My Tahoe is the GMT800 truck chassis from Chevrolet. The rear brakes always seem overworked and hard braking leaves something to be desired. If you also have a 4 wheel drive GMT800 SUV and are wanting to upgrade your brakes then this is the right place.
GMT800 Brake Timing Enomoly
I’m told the GMT800 has a system where under light braking the rear brakes are applied before fronts. This is contrary to popular brake tuning practice, where the fronts are always biased more than the rears regardless of timing. However, evidence seems to point to a slightly advanced rear brake timing.
This lead me down a rabbit hole where I continually pull over and check heat on front and rear brakes. One thing is clear the rear disc brakes work much harder on my truck when on slow descents from high elevation. In this testing on mountain roads, the rear rims were too hot to touch yet the fronts were cool!
Searching forums I’m not alone. These trucks seem to consume rear brakes at a much faster rate than the fronts. In 55,000 miles I barely wore my front brakes, yet had to do rear brakes twice!
Some (if not all?) of the GMT800 pickup trucks came with larger brakes. Specifically after the split model year, 2003. However, the SUV variants didn’t seem to get them till the GMT900 chassis was released. I theorize the original 16″ wheels on those vehicles wouldn’t fit the larger rotor so the engineers at GM held onto with the smaller brakes until they released the next revision GMT900 chassis.
Brake tuning
There’s a brake balance built into the brake system where the rear brakes less than the front (e.g. 55% front 45% rear). More braking force in the rear can create an unbalanced condition should the rears lock before the fronts. This can lead to an unrecoverable oversteer condition. Ever try pulling the parking brake at high speed? Then you know what I’m talking about.
Without theoretical models of the vehicle and track testing I cannot say with much certainty what will happen swapping parts like this. You can do some static modeling based of of applied torque & pad size since. However, there’s likely more to the picture than this basic math would tell us.
I did try to compare part numbers between GMT800 and GMT900 master brake cylinders (the proportioning valve). It would have been a no brainer if the part numbers were the same for rear brakes and the master cylinder but they are not. There’s also very little if any public information to be had on the brake bias for the factory master cylinders.
The GMT800 to GMT900 front brake swap is very popular though. After speaking with multiple owners who have done it I’ve heard of no adverse issues leaving stock braking tuning / bias as is. There are also people are swapping MUCH larger brakes from the C6 Z06 Corvette, the first generation Cadillac CTS-V, or the 4th generation Silverado. These are not direct fitment though.
Should I have chosen a larger front brake system then I’d want a tunable brake system as well as doing calculations to adjust bias then track testing. Likely, probably prudent regardless. More on that later.
GMT800 versus GMT900
Before you do this swap you’ll want to check which size rotor you have on your existing setup. Some of the Truck builds came with larger rotors already. The calipers on those are slightly different than the GMT900 but upgrading might not be worth the hassle in that case.
Rotors Differences
GMT800 rotor is approximately 1″ smaller than the GMT900
You have to have 17″ rims or larger to fit the GMT900 brakes. The 16″ rims will not fit the larger rotor! I purchased the OEM snowflake style rims. Make sure you’re spare is also a 17″ rim or you won’t be able to use it on the front of the vehicle otherwise!
| GMT800 (2001 Tahoe) | GMT900 (2010 Tahoe) | |
| Caliper Pistons | 2 | 2 |
| Rotor diameter | 12″ | 12.99″ |
| Rotor Thickness | 1.14″ | 1.18″ |
Brake splash guard is slightly too small from the GMT800. Cannot find one that is bigger and fits.
The splash guard (sometimes called dust shields) will won’t cover the entire rotor as it ideally should. I researched GMT900 splash guards (GM PN 25918337 left, GM PN 25918338 right) to discover they are discontinued! That aside, I’m not sure of the hub bolt pattern matches for the GMT900 versus GMT800. It’s possible some of the GMT800 Truck (with larger rotors) may fit.
Long story short, I used my old splash guards for now.
Caliper Differences
GMT900 Caliper sticks out farther from the steering knuckle to fit the larger rotor.
Both GMT800 and GMT900 calipers are a twin piston design. I understand the brake pad on the GMT900 is larger. This in combination with the larger rotor provides more braking force. The GMT800 brake hoses and banjo bolt mate up perfectly to the GMT900 design. Which makes this a direct swap!
Use the longer caliper bracket bolt on GMT900
It’s important to note the GMT800 caliper brackets are thinner. Make sure to use the correct length bolts when you install the GMT900 calipers to the steering knuckle.
Police Pursuit Vehicle (PPV) Parts
Police Pursuit Vehicle PPV Rotors with vented hat
An easy OEM upgrade is to research the PPV parts in the catalog and use them.
