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rear disc brake issue
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1newvwguy
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PostPosted: Sat Jul 14, 2018 9:54 pm    Post subject: rear disc brake issue Reply with quote

i recently installed a rear disc brake conversion on my sandrail with irs suspension .i purchased the correct empi kit with mechanical e brake .the kit went on just fine i have anew cnc master all new hard lines and hoses .ok heres the issue i have bled and bled im sure no air in the system but yet it still doesnt stop worth a darn it stopped twice as good with the drums still on it .....ive also tried 2 different masters can any one pleaseeeeee help me solve this issue its to the point im ready to just sell the dang thing and the brakes are the only thing left before i can put plates on it and start driving and enjoying ......thanks
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jspbtown
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PostPosted: Sun Jul 15, 2018 6:32 am    Post subject: Re: rear disc brake issue Reply with quote

"stop worth a darn" meaning what exactly?

Good pedal firmness but just stopping power? Poor pedal firmness? Spongy pedal? Lots of travel?

You might want to list the parts (with numbers) you used.
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1newvwguy
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PostPosted: Sun Jul 15, 2018 6:43 am    Post subject: Re: rear disc brake issue Reply with quote

do not have the part number as far as the pedal it seems to travel pretty far and just doesnt seem to ever hit the point where it feels hard enough to stop the rail the rotors had just a little bit of rust on them from sitting and i can see where the pads have cleaned it off but at 10 mph it takes 4times the distance it should to come to a complete stop
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slalombuggy
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PostPosted: Sun Jul 15, 2018 6:57 am    Post subject: Re: rear disc brake issue Reply with quote

IF the pedal is feels soft you still have air in the system. Do you have any humps in the brake line that can trap air? This is a common problem in custom built cars. Try lifting the rear of the car as high as you can. Also, sometimes it helps to take the calipers off and bleed them lifting them as high up as you can with the bleeder screw as high as you can get it. MAke sure to stick something in between the pads if you do this, even a piece of 3/8" plywood will do.

What bore is your brake master cylinder? 5/8 or 3/4? IF it's 5/8 you may need to go to a 3/4" master. I've stopped my buggy and my race beetle down from 120mph with only Empi rear brakes, no problem

brad
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1newvwguy
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PostPosted: Sun Jul 15, 2018 7:05 am    Post subject: Re: rear disc brake issue Reply with quote

had the front end lifted high enough it was foot and a half higher or better than the calipers and i also tried bleeding with calipers off as well i have 5/8 bore as far as the lines all new with only the junctions that have to be there and as straight and level as can be i worked as a mechanic in a suspension/brake shop for years so i understand all that but thats why this just has me baffled
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1newvwguy
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PostPosted: Sun Jul 15, 2018 7:08 am    Post subject: Re: rear disc brake issue Reply with quote

its not spongy and doesnt drop when u hold pressure on the pedal like it has air in the lines or a leak
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slalombuggy
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PostPosted: Sun Jul 15, 2018 8:58 am    Post subject: Re: rear disc brake issue Reply with quote

You need the calipers higher than the master cylinder not the other way around.

Your master is too small to move enough fluid for the calipers. I would go to a 7/8" master . The 5/8 master in my race car is barely big enough for my Kennedy clutch

brad
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1newvwguy
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PostPosted: Sun Jul 15, 2018 11:41 am    Post subject: Re: rear disc brake issue Reply with quote

ok i can try to bleed it that way and i understand what you are saying about the bigger bore but why would the e brake work the same way i now have that adjusted to the point it wont move anymore on the caliper and its mechanical
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cbeck
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PostPosted: Sun Jul 15, 2018 1:04 pm    Post subject: Re: rear disc brake issue Reply with quote

My flaps recommended I put a 2psi residual valve in my rear brake line. Keeps the pads closer to the rotor? I have a single 3/4 cnc cyl running my f/r empi discs w/rear e brake.
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bob cook
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PostPosted: Sun Jul 15, 2018 5:24 pm    Post subject: Re: rear disc brake issue Reply with quote

yes a residual valve is needed also a proportioning valve is good to have also
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1newvwguy
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PostPosted: Sun Jul 15, 2018 6:39 pm    Post subject: Re: rear disc brake issue Reply with quote

Even with just rear brakes only?
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oprn
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PostPosted: Mon Jul 16, 2018 4:10 am    Post subject: Re: rear disc brake issue Reply with quote

1newvwguy wrote:
Even with just rear brakes only?

