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Unread 01-30-2014, 03:54 PM   #1
DGRobles
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1986 CJ7 
 
Join Date: Apr 2005
Location: Mexico City
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No braking power with all new components... HELP!

Please help!... I never thought to say this but I am about to quit... I can't solve my problems with brakes and taking the jeep outside the city with this conditions make me evaluate other alternatives (TJ)...

So here is the background... I upgraded to vacuum booster brakes but I can't get enough braking power to block the tires or do emergency braking...

I changed my proportioning valve, I have the 8" diameter booster, brand new master cylinder from Chevy Astro, new brake lines, new valve check on the booster, hose for vacuum is new and is not collapsing... new pads...

Man, everything is new now and I still have problems...

I tested the booster to see is that was the problem but no, no leaks at all.

Braking power (assisted) came occasionally and I do not know under what conditions, with it I can block and make an emergency stop really easy but then suddenly I have no assistance...

So... pressing the pedal at half brakes good, but when I floor it it behaves like mechanical...

Any suggestion?... What could it be?


DG

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Last edited by DGRobles; 01-30-2014 at 04:37 PM.. Reason: Title wrong...
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Unread 01-30-2014, 04:02 PM   #2
LumpyGrits
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Where did you run the vacuum line for the booster to?
Can you in fact 'pull' vacuum on the booster?
LG
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Unread 01-30-2014, 04:18 PM   #3
DGRobles
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I run it directly from the manifold... and yes I can pull vacuum on the booster...

here is the setup,

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Unread 01-30-2014, 04:44 PM   #4
LumpyGrits
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With the altitude of Mexico City. Have you taken a vacuum gauge reading to see how many 'inches' of vacuum you have?
Does your engine run a stock profile camshaft?

LG
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Unread 01-30-2014, 04:46 PM   #5
Spieg8
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Are you using stock brakes (disc/drum)? Curious why you went with that MC? Not being familiar with the specs... what are the piston cylinder dimensions (volume)? Also, what proportioning valve did you use to replace the stock unit?
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Unread 01-30-2014, 04:56 PM   #6
DGRobles
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The engine is completely stock 258, no modifications on camshafts... also brakes are stock disc/drum setup.

Originally I had the MC1321H kit



but had problems with the MC, so I checked the specs on the ports and bore diameter (1") and the chevy astro has exactly the same specs but 50% lightweight.

the proportioning valve was bought at Morris, and was marked as the direct OEM replacement for the one I had installed...
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Unread 01-30-2014, 05:13 PM   #7
Knucklehead
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Had a similar problem when I swapped in a new master cylinder and booster - found that the problem to be inadequate bleeding of the master cylinder. Had to work hard at getting all the air out of the MC bore but once done, and bled the entire sytem again, the brakes worked great.
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'45 Ford GPW; '73 CJ5, 350/NP435/D20 w/Terlow gears, locked D30/D44; '13 CJ8, 304/T150/D20/D30/AMC20 w/locker and limited slip (T18 and Teralow gears in future); '88 Dodge RC, 360/NP435/NP205/D60s
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Unread 01-30-2014, 05:20 PM   #8
LumpyGrits
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I vote to 100% rebleed the system.
Can you do a pressure bleed?

LG
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Unread 01-30-2014, 05:41 PM   #9
DGRobles
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I can do pressure bleed as I do not have the hardware, however I can try to get it here to do it...

Is this the more recommendable procedure?... pressure bleed?
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Unread 01-30-2014, 07:30 PM   #10
LumpyGrits
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Quote:
Originally Posted by DGRobles View Post

Is this the more recommendable procedure?... pressure bleed?
At this stage, I feel it's your best option.
Just make sure you have a hose coming off the bleed-nipple into a bottle with some brake fluid already in it.
Do one wheel at a time, and do the whole procedure twice.
Best of luck and post up results.
Fingers crossed
LG
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Unread 01-30-2014, 08:24 PM   #11
DGRobles
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Thank you LG! Keep you informed!


This is the toy in problems...

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Unread 01-30-2014, 08:31 PM   #12
LumpyGrits
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Kool picture-Where was it taken?
LG
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Unread 01-30-2014, 08:53 PM   #13
DGRobles
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Quote:
Originally Posted by LumpyGrits View Post
Kool picture-Where was it taken?
LG
Mexico City, outside the city, a place called Ajusco....
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Unread 01-30-2014, 09:00 PM   #14
LumpyGrits
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IIRC, from when I lived in Mexico City as a kid. It's south of the city isn't it? One of the highest mountains in all of Mexico.
Beautiful country for sure.
LG
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Unread 01-30-2014, 09:22 PM   #15
DGRobles
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Quote:
Originally Posted by LumpyGrits View Post
IIRC, from when I lived in Mexico City as a kid. It's south of the city isn't it? One of the highest mountains in all of Mexico.
Beautiful country for sure.
LG
That's right!...
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