There’s some rumors about PPV calipers with upgraded seals in them. Unfortunately, I couldn’t validates those as there were no unique part numbers to be found as such. It’s easy to mix that rumor up with AC Delco Gold calipers but I found no difference between those and the aftermarket castings other than their paint scheme.
The PPV rotors have holes machined into the hat for additional cooling. The catalog leads one to believe they might not fit but I can assure you they will.
AC Delco and Power Stop sell a slotted rotors but I’m very careful about slotted rotors. The last set I bought immediately warped on me. I’m told much of the industry went to cast rotors which could be the issue there. If you can confirm the slotted rotors are not cast then they maybe okay.
Rebuilding Calipers
Rebuilding used calipers
Few quick notes here. I thought I could get the GM OEM original castings for cheaper by purchasing them from a junkyard.
The the ones I bought were on discount because they were rusted. I got both shipped to me for $85, well under half price. With rebuild kit (seals) it was close to half price. It took forever to clean them up which probably wasn’t worth my time.
The only difference I saw with the top shelf AC Delco Gold brake calipers was the paint scheme. I was able to get that same paint scheme. If you figure that in, I got a screaming deal.
I used a enamel paint with high ceramic content. The ceramic is for heat resistance. The Enamel apparently is more resistant to brake fluid. Researching parts store caliper paint I noticed it’s an enamel based.
This paint is not 100% resistant so BE careful when bleeding your brakes! Also if you paint them you’ll want to let the paint cure for a GOOD week prior to install.
Part numbers
They stopped making the GMT800 truck chassis in 2006. That makes these trucks all well past due for new brake fluid and brake hoses.
I couldn’t recommend Classic Tube enough. They have a steal braided brake hose kit that’s direct fitment for our trucks. I highly encourage this upgrade when you change your hoses out. Then I used a 2011 Tahoe as a catalog index to purchase pads, rotors, and rebuild items for the calipers.
Shopping list:
- Classic Tube brake hoses (lookup for your year)
- GM PN 85569601 Front Left Caliper
- GM PN 85569602 Front Right Caliper
- 18K17004 Caliper Bracket Bolts
- BD180409E Wagner PPV Rotors
- Wagner OEX1363 Ceramic Pads
No compromises list (stop FAST but chews up rotors)
- 18A1705SD AC Delco Slotted Rotors (note non PPV style)
- 17D1367SDH AC Delco (Metallic Pads)
- Same calipers, bolts, & hoses as above
Note: Not going over caliper rebuild parts. They’re stupid simple to rebuild but some brevity in this post.
Concerning non-OEM, I’m not a big fan of aftermarket parts. Researching these you can see the same casting numbers from AC Delco to off label are all the same! I found many people who purchased off label and used them with no issues. The only authentic OEM ones are the part numbers I’ve listed and used myself which I don’t think they’re making anymore.
Brake Performance (conclusions)
GMT900 Brake setup installed on knuckle.
In testing, I have some concerns about induced oversteer as anyone should! However, I press on the brakes hard and haven’t been able to induce an oversteer condition yet.
I did try aggressive braking while entering a corner which was scary! I think even an OEM setup would be tricky there too, as our trucks aren’t much optimized for high speed cornering. The real test would be snow and ice though which I don’t have access to in the Sonoran Desert where I live.
With normal braking as in traffic, the brakes feel a bit improved. Under aggressive braking they clearly provide more authority. I’d describe the factory GMT800 brakes as lazy, perhaps spongy. Press this setup with GMT900 brakes aggressively and you feel the truck fighting to stop.
I’d imagine a metallic pad would greatly improve step in response. I’m using ceramic and the initial bite isn’t that hard but gets progressively better with more brake pedal pressure.
I have yet to find the correct dust sheilds, although I’m not in a great hurry because swapping them will be a ROYAL PITA. It requires unbolting the hub, and axle, possibly also separating the control arms. YUCK, I can see why nobody else I talked to had bothered doing that.
Related platforms
This project isn’t limited to my my 2001 Chevy Tahoe. It should work on any of the following so long as you have the smaller 12″ front brake rotor. Otherwise, probably not worth it if you already have 13″ rotors.
Most if not all the GMT800 Suburban, Tahoe, Denali, Yukon, Escalade have the 12″ rotors
Years 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006
Most of the GMT800 Pickup trucks seem to already have the 13″ front brake rotor but if they don’t this would be a viable upgrade.
Suspension specifically steering knuckle maybe different on the two wheel drive variants. You’ll need to research that more as my scenario involves a four wheel drive suspension.
Rumor has it these brakes may also work on the GMT400, that’s the model before the GMT800 years listed above. Let me know if you’ve done that swap and how it worked out.
Feel free to message me with questions.
