Brake booster/MC upgrade

[IrishCJ6]

I'm looking into buying a new brake booster/MC setup as I'm not happy with mine (soft pedal and not enough pressure to lock up). Before I get the whole "its just air" or "adjust the pushrod" posts it's not, its been bleed properly and there is no adjustment on the pushrod. The brakes work its just seems like there is insufficient pressure/fluid being applied to achieve a good brake action and has been worsened since I did a rear disc conversion. My Jeep was butchered before I brought it and it does not have the original booster/MC combo instead its been fitted with Mercedes parts (early 300d) and now I'm wanting to get back to a Jeep/American setup THAT WORKS.
The Jeep is running a SSBC 12" Disc conversion on the front with the GM 1/2 ton calipers, and the Suzuki/Nissan calipers on the rear. Oh and running 33" tyres
I've been looking at kits shown on eBay but I'm not entirely sure what will work the best with my setup.
Boosters: 7", 8" or 9"? dual or single diaphragm
MC: 1" or 1 1/8"?
My pedals are not the factory CJ ones but the Mercedes ones but it does give me a 4:1 ratio pedal thus I believe I don't require the adaptor? The pedals locate in the same fashion and have very similar pushrod connections points.
As I'm in Ireland and will be purchasing this online, I need to know what I'm buying is going to work (tried and tested) so if anyone has a similar setup that works could you please let me know what I need.

 

[Purple77CJ7]

Brakes


You might check this site out. He has booster kits for Jeeps with and without disc brakes.

 

[ThisGuyUKnow]

http://www.jeep-cj.com/forums/f2/hydroboost-install-pics-7406/

If you already have power brakes you can reuse your mc, if you go to the junkyard for the other parts you can do this swap for under 50 bucks

 

[tarry99]

I'm looking into buying a new brake booster/MC setup as I'm not happy with mine (soft pedal and not enough pressure to lock up). Before I get the whole "its just air" or "adjust the pushrod" posts it's not, its been bleed properly and there is no adjustment on the pushrod. The brakes work its just seems like there is insufficient pressure/fluid being applied to achieve a good brake action and has been worsened since I did a rear disc conversion. My Jeep was butchered before I brought it and it does not have the original booster/MC combo instead its been fitted with Mercedes parts (early 300d) and now I'm wanting to get back to a Jeep/American setup THAT WORKS.
The Jeep is running a SSBC 12" Disc conversion on the front with the GM 1/2 ton calipers, and the Suzuki/Nissan calipers on the rear. Oh and running 33" tyres
I've been looking at kits shown on eBay but I'm not entirely sure what will work the best with my setup.
Boosters: 7", 8" or 9"? dual or single diaphragm
MC: 1" or 1 1/8"?
My pedals are not the factory CJ ones but the Mercedes ones but it does give me a 4:1 ratio pedal thus I believe I don't require the adaptor? The pedals locate in the same fashion and have very similar pushrod connections points.
As I'm in Ireland and will be purchasing this online, I need to know what I'm buying is going to work (tried and tested) so if anyone has a similar setup that works could you please let me know what I need.

Irish.........Good brake systems are made and just not thrown together. I've trouble shot many brake systems in the past .....on yours I really don't know where to start but here are some basic's:
You need at least 19-21 lbs of vacuum. A dual chamber booster is better than a single especially if your vacuum is down or you run the Jeep at altitude.
You need to run all the numbers in your system pertaining to volume. From the master cylinder bore and stroke to the piston sizes at each end and even the volume in the lines........every wonder why some dual systems have two different sized lines going to the front & Back?........Not knowing whether you have a 1" or 1-1/8 " inch MC bore is your first mistake................
All the components have to be matched. Standard true pedal ratio at the Master for power is about 4-5:1 but again all of the components of the system have to be matched together a standard person can push about 60-80 lbs of force at the brake pedal.........general rule on hydraulics is large bore more volume and less pressure and the reverse is small bore less volume and more pressure. A 1.125 bore master sounds big.........most I've seen on Jeeps with Power and disc's are 13/16" to 7/8" bore........proper sized residual valves also have to be in place.
How big is the reservoir in the master? Is one chamber bigger than the other? Disc brakes take more fluid volume than drums and that's because the pistons are floating and self compensating for wear.............do some home work on your old system before you buy new.

 

[IrishCJ6]

Thanks Tarry99,
I understand there is a logical method to work out the ideal system, I thought by now someone else out there would have the same/similar setup and thus could tell me the parts they used (rather than reinventing the wheel). To answer a couple of your questions

I'm running around 18.5HG at idle, so running a lower vacuum level I would have thought would give you a harder pedal (i.e. not as much assistance). How would I go about increasing this reading and what will this achieve?

