• Sign Up! To view all forums and unlock additional cool features

    Welcome to the #1 Explorer ST Forum and Explorer ST community dedicated to Explorer ST owners and enthusiasts. Register for an account, it's free and it's easy, so don't hesitate to join the Explorer ST Forum today!


GT500 front brake upgrade

Messages
57
Reactions
46
Points
17
Location
Nashville, TN, USA
Vehicle
2021 Explorer ST
#1
I bit the bullet and did the GT500 front caliper/rotor upgrade. Here’s what I learned, in no particular order:
1) This is almost entirely a direct bolt on using the brackets from Tony Hernandez
2) The only modification needed is trimming the backing plates slightly to clear Tony’s brackets. I used a cutoff wheel on a grinder, but tin snips would work too. You could also leave the backing plates off altogether if you wanted, as they are massively undersized with the new 16.5” front rotors
3) You will need at least 1.25” spacers with the 21” wheels to clear the calipers, or aftermarket wheels with a similar offset to what you gain with the spacers. 20” wheels are a non-starter, as would (I assume, but haven’t tested to confirm) less than 1.25” spacers with the factory 21” wheels
4) To do the ungrade you’ll need rotors, calipers, GT500 pads, GT500 banjo bolts, the four GT500 caliper bolts pads plus Tony’s brackets. You will reuse your existing ST brake lines, although I’d recommend fresh crush washers
5) If you’re buying new calipers don’t forget that you’ll also need two of the caliper retainer kits (KR3Z-2069-B)
6) I purchased the GT500 calipers and rotors off a car with 25K miles. I was fortunate in that the calipers came fully loaded with the pads, retainers, and GT500 brake lines which is where I got the GT500 banjo bolts. I paid $900 for the calipers/rotors plus shipping
7) The GT500 rotors looked good, but since I hade time I had O’Reilly’s turn them just to make sure everything was fresh. The rotors were the limit of what their lathe can do. They charged me the rate for the truck rotors which I half thought about calling them on since these are technically car rotors, but they’re truck-sized I guess so that’s fair
8) While I was doing the upgrade, I took the opportunity to do the Racing Brake braided lines and flushed the system with fresh fluid
 

OP
THNX SVT
Messages
57
Reactions
46
Points
17
Location
Nashville, TN, USA
Vehicle
2021 Explorer ST
Thread Starter #2
Pictures of the original calipers and rotors as compared to the GT500 stuff. The stock front calipers look comically small compared to the GT500 calipers. Stock rotors are 14” vs 16.5” for the GT500
 

Attachments

OP
THNX SVT
Messages
57
Reactions
46
Points
17
Location
Nashville, TN, USA
Vehicle
2021 Explorer ST
Thread Starter #3
Pictures of the trimming that I did to the backing plates. I originally did not do this as Tony’s brackets just barely push into the backing plates, but that minor amount was still enough to push the backing plates into the rotors until I trimmed them.
 

Attachments

OP
THNX SVT
Messages
57
Reactions
46
Points
17
Location
Nashville, TN, USA
Vehicle
2021 Explorer ST
Thread Starter #4
Final result plus a few glamor shots of the brakes
 

Attachments

OP
THNX SVT
Messages
57
Reactions
46
Points
17
Location
Nashville, TN, USA
Vehicle
2021 Explorer ST
Thread Starter #5
This can get expensive when buying everything new, but here are the part numbers for anyone that would like to go that way:
GT500 adapter brackets from Tony Hernandez (mofospeedengineering@gcom)
GT500 left caliper (KR3Z-2B121-C)
GT500 right caliper (KR3Z-2B120-C)
GT500 left rotor (KR3Z-1125-F)
GT500 right rotor (KR3Z-1125-E)
GT500 brake pads (KR3Z-2001-C)
(4) caliper bolts (W717394-S439)
(2) caliper/pad retainer kit (KR3Z-2068-B)
(2) GT500 banjo bolts (W712276-S430)
(4) GT500 crush washers (W711784-S300)

Optional: Braided front brake lines. This will likely come with new banjo bolts and crush washers, but those are meant for stock ST calipers which are a different thread size and pitch. If you contact Racing Brake they might be able to substitute in the GT500 banjo bolts and washers.
 

