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MG MG Y Type - Brake Upgrade YA/YT

As we all know, the Single Leading Shoe (SLS) brakes on our cars compare poorly with the Twin Leading Shoe (TLS) brakes on the YB.

In an effort to understand what we already have AND what relatively simple (bolt in/out) changes could improve the system, I drew up a calculation sheet (see attached).

The top half of the sheet shows the existing system, and the bottom shows a proposed modification. I can enter any number of combinations and compare back to the original for the baseline.

I am also investigating brake shoe lining materials. Our cars have soft woven linings originally (to suit steel drums), but these are now almost impossible to source due to the asbestos within.

I invite discussion from other owners who have already made changes to brake cylinder sizing, and your results.

I am particularly interested to discuss altering the Front/Rear bias, as the 80/20 bias appears to be part of the problem - should it be closer to 60/40?

Thanks in anticipation....

Tony Slattery
The Classic Workshop
Black Mountain
Australia


A L SLATTERY

To determine the front/rear bias, it is only necessary to calculate the ratios of the cross section areas of the front and rear cylinders.
The front 1.125" cylinder has an area of (almost exactly) 1 sq.inch.
The rear 1" cylinder (and the master cylinder) has an area of 0.7857 sq.inches.
Thus the split of any braking force will be 56% to the front and 44% to the rear.

To determine the actual forces, the force of 50kg applied to the brake pedal will be increased by a factor of 243/52.4 = 4.6374 due to mechanical advantage.
So the force on master cylinder will be 50 x 2.2 x 4.6374 = 510 lbs.
The pressure generated will be 510/0.7857 = 649 psi.
As the front brake cylinder has an area of 1 sq.in, it will exert a force of 649 lbs.
As the rear brake cylinder has an area of 0.7857 sq.ins, it will exert a force of 649x0.7857 = 510 lbs.
(The above will be the same as applied to the master cylinder as they have the same diameters)
R WILSON

Thanks for your comment - I will revise my calculations on bias and adjust the calculation sheet.

What are your thoughts on the proposed upgrade ?.

Tony
A L SLATTERY

Hi Tony Would it be easier to fit a VH 44 brake booster/servo It would give you the increase in brake pressure but does not fix the front brake design that was dumped on the YB.
Bob Wood

Fellow Typers
Can you enlighten me on this topic of brakes , regarding the drums .
Whether it be hearsay or truth , I am led to believe a superior drum for improved braking would be made of cast iron and modern today lining.
There are some cars that can have drums adapted if one is prepared to fill and drill to correct PCD.
Can this be an way(easier maybe) to improve braking performance .
Clive
Kimbers Kastle Klub
CR Dickinson

M/C = 15/16" dia. Area = 0.69 sq.ins. Pressure generated = 510/0.69 = 739 psi.
F/C = 1,1/4" dia. Area = 1.228 sq.ins. Force = 907 lbs (increase of 40%).
R/C = 1,1/8". Area = 1 sq.in. Force = 739 lbs (increase of 45%).
Ratio F/R = 55/45.
However, increasing the size of the slave cylinders and reducing the size of the M/C means that the stroke of the M/C, and the pedal, will increase.
If it is assumed that each slave piston must move 0.25mm (0.01") before its brake shoe touches the brake drum, then with the original system the pedal stroke will be 0.4".
With the altered system, the pedal stroke becomes 0.6". However, the 0.25mm (0.01") piston movement is a bit of a guess - it is better to work on the basis that the pedal stroke will increase by 50%.

If the original M/C is retained and only the F & R cylinders are increased in size, then the following applies;-
M/C + 1" dia. Area = 0.7857 sq.ins. Pressure generated = 649 psi.
F/C = 1,1/4" dia. Area = 1.228 sq.ins. Force = 797 lbs (increase of 23%).
R/C = 1,1/8". Area = 1 sq.in. Force = 649 lbs (increase of 27%).
Ratio F/R = 55/45.
Pedal stroke = 0.5", or safer to say that pedal stroke will increase by 25%.