The Merc MC can be one of 3 bore sizes, 3/4, 15/16 & 3/4 (split) or 15/16, without disassembly I'm not sure how to tell the diff. I'm thinking that if it was either the 3/4 or 15/16 & 3/4 units maybe there is insufficient volume/pressure. Possibly the 15/16 would work?

There is no proportioning valve on the system as there was never one when I brought it from the PO and from investigation the Merc's don't use one, however I would have thought if it was incorrect I would have more effort being applied to either the front or the rear which neither I believe is happening. Both front and rear lines on the MC are the same size (3/8 fitting 3/16 pipe) there are 2 ports for the front (LHS/RHS) and one for the rear. The lines are new (I made them during the rebuild) and there is no pressure reducing valves within this.

The reservoir on the MC is big and does not seem to drain out if the brakes are applied. There are 2 sections and 2 inlets to the MC and both are filled from the same opening.

 

[IrishCJ6]

Update to this, with the help of a chap on "Pirate" I have now completed a booster/MC upgrade using WJ Jeep factory hardware. It has worked a treat and I've now gone from having terrible brakes to fantastic ones without breaking the bank. For anyone wanting to know more please PM me and I'll let you know the in's and out's.

Will update with some pics later as my camera is dead

 

[Petescj]

Update to this, with the help of a chap on "Pirate" I have now completed a booster/MC upgrade using WJ Jeep factory hardware. It has worked a treat and I've now gone from having terrible brakes to fantastic ones without breaking the bank. For anyone wanting to know more please PM me and I'll let you know the in's and out's.

Will update with some pics later as my camera is dead

Please share.

 

[mtnwhlr]

Please share.

put it out here for all to see and learn thats what this site is all about.

 

[IrishCJ6]

Ok, so here goes.

First my setup:

Front - GM/Jeep 1/2 ton Calipers (2.9" piston) and 12" rotors
Rear - Suzuki/Nissan Maxima combo (1.34" piston/11.5" rotor)

So the parts required from the WJ were:

Brake booster
Master cylinder
First section of pipe - from MC to Prop valve or ABS
Proportioning valve (WJ/ZJ) or adjustable
Brake pipe and unions

First off I compared the pedal ratio between my current setup and that used in the WJ, I had been given the WJ pedal on the off chance I needed it. The WJ ratio is 3.8:1. I then checked mine and found I was running 4.5:1 (Merc pedal box). I then calculated what it required to achieve the WJ ratio. I had to lower the pushrod attachment point by 1/2". I also had to offset the pushrod by 1/4" to allow connection to the side of the pedal.

There is no reason why the same principle couldn't be used for a factory Jeep CJ/other pedal. It may just mean raising or lowering the booster assembly.

I then compared the bolt pattern of the two boosters (the WJ was larger). I made a quick template that utilised the existing bolt pattern and then the new bolt pattern taking into account the lowering and offset required. I then offered this up to the Jeep and redrilled the corresponding holes.

Once the booster was bolted in place I found that the pushrod on the WJ booster was 5/8" shorter than my current setup but that wasn't an issue as it made it easier to connect to the back of the pedal. I found that a shouldered 1/2" course thread bolt fitted snuggly in the WJ booster pushrod hole. Simply drilling out a corresponding nut (1/2") and welding to the back of the pedal sufficed with the correct pushrod length. A simple fibre washer either side of the pushrod and then the bolt placed through made a very usable connection to the pedal.

Next was mounting the MC (simple), I opted to use an adjustable proportioning valve as I already had one but a WJ/ZJ factory one is fine also (so I'm told). I quickly made up a bracket utilising the MC bolt holes and mounted the prop valve to this.

Next off was a simple case of making the pipes and connecting them to the existing system. I had to alter my front line by adding in a tee as the previous MC had provision for both LHS/RHS at the MC. The WJ MC uses metric threaded unions (M12x1.0 and M10x1.0). Make sure you get the M12 union with the MC as it's a Jeep/Chrysler only part.

After that is a simple connect up. I made one simple mistake by getting the front/rear lines the wrong way round on the MC (was mislead by the chap on Pirate "by mistake") which lead to a stiff pedal and not enough force to stop the Jeep. The smaller M10 union (closest to the booster) is the front connection, the M12 union (closest to the radiator) is the rear connection. The rear line on mine goes from the MC through the adj prop valve and to the rear lines. The front goes from the MC to the tee and is split to the 2 front brakes.

A quick bleed and run found that I needed full pressure to the back anyway so you may be able to eliminate the prop valve if you have the same setup as me.

Below are some photos during the build, the last photo shows the incorrect line positioning but I haven't taken one of the corrected version yet, but it will give you an idea on how it goes together.

WJ booster in place





Pedal connection





Prop valve





And the final mock up (remember the front/rear lines are the wrong way round)

 

[BIGTRUCKNUT]

Great write-up, appreciate the follow-up on your solution to your brake problems.