Brake BiasI have a ’00 XJ on 35-inch tires running Dana 44 axles from a ’07 JK Rubicon. I have replaced all the hard lines with stainless steel tubing and all the flex lines with braided stainless hoses. I am still running the factory master cylinder and proportioning valve that was on the vehicle when I bought it. The axles I removed were the original Dana 30 front (disc brakes) and a Dana 35 rear (drum brakes). I have never been happy with the off-road braking since completing the axle swap. On-road performance isn’t bad, but the brakes just don’t feel up to the task on steep inclines when in low range. There are a million different internet opinions on whether or not the proportioning valve needs to get swapped for a disc/disc valve and an equal number of “grab this valve from this vehicle in the junkyard” to make it work ideas. In researching the problem, there are a number of folks that say the OEM master cylinder/brake booster isn’t capable of pushing the volume or pressure of fluid I need to handle the larger JK calipers. They claim the root cause for the weak brakes is the master cylinder, not the proportioning valve. Before I spend a big stack of bills on all new aftermarket calipers and a big brake kit for a JK (of which there are several options), I want to make sure I have optimized my current setup before buying a solution and not actually fixing the original issue and still not getting the best performance.
Axle swaps can often cause brake system issues. Several things need to be considered before attacking the problem. First and foremost, you have to make sure the brakes are properly bled. Any air in the hydraulic brake system will cause the pedal to be spongy and significantly diminish braking performance. Removing all of the air from the system can be even more difficult when all of the hard brake lines of a vehicle have been replaced. It’s best to start the bleeding process from the wheel that is farthest from the master cylinder. In your case, this will be the passenger-side rear wheel. Then move to the next farthest wheel (driver rear), and so on once you think you have removed all the air from each brake. You will likely need to go around the vehicle several times and bleed through at least a quart of brake fluid before all the air is removed. A proper brake bleeder will make this process more efficient and reduce brake fluid waste.
Several things need to change when swapping from drum to disc brakes, and it sounds like you have skipped out on all of them, which could be the reason for your braking troubles. Upgrading to brake calipers with larger-diameter pistons or multiple-caliper pistons will usually require more brake fluid volume than smaller single-piston brake calipers. Your XJ factory front brake calipers featured 2.6-inch single pistons. The JK axle comes with 2.6-inch single-piston calipers as well, so I don’t believe your braking problem is up front. However, your factory rear XJ brakes were drum brakes, and the new JK rear axle has 1.9-inch single-piston disc brakes.
Drum brakes require a residual pressure valve either in the rear brake master cylinder port or in the combination valve. The residual pressure valve retains a small amount of line pressure to keep the drum brake shoes close to the drum. It decreases the pedal travel required for the brake shoes to make contact with the brake drums. Retaining the drum brake residual pressure valve will cause the new rear disc brakes to drag. I realize this is not the problem you are having, but it should be addressed.
The JK 1.9-inch-diameter piston rear disc brake calipers will require a higher brake line pressure and more brake fluid volume than the wheel cylinders in the factory rear XJ drum brakes. The factory wheel cylinders likely have a piston diameter of around 1 inch. Your factory XJ combination valve is designed to work with the rear drum brakes, which you no longer have. This valve is significantly decreasing line pressure to the rear brakes under hard braking. I suspect that your front brakes are currently doing more of the brake work than they should be, which could also cause poor handling when braking. To solve this problem, I would recommend removing the factory XJ combination valve. You should plumb in an adjustable proportioning valve on the rear brake line. Companies such as Russell Performance (russellperformance.com), Tilton (tiltonracing.com), and Wilwood (wilwood.com) offer simple, easy-to-install adjustable proportioning valves. Once you install the valve, you’ll need to find a large, empty parking lot or unused road to test the brakes and dial in the rear brake pressure. If you jump on the brake pedal and the rear brakes lock up before the fronts, you’ll need to dial out some pressure from the rear. If the front brakes lock up before the rear, you’ll need to increase pressure to the rear. There is some room for personal preference when tuning your brakes, so you’ll have to fine-tune the dial to meet your driving habits. You may find that you prefer to have an on-road setting and an off-road setting. If you want to retain the function of the original combination valve and still be able to make adjustments to the rear brake pressure, Wilwood offers an adjustable combination proportioning valve (part number 260-11179).
Now, if you are sure you removed all of the air from the system and the adjustable proportioning valve still doesn’t get your brake performance where you want it to be, you’ll likely have to start looking at swapping out the master cylinder. However, I really don’t think that you’ll need to go this route until you upgrade to aftermarket front brake calipers with bigger pistons.
