Drum brakes and servos

Post by **grainger** » Sun Aug 10, 2003 4:43 pm

no ive heard of lots with drums and servos ... anyway if the shoes locked on its better than locking OFF !!

my traveller has drums and a servo (dont know where it came from) and it is excellent, ive been told it might stress the rubber pipes and cylinder seals but thats all. going down a BIG hill with four BIG adults is still a bit hairy but much much better than not having a servo

cheers
grainger

Post by **Peetee** » Sun Aug 10, 2003 7:33 pm

....."if drums , no do not fit a servo as this set up is positively dangerous as the shoes could lock on having opened further than allowed on the snail cam".

I've read this quote too and found it equally puzzling. This is surely more relevant to worn out brake shoes than the suitability/not of a servo?

Post by **Gareth** » Mon Aug 11, 2003 9:42 am

Well, discs don't need as much maintenance as drums, do they, and I think they don't have any adjustment. So there would be no problem with the servo pushing the shoes off the cam... maybe it's just something to be aware of, if you make the mod.

Post by **Peetee** » Mon Aug 11, 2003 11:58 am

But you'd still have the rear drums.

Post by **Gareth** » Mon Aug 11, 2003 12:44 pm

hmmmm... maybe the extra fluid needed for front discs removes the liklihood of the drums locking on - especially since the front brakes come into play more often than the rears, I think.

How does it work on a Metro, then? There's front discs and rear drums on those... I might have a poke about when Dad comes home, and see if there's anything with the pipe routing &c

Is it a split-circuit, I wonder...?

Post by **grainger** » Mon Aug 11, 2003 1:15 pm

well my servo is apparently only on the front, which is usual. as the only function of the servo is to assist with the operation of the pedal, i dont see how you could do any damage with a servo that you cant do with a really BIG foot !!!

cheers
grainger

Post by **Kevin** » Mon Aug 11, 2003 1:26 pm

All you need to do is check the cylinder rubbers closely when servicing as there is a bit more pressure applied and the rubbers may not last quite as long as without the Servo, its not a major issue as long as you check properly when servicing.

Post by **Cam** » Mon Aug 11, 2003 6:51 pm

i dont see how you could do any damage with a servo that you cant do with a really BIG foot !!!

I totally agree, grainger. All the servo does is make the pedal easier to press. It does not increase the braking force. A non-servo'd car will stop just as well as a servo'd car.

As for the comment about the cam......I think that is best ignored!! It sounds like another 'practical' classics pearl of wisdom!! So, it can open up further than the internal diameter of the drums?????? maybe not, eh?

Post by **Chris Morley** » Mon Aug 11, 2003 10:28 pm

As Cam said, how does a servo magically expand the size of the drums? I doubt we are talking about more than 1 or 2mm clearance between the shoes and the drums. Also I can't see how the snail cams could be displaced as they are held in place by the flanges on the top of the cylinder.

Dr.B.B, where did you find this statement?

My only worry about servos is that you might forget that you still have brakes likely to fade. Anyway, what's wrong with having a well defined calf muscle (on one leg only)?

Post by **Kevin** » Tue Aug 12, 2003 12:50 am

Anyway, what's wrong with having a well defined calf muscle (on one leg only)?

I am relieved that I am not the only one shaped like that Chris

Post by **Chris** » Tue Aug 12, 2003 12:57 am

I can't comment on the morris side, but Land Rovers (and I'm sure many other vehicles) have been fitted with drums all round and servos for years, without any problems.

But how would a servo fit? isn't the master cylinder under the floor, or would that have to be moved?

Cheers,
Chris

Post by **Chris Morley** » Tue Aug 12, 2003 1:09 am

Chris

I think the servo is fitted in the Minor engine bay and the master cylinder is downgraded to being a simple brake fluid reservoir.

Post by **grainger** » Tue Aug 12, 2003 11:54 am

hi

my servo (which may have come from a land rover ?) sits on the drivers side of the engine bay on top of the chassis leg, with the fluid pipes leading TO the front brakes and FROM the master cylinder, and a large rubber pipe leading from the inlet manifold so it is tapping vacuum from the engine. you have to get the idea that cam explained to me that the servo is only ASSISTING the pedal and master cylinder. it doesnt force fluid through the pipes on its own, the master cylinder is not changed at all nor is it under any less pressure than before. i can pull the rubber pipe off, or turn off the engine and the brakes still WORK exactly like they did before the servo was fitted.

cheers
grainger