nitram38
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| posted on 30/6/06 at 01:02 PM |
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Service brake?
On my sva fail the form says service brake.
What is the service brake, is it the main brakes or the handbrake?
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DaveFJ
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| posted on 30/6/06 at 01:05 PM |
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I beleive it means the hand brake
Dave
"In Support of Help the Heroes" - Always
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Ketchup
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| posted on 30/6/06 at 01:09 PM |
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yup, 2nd that
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nitram38
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| posted on 30/6/06 at 01:10 PM |
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I am a bit confused because I am sure on the sva he mentioned my rear brakes were only 50% efficient, yet the brake/design weight sheet he gave me,
showed my brakes had passed.
I did not get the full failure sheet until today.
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David Jenkins
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| posted on 30/6/06 at 01:14 PM |
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No - service brake is the main one under your pedal. Parking brake is the handbrake.
Check out the list on the right of this MOT guide
HERE
David
[Edited on 30/6/06 by David Jenkins]
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nitram38
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| posted on 30/6/06 at 01:16 PM |
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Cheers
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Ketchup
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| posted on 30/6/06 at 01:19 PM |
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gonna show my local mot station that.. on the failure sheets they do.. rear service brake is the handbrake as far as they are concerned! obv not 
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stevec
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| posted on 30/6/06 at 01:56 PM |
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I did Motys for years and as said service is the footbrake.
Steve.
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02GF74
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| posted on 30/6/06 at 02:01 PM |
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service brake - main brake
parking brake - hand brake
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nitram38
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| posted on 30/6/06 at 02:03 PM |
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It is a bit of a bummer really as now I need to pull my rear brake system apart. I am hoping that it is not a problem with the master cylinder on my
brake bias setup.
It feels firm to me.
It could be just new pads and discs as the car has only done 2 miles.
Looks like my week off next week is going to be busy!
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britishtrident
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| posted on 30/6/06 at 02:53 PM |
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Reading bwteen between the lines of what you have told us I suspect your total foot brake efficiency is only 50% ie 0.5 g --- should really be
nearer 90% plus ie 0.9 g.
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nitram38
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| posted on 30/6/06 at 04:15 PM |
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For SVA the pass is 60% and for MOT 50%........go figure!
It is only my rears that failed
[Edited on 30/6/2006 by nitram38]
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britishtrident
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| posted on 30/6/06 at 07:38 PM |
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Even a 45 year old Ford Anglia with skinny 8" drum brakes will show a peak 80% to 90% efficiency on a brake test, it is not just a case of
lack of effectiveness of the rear rear brakes.
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Danozeman
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| posted on 30/6/06 at 07:58 PM |
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Have u given your rear brakes a good bedding in session??
Dan
Built the purple peril!! Let the modifications begin!!
http://www.eastangliankitcars.co.uk
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britishtrident
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| posted on 30/6/06 at 08:03 PM |
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Looking at your archive it is fairly obvious what is wrong the front calipers have about 4 times the effective hydraulic area of the rears. With your
cars weight distribution the rear should supply about 40% of the braking effort in the dry but you have a braking setup more suited to a very nose
heavy fwd car.
You can fiddle it by changing to a smaller master cylinder on the rear circuit (say 0.625" and a larger on the front (say 0.75" but
this will work for SVA but isn't the full answer as the brakes will warm up up at different rates with obvious consequences in brake response..
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nitram38
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| posted on 30/6/06 at 10:06 PM |
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I don't think this is a maths problem!
I highly suspect that the rears are not bedded in and I have a bias adjustment to do. I wound the bias over to the rears slightly and drove the car.
I could definitely tell that the fronts were not working as well and that the rears were not doing a good job of stopping the car.
I will start tomorrow by removing the pads and seeing if the pistons move out. I have also noticed that my handbrake balance yoke is pulling more on
one side than the other, so the self adjuster in the caliper could be faulty.
