AC Ace steering box?

[Michael Trotter]

Jonas
If you are going to solve your problem you have to start from a baseline of certainties. I presume you are satisfied that bearings, king pins and bushes,all suspension bushes, ball joints, rear end (the tail not wagging the dog) and steering box (come back to that) are all OK.

Tyres - I have no knowledge about how current Michelin X compare with those of 60 years ago. I have always thought Michelin are expensive but are the best. I think that tyres are not an issue, but what tyre pressures are you running? AC standard (normal) were F22/R24. I think for high speed you could go to 28/32. Might be worth trying, say, 26/29 to see if pressures have an effect.

Wheel geometry - AC figures are castor 5, camber 1 to 2 positive, KPI 9 and static toe-in 1/16 inch. Castor 3 to 4 is a bit short of 5 but I would settle for that unless all else fails. You haven't mentioned cambers but these can be measured accurately enough on a DIY basis with a spirit level (my method on application). Since stub axle and king pin trunnions are one machined part it follows that if cambers are OK then KPI's will be OK.
Now to static toe-in. The principle is that, when driving, rolling resistance at the tyres will 'pull them back' so they become parallel and roll true without generating slip angles when driving straight ahead. I guess you took the car to your local wheel alignment shop to have the toe-in set. 1/16 toe-in can be restated as 1/32 and angle A at each wheel. You state A as 0.25 degrees. I don't agree. My calculation is that A = 0.1 degrees. (Since you ask - rim lip to lip diameter = 17 and 3/8 inches.   A=1/32 divided by 17.375 radians = 0.001798 radians = 0.001798 x 360/ 2pi degrees = 0.1 degrees.) So the question is whether the toe-in is set at 1/16 or 0.25 at each wheel? If the former why did 0.25 come in to the conversation? If the latter my calculation suggests you have 5/32 toe-in which is too much by a factor of 2.5. I think this (?) error, apart from producing transverse 'feathering' of the tyre treads, would be significant at high speeds.
To check whether the toe-in is OK you don't want to spend months and miles examining the treads for feathering. I suggest a wheel alignment gauge which gives an instant answer. I have a Gunson Trakrite which I recommend. It detects the transverse force arising from slip angle. (Happy to lend you mine but Malmo is not just down the road from Hampshire). You put the Gunson ahead of one front wheel, drive the car gently over it and your assistant sees the pointer showing OK, to much toe-in or too little toe-in. (Advice : Don't ask her when she is busy cooking a nice dinner for you). Incidentally, the other wheel rolls true without slip angle on your workshop floor and any misalignment when the car is driven shows up on the wheel going over the Gunson. If the Gunson does not show OK it's trial and error adjustment until it does show OK, but each test only takes minutes. I guess the cost of a Gunson is about the same as a visit to your alignment shop or, if they 'messed up' with the 0.25, nil after a full refund.

You should check the spring mounting bolts are tight. A broken leaf would be obvious but over time the spring can flatten. I wouldn't think it would at 80,000km and am not sure what the effect of flattening is.

