem.
A nut and washer fit onto the thread on the body to secure the choke body into the veneered plywood dash. The plywood is clamped between the nut and the flange on the choke body. This arrangement works fine when first assembled but after a few of these knob rotating operations the nut has a tendency to work loose. When the body is not firmly secured into the dash it rotates readily in the dash rather than the control shaft rotating within the choke body and it becomes impossible to lock the choke.
 Just to make the correction of this situation a little more difficult the back side of the dash is counterbored, probably so that a standard choke control could be used rather than having one with a longer body especially developed. This counterbore makes it impossible to fit a normal box spanner (wrench) onto the nut to rectify the aforementioned looseness. THIS IS QUICKLY BECOMING A VERY FRUSTRATING EXERCISE.
 The only way I have been able to correct the problem is to start by disconnecting the choke cable from the splitter on the bulkhead.

Then I thread 5/8” spark plug socket over the cable and up to the dash where, using a spanner on the hex on the top of the plug socket, I can tighten the nut on the choke control again. To prevent the control coming loose again I then fit a 5/8” UNC Palnut. 
  

These are stamped out of spring steel and they really serve to lock that sucker in there. I’M NOT GOING TO GO THROUGH THIS AGAIN.!!!!!
 The most difficult part of the operation can be reinstalling the choke cable to the splitter. This is most easily achieved by removing the two 10/32 screws which secure the splitter to the bulkhead and then threading the cable end through the hole in the bulkhead and into position in the splitter before resecuring the splitter to the bulkhead.

Alan has commented that his original BJ8 choke control was of this type which has a round knob with picture somewhat like a fan on it:

 

I was of the opinion that this is a later version of the locking choke mechanism but could be wrong. The one pictured is from of my 1970 UK Market MGBGT. The original BJ8 choke knob was round and fairly flat with a white circle close to the outside edge and the word “CHOKE” across the center.

A couple of point that I have remembered about this operation which may be of help to anyone working on the choke control of their BJ8.

1. When the handle is pulled completely out of the body the inside of the body will acceptan Allen key which is of great help when tightening things up.

2. It is a lot easier to work on the choke control whith the tachometer removed.

Comments welcomed.

3 Comments »

Dave Porter, long time Healey nut and general all round good guy, suggested that I take some time to enlighten readers as to the finer points of antifreeze which, like most things in our world, has become a much more complex subject that it was just a few years back. He pointed me to an article on the Master Technician site by Bob Freudenberger which surely emphasized that!!

In the old days, well since WWII, all we had was the old reliable “green stuff”. (Prestone used to dye theirs yellow-gold but it was the same stuff to all intents and purposes) “Green stuff” consists of about 95% ethylene glycol and the rest is corrosion and erosion inhibitors like silicate phosphate and tolytriazole, sodium benzoate which is an organic acid that is also added to Coke (the drinking kind), some dyes and 1 or 2% of water. This brew works very well although over time the corrosion inhibiting properties deteriorate over time. So you should do a flush and refill every 3 – 4 years.
Unfortunately many of today’s manufacturers and less than enthused about these concoctions and all manner of new and fancy antifreeze mixtures have appeared on the scene in the last few years.
These of course include GM’s DexCool which has gained something of a bad reputation and at last count there were at least 14 class action lawsuits filed in state and federal courts throughout the U.S. representing GM vehicle owners angered over their experience with this product.
Dexcool is based on OAT (Organic Acid Technology), and its additive package according to GM’s literature can keep corrosion away for up to 150,000miles. It seems that the big problem is that Dexcool doesn’t like air. Everything is hunky-dory just so long as the cooling system remains completely full of coolant but introduce some air and things go seriously pear shaped and the additives in these OAT type antifreezes produce a guckey goop which clogs coolant passages and generally creates havoc in the victim’s cooling system.
Additionally, one of DexCool’s ingredients is sodium 2-ethyl hexanoate which is a “plasticizer” . Plasticizers soften plastics which, as you can imagine, isn’t exactly ideal for use in engines which have water heated intake manifolds made from the plastics that these ingredients soften.
There are other OAT based antifreezes out there and these include Prestone’s new Extended-Life gold is and Wal-Mart’s Super Tech brand. I would suggest avoiding the use of these in any vehicle. However…I digress.
So what should one use for antifreeze in a Healey? The short answer is “The green stuff and not too much of it”.
Based upon the number of questions posted on the Healey newsgroup about overheating problems this does seem to be a major issue with Healeys. I distinctly remember participating in the rally during an event in Tahoe a few years back during which the last section was a long climb in the desert heat. The further we climbed up the slope the more the side of the road was littered with steaming Healeys. At one “Kodak Moment” vantage point it was difficult to find a place to pull off to take a photo!!
It has been my experience that if the cooling system of a Healey is in good condition overheating is not a problem and as many of us don’t drive our cars in the winter here is something to consider. 
                                   Water     Ethylene Glycol       50/50 mix
Freezing Point              32F                8.6F                       -36F
Boiling Point                212F               387F                     225F
Specific Heat               1.00                 .57                        .81
Thermal Conductivity    .60                  .25                        .41

I’m no thermodynamics specialist but as I understand it the specific heat value is a reflection of the amount of heat a given weight of fluid (coolant) can transport. Now if the 50 / 50 water-antifreeze mixture in your cooling system can only carry 80% of the energy pure water can it seems obvious to me that I would want water and just water in my cooling system. Sure it may boil at a 13 degree lower temperature but if the system is working 20% better it probably won’t ever get that hot.
There is no question that if you live in a part of the world where the temperature drops significantly below freezing on occasion you need to have some type of anti freeze protection in your vehicle’s cooling system but this sure isn’t required in summer when overheating is the “issue of concern”.

