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Brakes, Master Cylinder Issues

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rohanlakhotia46 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rohanlakhotia46 Quote  Post ReplyReply Direct Link To This Post Topic: Brakes, Master Cylinder Issues
    Posted: Mar/01/2011 at 1:02pm
We are using Disc brakes for all the four tyres. However we have been facing issues on the master cylinder system to be used. I'm posting a picture of our current arrangement.



We have used two cylinders because in case if there is a brake failure, we still have atleast two of tyres to lock.

Due to the system, we are finding it difficult to apply equal pressure on both the cylinders through the brake pedal.
Could someone help us out by telling us where we are going wrong for the brake pedal design?

So far we have to decided to use two brake pedals and to have a common foot plate, so that both can be operated at once.

Also, am I going wrong by using two cylinders instead of one?

Can we switch to the single cylinder system?

Also, can any other team who has used a similar system suggest some changes that we should make for the brake system design?





Rohan Lakhotia

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Post Options Post Options   Thanks (0) Thanks(0)   Quote collinskl1 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/01/2011 at 1:22pm
NO you can not use a single cylinder system.  Read the rules!
 
You should do some research on brake pedal balance bars.  Also, if you are having trouble actuating the master cylinders you could move the pivot point on your pedal closer to the master cylinder.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ErikHardy Quote  Post ReplyReply Direct Link To This Post Posted: Mar/01/2011 at 1:26pm
I can't say we are shooting for equal pressure Front to Rear, I'm going to guess somewhere in the neighborhood of 70/30.  We use a balance bar on our pedal assembly, similar to one found at the of this page: http://www.summitracing.com/parts/WIL-340-1757/ 
 
A split brake pedal works, It might help with laptimes with the right driver too.
 
B11.2 In the rulebook states that you must have independent brake circuits. So don't switch to a single master cylinder.
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rohanlakhotia46 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/01/2011 at 1:26pm
@kyle and @erik thanks for the information. I was confused on the use for the second cylinder in case of dammed reservoirs.

Thanks alot for the information again.



Edited by rohanlakhotia46 - Mar/01/2011 at 1:27pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hop11 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/01/2011 at 1:27pm
The SAE rules require the use of 2 cylinders for exactly the failure scenario you described. The normal solution to the problem you are describing is a balance bar. You can google Brake Balance Bar and see some examples of how they are usually implemented, here is a quick description of how they work: http://www.bicknellracingproducts.com/index.php?option=com_content&view=article&id=9:brake-balance-bar-set-up&catid=5:brp-dirt-modifieds&Itemid=11

This can be done very well, with correctly designed bearings to ensure the proper amount of force is directed forward and backwards, or quickly and easily by increasing the clearance room around your bolt connecting the pedal to the cylinders. The second method isn't good practice but works in a pinch if you are pretty close to locking all 4 wheels but can't quite make it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jeiB Quote  Post ReplyReply Direct Link To This Post Posted: Mar/01/2011 at 1:31pm
Originally posted by rohanlakhotia46 rohanlakhotia46 wrote:


Due to the system, we are finding it difficult to apply equal pressure on both the cylinders through the brake pedal.


Is your goal to make your brake line pressures equal? How do you know they aren't equal right now? Like others have said, you usually want to bias your brake pressure to account for longitudinal weight transfer, so making the brake line pressures equal is not the way to go.

Your design looks cumbersome and not too elegant but it would seem that the master cylinders would be actuated by the same force/displacement. So maybe your front/rear calipers or front/rear setup is different which might account for the different line pressure you might be seeing.


Edited by jeiB - Mar/01/2011 at 1:32pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rohanlakhotia46 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/01/2011 at 2:02pm
Guys we know different pressure is needed to lock the front and back brakes. But it's tough to get balance brake bars in india. can it be fabricated. Or is there any other solution ?. Can someone post a picture.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jeiB Quote  Post ReplyReply Direct Link To This Post Posted: Mar/01/2011 at 2:09pm
Ok, so why did you design your pedals this way in the first place since you now have to redo it?