Now to the steering box - your first but my last resort. Let's get the terminology right. We all have a Bishop cam and peg box. The bit inside which turns is not a worm which has a uniform cross section along its axial lenghth. I quote from my Automobile Engineer's Reference Book (1959). ''A truncated conical peg pressed into the rocker shaft engages a cam of varying depth. The method of manufacture of the cam involves a finishing operation by a cutter of the same form and rotating on the same axis as the peg. This cutter also moves through the same arcuate path as the peg and by so doing ensures uniform contact between the peg and cam. Slight clearance is allowed on the full lock positions to cover adjustment which may be necessary for concentrated wear at straight ahead.''  So, complicated machining.
I have known Barrie Bird for many years and regard him as the authority in all matters AC. However he said above 'the cam is machined to give more clearance in the straight ahead area'. This is wrong as Barrie, on reflection, will confirm. Just goes to show that elderly folk like us get confused sometimes. Steering box adjustment is delicate, particularly as things can change as you tighten the locknut. You must follow the procedure set out in the AC instructions. In spite of references to 'slightest drag' and 'no lost motion' I would aim to have very slight free play at straight ahead - say 1/8 inch at the steering wheel rim. Unless your steering box has been abused ( eg lack of oil or faulty adjustment) it should be good for many more miles. I wouldn't change the peg at this stage without clear evidence - maybe later if all else fails. You should check the steering box mounting bolts going through the aluminium block but note the  warning in the AC instructions not to 'overtighten' them. However they didn't tell us how tight is too tight.
I picked up a warning signal when you said 'the peg is past the centre of the cam in the straight ahead position'. You later say you have adjusted the angle of the steering arm relative to the box. The only adjustment I know is to pull the drop arm off its splines and replace it on different splines. Sounds like you have got this right. In straight ahead the idler should be on the car centre line, the drop arm should be parallel to it and the steering wheel should have the same number of turns to the left and right full lock stops.

I hope some of this will be helpful. Good luck and remember the Golden Rule - only change one thing at a time.

If any of you are still reading this I have a question. Years ago the club did a batch of bracing struts to go diagonally from the steering box to the suspension tower. I have always thought that the steering box mounting was a bit 'flimsy' and bought a kit but never fitted it. My current Aceca (ex factory demonstrator) has an identical bracing strut fitted. I have never seen this referred to as a factory option. I wonder if AC fitted it after the Autocar reference to high speed wander or or was it out of the club batch and fitter by a subsequent owner? Now here's the interesting bit - my memory is that Barrie was the instigator of the club batch but I can't remember  what the claimed benifit was. So, Barrie, if you are reading this do you plead 'guilty' and can you remember the intended benefit and whether the strut delivered it? Subject to Barrie enlightening us about bracing struts, perhaps this is what you, and maybe every owner, should have.

Michael

[AC Ace Bristol]

.
Michael. &  Jonas
Steering Box Steady Control Arm
A very in depth interesting  analysis,  You are definitely right , change one thing at a time.
You mention in your last paragraph  " Steering Box Steady Control  Arm " ..........These are available from:
Classic Autos Ltd
10, High Street.
Kings Langley.
Hertfordshire.
WD4 8HB
England
Tel: 01923 262994
Aubrey or Nik Finsburgh


PLEASE NOTE:  They are handed,  You must state Left Hand Drive  or Right Hand Drive.

I supplied Classic Autos with a full size drawing after I ordered mine, as I was  incorrectly supplied a RHD unit
for my LHD BEX333.
I bought and fitted mine to BEX333 some 20 years ago, it definitely Supports  the steering box.   
Hope you solve your Steering Box problem.

Keith

[AEX 31]

Michael,

Thank you very much for sharing your thoughts and experience in this matter, much appreciated. I also thank you for the kind offer to use your Trackrite. I am somewhat confident that the bearings, king pins and bushes, all suspension bushes, ball joints and steering box are fine since most parts are more or less “new”.

I will give you some more data about the Wheel geometry, well the caster is a little bit off as I think I mentioned 4 degrees and 02 minute degrees on the left and 3 degrees and 42 minute degrees on the right side. So 18 minute degrees difference, if that is too much I don’t know.

The camber on my car was at least – 23 minute degrees on the left and - 10 minute degrees on the right side; again if this is acceptable or not I don’t know but I have seen a couple of Ace’s that race that are set up with negative camber.
When it comes to the toe-in I have made the assumption (right or wrong?) that when the handbook states 1/16 toe-in that is per side, so my calculation is that the total toe-in should be 1/8 inches. I recently bought a Track ace alignment gauge, http://www.trackace.co.uk/ and when I use their guide to converting the 1/8 to degrees I end up with a total toe-in of 27 minute degrees.