As for all the theory about Rear engined cars and discs, I have raced single seaters and they have discs all round. The fronts always being larger
than the rears. The brake bias on these consist of 1 turn from wet to dry settings and I suspect that my bias is also going to be the same, on a knife
edge.
Once I have proved that the rear system is working mechanically, I am going to attach my cable adjuster and take it to my local MOT station.
I will dial the brakes in there and then lock them off and remove the cable again for sva.
The problem with bedding the brakes in is where to do it. The car is insured only for sva tests and MOT station visits. Unless I book an MOT 100
miles away....theres an idea!
Cheers Guys
[Edited on 30/6/2006 by nitram38]
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Liam
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| posted on 30/6/06 at 11:19 PM |
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Was gonna post about this on your other brakes thread but BT has beaten me to it here! I'm also of the opinion that your problem is due to a
very unbalanced brake system rather than just a lack of bedding in.
Assuming your donor bits are from a front engine production car they are designed to give a huge front brake bias. With equal sized mcs you'll
have that same bias on your car which I imagine is rear heavy. This is your problem - i've never heard of new discs/pads giving only 50%
braking just cos they aint bedded in. I've sailed through MOTs with brand new brake bits.
You might have enough adjustment on your balance bar but it isn't an ideal solution. Also by biasing your effort away from the fronts to the
rears you'll increase your overall pedal force required. You really need a smaller rear mc if you have to keep these calipers.
You need to do the calcs for your car and sort the problem properly. I used an excellent spreadsheet which I think originally came from the locost
yahoo group (see attachment). My requirement incidentally ends up being a 0.7" on the front and a 0.625" on the back with sierra XR4x4
brakes. You should have a good idea of your axle weights from the SVA so should get some accurate figures from the spreadsheet.
Liam
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Liam
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| posted on 30/6/06 at 11:29 PM |
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Er here's the spreadsheet...
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nitram38
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| posted on 30/6/06 at 11:33 PM |
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Thanks for the spreadsheet. I am at work at the moment, so I'll check it out in the morning.
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nitram38
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| posted on 1/7/06 at 03:51 AM |
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Just thought you would like to see the aerial atom brakes.
The car has an engine at the rear about the same weight as mine (both k-series).
I would say mine had more weight at the front because of my bodywork etc.
Fronts:
I have single discs at the front.
They also have brake bias setup:
Rears:
[Edited on 1/7/2006 by nitram38]
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nitram38
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| posted on 1/7/06 at 12:25 PM |
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Update:
Took calipers off and checked that piston ejected properly. Found a problem with handbrake adjuster in that it was not returning. Freed it off and re
adjusted handbrake. Pedal felt different and better than before.
Connected bias cable and drove it around on different settings.
I can difinitely feel a point where the brakes work front and rear and the car brakes horizontally (it does not dive at the front.
I am going to take it to the MOT station on Monday and adjust it there.
If it cannot be adjusted properly, then I will go down the master cylinder change route.
I have read that the rear cylinders should have a bigger master than the fronts and not a smaller one as suggested
CLICK HERE FOR INFO. Please correct me if I am wrong.
Both cylinders are 0.75.
Do I reduce the fronts or increase the rears?
[Edited on 1/7/2006 by nitram38]
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Liam
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| posted on 1/7/06 at 01:00 PM |
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Just had a quick read through that. Can't see where it says the rear cylinder should be bigger. Even if it did say that the author
hasn't done calculations based on your specific car with your brake parts has he! No rules of thumb can be applied - you need to do the calcs
and your requirements will be in front of you.
Just from the behavior of your brakes though you can see what way you need to go. You have very low rear brake effort (compared to your fronts) so
you either need to increase the rear caliper piston area, or since you probably dont want to change the calipers, increase the rear line pressure by
using a smaller rear mc. A bigger rear mc will make your problem worse. Of course you could also correct the balance by increasing the front mc size
hence reducing the front braking strength, but you'll end up needing legs of steel to stop the car.
Liam
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