Anyways, a bias bar is basically a spherical bearing with a threaded insert. A threaded rod can be moved through that insert towards the right or the left providing more leverage to one master cylinder. The spherical bearing provides the misalignment.

EDIT: disassembly of a bias bar

http://www.walkers-garage.co.uk/shop/contents/media/l_Balance%20Bar.png


Edited by jeiB - Mar/01/2011 at 2:10pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rohanlakhotia46 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/01/2011 at 2:25pm
@jeib,  actually our original master cylinder with two parallel cylinders actuated by a single fork with rods of different lengths broke. So we were using the  system posted in my first post  and were unable to figure out how to provide different pressures for that system.
our original system:

we are unable to find a similar system in india , and it has two independent parallel cylinders with a common dammed reservoir.

I really appreciate your help and i hope you can help us a bit more on the balance bar issue.

Thanks A lot.

edit: Thanks for the link


Edited by rohanlakhotia46 - Mar/01/2011 at 2:31pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tp Quote  Post ReplyReply Direct Link To This Post Posted: Mar/01/2011 at 2:32pm
You can always try a proportioning valve
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jeiB Quote  Post ReplyReply Direct Link To This Post Posted: Mar/01/2011 at 2:42pm
Originally posted by tp tp wrote:

You can always try a proportioning valve


Yea....thats really a bandaid fix but as long as you know it, then I guess....

rohanlakhotia46, what questions do you still have?

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Post Options Post Options   Thanks (0) Thanks(0)   Quote rohanlakhotia46 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/01/2011 at 2:51pm
Originally posted by jeiB jeiB wrote:

Originally posted by tp tp wrote:

You can always try a proportioning valve


Yea....thats really a bandaid fix but as long as you know it, then I guess....

rohanlakhotia46, what questions do you still have?


we'll try fabricating a similar system (brake balance bar). If it works out i'll let you know. 

Thanks alot for the help!
Rohan Lakhotia

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Post Options Post Options   Thanks (0) Thanks(0)   Quote VivaLaShay Quote  Post ReplyReply Direct Link To This Post Posted: Mar/02/2011 at 1:35pm
Wouldn't a split pedal system defeat the purpose of 2 master cylinders? You could have one cylinder fail and then try to press that pedal in an emergency situation...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ErikHardy Quote  Post ReplyReply Direct Link To This Post Posted: Mar/02/2011 at 1:41pm
Push both of them

Edited by ErikHardy - Mar/02/2011 at 1:41pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Red_Beard Quote  Post ReplyReply Direct Link To This Post Posted: Mar/02/2011 at 2:22pm
Originally posted by ErikHardy ErikHardy wrote:

Push both of them


You know rounds wouldn't let that fly...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote collinskl1 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/02/2011 at 2:35pm

I seem to remember a picture of that in the rules with a big red X through it.  And I doubt it would pass tech anyway, let alone you'd be able to lock up the brakes with two separate pedals.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote ErikHardy Quote  Post ReplyReply Direct Link To This Post Posted: Mar/02/2011 at 2:44pm
Looked up the rules again, clearly says one single foot pedal only Whoops. I thought I remember seeing a car at michigan tech with a split pedal, could have been allowed back in the day??
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tech.tmr11 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/14/2011 at 12:36pm
hey rohan this is ritwik from manipal whom u asked for the fuel tank. .. .. m the brakes guy of the team. if u want i cn help u in this.. may be a better feasible solution ...i m nt able to get a clear idea of ur assembly from the picture... i guess u have used 2 tandem master cylinders or maruti ..?..

 u cn contact me at 09008417770

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Post Options Post Options   Thanks (0) Thanks(0)   Quote LukeS Quote  Post ReplyReply Direct Link To This Post Posted: Mar/14/2011 at 10:16pm
The old Baja vehicle in our shop uses a simple proportioning bar made by students.  It worked well.  I'll grab a picture of it next time I'm in the shop.

Something to check would be the way your using your master cylinder.  It looks like your master cylinders each have 2 outputs, one meant for the front and one meant for the rear.  It also looks like you have both lines connected which I'm assuming is one for each side.  They might be setup from the factory to proportion braking differently (70/30).

