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[IrishCJ6]

Guy's I need some help, my brakes are still rubbish in the 6 and are worse now after the rear disc conversion. You probably no by now but it's running a Merc pedal/booster and MC (disc/disc) but the pedal is soft and very long. The brakes work but there is no way they will lock up and it's just doesn't feel right. I'm wanting to bin the Merc stuff and put in a Jeep designed system. I have been looking around and reading up on the old forums and think I have the right info, but want to check first before purchasing.

1 1/8" corvette style MC (disc/disc)
8" dual diaphragm booster

Does this sound right?
 I'm running a SSBC 12" disc front (1/2 ton calipers) and the Suzuki/Nissan Maxima setup on the rear.

I just want to make sure this will work before I spend my money. Oh the Merc pedal has a 4:1 ratio.

[Dave69]

It might be a case of looking at pirate4x4 to see what systems the yanks run, as i see it the disks are not in the equation, you need a compatible ratio of m/c to caliper. if these are not matched then the brakes will not work effectively as you have found out.
 i tried a similar thing with a bike brake system, i replaced the m/c with an all singing/dancing AP Lockeed brand but found out that it was too fierce and required a full race sighting lap with it dragging to get the brakes hot for it to work effectively, which in fact the ratios were totally wrong which forced me back to the std system.
 I have been looking at a brake booster system for the CJ7 and to be honest there are some off the shelf products that will fit the std install and create an improved brake application, but the brake effort will remain the same until more effective calipers are used but then you could be back in the same situation as you are in now.

[JamesH]

There's a good billavista article on Pirate about the balance between M/C , booster, pedal travel and pedal feel / pressure needed on the pedal. For my setup it help me to understand that I could reduce pedal travel but only in exchange for needing to put more force in through my leg to get the same effect on the brakes. In the end I've learned to live with a bit more travel because it works better offroad.

[bigjeepzj]

it all to do with physics



it's like a lever to move a load
if you move the long end a grater distance you pull more force on the load
simples

[wildwood]

I used a MasterPowerBrakes servo.......about $400 twice the size of a YJ and nearly twice size of TJ......It was needed as 35s and a YJ would not pass an MOT. But had been just about OK with33s.
Did the Job well........ Noŵ I have massive 1 Ton Discs and calipers at thefront and 3/4 ton discs at rear the amount of fluid needed is vast so pedal goes half way down but brakes are monster .......and handbrake which is hydraulic can hold anywhere......... To improve on what I have would require Ford F350 resesevoir to fuel the fluid hungry calipers.....

As the guys say above Pirate is your answer as they go into detail as to what works......

[Delk]

I have big Chevy front brakes and transit rear calipers. The pedal travel was drastic until I swapped in a larger master cylinder from a Dodge pickup. Once I did that it stops like a treat and can lock up wide 36's with ease.

The Dodge cylinder had the same fittings and I only needed to make a longer adjuster bolt.

[JamesH]

I have big Chevy front brakes and transit rear calipers. The pedal travel was drastic until I swapped in a larger master cylinder from a Dodge pickup. Once I did that it stops like a treat and can lock up wide 36's with ease.

The Dodge cylinder had the same fittings and I only needed to make a longer adjuster bolt.

[JamesH]

I have big Chevy front brakes and transit rear calipers. The pedal travel was drastic until I swapped in a larger master cylinder from a Dodge pickup. Once I did that it stops like a treat and can lock up wide 36's with ease.

The Dodge cylinder had the same fittings and I only needed to make a longer adjuster bolt.

This is where I got to - pedal travel probably not quite as bad with WJ front calipers and ZJ rears but needed more fluid than stock. The master cylinder upgrade doesn't give extra power but does mean the pedal travels a lot less so the brakes bite quicker and it feels more car like. A new booster is needed for more power.

For older XJs it's quite common to swap in the later booster and master cylinder for better braking. This is what's in mine and works well for disc / disc - I have a non-ABS proportioning valve but otherwise stock facelift XJ.