Straight Spring SwapI have a question regarding setting up leaf springs on my CJ-2A. I have been scratching my head mocking up the spring hanger and shackle hanger locations, as I am unable to square things up and keep my axles perpendicular to the frame. I have the leaf springs bolted onto the axles and perfectly parallel, but in order to keep the axles exactly perpendicular to the frame and square, I am having to locate one side spring hanger slightly offset or out of alignment from the other side when measured from a fixed point on the frame. Is this the correct approach to take? Should I instead locate spring hangers in an identical location on each side of the frame even though the axle will not be exactly perpendicular to the frame? I hope to use this Jeep as a daily driver/weekend warrior and would like decent street manners.
It sounds as though you may have a bent frame or maybe a kink in one of the leaf springs. You should check for crumpled areas along the framerails and carefully inspect the leaf springs for kinks and bends. If you don’t see any crumpled areas on the frame, measure the frame diagonally on each side to see if it has been pushed into a diamond shape. If you see uneven measurements, you may want to have the frame straightened before attaching any suspension brackets.
It’s also possible that the leaf spring center pin holes are not centered on the axle. I typically mount the springs to the frame prior to bolting up the axle. Sometimes just a little bit of slop in the center pin holes can translate into a lot of mismeasurement. The leaf spring pivot mounts are the most important to get correctly located. In the past, I have attached all-thread rod through the bolt holes in the mounts to keep them in line with each other and square with the frame. Use a plumb bob to help locate the spring centers where they should be on the frame.
Keep in mind that this isn’t a race car; some variance is completely normal for most Jeeps. I’ve had Jeeps with frames that were up to 3 inches out of whack that still drove straight down the road with no hands on the wheel. If you can keep things within a 1/4-inch or so, you’ll be doing better than most of the older Jeeps still on the road today.
4.3L Swap AccessoriesI can’t wait to hear how the Garage Project GPW handles itself. I noticed that you installed a ’02 Chevy Silverado serpentine group on your 4.3L engine. Can you describe your thought process and if possible provide the part number?
So far I’m really happy with the GPW. As with any new Jeep project, I still have a few small bugs to work out, but it’s been on two weekend trips so far and has yet to leave me stranded, so that’s a good start.
As for the front accessory group, I have dealt with mix-and-match parts and some aftermarket accessory brackets that resulted in poor belt alignment on past projects. I promised myself I would never do that again. I wanted the simplicity and reliability of a factory front accessory group with only one belt. One serpentine belt is far less problematic than multiple V-belts, and I only need to carry one spare. Chevy Performance (chevrolet.com/performance) offers a complete serpentine kit for GM V-8 engines (part number 12497697). It runs around $700-$800, but it won’t fit the later-model 4.3L. So for my GPW I pieced the accessory group together from a combination of used ’02 Silverado parts from eBay (ebay.com) along with new parts from GM and other sources. The idea is that I should be able to easily find replacement parts at any dealer or parts store if I ever need them.
Now, the one hiccup I had was with the large-diameter factory crank pulley. I had to replace it with a smaller pulley from March Performance (marchperformance.com) to allow the axle and front suspension to compress as far as I wanted. I'll eventually replace the stock GM power steering pump pulley with a smaller one from PSC. This will put it closer to a 1:1 ratio with the crank pulley and return power steering performance at idle.
CJ SpecificsI'm not the best with computers so please bear with me. I'm rebuilding an ’85 Jeep CJ-7. I bought a new frame from Throttle Down Kustoms. I then had it powdercoated and it looks great. I'm looking to upgrade to one-piece axles in the AMC 20, which shouldn’t be a big problem as there are lots of choices. The problem comes in when I try to find a rear disc brake conversion kit to work with the axle upgrade. Nobody will tell me if the axles I want to buy will work with the disc brake conversion kit. I'm trying to build a show vehicle and I want the front brakes, which are already disc to match the rear. I don't want red calipers in the back and blue ones in the front. I don't know if I'm not asking the right question or what, but people just never get back to me with the answer.
I would like to buy from one supplier. I need a one-piece rear axle kit, a rear disc brake conversion kit that fits the one-piece rear axles, front brakes, calipers, rotors, and pads that match the rear conversion kit, a new master cylinder, a proportioning valve, pre-bent stainless steel brake lines, and stainless steel braided flex lines. I don't do this every day so if there is something that I have overlooked please let me know. Such as do I need clips and hold downs for the brake lines? Please keep in mind I'm trying to end up with a show vehicle in the end. If you could be so kind as to send me a list of parts or where to go I would sure appreciate it very much.