So to answer your question where the 0.25 comes from it’s from the fact that I used to have the total toe-in set to 0.25 degrees. After trying this, which I believe corresponds to the factory specification, I have increased that to, at the wheel alignment shop 47 minute degrees, and when I measure it at my workshop with the Track ace, it’s roughly 40 minute degrees. I increased this after consulting with people with a lot more experience than me. When looking at the recommended toe-in for other English sports cars of the same era with 15 and 16 inch wheels, many of them seem to have a recommended total toe-in of 1/8 inches.
Anybody else out there with any ideas about this?

I very much regret that I didn’t check what toe-in 31 had before I pulled everything apart since it used to be less prone to high speed wander.

Furthermore what I meant about the angle of the steering arm relative to the box was that the arm, which I believe should be 3 degrees to the right, on a left hand drive car. If you look closely at the drawing in the handbook you can see that the arm is not straight in comparison with the column when in the dead ahead position. I’ve enclosed an image of a TR 3 steering box as well as the image from the handbook.
I do have a bracing strut that I have had for a very long time, I maybe got it when I had AE 25 in the early 1980’s but so far I haven’t fitted it, maybe I should?!

Thanks a lot for all the comments and help.

Jonas

[Michael Trotter]

Jonas

You are right about the 3 degrees on the drop arm. The AC drawing you posted is identical to the one in my Service Instructions and my guess is that AC fitted the same box to left and right hand drive cars. I have measured 3 degrees on the AC drawing and the TR one is explicit in this respect. I wonder whether Triumph and AC independently specified this or did they take standard Burman boxes as supplied in large quantities to Austin for (was it?) A40's. On my car the drop arm poking out from under the box 'looks' parallel to the centre line but I couldn't detect 3 degrees by eye. If the drop arm was on the wrong splines (you talked of 'adjustment') this would move the arm by 15 degrees or so per spline which would be obvious. So please correct my statement to 'parallel or thereabouts'. In my view this is not relevant to high speed wander.

Now to castor and camber. I think the fact that you have about the same figures on both sides is more important than the variances from the AC figures. I think your figures will be fine and I don't think the variances are relevant to high speed wander. We don't know how 'sophisticated' the AC chassis jig was. Perhaps every car has different wheel geometry and maybe no two cars are identical. Has anybody got info on this?

Now to toe-in which I think is relevant to high speed wander.
1. Toe-in is not a design calculation. It reflects a concensus view that for rear wheel drive cars 1/16 to 1/8 toe-in will achieve the desired result which I stated as ' driving straight ahead / wheels parallel / rolling 'true' / no slip angles'.
2. Definition - I believe AC's 1/16 is on the basis of the classic definition ' Distance between the rims at hub height behind the hubs less the corresponding distance ahead of the hubs'. On that basis 1/16 is 'total' and not at each wheel. You interpreted AC's 1/16 as 1/8 total - this is wrong.
3. I have no knowlwdge of current alignment kit. Probably use mirrors and laser beams (whatever they are). From what you have told us I understand that the desired toe-in is converted to an angular toe-in at each wheel. The track rods are then adjusted to give this angular toe-in at each wheel.
4. I said that AC's 1/16 could be restated as 1/32 and angle A at each wheel. I set out my calculation that 1/16 toe-in on 16 inch wheels equates to an angle A at each wheel of 0.1 degrees. Now this is important : do you agree with my calculation? If you do we can 'scale' it up for other toe-ins and angles. If not, I think we are wasting our time discussing the matter.
5. You told us that '31 is set up with roughly 0.25 degrees per side which should equate with the 1/16 which it says in the handbook'. You later told us you had increased A to 40' or 47' (say 0.75 degrees). My calculation showed  that 1/16 toe-in (total) gave A = 0.1 degrees. Scaled up it gives A = 0.25 degrees as 5/32 toe-in. At A = 0.75 degrees it gives toe-in as 15/32 - almost 1/2 inch. If you are driving AEX31 with, give or take a bit, 1/2 inch toe-in I am not surprised that it wanders at high speed.

