Seriously Scary brakes - Please help.

[simonc]

Mornin’ all, yes it’s another moan (but I think it’s serious) from simonc.

It’s the bloody brakes again. OK, rather than go through one of my long-winded diatribes I’ll put in down in point form and ask your diagnosis as well as recommendations to sort it.

1: When the engine is idling, and I’ve stopped (say at traffic lights) the pedal seems to go down.

2: If I take my foot off the brakes (after slowing down for a corner) the pedal comes up with an almighty clunk.

3: When I’m at traffic lights I have to pump the pedal to bring pressure back up.

4: Normal braking when the engine is on seems fine but I did have moment coming back from an errand this afternoon, where I came to a junction and the pedal did seem very soft. Sure it stopped but it was a bit of a hairy moment.

5: Like I say, it seems to be worse when I’m crawling forward in traffic and the engine is idling. It’s like the pedal is going down but nothing is happening.

Gentlemen, I would be grateful for any info because I am mightily p*****d off and frankly baffled at the moment. Does this all stem from the new booster and cylinder I had fitted last week?

Thanks so much, Simon.

[Donald]

Does sound like it hasn't been bled properly and a cylinder issue.

When the engine is off if you pump the pedal it should firm up and hold that pressure?

In a previous car I had the same issue and not long after I lost all brakes half way home TBH I'd be hesitant to continue driving it until the issue is resolved, it's no fun approaching a roundabout at 60 with nothing but engine braking and hoping nothing is coming.

[4th Gen Doug]

Hmm..
First port of call would be re-bleeding if it were me TBH - was the M/C primed before fitting?
It's worth checking for leaks around the M/C as well though, especially where it meets the booster and it might be worth checking the vacuum pipe to the booster as well while your there, but my money is on air in the lines as @Donald says.

[vanzep]

Rebleed them and if that doesnt work then have a read of this link about master cylinder
http://www.tegger.com/hondafaq/mastercy ... index.html


you say the brake booster that was fitted recently is larger than what was originally there - so you have gone from 15/16" brake booster to 1" brake booster. was the master cylinder also replaced at that time or did they swap you old mc onto the new booster?

[simonc]

@Donald and @4th Gen Doug first. Thanks guys and just to let you know that I've popped out to the car and pumped the pedal. Donald, unhappily I have to report that it does NOT stay firm but continues to go down.
Doug, you ask about priming and I'm afraid I cannot answer that question. I reckon to have looked for leaks and have moved the car away from the parking space and there's nothing visible on the floor. I've poked around with my finger and can't feel anything in terms of leaking (but don't trust me, I'm probably poking in the wrong place).
Doug again, I'm not sure what to look for on the vacuum pipe. Am I looking for a crack or maybe a hissing sound? Sorry to be gormless but if I look at the pipe is there something obvious a dimwit like me should see or hear or even feel?
@vanzep, I think they changed both the master cylinder and the booster mate because the original cylinder's piston was not long enough (or was it too long? ) sorry mate I can't remember. Thank you for the link, I will have a look but don't know if I can do anything to fix it myself given my sheer stupidity vis-a-vis things mechanical.
The irony of all this is that I've got a booster and a master cylinder stored in my little cubbyhole at home so I'm thinking that I should get these fitted. I must admit that the booster and the cylinder they fitted did look at little manky, especially that bit where the booster meets the cylinder. It looked rather rusty and mucky to me.
Bugger.

[simonc]

Guys, just to let you know that the brake fluid they put in is:
HD racing brake fluid. (made in Japan). All it says on the tin in English is "Dry 335 C Wet 221 C". Everything else is written in Japanese. I've got most of a metal bottle at the house.
Is this stuff kosher and right for my car or is it too "high spec" if you get my meaning?

[4th Gen Doug]

I'll probably get shot down for this, but you should be using a DOT3 fluid - anything else is just not worth the risk.
If it's DOT5 or 5.1, it will rot your lines (according to Google!)
If the Booster is rusty around the join with the M/C, then there is the possibility that fluid is getting in there from the M/C - but unlikely if it's just been fitted.
My advice would be to get some DOT3, and flush the whole system through with it before bleeding it until there is no more air in the system. If the fluid in your system is unknown at the moment - get it out ASAP. but that's just me!

Long story short? My money is still on air in the lines..
Who changed the M/C & Booster anyway?

[simonc]

@4th Gen Doug - Cheers for that sunshine. I'll pop down to a local lad tomorrow who I can trust with something like bleeding brakes and as you say, I'll just buy the normal stuff rather than this fancy-schmancy stuff that the guys at N1 put in.
To answer your question Doug, they were the guys that I went to last week to get it tested on the dyno which then caused these knock-on effects with the brakes.
Thank you everyone - just hope it's air trapped in there then.

[vanzep]

Yep replace the brake fluid and bleed the brakes and take it fom there.
There is a sequence to bleed them in as shown in the manual and there is also a couple of simple tests you can do to check if the fault lies with the booster,master cylinder or vaccum check valve if bleeding doesnt sort it.
I will try and find the links. If you cant do the work yourself you can share the info with the garage your going to or at least read up on a bit so you know what theyre talking about

[Sailor]

Yep replace the brake fluid and bleed the brakes and take it fom there.
There is a sequence to bleed them in as shown in the manual and there is also a couple of simple tests you can do to check if the fault lies with the booster,master cylinder or vaccum check valve if bleeding doesnt sort it.

This.