Excessive Understeer

[dick campbell]

Hi Gordon,

By measurement and calculation the original caster angle was 3.5 deg. (As per the technical manual). The shims that I installed gave an angle of 2 deg. rotating the axle forward so the current caster angle is around 1.5 deg.

Regards,
Dick

[gordon higginbotham]

Hi Dick,

Many thanks for your reply. It is great to see such good technical information published along with an evaluation of its effect.

Regards,
Gordon.

[dick campbell]

Hello, Alistair,

Nice to hear from you.....you have been very quiet recently.

I have a theory about Talbot steering but I will wait until I can carry out more road testing then I may do a write up on it.

sorry to hear about your gearbox......had a lot of issues with mine but now, fingers crossed, it is ok and even silent on tickover.

take care snd stay safe,

Dick.

[gordon higginbotham]

Today I went shopping in the 14/45 so It was the first time I had tried the car with wedges fitted between springs and axle. This reduced the caster angle from 4.9 to 1.9 degrees. Steering transformed - much lighter and runs true on a flat road without steering input. Thanks to Dick Campbell for allertng me to Talbots tendency for their chassis to take a set that increases caster angle. Also as Dick suggested with Perrot shaft brakes reducing the caster angle would require the front brake rod lengths to need resetting and I found the amount was significant. Also thanks to David Adams in New Zealand for suggesting that 'tuning' the caster angle could be quite productive.

[dick campbell]

I finally went tested my reduced caster wedges yesterday.

These were Land Rover caster correction wedges which are used on leaf sprung Series Land Rovers when the ride height is increased by 2" to restore the prop shaft geometry.

The wedges have a 3° taper so left around 0.5° of caster.

This modification gave the same result as Gordon's post above. It really transformed the steering and handling with no apparent negatives. I now have lighter steering, only sleight understeer, not a bad idea, and wander on undulating roads is much reduced......so it appears to be win, win.

The question now though is why.

My front springs are flat when loaded, the starting handle lines up perfectly with the dynamotor dog, so no distorted chassis.

I am pleased with the outcome but would be happier if I could understand what the original fault was.


Here are some photos of the general idea, showing the wedge as bought and then modified to go around the spring clamps and provide fore and aft axle location.

Regards,

Dick

[gordon higginbotham]

Dick,
Excellent news on the results. I am surprised that starting with just +.5 degrees on spec caster angle should have given so much effect on your steering and handling. Do you think that the extra weight of your engine could be the critical factor here? Certainly a reduction of 3 degrees in caster on both our cars has had a significant beneficial result although the underlying cause for both of us is different.
Regards,
Gordon.

[dick campbell]

Hi Gordon,

I started with 3.5°. I have not measured it as now that the axle is tilted the slope of the spring will not be the actual caster angle, so the 0.5° is just an arithmetic deduction.....3.5° original minus 3° wedge angle.

Dick.

[gordon higginbotham]

Hi Dick,

And a very reasonable one too.

Gordon.

[gordon higginbotham]

There has been a recent posting on the STD forum, https://www.stdregisterforum.org.uk/...62/#post-14862 which reports on a Sunbeam with poor steering and what it took to put right. Makes interesting reading and confirms benefits of getting the caster angle optimised.

Hi everyone

As some of you would be aware, last month I became the current owner of Nigel Berlyn's superb 1928 20.9 Weymann Saloon (2400H). Also being the son of the late Kevin Piggott, I find I am now in possession of a wealth of Sunbeam data, including many STD newsletters stretching back across the decades.

The reason for this post, is that I recently came across the March 2007 (#175) issue of the Australian newsletter, in which there appears an article by Nigel, explaining how he fixed -after several tries - the initially unsatisfactory steering characteristics of his then car. In the hope that what Nigel wrote & shared 13yrs ago, will help other 20.9 owners in particular, and perhaps all Sunbeam, Talbot & Darracq owners in general, I am re-presenting Nigel's article here.

"I bought my 1928 Sunbeam Weymann Saloon in 1967. By then she had obviously travelled several times around the clock which resets to zero after each 99,999 miles.

"I used her for a time as a second car, but only on fine days. We also took her on rallies and I particularly remember a return trip from Sydney to the peak of Mt. Kosciusko when we seemed to use almost as much oil as petrol! Another memory of that trip is of the sheer exhaustion and constant attention needed to keep her on track on the then very narrow and busy Hume Hwy (now a dual lane carriageway). I made a mental note to do something about the steering during restoration that dragged on between 1972-1991, due to work and other pressures.

"I started by renewing all spring shackles & pins as they were very badly worn. I checked all steering ball joints but these seemed perfect. I then fitted new kingpins & bushes and also replaced the assembly of thrust washers that transfer the weight from the axle beam to the wheels via the stub axles. I also checked the steering box but found neither wear nor obvious means of adjustment. So it was cleaned & received new felt seals to combat a long-standing oil leakage problem.