So to progress matters we need to agree, or not, the definition of toe-in as used by AC and my calculation of the relation between toe-in and angle A at each wheel. Jason, I want to help you - AEX31 is an important car. An early Ace, the first one exported and the first LHD one isn't it? I hope the above doesn't sound confrontational but unless we agree the basics we will end up floundering about in a 'soup' of numbers. If we can agree the basics I am happy to advise you further and you are free to act on or ignore my advice. The important thing is that, in spite of the problems the club is facing, members and owners of our lovely AC cars continue to talk to and try to help each other.

Michael

[Ron Hollis]

Here's another bit of background. My car was supplied by Rudds; it was on Michelin X when I bought it in 69 and the handbook had a pencil note on the useful information page saying - Rudd recommends 28, 26 tyre pressures. Seems fine to me, whatever tyres.
          Cheers
                    Ron

[AEX 31]

Michael,

Again thank you for taking time to engage in this matter. I’m in no way offended. My main reason for posting on the forum in the first place was to find out what to-in other Ace drivers
have and if anybody else has had experienced any similar problems.

Let me also try to be clearer with what I meant concerning the degrees of the drop arm. What I did was to adjust the length of the arm that goes from the steering arm
to the idler, so that the peg in the box was dead centre when the idler was, since it wasn’t!

To answer your question I have, as you know,  made the assumption that the 1/16 toe-in as stated in the handbook, is per wheel since it states rim, not rims.
This might very well be a mistake on my part and this will obviously make a difference. I also have to admit that I was unclear in my previous post, I was and I am talking about the total toe-in,
i.e. the combined toe-in for both wheels.

I have since my last post talked with two AC Ace knowledgeable people and they have interpreted the handbook toe-in as referring to one wheel, when the 1/16 inch measurement is given.

But they can naturally have interpreted this wrongly. It would in this situation be interesting to hear how other members on the forum interprets the 1/16 inch toe-in statement;
if they believe it is per side, or the total toe-in?

I agree with your calculation under the fourth point, when I look at conversion tables for 16 inch wheels, from inches to degrees, 1/16 inches translates to 13 minute degrees which
is very close to 0.1 degrees.

At the moment 31 has a total toe-in of roughly 40 minute degrees, or 0,4 degrees which is too much regardless of how the handbook is interpreted. So I will definitely set the car up
with less to-in, after which I will post my experience of this.

One comment I have had during this “investigation” was that a problem could come from the fact that I’m using Penrite’s Semi fluid Steering Box lube and not a high viscosity oil…

I also feel I have to point out that I’m not an engineer, so any statement I make can obviously be wrong, I hope that that any possible ignorance on my part isn’t regarded as rudeness
since that’s the opposite of what I intended. I totally agree and hope that members and owners of AC cars will continue to talk to and try to help each other out as much as possible.
I am very grateful for all the comments and help I have received in this matter, as well as on other questions I have posted on the forum over the years.

Thanks also to Ron, the tyre pressure you stated is exactly what I have so that shouldn’t be the culprit!

Jonas

[B.P.Bird]

