Dana 60 Brake Caliper Grinding

I've finally gotten started on my 1st "hard core" 4x4 built specifically for the rocks. For most, that means you need big clearance, which means big tires, which mean strong axles and brakes. So, we step up to (or start with) 3/4 or 1 ton gear to reduce the time setting on the side fixing things, and to bring those big tires to a stop within a reasonable distance. So far, the only real question is whether you want to fork out for the ultimate in full-size beef, a Dana 60 front, or save some major cash and settle for a 3/4 ton front so that you can at least run a Corporate 14 bolt rear and you still get the stronger brakes.

Next thing you have to think about is those tires. That's what started the whole thing anyway right? What are your choices? Basically, it falls into 3 categories.

16.5" Wheels

You can run the common 16.5" rim which has been around for years, has MANY different sizes and makes of tires available, and can be readily found new or used for a good price. Only problem is, the area where the bead seats on the rims has no safety bead and the tire will frequently "un-seat" if you run the low pressures (10-15 psi or less) commonly found on rock-crawlers. The only way to run this tire with confidence at low pressure is to run a bead-lock. Unfortunately bead-locks are rather expensive (offsetting the cheaper tire), they can be a pain to fool with on a daily driver, and they are illegal for road use in most areas. 16.5 is a good choice for many people, but it is not ideal.

16" Wheels

Next, lets look at a 16" wheel. This is a much better design since it does have a safety bead to help keep the tire seated. That means you can air down without as much worry about un-seating the bead. The only way to be sure that you won't pop the bead is a bead lock, but the 16" wheel is much better than a 16.5, especially on a daily driver that will also see duty as a rock crawler. However, all is not good with the 16" wheels. The tire selection is still pretty limited, although it is getting much better as time goes on. As of this writing, the largest sizes are not even available for 16" rims. To make matters worse, they are also a bit more expensive than their 16.5" counterparts for the same tire size.

15" Wheels

15" wheels have the best of both worlds. They have the safety bead like the 16" wheel to help keep the tire seated. They also have the biggest selection of tires available, even in the very largest sizes. Plus they are often the cheapest for any given size. Unfortunately, while the 15" rims will fit fine even on a 1 ton rear axle, they will not fit over the heavy duty 8 lug disk front brake calipers. Contrary to what many people will tell you, including the people at tire stores, you can run a 15" 8 lug wheel on 3/4 and 1 ton GM axles. It just takes a little extra work. Specifically, you will need to grind down the outer surface of the brake caliper, caliper bracket, and sometimes the backing plate to clear the wheel. Many people think, as I do, that the merits of a 15" wheel make the extra work well worth the effort.

So, what does it take to run 15" wheels on 8 lug front axles? To begin with, you have to decide what wheels you will run. You can not run an aluminum wheel because the thicker wheel would require far too much grinding to make it fit. So, steel it is, no choice here. However, you can choose the amount of back space for the wheel. That is the amount of offset from the back of the rim to the wheel mounting surface. Your choices typically range from around 2" up to about 4.5". Less back spacing means less grinding. With smaller axles, wheels with minimal back spacing (which offset the tire to the outside) would put too much stress on various components, resulting in premature failure. In our case, the 8 lug axles can all easily handle this extra stress. However, there is are still problems with minimal back spacing that affect us. Since it increases the arc that the wheel follows when it is turned, it can require extra modifications to the suspension or body to prevent the tire from hitting the body. Offsetting the wheel to the outside also increases something known as the "scrub" radius. This results in making it harder to turn the wheels when your not rolling. Combine this with the additional effort required to turn the big tires to start with and now you need a whole new set of modifications to deal with that. I prefer to use a 4" back spacing and grind a little more. You'll have to decide what is right for you.

I started with an inexpensive set of white buggy wheels from Discount Tire. They are "Unique Series 21s" with 4" back spacing and they cost just over $30 each including shipping. They are a special order item that must be paid for in advance and there are no refunds. It took less than a week for them to arrive. I did the grinding before mounting the tire so that it would be easier to test fit the wheel as I worked on the caliper.

Read on as I describe the modifications necessary to put 15" rims on my Dana 60 front axle. You'll need some way to tighten and remove lug nuts, a jack and jack stand, some spray primer, and a hand grinder (4" or 4.5" typically).

