mk 6 special technical advice needed

Gary Andrews · Joined: 23 May 2016 Posts: 34

I've just joined forum .

getting close to finishing of my mk 6 special apparently shes not been

on road since around 1955

I've got a few issues I could do with some advice

shes 1948 early brake type

firstly mec servo missing do I need a servo or not ? and if so would

a hydraulic one on front wheels only be ok to fit. im rod braked still at

rear.

Also i note the wear adjusting mech is missing in rear shoes is that

a problem ?.

I've just fitted o/s king pin kit but unsure what torque king pin

top nut should be cannot seem to find this in w m. can anyone give

assistance please.

Gary

Christopher Carnley · Posted: Tue May 24, 2016 7:47 am Post subject:

Hi Gary,

The front brakes only operate via the servo motor, there is no direct connection to the foot pedal.

The braking mechanism has to be complete.

There were no torque figures for these cars, just make sure that the bottom of the king pin does not protrude below the bottom edge of the housing, tighten the odd sized fine threaded nut until it feels right, then lock tab.

The king pins were subject to 4 varieties of heat treatment during manufacture, but the threads are not hardened.

Gary Andrews · Joined: 23 May 2016 Posts: 34

Hi Chris

thanks for the quick reply

the brakes have been set up via rods to operate the front brakes

I was just wondering if a hydraulic servo might be worth fitting.

I take it the mech servo only worked on front brakes .

I am working on her today hopefully give her a test run later

Gary

John Robins · Posted: Tue May 24, 2016 8:18 am Post subject:

The Mk VI would do close to 100mph with 15cwt of pressed steel atop the chassis. Your special has the potential of high speed and needs to be able to stop accurately and quickly and I join Christopher in suggesting that the system needs to be complete.

The mechanical servo not only operates the front brakes by way of the hydraulics, but also augments the effort of the foot on the rear brakes. You may need less effort as your car is lighter than the saloon, but the drums would have been designed with the servo as part of the thinking and you may need to rethink all of it to change to a vacuum servo. There is a very clear diagram of the system in the workshop manual which would be worth a look.

Proof that the servo does a lot of work in the standard setup came home to me in the amazing difference in the brakes of my car after the servo was relined.

Gary Andrews · Joined: 23 May 2016 Posts: 34

thanks John

I dont have the original servo so cannot go the original complete root.

will set it up today and see how it feels without a servo otherwise might

go with hydraulic vacuum

I dont intend doing 100 in her. just pottering about 50 60 ish

having seen brian johnson go for a ride in 3 litre supercharged car with

only rear brakes Im hoping mine will be ok providing you drive it

sensibly .

Im guessing that wo cars did not have servos just bigger drums

James O'Neil · Posted: Tue May 24, 2016 10:28 am Post subject:

Hi Gary,

Another point to bear in mind is that when the car is statiorary the front brakes are wholly ineffective (and indeed they do not begin to work until the car is moving at around 3 mph). An MOT tester trying to test the brakes using the normal set-up (car at rest and front wheels on rollers) would record that the front brakes were unserviceable. The car needs to be road tested, a decelerometer (usually a Tapley meter) being used to test brake efficiency.

Regards,

James

John Robins · Posted: Tue May 24, 2016 2:19 pm Post subject:

IIRC didn't some Mk VI specials have back axles from Jags?

That would mean a full hydraulic system so maybe that's worth a look, especially as to whether the builders felt a vacuum servo to be necessary.

(Before anybody shouts at me Jags did have solid rear axles in the Mk 7, 8, or 9.)

James O'Neil · Posted: Tue May 24, 2016 3:54 pm Post subject:

John,

You are right, of course, the Jaguars you mention did have live rear axles, and good ones, too, with limited slip differentials. The Mark X was the first saloon with independent rear suspension, similar to the E-Type's, although (I think) without the inaccessible inboard disc brakes.

Given the current climate, I wonder how amenable the DVLA would be to approving a Jaguar axle on a Bentley special?

Best regards,

James

Gary Andrews · Joined: 23 May 2016 Posts: 34

jag back ends have been used but im happy with the Bentley axle .

Ive trued up the shoes have a brake pedal that now seems good .

just been for a spin and everything ok car breaks reasonable no more

binding of brakes

but i have a problem with the rear suspension. its to springy I've had the

springs redone as they were very bad with leaves missing

think the problems now with dampers . the soft hard ride

system has been disconnected Im wondering if its worth reconnecting it

Can any one tell me what difference in adjustment it makes.

Christopher Carnley · Posted: Tue May 24, 2016 5:10 pm Post subject:

The problem comes with the thinned out springs, in that the individual leaves lose the support of the missing others.

Gary Andrews · Joined: 23 May 2016 Posts: 34

Chris

your right and Ive had the springs refurbished to standard spec

my issue seems with dampers now

Stephen Blakey · Posted: Tue May 24, 2016 8:41 pm Post subject:

Hi Gary,

Welcome to the forum.

Some of the Mallalieus used a vacuum servo with the original rod rear brakes actuated by a single slave cylinder in the manner of the Austin A30 and various early post-war light commercials. Owners of Mallalieus thus equipped report that the brakes are jolly good. I'm planning on using a variation of this system on my own special, with dual master cylinders and a bias bar. I'm hoping to get away without servo assistance but will soon find out once I try it. The maiden voyage is a way off, sadly.

The word on the street is that the rear dampers are quite sensitive to the viscosity of the oil so you may be able to improve things by going to a heavier grade. It must be possible to convert the bellows gubbins to a screw adjustment of the damper rate though I have yet to find anyone who has done that. Lots of folks fit tele's and good luck to them but I prefer the look of the lever arms.