Some of the specifics you are asking for are hard to provide. For example, the pre-bent stainless lines may interfere with the aftermarket frame and may need to be modified. Also, the factory CJ-7 rear axle and chassis generally have small metal brake line retainers already installed. Of course they are more than 30 years old and have likely broken off by now. Regardless, I can at least get you going in the right direction so you can figure out the small details as you go.
You have the option of going with any number of one-piece AMC 20 rear axle kits. If it’s the original rear axle, it will be the more desirable Wide-Trac axle housing. Look for a one-piece axle kit that includes axleshafts with rolled splines, such as the kits available from Alloy USA (alloyusa.com), G2 Axle & Gear (g2axle.com), and TEN Factory (tenfactory.com). These kits include all the bearings, seals, retainers, and other hardware that you’ll need.
TSM (tsmmfg.com) offers a rear disc brake conversion kit for your AMC 20 rear axle. The kit will fit both the factory two-piece axleshafts and any aftermarket one-piece axleshaft kit. The correct flexible stainless steel rear brake lines are available from TSM, as are the rear brake calipers, but you could purchase the brake calipers at your local parts store. The calipers generally come in raw steel, but brake calipers can be painted any color you choose with high-temp brake caliper paint from companies like VHT (vhtpaint.com).
Classic Tube (classictube.com) offers a complete pre-bent stainless steel hard brake line kit for your CJ-7, as well as kits for many other Jeeps. Unfortunately, the kit is designed to work with the factory rear drum brakes, so you will have to modify the brake lines and attach them to the rear axlehousing to accommodate the flexible braided stainless lines that are used to plumb the calipers.
Flexible stainless braided brake lines to replace the factory rubber lines are available from a few sources. Companies such as Goodridge (goodridge.com), Russell Performance (russellperformance.com), and Skyjacker (skyjacker.com) offer stainless braided brake lines. The length you choose will depend on the amount of lift your Jeep has.
The front brake components and master cylinder can all be replaced with over-the-counter parts from your local auto parts store. Again, you can paint the calipers any color you desire.
It will be difficult to find one retail source that carries all of these manufactures, although you may be able to special order the parts in some cases. Your best bet will be to try some of the bigger retailers such as 4-Wheel Parts (4wheelparts.com), 4Wheel Drive Hardware (4wd.com) or Quadratec (quadratec.com).
Unfortunately, you will likely find that a project like this is not a straight bolt-together deal, so it’s nearly impossible to provide you with an exact list of the parts you will need to complete your project. It is not at all unusual to have to modify the factory and aftermarket parts to fit your application. Rest assured that there will be times that a project like this will wear your patience extremely thin, but when it’s done the results will be tremendously rewarding. Good luck with your project.
Flattie Gold StandardI love the Garage Project GPW. I have been working on a CJ-3B project for years and I am finally getting close to being done. It has a boxed frame, small-block Chevy V-8 engine, SM420 manual transmission, Wagoneer axles, YJ leaf springs, power brakes, and power steering. I have been thinking about different tire sizes. Why did you end up going with 33-inch tires instead of 35-inch tires, which is what I thought was the gold standard for flatfenders?
Via Instagram @cappaworks
It sounds like a fun project you have there!
I usually try to build my Jeeps around a specific tire size. I wanted to keep this Jeep relatively lightweight and low. I’m sure the Dana 44 axles could survive with bigger tires behind the V-6, but they should have absolutely no problem living with 33s. In the past, I've had a flatfender with 31s, 33s, 35s, 36s, and 37s. I’ve always liked the way the 33s looked and worked off-road. I'm not planning to compete with rock buggies in the boulders, so I don't really need the larger-diameter tires or the ground clearance that they provide. I also don’t need the raised center of gravity that goes with them. Plus, the 35s don't fit in the flatfender rear wheelwells all that great without lots of trimming. I kind of wanted to keep the bodylines at least somewhat close to stock, even though the body on my GPW is full of dents and hack body mods made by previous owners. The 33s look more proportional, at least they do to me. I also like the tires really wide. Some might say that I’m stuck in the ’90s with my extra wide and knobby tire and wheel selections, but I like it, so that’s really all that matters I suppose.
M38A1 Data PlatesI just got an M38A1. Where can I find the data plates that go on the dash for the transmission shift pattern, transfer case shift pattern, vehicle dimensions, capacities, and more? Right now all I have is the serial tag.
The old factory military and civilian Jeep data plates have become highly coveted items. Weathered original pieces often show up on eBay (ebay.com), but you can purchase new reproduction Jeep dashboard data plates from companies like Army Jeep Parts (armyjeepparts.com), Data Plates 4 U (dataplates4u.com), and Kaiser Willys Auto Supply (kaiserwillys.com).