Michael and Jonas,
My apologies for a long pause in contributing to this essential topic. My poor defence being the hours I am wasting on setting up a new lap top, demonstrating my ignorance of all things digital.
To begin with, when reading Michael Trotter's posts, I realise what a chasm exists between a proper engineer, like Michael and an amateur fitter, like me. Thus I have no doubt that my opinion on the clearance of cam to peg is quite wrong and the cam is machined with more clearance on lock as compared to straight ahead. Which being the case I am now puzzled by the too often observed, incorrectly adjusted Bishop Cam steering box, binding as lock is applied. In my experience there is a tendency, during adjustment, to reduce straight ahead free play too much and this seems always to result in the peg binding in the cam as the rocker arm travels from the straight ahead position. This prevents the self centering action of the caster angle operating and makes your Ace or Aceca an absolute pig to drive....
To address the specific problem described by Jonas, one of the symptoms of excessive toe in is poor straight line stability. If, as Michael suggests, this is the situation with AEX 31 then it will be interesting to hear the results of a revision to the toe in adjustment.
Turning to the general question of toe in I used a tracking pad for many years, such as Michael describes, but eventually concluded that the drag due to tyre rolling resistance probably varied as the square of speed and any slip angle detected at walking pace might be misleading at sixty or seventy miles an hour. The other doubt in my mind was repeatability, or rather the lack of it: Slip angles measured on each run seemed to have quite a large scatter. I now use the 'Trackace' system mentioned by Jonas. The other thing about the effects of drag on front wheel alignment concerns the early versus the later Ace chassis: The early cars, including '31, have hard mounts for the inner wishbone whilst the later car uses rubber bushes which one might suppose give  greater compliance. As far as I am aware the toe in setting remained the same for both when you might expect the early 'solid' wishbone to require less toe in angle ?
Jonas mentions choice of steering box oil and I don't believe that this will have any effect on straight line stability. In the interests of longevity I use a synthetic gear oil - Mobil SHC 75W - 90, but I'm sure his Penrite is satisfactory.
Steering box brace: It was not me that was involved in a batch, but I have made a couple for myself. I remember David Sanderson telling me that the LHD Ace steering box mount is far less rigid than the RHD mount and I think the steering brace requirement could have come from SCCA racing. Whatever the instigation you can't have too much of a good thing so braces all round - RHD and LHD. However I doubt that the brace would affect straight line stability as any flexing would be more likely during brisk cornering.
Finally (sigh of relief) I am wondering about some of the calculations shewn in this thread. Mixing fractions of a degree with decimal points is not a good idea. It does seem to be the modern way, but 2.5° is not 2° 50' it is 2° 30' . On this basis '31 with 40' of toe in (0.66°) then it is over 3/16 of an inch
Barrie

[AEX 31]

Barrie,

Thanks for your comments. First I have to admit to being guilty of mixing up fractions of a degree with decimal points. I’m aware of the difference, and I did try not to make this mistake, but I did. Sorry.

Since I’m travelling at the moment I haven’t had a chance to set the toe-in to lesser degrees.

However I’m still wondering what the verdict is concerning the statement in the handbook, is 1/16 intended as the overall toe-in or is it per wheel?

I’ve also enclosed the Track-ace conversion table which is what I have used as a base to decipher what the setting 31 has.

Thanks Jonas

[B.P.Bird]

Jonas,
Who knows what was in the author's mind when the original 1/16" was specified ? In any event I think Michael has a very persuasive argument that A.C. meant total total toe in. In addition that dimension is not a critical, engineering law of physics: It is really an arbitrary guess - if manufacturing teams thought that their suspensions would drag back to the tune of 1/16" toe out then best start off with 1/16" toe in. I doubt there was much calibrated testing carried out in the early days, but by experiment and experience manufacturers came to recommend a static toe in figure. There is no reason why you and your highly accurate Trackace cannot do the same thing, coupled with your assessment as a driver and an observation of tyre wear patterns. So I would start off at 1/16" total toe in and then see how she drives and how the tyres wear.
The nice thing about having the Trackace is knowing exactly where you are with these adjustments - once you have got a satisfactory setting of toe in you can return to it with great accuracy.
Do let us know what you discover, I will need to set the toe in on '22 shortly
Barrie

[shep]

I'm with you on that Barry, try 1/16" total toe in at the front and see how that feels. I normally run parallel at the back on an Ace and a gnat's of toe out on the Cobra.

[Michael Trotter]

Jonas

You say you are still 'wondering what the verdict is ' re AC's 'Toe-in 1/16 inch' - did they mean total or per wheel? I set out above  what I described as the classic definition of toe-in. The same definition appears in my Automobile Engineers Reference Book (1959, edited by George Lanchester) and in 'Racing and Sports Car Chassis Design' (1965, by Costin and Phipps). I regard both as authoritive and both are 'in period'. I cannot believe AC did not follow the convention of the day- ie 1/16 was total.