Why not convert to twin leading shoes at the front only - I am sure that this has been done to YA backplates.
R WILSON

RW - I think that's what Chris Pick in Yorkshire did (among other upgrades) when he fully restored his YA which I believe is now in New Zulland. I don't, but someone might have his contact details.
John.
J P Hall

I agree that an upgrade to TLS would be a significant upgrade, but YB and TD parts are not thick on the ground in Australia.

I have a large stock of YA/YT wheel cylinders, master cylinders, brake shoes/drums and backing plates, so would prefer to use those up first.

If this little exercise delivers an easy (bolt in/out) and cost effective upgrade, many YA/YT owners will benefit and enjoy safer motoring. Remember these were "parts bin" cars, and not always had the best of everything in their construction.

I have revised my calculation sheet to all imperial results - see attached - there is more development coming to this sheet too, so I can understand where the original system needs improvement.

Safety Fast

Tony Slattery
The Classic Workshop


A L SLATTERY

Good work Tony - I plan to keep Y3348 on the road for many years, so twin leading shoes at the front is attractive to me. I see it as an "improvement", not a "mod" - it's down to how we want our cherished car to act and feel.
John.
J P Hall

Not being the purist type, a question--has anyone tried Holden brakes
William Revit

Somehow I need to re-phrase the question it seems.....
A L SLATTERY

Hi Tony,
You asked "what are your thoughts on the upgrade?" and my answer to that is, if it can be done quite simply as a bolt-on job then I'm for it, and I'll do it.
Y can't a Y (or YA, if you prefer) have the same twin leading shoe braking system of the YB?
I have two YB front drums etc spare under a tarpaulin, and I 've looked them out to speculate on the matter and how it might transfer to the Y.
When I've done the loom etc.
A J R Felthouse

Don't know how you'll rephrase your question when you didn't really ask one Tony
The brakes are either std.original -
or
modified/non original

I thought you were inviting discussion-?
Cheers
willy
William Revit

Are you aware of the article regarding front brake twin leading shoe conversion undertaken by Steve Priston. It's available on the MG T Society Totally T Type 2 website, a superb bimonthly production web magazine.
A J R Felthouse

Thanks for your comments.

As I said, the TLS upgrade is probably the ultimate upgrade, but I am trying to first understand where the existing system is "short in performance". Is it the mechanical advantage in the hydraulics, or the friction of the shoes with the steel drums.

I am seeking a simple "first step" upgrade that is available to YA/YT owners everywhere.

Does anyone have a Tapley Meter to measure the g-force in braking a YA/YT or YB?

In "The Sports Car" by Colin Cambell, he uses a g-force of 1.0 to calculate the braking pounds required in the hydraulics for a Sports Car. As you can see in my latest calcs above, the standard YA/YT system can only deliver 0.43g - I think it should be up near 0.75/0.8 for a small sporting saloon of 1,054kg.

I will eventually move on to calculations on the TLS options, but for now would like to limit the discussion to SLS system/upgrades.

Cheers

Tony
A L SLATTERY

Tony
You can get a G force app for your phone from the app store
willy
William Revit

Thanks Willy
A L SLATTERY

Tony

The man, I bought my YT from in 1979, gave me an invoice that quoted all that had been done to the car before it was sold to me.
It might be of interest to you that the workshop used Suzuki brake shoes. Maybe this gives you new ideas about the mechanics of our brakes (even TLS)?!

Kind Regals
Anton



Anton Piller

AJR

In what issue of the TTT2 newsletter, the TLS article was published, please (by Steve Priston)?

Anton
Anton Piller

Aug 2019 issue 55, and Feb 2021 issue 64.
R WILSON

Thank you, R
Anton
Anton Piller

Steve Priston's two articles referenced above by R Wilson have been added to the Hints and Tips page on the International MG Y Type Register website by kind permission from Steve Priston and John James.

https://www.mg-cars.org.uk/imgytr/hints&tips.shtml#TLS

Paul
Paul Barrow

This thread was discussed between 07/11/2022 and 22/11/2022

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