Last edited:

2020FordRaptor

1000 Post Club
Messages
1,227
Reactions
591
Points
162
Location
Nevada
Vehicle
'20 Raptor, '22 Explorer ST, '14 GT500, '03 F150
#6
This is the best writeups for this brake swap! I love the look of that wheel setup! Also, you can fit 20” wheels but like you said spoke clearance would need to work. They look awesome! Been trying to find some photos of them on with stock wheels. I wish they would fit with just 1” spacers like the GT350 swap but oh well.
 

Messages
186
Reactions
95
Points
27
Location
30122 Woodward Ave
#7
Any chance you did before and after brake testing maybe 60-0 or 100-0 or overall feel between the two setups. Awesome write up.
 

I Bleed Ford Blue

Active Member
U.S. Navy Veteran
Messages
737
Reactions
508
Points
182
Location
Ohio
Vehicle
23 Rapid Red Explorer ST
#8
You should seriously consider the racing brake rear brake upgrade. With the huge GT500 brakes up front and the factory street pack rears your brake system is going to be unbalanced.
 

Messages
297
Reactions
175
Points
37
Location
San Francisco
Vehicle
2022 ST
#9
You should seriously consider the racing brake rear brake upgrade. With the huge GT500 brakes up front and the factory street pack rears your brake system is going to be unbalanced.
Absolutely right. I would not run a system so wildly unbalanced.
You might as well have stock fronts with read drums... :LOL:
 

I Bleed Ford Blue

Active Member
U.S. Navy Veteran
Messages
737
Reactions
508
Points
182
Location
Ohio
Vehicle
23 Rapid Red Explorer ST
#10
Even with the racing brake rears, the biggest I would go is the GT350 fronts at 15.5" Any bigger than that and you still will be unbalanced.
 

Messages
297
Reactions
175
Points
37
Location
San Francisco
Vehicle
2022 ST
#11
Even with the racing brake rears, the biggest I would go is the GT350 fronts at 15.5" Any bigger than that and you still will be unbalanced.
Listen, this all solved if you do GT350 Fronts, as rears, with GT500 fronts. :geek: :ROFLMAO:
 

2020FordRaptor

1000 Post Club
Messages
1,227
Reactions
591
Points
162
Location
Nevada
Vehicle
'20 Raptor, '22 Explorer ST, '14 GT500, '03 F150
#12
Absolutely right. I would not run a system so wildly unbalanced.
You might as well have stock fronts with read drums... :LOL:
Yah but the GT500 brakes look so good! Also, it has to be better than the stock system.
 

2020FordRaptor

1000 Post Club
Messages
1,227
Reactions
591
Points
162
Location
Nevada
Vehicle
'20 Raptor, '22 Explorer ST, '14 GT500, '03 F150
#13
Listen, this all solved if you do GT350 Fronts, as rears, with GT500 fronts. :geek: :ROFLMAO:
There would be no use doing that, although it’d be awesome. 70% of braking is done in the front so the rears would be locking up and tripping ABS from my understanding.
 

2020FordRaptor

1000 Post Club
Messages
1,227
Reactions
591
Points
162
Location
Nevada
Vehicle
'20 Raptor, '22 Explorer ST, '14 GT500, '03 F150
#14
You should seriously consider the racing brake rear brake upgrade. With the huge GT500 brakes up front and the factory street pack rears your brake system is going to be unbalanced.
Even with the racing brake rears, the biggest I would go is the GT350 fronts at 15.5" Any bigger than that and you still will be unbalanced.
Sure it is unbalanced but it’s better than the stock system I am sure. Our S197 GT500 had large 6-piston brakes up front and simple 1-piston rears. I understand a more balanced system is better for braking but this upgrade can’t be horrible. Also, Tony is working on a Dark Horse rear brake upgrade.
 