Shocked I trust you are not running this on the street! Shocked
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slalombuggy
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PostPosted: Mon Jul 16, 2018 5:11 am    Post subject: Re: rear disc brake issue Reply with quote

1newvwguy wrote:
ok i can try to bleed it that way and i understand what you are saying about the bigger bore but why would the e brake work the same way i now have that adjusted to the point it wont move anymore on the caliper and its mechanical


The ebrake has the same braking effort because it is not exerting enough pressure either. Typical braking systems operate in the 2000psi range and I have measured 2500psi on some luxury marques.

Yesterday I tested my new car out. Rear brakes only. Ghia calipers and 3/4" bore master. The pedal was rock solid but it took a long time to slow down as the braking effort exerted by the calipers was fairly low, which is exactly what I want but a larger bore master would shorten my distance and increase braki g effort AND reduce pedal effort.

brad
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1newvwguy
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PostPosted: Mon Jul 16, 2018 6:40 am    Post subject: Re: rear disc brake issue Reply with quote

I'm not driving it any where yet til I get the brakes fixed only in the yard just to test
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heywebonya
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PostPosted: Mon Jul 16, 2018 6:53 am    Post subject: Re: rear disc brake issue Reply with quote

There is a video on YouTube for technical tips of EMPI discs. https://www.youtube.com/watch?v=2rustBbto50

Basically you need to clock the brake calipers to the top to remove air because the bleeders are too low. Install the brakes as normal, remove the caliper mounting bolts, rotate to top of disc and bleed. Then move back to normal location.

Pain in the butt, but it worked for mine.
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vwracerdave
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PostPosted: Mon Jul 16, 2018 7:45 am    Post subject: Re: rear disc brake issue Reply with quote

oprn wrote:
1newvwguy wrote:
Even with just rear brakes only?

I trust you are not running this on the street!


You didn't answer the question. Are you planning on driving this on the street with rear brakes only because it is illegal. This may be part of the reason Sandrail and dunebuggy can no longer be registered and driven in Texas. The law requires all vehicles to have front and rear brakes. Not having front brakes may also be part of the reason your sandrail isn't stopping worth a darn.
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Last edited by vwracerdave on Mon Jul 16, 2018 9:03 am; edited 2 times in total
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1newvwguy
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PostPosted: Mon Jul 16, 2018 8:13 am    Post subject: Re: rear disc brake issue Reply with quote

Not really sure yet on driving it on the road but if I decide to do that at some point I will add 4 wheel disc brakes wouldn't feel safe with out them on the road
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oprn
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PostPosted: Mon Jul 16, 2018 11:27 am    Post subject: Re: rear disc brake issue Reply with quote

My sand rail has never has front brakes. I bought it that way, upgraded the rear suspension to IRS Bus including the rear drum brakes. This is basically an off road only trail machine that rarely gets out of third gear. I thought that was all I needed - Wrong!

I just about bought the farm coming down a mountainside through the trees at less than 5 mph. Back wheels were locked up, no room to turn because of the trees and picking up speed big time headed straight into the lake!

The weight shift on a steep down hill makes back brakes ineffective!
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1newvwguy
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PostPosted: Mon Jul 16, 2018 1:07 pm    Post subject: Re: rear disc brake issue Reply with quote

Well that's great advice since I'm a Newby to all this I think from what everyone is saying ii will just buy the front kit and be done with it the right safe way
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vwracerdave
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PostPosted: Mon Jul 16, 2018 2:38 pm    Post subject: Re: rear disc brake issue Reply with quote

One thing you might do before you spend any money is to ask the people in the HBB Off-Road forums and see what they suggest. I'm not trying to be mean but the description on this forum is for on street vehicles.



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