I worked through your Trackace chart 'Converting mm to degrees' starting with 1/16 inch and 16 inch wheels and got the result 13 minutes at each wheel. Given their roundings this is twice my calculated 0.1 degrees (6 minutes) so I deduce they are using mm toe-in per wheel. Do they make any reference to total / each wheel toe-in? It may be that with mirrors and laser beams the definition has changed but current usage is not relavent to your question.

I hope you will set 0.1 degrees toe-in at each wheel. Note Barrie's correction : 1 degree = 60 minutes and not 100 which you appear to use. So my 0.1 degrees = 6 minutes.

I look forward to your next report - we all hope you will eliminate the dreaded 'tracking'.

Michael

[Flyinghorse]

Toe in ( or out) is across the axle so for me all references are total.
I am sure the track ace measures total toe in/ out as it’s measuring one wheel relative to the other.( I have used a track ace since they came out).
Regardless of your tracking setting , the play in the box will dictate whether you control the car via the steering wheel or the road surface does the steering for you due to road surface changes and the play available to it.
I would Jack the car up and check ( with someone holding the steering wheel) how much slop you have at dead centre
My vintage 1929 Citroen had such an issue ( worm and sector) and it felt like I was driving a boat down the road.
Graham

 

[59 Aceca]

All,

This is a topic which grabbed my attention because I've always wondered if what I am experiencing with the original steering set up in my 1959 AC Aceca is normal.  Note that my suspension has been rebuilt, including tie rod ends.  I also have a Revington TR modified top plate installed on the top of my steering box.  All of these things have helped tighten things up to some degree, but it seems there is still a lot of excessive play at the center position.  In essence, I estimate to have about 5-1/2 inches of travel before I meet some moderate resistance in the steering wheel.  The "highly technical" photos attached demonstrate what I am experiencing.  All this play makes going through the twisties somewhat challenging, particularly when changing directions quickly.  Frankly, it's hard to imagine Aces dominating the race circuits back in the day with this kind of vague steering.  I should also note that the steering box was out and I was told that there was nothing obviously worn but I am second guessing that.  I've heard steering can be significantly improved by rotating the pin 90 degrees, exposing a fresh/unworn surface for it to engage with the sector.  Would appreciate any thoughts on my what the photos are demonstrating, pin rotation as a solution, and/or anything else obvious to check.

Thanks,
Greg

[AEX 31]

Dear all,

A sincere thank you all for joining in and helping out with the toe-in examination. It’s very pleasing that so many of you are sharing your technical knowledge of these lovely cars.

Michael, I do suspect that AC did follow the convention of the day so that 1/16 was the total toe-in. However I still find it interesting that it says “on rim”, that might very well be a linguistic detail that should be overlooked. As previously mentioned, other British sports cars of the period came with recommendations of a lot more toe-in.

Barrie, you most definitely make an interesting observation that the early cars have harder mounts for the inner wishbone. I believe I have the original handbook for 31 (that was delivered in the summer 1954) and that definitely states 1/16, as it does in later handbooks.

I’m just back from the UK so I will try to find time this week to set the toe-in to a total of 13’, or 1/16 of an inch, and test it! Hopefully with astonishing results.

Contrary to Greg’s experience I have to say that 31 is fantastic around winding roads, it’s only at higher speeds, on straight roads that the wandering manifests itself. The total play on 31, if doing Greg’s test would be, I’m guessing a maximum of 2 inches, if that.

Best regards

Jonas

[59 Aceca]

Dear Jonas,

Many thanks for providing some perspective as it relates to AEX 31.  This is really good information to validate my suspicions that something is amiss with my steering setup.

If anyone else has any experience with pre and post pin replacement/rotation as it relates to steering play I would greatly appreciate it.

Thank you,
Greg