Modifying a Dana 60 to run 15" rims

Now, time to start working on the calipers. Always remember, safety first! You can't wheel if your in the hospital or dead. So, set the parking brake, block the rear wheels, jack up the front axle and set it securely on jack stands, and then remove the front wheels. The next thing I did was to clean it up good with a wire brush and spray it with some gray rattle can primer I had setting around. I used this like a body man (used to be one) uses a "guide coat" to find high spots. With a nice uniform coat of dull primer on the caliper, any place that the wheel touches will be very easy to spot. Any kind of paint will work, but I prefer primer since it dries really fast and covers the ground areas in one coat. With primer, your ready for another test fit just about as quick as you can get the wheel back on the hub.

Next, put the wheel on. Push it as far back as you can. On mine, the caliper side lacked about 1/2 inch or so going all the way back. Look at the back side and estimate where the back of the wheel will be when this is completed. You do not need to grind any further back that that so pick up some visual queues (or mark it) to remember. Now, holding the wheel in place, turn it back and forth a few times and then pull it off. You should be able to see clearly where it is rubbing. Take a scribe (or the grinder) and mark fairly straight line at the point where the back of the wheel will ultimately set. When your done with the grinding, there will be a small ledge here. Then I took the grinder and hit every point that was showing contact with the wheel using the edge of the wheel. Take each one down about 1/16" in the beginning, digging in less and less as you get closer to the final fit. This "trough" also helps you keep up with the "high point" while grinding away. Don't get into too big a hurry, you don't want to remove any more metal than absolutely necessary. After you have turned all the "high points" into "low points" you need to blend those small troughs into the surrounding area till it looks uniform and smooth. If you keep the grinding area looking smooth and uniform, the "high point" will generally indicate a larger high area or dome. So, your blending area will be 1-2" in diameter around the high point. Again, don't get carried away, take your time. It will require many test fit and grind cycles to get it right, be patient.

Once you have all the troughs blended in, spray a light coat of primer, just enough to get a somewhat uniform dull color. Your not looking for full coverage, just the uniform dull color. Put the wheel back on, look at the back side to see where you are on your reference (back limit) line, turn the wheel back-and-forth a few times, and remove it. You should see a different pattern of scuff marks, grind them into troughs, blend them in, repeat. Again, as you get closer, reduce the depth of the troughs you cut on the high points. You don't want to over shoot.

Here is an example of what the scuff marks look like (indicated by yellow arrows) and how I am using the reference back limit line (indicated by the red arrows).

When you get it to a point where the wheel goes all the way back and you can turn the wheel without scuffing, put a couple of lug nuts on and snug them down. I had to repeat the sequence twice at the end to get it to turn free with the lug nuts on. When your done, take the grinder and smooth out any sharp edges to reduce stress points. A nice fat radius on corners is what your looking for. I primed mine after finishing just so the amount of material removed would be easier to make out in the pics. The ground surface just didn't give a clear perception of what was done. I also left the back ridge fairly square for the same reason. I will round it off and blend it in a bit before calling it done. Below you can see the results. It's hard to tell but there is still ALOT of material left in ground areas of that caliper. The area around the hole is the thinnest part and it gets much thicker as you move away from the hole. It's strength is in no way compromised by the modifications, it's still thicker than a 1/2 ton caliper.

So, the total job used less than 25% of a 1/4" abrasive disk on a 4.5" grinder to do each side. The second side went MUCH faster since I knew about what I was looking for. All total, I removed about 1/8" or a little more across the entire outer surface of the caliper. The largest amount of material (almost 1/4" depth wise) came off the outer ears of the caliper mounting brackets. No modifications were necessary to the backing plate.

One other thing to be aware of. The GM calipers align on the rotor and adjust automatically for pad wear. If you have worn out pads, the caliper will be pulled back toward the king pins to compensate for the wear. New pads will cause it to stick out further to the outside and, deeper into the wheel. If you have worn pads, you would do well to go ahead and change them now rather than risk having to grind more on it later just to clear after installing new pads. That's it, no big deal.

Disclaimer: As always, standard disclaimers apply. Making these modifications is your choice and yours alone. You should consider any modifications to the brake or steering system very carefully. If your not comfortable making these modifications yourself, take it to someone you trust, or don't do it at all. I do believe this modification is safe, after all, my son and daughter will be riding in this rig. However, I make no claims about the effect this modification will have to the caliper strength. I can only say that the modified caliper appears to still be much stronger than the 1/2 ton caliper, even after removing all that material. I can also say that many people have made this modification and I don't know of any caliper failures due to the modification. This modification is intended for off-road use only.