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Unread 06-26-2013, 07:06 AM   #1
gabbagabba
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CJ7 brakes and disc conversion, poor performance

Myself and my mech. could use some input on my CJ7. The brakes are terrible, I just bought it a few weeks ago from a jeep shop who told me 'that is how brakes are on a cj7'. I have my mech looking at it this week and he found the master cyl leaking and plans to replace that but was inclined to put a diff type in there.

It has a disc brake conversion and my mech feels like the OEM style master cyl for drum brakes may be part of the problem. However, he notes that conversion kits do not spec a new master cyl typer and he also talked with a buddy at a 4x4 shop who also told him to stick with an OEM style master cyl

help?

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Unread 06-26-2013, 10:33 AM   #2
LumpyGrits
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Any mech worth a dang should know that it takes far more PSI to 'work' disc brakes that shoe type.
Any parts house worth a dang will show you that there are at least 2 different M/C's for your Jeep. One with, and one WITHOUT disc front breaks.
Go to NAPA online and you can see this for yourownself.
LG
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Unread 06-26-2013, 11:04 AM   #3
Mr_Ranger
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If this is a front disc brake conversion, then I agree with LumpyGrits.
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Unread 06-26-2013, 11:11 AM   #4
SLO_Ken
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Quote:
Originally Posted by Mr_Ranger View Post
If this is a front disc brake conversion, then I agree with LumpyGrits.
Didn't most, if not all, CJ7's come with front disk brakes from the factory?
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Unread 06-26-2013, 11:27 AM   #5
LumpyGrits
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OP never said if the disc's were front or rear
IIRC, disc's were std in '79 on the '7'.
LG
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Unread 06-26-2013, 11:33 AM   #6
SLO_Ken
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From the OP's other post...

Quote:
Originally Posted by gabbagabba View Post
Just bought a 86 cj7 a few weeks ago. The brakes are terrible, no way I could stop in a hurry if someone pulled out or whatever. Downshifting actually stops it better

My mechanic is looking it over and plans to replace the currently leaking master cyl. He thinks the one in their now is OEM or similar spec and looks to him to be a drum brake style master cyl

He notes that disc brake conversion kits for these do not spec a new or diff type master cyl and a mech buddy of him who works at a 4x4 shop also told him to continue with OEM style master cyl, not upgrade to a disc style one?

Thoughts?

I was told when I bought it from a jeep shop that I would have to learn to live with sh**tty brakes on a CJ7, but it seems that something can be done?

Thx!
'86 definitely came with front disks, so the conversion would have to be rears.

Gabba, you didn't mention anything else about your Jeep. How big are the tires? Does it have any mods/armor/recovery equipment that would increase the weight significantly? These can significantly affect braking performance.
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Unread 06-26-2013, 11:39 AM   #7
LumpyGrits
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SLO, yes OEM front disc.
Rear was a D/44.
But, who knows what's there now........
X2 on need'n more info........
LG
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Unread 06-26-2013, 11:43 AM   #8
gabbagabba
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info

It has 35's (wrangler MTR), winch, steel rock crawl type bumpers, heavy duty axles (some kind of hvy duty version of the 44's). Ox lockers. It also has a cast iron tx case which my mech felt looked very hvy duty and def not stock (not a dana 300 he said whick would be alum?)

I am not too knowledgable with regard to car mech stuff but I have a feeling I'll be learning...

It has a rear disc conversion. My mech thought the current master cyl looked kind of wimpy and was thinking about changing it out to something else. It was also leaking so maybe a new one in itself will help? He chatted with a buddy of his who supposedly knows a lot about CJ's/4x4's that advised him to stay in OEM spec for the master cyl. I dont know the reasoning there


I see info on the web re: corvette MC's for these?
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Unread 06-26-2013, 11:51 AM   #9
SLO_Ken
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Quote:
Originally Posted by gabbagabba View Post
It has 35's (wrangler MTR), winch, steel rock crawl type bumpers, heavy duty axles (some kind of hvy duty version of the 44's). Ox lockers. It also has a cast iron tx case which my mech felt looked very hvy duty and def not stock (not a dana 300 he said whick would be alum?)

I am not too knowledgable with regard to car mech stuff but I have a feeling I'll be learning...

It has a rear disc conversion. My mech thought the current master cyl looked kind of wimpy and was thinking about changing it out to something else. It was also leaking so maybe a new one in itself will help? He chatted with a buddy of his who supposedly knows a lot about CJ's/4x4's that advised him to stay in OEM spec for the master cyl. I dont know the reasoning there


I see info on the web re: corvette MC's for these?
yeah, those 35's are not doing you any favors as far as braking performance. I have the same 35's, and I almost killed a poor girl when she stepped out to cross the street from behind a delivery truck .

The D300 is a cast iron case, not aluminum. The winch, steel bumpers, heavy duty axles, and big tires/wheels all add to the weigh that the brakes are trying to stop. Disk brakes in the back might help, but the lion's share of the braking is done by the front brakes.

I'm in the process of upgrading to a hydroboost brake boster and master cylinder from a 90's Chevy 1-ton truck.
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Unread 06-26-2013, 11:53 AM   #10
LumpyGrits
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First, Dana 300 t'cases are cast iron.
Your OEM t'case was a d'300.
Second, you will need a M/C that is built for front and rear d'brakes.
I have heard Vette an Lic. Cony M/C's may work. NOT SURE.....
What tranny you run'n?
LG
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Unread 06-26-2013, 11:56 AM   #11
John Strenk
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4 wheel disk brakes will have the same appearance as 4 wheel drum brakes.

Inside will be a lot different.

But I would not go with an OEM MC for a CJ. they never had 4 wheel disk.
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Unread 06-26-2013, 12:09 PM   #12
gabbagabba
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Snds like I need a new mechanic who knows CJ's better, until I know more
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Unread 06-26-2013, 12:12 PM   #13
John Strenk
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At least your mechanic looked for info when he didn't know, he just needs a better informed "Buddy"
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Unread 06-26-2013, 12:22 PM   #14
Jim1611
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In rebuilding my CJ I went with rear disc brakes, already had them up front. I also am converting to power brakes. In doing this I knew a different master cylinder was in order so I did some checking. I ended up calling Tuff Stuff Performance Assecories and talking to their tech dept. They sell brake parts and supplies. They suggested one of theirs that's a dual resevoir with a 1 1/8" bore. This also happens to be close to the same size as the Corvette cylinder, maybe even the same. I have yet to use it set up this way so I can't give you first hand info on how it works. You also may need to change the proportioning vavle too. I'm going with an adjustable one that I can fine tune.
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Unread 06-26-2013, 12:47 PM   #15
gabbagabba
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Quote:
Originally Posted by John Strenk View Post
At least your mechanic looked for info when he didn't know, he just needs a better informed "Buddy"
fair enough, maybe I'll wil hold judgement until I see the end results of his work this week and the bill.....
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