Rear Drum Brake Issues and Brake Servo

Sun Mar 30, 2014 7:02 pm

Took my car in to get an MOT and my nearside rear brake has little to no effect under regular braking or when the hand brake is pulled...

I'm also having issues with my Brake servo where it makes a "hiss" noise when i press the brake down, just a quick hiss, not a continuous one...

If i need to replace the servo i'd rather go with a servo-less setup and delete that headache all together... has anyone ever gone that route? yes i understand the amount of brake pressure you must apply manually is a bit more, i've driven cars without the servo...

also if this nearside rear brake issue costs more than it would to put rear disc brakes, I may go that route...

I've bled the brakes, checked all the lines and thoroughly checked all vacuum lines from the servo, unless there is a common issue i am unaware of...

Sun Mar 30, 2014 8:02 pm

Brake servo is supposed to hiss when you press the pedal. Perfectly normal.
If one rear brake is ineffective, then either fluid is leaking and lubricating the shoes, or the automatic adjuster isn't working.

Sun Mar 30, 2014 8:40 pm

Well the problem is, it was written up as one of the reasons my MOT was refused, 'Brake Servo leaking' was the write up... How am i supposed to explain that, it's supposed to hiss?

Ask how to adjust the automatic adjuster? I already replaced the drum brake cylinder and tightened the lines, then bled them... So i know brake fluid isn't getting on the shoes...

Sun Mar 30, 2014 9:32 pm

Unusual, but it's not unknown for a rubber brake hose to start de-laminating internally and block the pipe under pressure.
A brake servo is definitely supposed to hiss when the pedal is pressed, but it's possible that there is a leak somewhere as well. Without seeing the car I can't really say further.

Sun Mar 30, 2014 10:51 pm

As Brian said a prompt hiss from the servo is perfectly normal when the brake is depressed.

If it is failing due to a leak though (potentially un-associated with said hiss), highly recommend replacing it with a new or good used part. It's not overly complicated and driving without a servo (without making other modifications, i.e. swapping calipers for bigger ones with more cylinder surface area and/or increasing mechanical pedal ratio) will be more of a headache than you know! It's quite different from driving cars with unassisted brakes from the factory. A 'proper' servo delete setup will set you back a lot more money than £25 or so for a used servo and few hours fitting it

Plus if you ever come to sell the car, it raises a lot of questions.

Mon Mar 31, 2014 12:53 am

well there aren't any plans for selling, i currently have a Honda that doesn't use a Brake Servo (i removed it and installed a booster delete) and have no issues stopping even abruptly... The E30 will be used as a daily driver and for comfort purposes, it won't be seeing any circuits or tracks as my other car does...

i don't think it's failing for a leak in a hose though, as i checked all the hoses, disconnected and verified they weren't frayed or cut anywhere, didn't see the need to replace the clamps that held them in place either as they were fully capable of doing their job... it's just that quick hiss when you depress the pedal...

Also if the rubber brake hose was delaminating wouldn't it also prevent me from bleeding the brakes? or keep the fluid from releasing?

Mon Mar 31, 2014 9:15 am

Fair enough, if you're happy with the way it drives

One more thing I forgot to mention though is 'lack of a servo when fitted as standard' is an MOT failure now too. Although if you can get your Civic MOT'd, then I'm sure you can get around this!

Mon Mar 31, 2014 10:07 am

powerwheels86 wrote:
Also if the rubber brake hose was delaminating wouldn't it also prevent me from bleeding the brakes? or keep the fluid from releasing?

Not necessarily. The pressures involved with brake bleeding are only a fraction of those when the brakes are used in anger and don't stretch the rubber.
If your Honda is substantially modified for track use then it may be exempted from the MOT OE brake servo requirement under a 'grey' area of the regs. that can be applied to 'competition' cars, or of course, it may just have a dodgy MOT certificate, which is fine until circumstances occur when the authorities take an interest.
I certainly wouldn't like to stop an E30 without a servo, and I've driven cars more than half my life that didn't have servo assistance.

Mon Mar 31, 2014 10:49 am

Brianmoooore wrote: I certainly wouldn't like to stop an E30 without a servo, and I've driven cars more than half my life that didn't have servo assistance.

From my fag packet calcs I get about 90kg required on the pedal to execute a 0.9g stop - typical emergency stop I guess. It's not so severe as I thought, perfectly doable for a big bloke

Mon Mar 31, 2014 12:48 pm

Motorhole wrote:
Brianmoooore wrote: I certainly wouldn't like to stop an E30 without a servo, and I've driven cars more than half my life that didn't have servo assistance.
From my fag packet calcs I get about 90kg required on the pedal to execute a 0.9g stop - typical emergency stop I guess. It's not so severe as I thought, perfectly doable for a big bloke

An F1 car is about 80kg of pedal pressure for a standard braking situation (basically slow as fast as you can) IIRC. But then they're creating about 5g of braking force (although part of that is aero drag).

Mon Mar 31, 2014 8:36 pm

Well how do they know if older cars have servos? It's an older honda... I actually didn't know it would fail an mot without it...

I'm sure the e30 servo is fine, I'll double check the brake lines..