It sounded like this might have been mentioned earlier in the thread.  Either way I'll grab that picture of the proportioning bar on our old car.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tech.tmr11 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/15/2011 at 12:24pm
i guess u hv used 2 tandem master cylinders for the each of the rear and front...which might be the problem with this..generally the tandem cylinders have a biasing of 40-60 ..so u should consider changing to one master cylinder only... using T joints to separate the circuits and use 2 different reservoirs...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote LukeS Quote  Post ReplyReply Direct Link To This Post Posted: Mar/15/2011 at 11:46pm
Here's a gallery of the setup our school used back in the early 90's.
http://img691.imageshack.us/g/img20110315201913.jpg/




Edited by LukeS - Mar/15/2011 at 11:47pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MMBRETTS Quote  Post ReplyReply Direct Link To This Post Posted: May/24/2011 at 12:16pm
we ran two pedals at birmingham this year. lockup was tricky getting your foot balanced between the two right.  they were close enough to get a foot on both of them, but centered enough to be able to hit only one also.  inspectors didn't say a word about it besides "you can it them both at the same time right?"
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Post Options Post Options   Thanks (0) Thanks(0)   Quote collinskl1 Quote  Post ReplyReply Direct Link To This Post Posted: May/24/2011 at 2:08pm
Yeah, that is really surprising to me... That used to be absolutely not allowed.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CobraCommander Quote  Post ReplyReply Direct Link To This Post Posted: May/24/2011 at 3:44pm
Just read down the page a little further... You're good with two pedals

B11.4 Cutting Brakes
Hand or feet operated “cutting brakes” are permitted provided the section (B11.1) on “foot brakes” is also satisfied.
A primary brake must be able to lock all four wheels with a single foot.
If using two separate pedals to lock 2 wheels apiece; the pedals must be close enough to use one foot to lock all four wheels.
No brake, including cutting brakes, may operate without lighting the brake light.


Edited by CobraCommander - May/24/2011 at 3:44pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CobraCommander Quote  Post ReplyReply Direct Link To This Post Posted: May/25/2011 at 8:45am
I had to check... You guys gave me a panic attack...Confused
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ErikHardy Quote  Post ReplyReply Direct Link To This Post Posted: May/25/2011 at 9:08am
Guessing you are running a split pedal? 
 
Between B11.1 & B11.4 They almost seem to contradict each other

B11.1 Foot Brake

The vehicle must have hydraulic braking system that acts on all wheels and is operated by a single foot pedal.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote tp Quote  Post ReplyReply Direct Link To This Post Posted: May/25/2011 at 11:25am
Ambiguous Baja rules strike again!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CobraCommander Quote  Post ReplyReply Direct Link To This Post Posted: May/25/2011 at 11:57am
We are indeed running a split pedal... It is set up however that only the rear brakes can be applied independently. Our backup plan for tech is to just lock them together if things go south...

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Post Options Post Options   Thanks (0) Thanks(0)   Quote tp Quote  Post ReplyReply Direct Link To This Post Posted: May/25/2011 at 12:43pm
While using the "it exists in industry" logic rarely works in passing tech, our John Deere 770 has a split brake pedal. There is a little link that flips down to lock the pedals together. Only difference is on the tractor one pedal is for the left brake and the other is for the right. Someone should run that setup on a Baja car!!!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bettner12 Quote  Post ReplyReply Direct Link To This Post Posted: May/25/2011 at 11:25pm
Originally posted by tp tp wrote:

While using the "it exists in industry" logic rarely works in passing tech, our John Deere 770 has a split brake pedal. There is a little link that flips down to lock the pedals together. Only difference is on the tractor one pedal is for the left brake and the other is for the right. Someone should run that setup on a Baja car!!!

i'm sure many teams have been tempted to do that... maybe i'll try it out next year...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote collinskl1 Quote  Post ReplyReply Direct Link To This Post Posted: May/26/2011 at 8:55am
That is what true cutting brakes are, as referenced in the rules.  Independently controlling right and left brakes can greatly improve maneuverability (of course when coupled with a differential and not a spool)
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