Front twin piston brake conversion.
I was un-happy with the Jeep stock brakes even when new and with the standard tyre height. There was a lack of travel in the pedal and a very wooden feel suddenly part way down. This only got far worse as bigger tyres were fitted as they give greater leverage on the whole system showing up the faults more. I improved this a lot when I designed, many years ago, a rear disc brake system using the local Ford Falcon parts to replace the drums and now even a newer rear kit using current BA-BF Falcon rear brakes, but always want to do the fronts as well. The opportunity came when discussing my ideas with owner of Ultra Performance Components & Competition Engineering, Tony Edwards, who makes up grade kits for Holden's and Fords. He was willing to lend me the brake parts and the much needed contacts to get this sort of a job done and even invest in the first batch of 50 brackets to be laser cut. I went with choosing the latest twin piston Ford Falcon BA caliper by PBR and the matching rotors, which at 300mm, 20 mm bigger than the stock Jeep ones, give a much greater mechanical advantage. These also have the same stud pattern so can be used un-modified for ease of replacement. These calipers were also a good choice as the master cylinder didn't need changing as they were designed to run with the same bore diameter that the Jeep has. Two small pistons are used in each caliper instead of one large one in the Jeep. This better distributes the force over a wider area of the pad and prevents the large single piston cocking as they are prone to do in the stock ones. I spent quite some time working out the best way to make the caliper bracket and to fix it to the knuckle without having to change it for a completely new one. There was nothing out there to follow but was very pleased with the end results after much hard thinking and working around obstacles as they arrived. Once the brakes were fully bedded in I found the faster I needed to stop, the more I noticed the difference over stock. The brakes really shine when emergency stops are called for when they grip very well and can even cause 33" tyres to lock if you so choose to do it which cannot be done on the stock system due the taller tyres extra leverage. The larger rotors give leverage back to you to help you stop rather than working against you like taller tyres do.
The conversion has worked out so well that the kits will now be made and sold through Ultra Performance Components/Competition Engineering as a complete kit to suit all Jeeps with a unit bearing hubs which include the XJ Cherokee, ZJ ( ZG ) Grand Cherokee, TJ Wrangler and Rubicon. He can be contacted at: firstname.lastname@example.org or through his eBay store at: http://stores.ebay.com.au/MR-SPARES_W0QQssPageNameZstrkQ3amefsQ3amesstQQtZkm
The polished calipers will fit 15" rims with 4.75" of back spacing or less ( stock is 5.25" and only some of the stock ones clear ). Or you can pay extra for the painted PBR Sports calipers in black, red or yellow, ( see below ) which only fit 3.75" of backspacing or less for 15" rims ( for the coloured calipers only and not the polished ones supplied with the kit ) or any BS with 16" or larger rims. Chris in the USA has also put together a group buy which included a full spare set of pads with each kit and shipped over a pallet load along with spare rotors and pads etc. You can contact him at: email@example.com
The braided stainless steel lines can also be asked for in red, silver, blue or black as well. You must state the year of the Jeep because the hub offset changed in 99 ( see bottom of this write up ) as they later have 5mm less offset which much be accounted for in the bracket. If you have a pre 99, it is a good opportunity to change to the stronger later model hubs also and order the later model braking kit to match. The hubs also having longer studs and centre spigot to for cast rotors such as the kit comes with.
There is also a 325mm rotor kit available with FPR calipers that will fit some 16" rims ( less backspacing the better ) or 17" rims or larger for around for extra cost. These calipers are better again as are C6 Corvette ones with just a slightly different mounting cradle to suit the Ford mounting points.
Start by removing the hub as shown here. If not changing hubs at the same time you can actually leave the hubs attached to the axles saving you from buying a 36 mm socket and removing the axle nut. The axle will just pull free once the three hubs bolts have been removed complete with the hub attached if the axle nut was left in place without any need to remove the diff cover as no C clips on the front axle. Un bolt ABS sensor if so equipped. Remove the two ball joint nuts after taking out the slip pins. Remove the steering arm, like shown here, with a swift blow to the front of the steering arm. The knuckle can then be removed by giving a hard downward blows on the cast in flat area made for this purpose as shown in the photo using a heavy ball peen hammer. Use the other way around though as this was just to show the flat area under the hammer in the photo. Hitting the back of the joint and shocking it out like a tie rod can also be used. I would recommend soaking the two joints in penetrating oil in the week prior. It maybe possible to so the cutting with it left on the axle too. Some have reported to me that they have done this conversion now without removing the knuckle at all and cutting the knuckle while still attached. Might be able to leave the hub and axle still in place too which will save having a 36 mm socket. It is up to you which way you prefer to do it.
The first photo above can be enlarged ( just click on it ) to show the area marked to be cut off as viewed from the back. I just used a 9" angle grinder with a cut off wheel ( only took a minute a side ) but smaller ones can also be used. Even a hacksaw if nothing else is available. The mark runs down hard against the back of the upper ball joint mount and then stops about 10 mm shy of the hub ring area leaving a similar thickness to the area between the caliper mounts. The top part of the bottom mount was done the same with the lower hard against the lower ball joint mount.
The photo above viewed from the front shows the thickness left around the ring as well as the web left about 5 mm thick at the top. The next photo shows a early knuckle ( thanks Ryan Brown for the photo ) that had the bolt on caliper bracket showing how much more can be safely removed. Those with this knuckle just need to remove the caliper tabs.
The knuckle can now be bolted back into place ( upper nut 101 Nm or 75 ft. lbs, lower nut 109 Nm or 80 ft. lbs ). Slide the axle and hub back into place leaving the dust shield off and torque axle nut down now or later with the wheel in place to 237 Nm or 175 ft. lbs if it was removed. I have chosen to run the later hubs at the time of this install so I do not increase my track from the thicker rotors by 5mm each side and you gain the extra length in the wheel stud length as well. Next is to select the correct caliper bracket that will have the spacers facing towards you once positioned over the back of the hub.