Brake Rotor Upgrade

[Jonnyslim]

Hi All,

I am looking to upgrade my pads soon on my 21 3.5 SCREW. I was looking at the factory brake specs for 2021 and it looks like the primary difference between the standard HD brake spec and the Max Brake spec is rear 350x24mm rotors. The pads and calipers look to be identical through the spec range.

As I do a rotor/pad replacement would it stand to reason I could upgrade the rears to the larger rotors using stock calipers? Has anyone else done this modification?

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[Jonnyslim]

Alot of views but nobody seems to know an answer. To me it seems like it could work, maybe there is a Ford tech on the forum who knows?

 

[Gros Ventre]

While my truck was up on a lift I inspected the brakes. Given that the caliper is identical as appears above, the only difference between the front and rear brakes was the disc thickness and possibly the diameter. I didn't measure the diameter, so look above.

 

[HammaMan]

The axles and caliper mounting brackets are different. That disc offers marginal gains at best. Aftermarket options are limited due to the popularity of smaller wheels (brakes are as large as they can be for 18" and under wheels). If someone made new larger diameter rotors with 'new' caliper mounting brackets, that'd be rather attractive if priced appropriately by retaining factory calipers which are more than adequate.

 

[HammaMan]

I'd say there's a 70% chance of it fitting (350mm rotor on rear in place of 336 rotor). The actual specs vary a bit from ford's literature.... 2.85mm thickness

 

[Jonnyslim]

I will probably end up getting a set of 336 and 350s just to try it. I'm not ready to do brakes just yet but probably just before summer.

Once I do I will report back.

 

[Gros Ventre]

Looking more closely at the above, the rear disc has a larger diameter by 14mm. So the axle mount points may not be properly located even though the caliper appears to be the same. Also the Standard axle has a lower rated parking brake. My gut reaction to these differences says you may have to replace the axle itself to get where you want to go.

 

[nitrobass24]

Call me stupid but if you are using the same calipers and pads, the contact surface area will be same, so how would get improved braking performance?
If anything you are just adding unsprung rotating mass to rear axle.

 

[HammaMan]

Call me stupid but if you are using the same calipers and pads, the contact surface area will be same, so how would get improved braking performance?
If anything you are just adding unsprung rotating mass to rear axle.

Indeed, without moving the pads out a bit to take advantage of the larger diameter the gain is zero.

It's why I'm surprised that someone doesn't just make larger rotors and new caliper mounting brackets to move the calipers further out. This would work by increasing the authority the calipers have by extending the moment arm. If someone were to make 400mm rotors while retaining the same calipers, braking would increase by 8% just in the additional authority. When combined with the larger surface area, there's cumulative effects by needing less heat for the same braking force, while also providing a cooler rotor for a given brake amount. Combine that with a higher friction pad and braking could be improved just over 30% while reducing brake fade due to better cooling, all while retaining factory calipers. The rotors and caliper mounting brackets would come in around $1k or so while offering tremendous benefits under heavy braking.

Sure it'd only work with 20s, but most of the trucks already have them.

 

[amschind]

The only thing that upgraded rotors can do is shed gas. If you are REALLY laying on the brakes, which in these trucks means that your trailer is propelling your truck into stopped traffic and your sphincter into a degree of tightness approaching a singularity, then the brake pad will vaporize from the heat. That vapor, if trapped, will lubricate the pad and result in decreased friction or "fade"; the braking force will decrease right when you need it most. Pads are much better at avoiding that today, but slatted/cross drilled rotors give the gas somewhere to go. Likewise, pads can provide more stopping power, but usually at the cost of reduced performance when the pads are cold. The Powerstop kits are matched pads and rotors and pretty affordable.

 

[Gros Ventre]

Call me stupid but if you are using the same calipers and pads, the contact surface area will be same, so how would get improved braking performance?
If anything you are just adding unsprung rotating mass to rear axle.

Given the Ford Information... The improvement in braking comes from the greater heat dissipation capability of the larger disc coupled with the greater swept area of the pads. Don't discount the heat dissipation factor.

 

[Jonnyslim]

Great insight from everyone. Im new to F150's and just coming out of a VW Touareg, which had excellent brakes, even on a 5000 lb vehicle. I was looking to maximize stock performance on the new truck and this looked this might have been an easy way to do it.

The current performance seems fine but for vehicles who's real purpose is for towing and hauling, they could probably be a little better.

In my experience, using semi metallic pads really helps with performance on their own. I can live with the brake dust.

 

[nkyhunter]

Hi All,

I am looking to upgrade my pads soon on my 21 3.5 SCREW. I was looking at the factory brake specs for 2021 and it looks like the primary difference between the standard HD brake spec and the Max Brake spec is rear 350x24mm rotors. The pads and calipers look to be identical through the spec range.

As I do a rotor/pad replacement would it stand to reason I could upgrade the rears to the larger rotors using stock calipers? Has anyone else done this modification?

so what was the outcome of the size of the front and rear rotors?

 

[Calson]

Performance depends on the rotors and the pads and the calipers. My Chevy truck had warped rotors at only 28,000 miles. I replaced them with aftermarket racing grade components which did not cost all that much more than buying GM parts and the labor was the same either way. Brakes were in great shape when I sold the truck with more than 170,000 miles on the odometer. The brakes are an easy place for auto manufacturers to cut corners and save a few dollars.

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