MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGF Technical - Brake Servo Position

Hi all,
Ive just bought B+G's stiffened servo bracket, and was miffed to see that there is still an amount of movement in the servo when applying the middle pedal!

If Im right (not offen!), Then the servo is remotely sighted, and the brake pedal operates the rotation of the bar, which inturn, pushes the piston rod into the servo, all this requires the bulkhead to take the strain, which it obviously cant!

Why isnt the servo infront of the driver? directly linked to the brake pedal and bolted to the pedal box, limiting movement and flexability from a large flat panel!???

Or,can/ could a hydrolic slave to piston arrangement be concocted to to replace the mechanical linkage altogether?

again, everyones thoughts would be appreciated.
(and a spelling lesson!)
Many Thanks
John
John Reed

I'm not convinced that the amount of flexibility in the servo mount is as bad as it's painted. It's still stiff enough to allow maximum braking up to wheel locking, and the effect of the flexibility is to allow an amount of pedal travel proportional to the load being applied. There will also be part of the travel caused by elastic distortion of all the other braking components - long pipes, and hoses for instance. All this adds up to a system that the driver becomes accustomed to by feel, and will use the sensory feedback of load and position to modulate the braking. If there was no give in the system, there would be only the applied force to give the feedback, and no more actual braking performance. I seem to recall that the original Citroen DS19 with its power braking system had a brake 'button' instead of a conventional pedal, and people found it difficult to drive with - it had no travel, just force, and they eventually replaced it with a pedal.
Anyway, there are other things I would prefer to spend my money on!
Mike Cunningham

I'm not sure that the culmination of several components shortfalls is the right way to obtain pedel feel?
But i will find out!
And i think the DS was over servo'd to reduce the effort needed to stop to a gentle squeeze, and unfamiliarity with the new system lead to the on off brake reports.
Fluid displacement isnt affected by pipe length, efficency may be affected by pipes swelling under pressure, reducing the end movement though.
The servo isnt on the pedel box to maintain its high safety rateing, apparently the servo pushed the pedels into the drivers feet and legs during crash tests so it was moved, and there it can stay!
I think a tandem master to tandem slave cylinder would be an ideal set up, and remove stress from across the bulk head.
as for the cost, the ability to stop is priceless, imho :-)
John
J E Reed

Rob's site discusses this topic extensively (he'll be along soon no doubt).

He also found that there was still movement in the servo after fitting the bracket. Now, after a few experiments, he has managed to relocate the servo just above the pedal box almost eradicating movement.

http://www.mgf.ultimatemg.com/group2/common_problems/brake_servo.htm#Update

The link indicates Rob's penultimate solution.

Tim
Tim

Yes, the triangulated bracket was certainly better, but not quite there. Relocating the servo in front of the driver has helped a little more - this time using a LHD B&G bracket. It uses the existing torque tube (it's designed to be the same for both LHD and RHD installations and therefore perfect to retain), and in doing so, simplifies the pedal to servo linkage (which is essential OEM, albeit on the same side as the pedal box!)
Rob Bell

Hi Rob
Not sure i know what you mean?
By torque tube do you mean that great big bar which runs from driver to passenger side of the car?
why retain that?
cant a link/rod be made from the pedel directly to the servos clevis pin ended piston rod?
a write up cant be far away?
John
John Reed

Hi John, yes, that's the one. It's needed so that there is an easy connection twixt the pedal and the servo input piston. The MGF Cup cars had a pin of some description that I wanted to use, but they're no longer available, and the OEM has apparently lost the blue prints for it, so can't be remanufactured. Irritating.
Rob Bell

Stop saying can't!!!!
It would just be daft for some plank to try and remake them,
so
Im asking around for one of a cup car to act as a patern.
If anyone knows where there is a cup car, please get in touch.
Will any be at silverstone on Aug 4th?
Any Mgs on Track fella's know of a regular attender to track day's?
John
John Reed

That's exactly what Roy Ford attempted to do for me - locate a Cup car to retrieve the part to use as a pattern... Ran out of time (I did eventually need the car back!), so ended up with this very neat 'half way house' solution. Of course, if you could delete the torque tube, you could loose some additional weight - very tempting for Project Shed!
Rob Bell

This thread was discussed between 07/07/2009 and 24/07/2009

MG MGF Technical index

This thread is from the archives. Join the live MG MGF Technical BBS now