Messages
297
Reactions
175
Points
37
Location
San Francisco
Vehicle
2022 ST
#15
There would be no use doing that, although it’d be awesome. 70% of braking is done in the front so the rears would be locking up and tripping ABS from my understanding.
I'm just making jokes.
Hell, in this GT500 fronts / street package rears setup the front is doing 90%... :ROFLMAO:
The balance just isn't there.
If you are that off-balance you can cause some serious braking issues. In low-friction scenarios like water/snow/ice/mud, the inherent nose-diving is going to cause an accident.
You will also be wearing out and breaking the front suspension way faster. Hell, you might even actually need the upgraded front sway bar in that scenario.

The real balance would probably be the street package fronts as rears with the GT500 fronts.
 

2020FordRaptor

1000 Post Club
Messages
1,227
Reactions
591
Points
162
Location
Nevada
Vehicle
'20 Raptor, '22 Explorer ST, '14 GT500, '03 F150
#16
I'm just making jokes.
Hell, in this GT500 fronts / street package rears setup the front is doing 90%... :ROFLMAO:
The balance just isn't there.
If you are that off-balance you can cause some serious braking issues. In low-friction scenarios like water/snow/ice/mud, the inherent nose-diving is going to cause an accident.
You will also be wearing out and breaking the front suspension way faster. Hell, you might even actually need the upgraded front sway bar in that scenario.

The real balance would probably be the street package fronts as rears with the GT500 fronts.
I’m not denying that there is unbalancement there, it just isn’t horrible unless you’re racing and the best braking distance is needed. It’s better then the stock brakes is all I am saying.
 

OP
THNX SVT
Messages
57
Reactions
46
Points
17
Location
Nashville, TN, USA
Vehicle
2021 Explorer ST
Thread Starter #17
Any chance you did before and after brake testing maybe 60-0 or 100-0 or overall feel between the two setups. Awesome write up.
Sorry, no before/after tests as far as different stopping distances. Feel wise, the new brakes feel a bit more firm which could partly be the hoses. The GT500 setup doesn’t feel as wild as you would expect in normal driving.
 

OP
THNX SVT
Messages
57
Reactions
46
Points
17
Location
Nashville, TN, USA
Vehicle
2021 Explorer ST
Thread Starter #18
I’ll do the rear upgrade when someone comes up with a way to do it cost effectively. To me, I can’t see paying a minimum of $1700 for just a pair larger rear rotors and brake caliper brackets, but am hopeful someone will come up with an setup for the rear that uses OEM components of some sort to make the kit more reasonable.
 

OP
THNX SVT
Messages
57
Reactions
46
Points
17
Location
Nashville, TN, USA
Vehicle
2021 Explorer ST
Thread Starter #19
Sure it is unbalanced but it’s better than the stock system I am sure. Our S197 GT500 had large 6-piston brakes up front and simple 1-piston rears. I understand a more balanced system is better for braking but this upgrade can’t be horrible. Also, Tony is working on a Dark Horse rear brake upgrade.
Yes, lots of concern from people with the front/rear not feeling balanced. From what I can tell the brakes feel great both at threshold braking and beyond where I’ve purposely engaged the ABS.
 

OP
THNX SVT
Messages
57
Reactions
46
Points
17
Location
Nashville, TN, USA
Vehicle
2021 Explorer ST
Thread Starter #20
This is the best writeups for this brake swap! I love the look of that wheel setup! Also, you can fit 20” wheels but like you said spoke clearance would need to work. They look awesome! Been trying to find some photos of them on with stock wheels. I wish they would fit with just 1” spacers like the GT350 swap but oh well.
Thank you for your appreciation and good call on the 20” wheels maybe being a possibility. With how tight things seem with the 21” wheels I didn’t see how the 20” wheels would be an option, but I suppose that’s possible since the GT500 comes with 20” wheels so the rotors/calipers could fit. Someone is welcome to figure out that part along with what spacers are needed to make that work. I’m sure aftermarket 20” wheels would have a better shot of fitting well too.
 



Top