 One consideration of course is that pure water doesn’t provide much in the way of corrosion protection, but you can buy straight corrosion inhibitors to add to your coolant to solve that problem. One source is:Here and I’m sure thare are plenty of others.
The reverse situation also applies. At the beginning of the cold weather here in the Great White North most auto repair shops get a number of customers coming in complaining that their heaters aren’t working. The most common diagnosis is that the heater core is plugged and the customer has to either put up with freezing feet for the duration of the winter or part out with a hefty wad of dough to have the core replaced. The fact is that in a fair percentage of cases the problem could be resolved by just checking and adjusting the percentage of antifreeze in the cooling system. We used to check the antifreeze concentration as part of a regular service and many was the time when we would discover that the cooling system had more than 70% antifreeze. Definitely a case of more is not necessarily better!!

4 Comments »

For many years now aftermarket vendors have been extolling the virtues of polyurethane suspension bushes. I have yet to be convinced. Several years back, at the request of a Healey owner we installed a set of these which he supplied. They came from a reputable supplier and were touted to be the best thing since sliced bread. Unfortunately I don’t have a photo of the bushes he supplied but they were red and looked to be of good quality.

I’m always hesitant to install customer supplied parts because if something goes wrong there is always some concern as to who is responsible for the problem and who will pay for the necessary corrective action.

After making my position clear I got the go ahead and installed these front suspension bushes in said Healey. Anyone who has worked on a Healey which has spent time in Eastern Canada is well aware of the difficulties that removing the lower inner suspension bushes can present and this car was no exception. As I recall this one was so bad that I ended up having to change all four pivot pins and washers after having to resort to using the great blue wrench to get out the original rubber bushes which, before my attack, were in great shape despite their age.

Polyurethane bushes replaced the anti roll bar bearings, the anti roll bar link bushes (which required that the links be replaced because the ends of the threads were badly damaged) the upper trunnion bushes and the afore mentioned inner lower bushes. No lubricant was supplied with this set but as per the instructions we applied silicone grease to the bushes.

In less that one week the owner was back complaining of creaking noises from the front suspension; however, despite the creaking noises, he swore that the handling of the car had improved immeasurably.

I took it all apart and re-applied the lubricant and reassembled everything. This fix lasted about 10 days before the creaking started up again and one of the threads broke off one of the new anti roll bar links. The car was back and I was on vacation. My chief mechanic of the era was a distinctly crusty individual who was somewhat disinclined to “humour” customers and, without discussing the options with the owner, fixed the problem and sent him on his way.

When I ran into him at the next club gathering the owner was to be heard extolling the virtues of the “genius” I had working in the shop while I was on vacation and how he, the mechanic, had managed to correct the creaking problem in his suspension. He took pains to point out that this was something that I wasn’t able to do, and how wonderful the handling was with the polyurethane bushes. When back at work on the following Monday I mentioned the praise to mechanic he said “Wait till he finds out that the bushes are rubber”.

I think this incident says a lot about polyurethane bushes in Healeys and MGs for that matter.

The problem with these bushes, as I see it, is that joints are not designed for polyurethane bushes and without a major reconfiguration are completely inappropriate for them.

Take for example the upper trunnion of a Healey or, for that matter an MGB which is virtually identical. The same issues apply to the lower inner joints. This is what a cross section of the joint looks like.

The brilliance of the design is that there is no relative movement between the surfaces. All the movement is taken up by the compliance of the rubber bush. No movement means no maintenance, no squeaks and no wear. What more could you ask for? The bush design is far cleverer than it at first appears. When the joint is tightened up with the suspension in mid range there is just enough rubber in there that it remains within its elastic limit throughout the entire movement of the joint and the rubber is squeezed in so tightly that it keeps moisture out. It’s brilliant!!

Now let’s consider the concept of installing polyurethane bushes into the same place. This is a scan of the instructions received with a set of such bushings.

And this is what the “improved” joint looks like.
 

Unlike the original rubber bushes, polyurethane requires sliding contact somewhere. In the case of the ones used in this application the sliding is meant to take place between the sleeves and the polyurethane and between the shock arms and the polyurethane.

The first problem is that there is no sealing medium at the edge of the sliding joint at the shock arm with the result that any lubricant in there gets squeezed out and replaced by moisture.

The next problem is that the force required to hold the bushes into the tapered holes, which is a factor of the compressibility of the urethane, the excessive length of the urethane which gets compressed to tighten the bush into the cavity and the length of the sleeve is quite substantial. This force produces friction at the shock arm to urethane intersection. Decrease this force and the bushes will start rotating inside the upper trunnion because they are a loose fit.

Way back in 1962 Triumph redesigned the suspension used in their TR series of sportscars and used nylon bushes in the then new TR4A. Around the same time they also launched the Spitfire which used a similar system also incorporating nylon bushes. I know that nylon isn’t exactly the same as polyurethane, but it does have very similar properties. The joints in these cars were redesigned to incorporate the nylon and this redesign included fitting a complex “O” ring sealing system to keep moisture out and lubricant in. They worked fairly well, although they do wear out frequently and are often reassembled incorrectly during maintenance which does not improve matters. 

I have no doubt the polyurethane is a wonderful material for suspension joints BUT the joint must be designed appropriately and not cobbled up from something designed to operate entirely differently.

18 Comments »