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Robert Yates got together with Blaine Johnson (both wheelin' friends of mine from SoCal) to address Robert's desire to have better brakes on his 35" tired TJ. During my last visit to Robert's place (Blaine was helping me relocate my rear shocks), I stuck my head under the TJ's hood to take a look at what they came up with. I snapped a few pictures and asked Robert to write up a description so the rest of you could get an idea that some folks go just a bit further when it comes to restoring good braking performance on their TJ. Here is what Robert had to say about the hydro-boost project on his TJ. (Thanks to Robert and Blaine for sharing this good information!)
The Jeep is using the stock master, prop. valve, stock front brakes (using Performance Friction pads) and has a ZJ rear disc brake conversion with the o-ring in the prop valve removed. The Jeep still utilizes the stock power steering pump and box, with the steering links still in the stock design parameter, ie no high steer or trackbar locational changes.
While the rear disc brake conversion was an improvement and generally acceptable, pedal feel was spongy at best and required a vigorous amount of leg pressure in a hard stop situation. The Jeep also runs a TeraLow with an automatic transmission so brake performance in off road/rockcrawling situations required improvement as well. On steep downhill crawling situations (such as a drop off a ledge or waterfall) the TJ in some instances, would require a shift into neutral to recover braking power as the t-case and automatic transmission would "push" the Jeep by outrunning braking capability.
The intent of adding the hydro-boost was to provide for a firmer pedal feel, while obtaining additional braking performance by adding more line pressure than what was being achieved with the stock vacuum booster.
Hydro-boost & Adaption for Use:
The hydro-boost unit was sourced from a 1 ton Chevy truck application. Delivery of the unit revealed that modifications would have to be dealt with in order for the hydro-boost to accept the stock master cylinder rod as well as for mounting it on the firewall.
Accordingly, a flanged adapter was constructed (painted gray Hammerite and seen in pictures below) which would mount to the TJ master and accept the rod, and a firewall mounting bracket to adapt the different bolt pattern of the hydro-boost to the TJ firewall. Also required was a simple rod extension for the hydro-boost to actuate the master.
Lastly, the pedal rod on the hydro-boost unit was shortened in order to land the brake pedal in a reasonably close to stock position inside the cabin.
Installation was relatively straight forward once the fabrication of the adapter and bracket was completed - taking approximately 5 hours for the hydro-boost unit itself.
Initial disassembly included unbolting the master from the stock vacuum booster along with disassembly of the brake pedal rod inside the cabin. It should be noted that at no time were any brake lines opened thus no re-filling of the master or bleeding of the brake system occurred.
Additionally, the combination of the length of the hydro-boost with the flanged adapter, required that some of the EVAC components located on the fender be moved to accommodate the longer length of the hydro-boost assembly, thus the fender mounted bracket was also unbolted (see first picture and use as comparison to stock to see where EVAC was reoriented).
Since the hydro-boost utilizes the power steering pump as opposed to the vacuum booster to provide braking assist, it requires high and low pressure hoses to be constructed and plumbed into the Jeep. High quality Firestone line along with barbed hydraulic fittings were used throughout. The installation of the hydro-boost unit also included plumbing in a stacked plate style Hayden power steering cooler inside the grill in front of the a/c condenser. This added about 3 more hours to the overall installation time.
Initially, the stock power steering hoses were all removed and the intent was to install all new hose for each connection. Trying to plumb in a "tee" off the top of the stock pump for the hydro-boost high pressure line (pump to hydro-boost) proved to be difficult and in looking at the situation, it occurred to us that the stock high pressure line (from the pump to steering box) could be flipped over and reused for the pump to hydro-boost connection. This will save both time and money and I like the idea of re-using stock parts if possible.
The remainder of the lines were then constructed with time taken to route hose and orient fittings so that no interference issues would occur. The power steering system then required new fluid to be added (I used Valvoline Syntech) and the entire system was bled to remove air.
The difference in braking power was dramatic. While I do not yet have any scientific data, such as a line pressure comparison, it is clear from a seat of the pants perspective that braking power has been greatly enhanced. The pedal is now quite firm and it is possible to lock up all 4 tires in a controlled fashion, ie. the fronts lock up first and then the rears. I did fiddle with tire pressure a bit, running 2psi more in the rears than the fronts to further enable good proportional response.
My stock power steering pump has over 67k miles on it and while it has so far stood up to the additional stress of the hydro-boost unit, I plan to eventually swap in an aftermarket pump with remote reservoir. This will add both braking power as well as steering power in the rocks so in consideration of the steering, it probably would have happened anyways and is not absolutely necessary to the success of the hydro-boost modification.
See Stu's Hydroboost Conversion