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MG Midget and Sprite Technical - Sticky servo

my remote servo has a habit of staying on after the brake pedal has been released, most noticeable at junctions. A hard jab of the brakes usually clears the problem, though any cars following me don't appriciate the near emergency stop.
Is this a servo problem or something to do with the twin choke set up?
The brakes work fine when the servo vac tube is disconnected; new master cylinder & calipers have also been fitted.
Anyone got any ideas?
cheers
Brad
Brad (Sprite IV 1380)

My best advice would be remove the servo.... You really don't need one on a midget

Regards

James

J A Bilsland

Do you have a one way valve installed, Im fairly certian one is needed...I wish I could offer more...I understand the concept, but reality is another topic.

Prop
Prop

The fault is the same with or without the one way valve in the vac line.
Brad (Sprite IV 1380)

Brad

It rings a bell, been there found that but it's a few years ago now. My recollection is that it was to do with the air intaker valve on the servo. But then my kids rev me up about my memory frequently now. (I just plan to live long enough to get them back!)
Paul Walbran

How about your flexible brake lines? Internal collapse of those hoses can cause the brakes to lock on.

-:G:-
Gryf Ketcherside

The brakes are fine without the servo connected though, aeoquip all round as well.
I was reading one of my old Cooper manuals & they advise blowing out the servo air filter every 12000 miles, so i've done that as its easy.
Just waiting for a new speedo cable before the car takes the maniac out again.
Brad (Sprite IV 1380)

Brad,

Are you using Silicone brake fluid? If so then this could be your problem.

I had this happening on my MGB and changed back to 'normal' dot 4 - no further problems.

If you search MGB archives it appears to be a regular topic.
John Turner (Midget & MGB)

I did use silicone for a year, but changed back to Dot 4 several years ago. Since then probably 3-4 litres of fluid have been through the system.

I'm thinking maybe the dellorto has something to do with it as i only take a vac off of one inlet tract now which isn't balanced to cylinders 1&2. The problem is worse at junctions when the car has stopped, so maybe i have too little / much vacuum?
Brad (Sprite IV 1380)

Thanks John,
had a read on the MGB pages, looks like the servo piston is sticking & i need to take it out & lubricate with dot 4,

cheers
Brad
Brad (Sprite IV 1380)

Pulled out the servo piston, it was covered in brown gunk, gave it & the bore a good clean up,the piston moves a lot easier in the bore now, quite an easy job actually.
Brad (Sprite IV 1380)

Been out for a rather wet drive today & the servo is still sticking, also the handbrake seems to be disapearing & i get chronic brake fade, from a firm pedal to nearly on the floor on steep desecents. I'm on standard MGB pads at the moment though i think the problem may be knackered drums again.

Anyone got any ideas on the servo front? I'm using a DHLA & only taking the vac from inlet 3/4, is that going to give less vac than from the SU system which has the vac shared from both inlet tracts?
Brad (Sprite IV 1380)

Hi Brad , re the servo problem !!! Ihave an MGA that i recentley fitted a servo on & had this same problem that i managed to cure by taking the air release valve out, wiping clean , covering in silicone grease & replacing , sorted, as this was a new unit i also lightly honed the bore making the job easier for the valve, i also use silicone fluid, hope this helps .
Colin
p/s i bought the grease @ a plumbers merchant as i got blank looks in several garages
colin daly

Hi Colin,
i've some 3M grease so i'll try that & have a look at the drums again,

cheers
Brad
Brad (Sprite IV 1380)

Brad, You sure your taking your foot off the brake pedal, in your old age you might be getting forgetfull!!!

On the serious side, I had the same sort of issue, serious brake fade including having to pump the brake pedal to get any sort of feeling in it to stop the car and that was due to the rear drums needing attention and now all is fine again.

Shaun
Shaun

Shaun,
i'll check the drums later today.
On another note, new RTL EN24 bolts ready on wednesday.
Brad (Sprite IV 1380)

Well the drums are still round, but both cylinders are weeping, also both the cylinders are wobbling around a lot, so much that the rubber has worn off & contaminated the shoes.
So new shoes & cylinders required & a mod to keep the cylinders in place.
Brad (Sprite IV 1380)

The best mod to keep the cylinders in place is to remove the roll-pin and tap an M5 thread into the hole.
You will need to open up the hole in the backplate and use an M5 button-head to secure the cylinder.
Dave O'Neill 2

Thanks Dave
Brad (Sprite IV 1380)

This thread was discussed between 21/07/2009 and 03/08/2009

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.