[IrishCJ6]

Anyone got a booster/MC off a WJ? Seems this combo will work so the US boys think

[IrishCJ6]

So I've taken the gamble on the WJ setup, seems a very common swap in the US for early Cherokee's and when I did the figures it turns out the discs/calipers on mine are very similar size/surface area to that on the WJ and its so much closer than those given on the Merc stuff I have currently. One of the guys I got talking to had the same exact setup on his Cherokee with the same brakes as I do and he's locking up 35's. Making it that bit easier is having the benefit of a different pedal/ratio combo than the normal CJ thanks to the Merc parts which again is very similar to that of the WJ and thus doesn't require the bulkhead ratio adapter normally required on CJ's. I did a quick search here in Ireland and found a guy scrapping a 2001 WJ with minimal mileage and very well maintained (engine went,?? uneconomical to fix) so for €45 only 10mins up the road, I got the pedal, booster, MC and pipes. All the other parts I had already from past projects (pipe, fittings, adjustable proportioning valve).

So here are some progress shots,

Removed the existing booster and MC and compared rod lengths and bolt patterns of both to see what would work. I also checked the pedal ratios. To achieve a similar ratio I moved the booster slightly lower and to allow the rod linkage to fit onto the pedal I moved it slightly offset from dead centre. I made up a small blanking plate that substituted as a template for drilling and offsetting the main rod hole.

New booster in place



Next I had to figure a way of connecting the rod to the pedal as the Merc system used a clevis style rod and pin system and that didn't suit the Jeep rod. Luckily I found a 1/2"UNC bolt with a shoulder fitted snuggly in the Jeep rod hole, I then drilled out a 1/2 nut and welded this to my existing pedal at the correct height (for the ratio) and depth for push rod connection (Merc rod was slightly longer).

Pedal connection - Little hard to see





Now the fun started with the modification of the existing pipes to suit the new MC, I have to change the front from individual lines to a combined system (simple tee) and then incorporate a adjustable proportioning valve into the rear line. A simple bracket held off the MC bolts sufficed as a prop valve bracket.

 



So I've got to finish off the front pipes and then bleed the MC, reinstall and bleed the entire system. Fingers crossed I get a good result.

[IrishCJ6]

I wish it was good news but its not, I have installed the WJ booster and MC into the Jeep, bleed everything and have a great pedal (about 1/2" before takeup). However I can not do an emergency stop and the brakes will still not lock up. The pedal feels like its getting full MC piston stoke (hits a wall, but not the pedal grounding out) and is firm like a modern vehicle. But is unable to produce either enough pressure or volume to adequately stop the vehicle. It will stop but it more of a gradual stop rather than a sudden stop, even if I do just jump on the pedal. It's better than the original setup but not by much. Any suggestions?

[Dave69]

apart from i was hoping for a positive result

[IrishCJ6]

The fix might not be so major, seems I have the brake lines to the MC backwards, won't know till next Mon/Tues when I get a chance to change them over. Fingers crossed 

[j33pky]

What front calipers have you got?

[isle of man]

MAN!! You need to go power boost, ask vanco.

[IrishCJ6]

What front calipers have you got?

Chev 1/2 ton

MAN!! You need to go power boost, ask vanco.

Haven't got the money to spend unfortunately, but time may change this.

[j33pky]

Changed the front axle on my 1974 cj5 for a early cj7 disked front axle, large calipers.  The stock mc just. Didn't move enough fluid to make them work properly. It would stop just not too well.  Moral to this story...  I had to buy the right mc to suit the calipers..

[isle of man]

What front calipers have you got?

Chev 1/2 ton

MAN!! You need to go power boost, ask vanco.

Haven't got the money to spend unfortunately, but time may change this.

You will know when you are ready, you can only swallow so much sword!!

[IrishCJ6]

I have a big mouth and the sword would have to be doing some serious internal damage to convince the other half to part with money for it. I'll persevere but thanks for the advice 

[IrishCJ6]

Brakes sorted 

Had some time today to change over the lines. Brakes are so good. Almost too good now and will easily lock up in the wet. Will have to get use to now only having to apply a small bit of pressure to the pedal. Must say best bit of money I have spent recently.

[Bulldog67]