Fitting servo to traveller

[PJR2601]

Hi all, got the brakes "sort of" working

Has anyone got the instructions for fitting a servo - would be helpful to have a read of these so that i can judge whether i am capable of doing the job

Thanks in advance

Peter

[svenedin]

Hi all, got the brakes "sort of" working

Has anyone got the instructions for fitting a servo - would be helpful to have a read of these so that i can judge whether i am capable of doing the job

Thanks in advance

Peter

Before you even consider whether you have the skills to fit a brake servo it is important to be clear about what a servo actually does.

A servo reduces the force you have to apply to the brake pedal in order to achieve maximum braking (which without ABS, is locking the wheels). A servo does not in any way improve the performance of maximum braking. In fact, a servo complicates the braking system with another component that can fail and can prove a source of irritation and annoyance with trapped air when trying to bleed the brakes.

Fitting a servo to a poorly performing braking system without diagnosing and rectifying the original fault will not improve matters at all.

A servo can be useful to reduce driver fatigue and for those with limited physical strength.

Stephen

[geoberni]

Before you even consider whether you have the skills to fit a brake servo it is important to be clear about what a servo actually does.

A servo reduces the force you have to apply to the brake pedal in order to achieve maximum braking (which without ABS, is locking the wheels). A servo does not in any way improve the performance of maximum braking. In fact, a servo complicates the braking system with another component that can fail and can prove a source of irritation and annoyance with trapped air when trying to bleed the brakes.

Fitting a servo to a poorly performing braking system without diagnosing and rectifying the original fault will not improve matters at all.

A servo can be useful to reduce driver fatigue and for those with limited physical strength.

Stephen

What he said up there.jpg (23 KiB) Viewed 5040 times

I totally agree.
In addition.....
So many people have their servo incorrectly fitted with the air valve on the top. I don't know if...
- it's because the installer didn't read the instructions
- the instructions didn't used to make it clear (they do now)
- the installer thought they knew better and it looked prettier their way....
The one on my car was upside down when I brought him and it was a PITA to reinstall it correctly.

[Bill_qaz]

Hi all, got the brakes "sort of" working

Has anyone got the instructions for fitting a servo - would be helpful to have a read of these so that i can judge whether i am capable of doing the job

Thanks in advance

Peter

You want them fully working and able to lock wheels before fitting servo. As Berni says it reduces the pedal effort not increases the braking force. Mine also came with a servo fitted but has disc front brakes, generally disc brakes need greater pedal effort, no self servo effect of drum brakes.

[svenedin]

This table is informative. It was originally posted some years ago by "Islipminor" and was written by the Design Manager of AP Lockheed.

Pink highlight: Minors with 7" brake drums all round
Blue highlight: later Minors with 8" front brakes and later master cylinder


The table below shows the front/rear brake balance and un-servoed pedal pressure to achieve 1g retardation for many of the likely BMC/BL brake component combinations fitted to a Minor

Stephen

Minor Brake Setup Summaries v3.jpg (166.39 KiB) Viewed 5004 times

[Bill_qaz]

So marina discs with same 13/16" master cylinder needs a lot more pedal pressure than 8" drums 118 lbs (with same diameter master cylinder).
Hence servo helps with front disc set ups.135 lbs requirement.

[svenedin]

So marina discs with same 13/16" master cylinder needs a lot more pedal pressure than 8" drums 118 lbs (with same diameter master cylinder).
Hence servo helps with front disc set ups.135 lbs requirement.

Yes but actually my drums all round but Wolseley 9" front brakes works out at 131 lbf and I can't say I even noticed an increase in the pedal pressure required from 118 lbf. Original Minor 7" all round 142 lbf.

It does show you have to push quite hard on a Minor brake pedal though!

Stephen

[ManyMinors]

And let us not forget that the "modern" disc brake equipped BMC 1100/1300 range, MG Midget and MGB plus the first Marinas managed perfectly well without servos

[Bill_qaz]

And let us not forget that the "modern" disc brake equipped BMC 1100/1300 range, MG Midget and MGB plus the first Marinas managed perfectly well without servos

Yes they did but with pendulum pedals, with a much higher leverage ratio from pedal pad to pushrod point.
I've owned both an 1100 and a Marina

[Bill_qaz]

So marina discs with same 13/16" master cylinder needs a lot more pedal pressure than 8" drums 118 lbs (with same diameter master cylinder).
Hence servo helps with front disc set ups.135 lbs requirement.

Yes but actually my drums all round but Wolseley 9" front brakes works out at 131 lbf and I can't say I even noticed an increase in the pedal pressure required from 118 lbf. Original Minor 7" all round 142 lbf.

It does show you have to push quite hard on a Minor brake pedal though!

Stephen

So Stephen am I reading the chart wrong?
Wolsey fronts, minor 7" rear 13/16" master 3/4 wheel cylinder is 104lbs pedal

[svenedin]

So marina discs with same 13/16" master cylinder needs a lot more pedal pressure than 8" drums 118 lbs (with same diameter master cylinder).
Hence servo helps with front disc set ups.135 lbs requirement.

Yes but actually my drums all round but Wolseley 9" front brakes works out at 131 lbf and I can't say I even noticed an increase in the pedal pressure required from 118 lbf. Original Minor 7" all round 142 lbf.

It does show you have to push quite hard on a Minor brake pedal though!

Stephen

So Stephen am I reading the chart wrong?
Wolsey fronts, minor 7" rear 13/16" master is 104lbs pedal

The 104 lbf figure is for Wolseley 9" fronts using Minor cylinders (this requires modification of the brake backplates). My Wolseley front brakes use Wolseley 0.8" cylinders so 131 lbf.

Stephen

[Bill_qaz]

Are I see cylinders changed as well
Funny you posted as I was editing including wrong cylinder diameter
Even with my servo discs when I get back in my mitsubishi the first few stops are headbutting the screen moments.

[svenedin]

Are I see cylinders changed as well
Funny you posted as I was editing including wrong cylinder diameter
Even with my servo discs when I get back in my mitsubishi the first few stops are headbutting the screen moments.

Yes I have to be very careful in my modern car. Not just the brakes but it's bigger and has more than 6 times the power. I quite often end up putting on the windscreen wipers rather than indicating.......people probably think typical Audi driver, doesn't bother to indicate!

Stephen

[Bill_qaz]

Are I see cylinders changed as well
Funny you posted as I was editing including wrong cylinder diameter
Even with my servo discs when I get back in my mitsubishi the first few stops are headbutting the screen moments.

Yes I have to be very careful in my modern car. Not just the brakes but it's bigger and has more than 6 times the power. I quite often end up putting on the windscreen wipers rather than indicating.......people probably think typical Audi driver, doesn't bother to indicate!

Stephen

Just looked up 35 to 50 lbs. pedal pressure for 1g deceleration on my modern. No wonder it takes a couple of applications to get used to the swap in feel