"I then rebuilt the complete front axle on the car without altering the geometry controlled by the track rod and drag link as these can only be adjusted by shims. I reasoned that they would have been correctly set-up during manufacture and was reluctant to make any changes at this stage. Shock absorbers were refurbished at this stage & fitted but I did not replace the steering damper added by a previous owner. I felt sure that a well-maintained Sunbeam would hardly need such a primitive device!

"Although the car was running again by 1991, it remained garaged in Canberra whilst I worked in Sydney. For this reason it covered less than 500 miles between '91 & early '99. On her rare outings I simply accepted her steering as typical of a vehicle of her age.

"My position changed when I drove the car to Sydney for our daughter's wedding in early 1999. The vintage Rolls-Royce owner who kindly drove the Sunbeam to & from the church was less than impressed with the steering, which he said was prone to wander, especially after hitting a bump in the road. At his suggestion I filled the steering box with a semi-liquid sold as Penrite Steering Box Lube. This certainly fixed the oil leak & stiffness but bump steering & tendency to wander remained.

"A run to Mudgee & back with the Illawarra Motoring Museum in Sept. 99, a distance of some 860km was the final straw. Loved the trip but it left me exhausted from fighting the car. However I did have the opportunity to drive Wendy & (the late) Ray Muddell's 1926 Sunbeam 25hp and also a vintage Alvis 12/50. Both cars steered impeccably and I finally accepted that drastic measures were required on my car.

"Ray Muddell helped me to check lots of measurements & angles. The only obvious discrepancy was excess front wheel toe-in measured at 17mm as compared to the generally accepted 3-6mm. This was corrected by removing 2 x 1mm shims between the steering arm & the brake back-plate to give toe-in of 5mm. The tendency to bump steer was reduced but wandering remained.

"So what was the problem? Why, despite all the care taken during restoration, did my Sunbeam steer so badly? I had realised long ago that the front springs had been reset about 30mm high (this had come to light after difficulties with the brakes in the form of bent Perrot shafts). Similarly the rear springs seem to have been raised by as much as 60-75mm but I have never seen data on their original settings. I think these adjustments were made by a previous owner to allow the fitting of 21" x 6.00 tyres as opposed to standard (?) 21" x 5.25. These are fine for city work but help to leave the car under-geared for modern highways.

"The critical point of all of the above is that raising the rear of the car has the effect of reducing the backwards inclination of the kingpins (Castor Angle) which is there to encourage the car to steer in a straight line. My rough measurements suggested that castor angle remaining was 0.3 degrees of an original 2 degrees!

"I had made some aluminium alloy 1.7 degree wedges to replaces the existing packing pieces between the front axle & springs. These made a marked improvement when fitted with the thin end facing forward. In fact I was reasonably content until my Alvis friend still felt the Sunbeam was fidgety & relatively demanding to steer. Reasoning that the 1.7 degree wedges had given a marked improvement I decided to try even more castor angle and hand made & fitted wedges of 2.4 degrees.

"At the time I was delighted and felt we had at last got it right. Bumps and rough surfaces could now be taken at speed with one hand on the wheel and no increase in driver concentration. But over time, I realised that we still had a problem. Freshly greased, the steering was a little heavy but otherwise excellent. But after only 100km or so it would stiffen and the old symptoms would start to reappear.

"I talked with anyone who would listen and particularly to vintage Sunbeam owners. It gradually dawned that most Sunbeams had ball thrust races between axle & stub axle while mine had 2 x hard steel washers with a fibre washer sandwiched in between. This is even shown in the 1928 20hp parts list. It seems that later cars reverted to proper ball thrust races and that is what I have fitted. This has been a huge success & subsequently allowed removal of the steering wedges with no adverse effect.

"My Sunbeam at last lives up to the reputation that these cars have always had. True, it had a temporary hiccup on the STD run to Wodonga. The symptom developing was an unpleasant notchy feel when steering slightly to the left. The cure was some light oil applied to the boss of the recently tightened steering wheel which, as a result, had moved down the shaft a fraction and was just rubbing on the top of the steering column. If only curing steering problems was always so simple! Finally I should say that the car is now fitted with 21" x 6.00 tyres and the ride is much improved. There is none of the previous owner's problem of scuffing against the wheel arches when cornering hard; a Panhard rod takes care of this. But that must be the subject of another article........."

Again, I do hope that this post will be helpful to many people.

FWIW, the few drives I've had of this car since purchased, it drives (and steers) as well as you could expect a 90yr old car to drive - of course being a Sunbeam, rather better than most of its contemporaries.

It must be said, it does require some minor corrections whilst on the road - but I put that down to my inexperience with cars of this era, and I'm assured by experienced friends, that it's better than most of that time.