I'm hoping the specials SIG will happen too.

Where are you?

Mark Taxis · Posted: Tue May 24, 2016 10:12 pm Post subject:

The variable damper setting in my Mk6 is still operational, but in all honesty I never use it, it is always on "soft"
If the ride hight is too high, take a leaf out, the car will be a lot lighter now that the steel body has been removed.

I am also hopeful that the SIG takes off, unfortunately I cannot assist with running it due to work commitments, living in Aus and very basic computer skills.
_________________
Mark Taxis
Sunshine Coast
Queensland 4560

Gary Andrews · Joined: 23 May 2016 Posts: 34

thanks Stephen

a very informative reply

I too don't wish to go tele's unless its the only alternative.

my car sits very high which I like , have concluded the dampers are out

of their normal travel position

I will fabricate longer connecting rods to leaf springs to

compensate for this and see if that helps

i put sae 30 oil in to start

Mark comments much appreciated

pic of my fast lady attached

John Robins · Posted: Wed May 25, 2016 12:37 pm Post subject:

Thanks for the picture. Looks good, from your early post I had a vision of a sort of half completed buckboard job, but this is far from that. Keep an eye on the mirror when you're out and about!

Gary Andrews · Joined: 23 May 2016 Posts: 34

Thanks John

Its getting there I like to think it looks like a late 20s early 30s race

style car now after a lot of blood sweet and tears

I also made the aluminium dash and all of the gauges except for the

original speedo and ignition switch pod and laced the steering wheel with

cord for the right look

Gary Andrews · Joined: 23 May 2016 Posts: 34

Stephen Blakey · Posted: Fri Jun 03, 2016 9:37 am Post subject:

Lovely pictures. How did you make those flanges on the front of the instruments? I've got a machinist pal waiting for me to produce a design for a little press tool to make some but there might be an easier way of doing it?

Re the dampers, I was reading Harry Rose's piece, Review 79 January 1966, on the Bradley MKVI, often referred to as the first MKVI special (do please all correct me if this is the usual case of the facts not fitting the story as I'm about to quote it elsewhere) and thought this extract might be of interest;

"The ride control has been discarded and the shock absorbers modified by the simple expedient of washering the valves and refilling with heavier oil."

P.S. There's a lot of Aldi tools being used on my project too e.g. I'm using their right-angle drill drive to drill the chassis where there is no space even for the air drill. The 8mm bits going through not-mild-steel must be way beyond its design remit but it's still going.

It makes you realise what a fantastic achievement it was for those chaps building specials 50 years ago when only a fraction of these DIY tools existed.

James O'Neil · Posted: Fri Jun 03, 2016 10:16 am Post subject:

Hi Stephen,

It's not just the special builders that managed to achieve great things with limited resources. I remember helping my father, when I must have been in my early teens, to decoke the engine of his current car, which was not such a simple task as it sounds, as it did not have a removable cylinder head. The facilities he had were primitive - all done outside, car raised manually and supported on wooden blocks, a very basic array of tools. No Machine Mart or Aldi in those days! He would have been green with envy if he could have foreseen what I now have in my garage (and he was an engineer, unlike me).

(Of course, this may be just another false memory, like my recollection of how a B60 engine should be expected to be capable of propelling the vehicle it's installed in.)

Regards,

James

Gary Andrews · Joined: 23 May 2016 Posts: 34

Stephen

I made the gauges using second hand aircraft / military gauge bodies

which had the bezels / flanges

fitted the gauges i wanted into these

made new dial faces to match the mk 6 speedo

the original mk 6 speedo I added a bezel taken from an old military

gauge.

the temp gauge was a real pain my original capillary tube was broken.

i first tried to make an electric sensor one but because im still +

earth it just did not seem to work correctly. so I went back to capillary

and built the gauge into a military housing

on ride height. hopefully tomorrow going to make new

longer rear damper connecting levers to compensate the higher ride

height . im thinking of reconnecting the old soft /hard ride

system possibly in the near future if the levers dont sort my problem

I agree the right angle drill drive is a very useful tool

I like good old tools but do use drill bit sets and cordless drills from

aldi .

my specials mainly been on breeze blocks with wooden packers whilst

working on her .

Gary Andrews · Joined: 23 May 2016 Posts: 34

last weekend made longer rear damper connecting levers and its

made a big difference. but i think i need heavier oil in dampers all round

used sae 30 to start any ideas what thickest I can go to 50. 80 90

140 ?

my wheels are said to be WO 3 litre they are 19 inch and running

6.00 x 650 tires is 36 psi front 38 psi rear pressure about right ?.

looking at new tires either 650/700-19 ENSIGN B5:

or blockley 650 -19 anyone have opinions on tires to suit

Christopher Carnley · Posted: Fri Jun 10, 2016 5:05 pm Post subject:

Try EP 80/90 gear oil, only Castrol sell straight EP140 .

John Murch · Posted: Fri Jun 10, 2016 7:52 pm Post subject:

WO 3ltrs would have had 21inch wheels when new, but many cars post 1945 did have their wheels rebuilt to 19 or 20 inch as 21 inch tyres were very difficult to find. So your wheels may well have come from a 3ltr. Were the hubs straight forward to fit to take the splined centres?

John

Gary Andrews · Joined: 23 May 2016 Posts: 34

Hi John

the 62 mm wheels where not an easy fit

new spline hubs designed from scratch had to be made on front and

rear. was a lot of work .

I would have gone 72 mm if I had known but I bought the 62 mm wheels

after being reassured by someone who should know whats what that

they were the type i needed.

to me it looks far better than the original mk 6 wheels or modern

type wire wheels and where possible i like to use old parts to give the

right look and feel although Spinners where made from scratch but to

old style