P38 Calipers on a D2?
 

Wondering if anyone has looked into this. The P38 front calipers have 48mm pistons and the D2 have 45mm ones. My P38 stopped way better than my D2. I know that the P38 barking system is unique but ultimately it still delivers fluid under pressure to the calipers.


On my D2 I have slotted and vented discs with Akebono ceramics all around, stainless lines, and the system has been completely bled but the brakes could still be better. When I stomp on the pedal I can get the ABS to kick in for the rear brakes on wet pavement but the fronts aren't close to locking up. I know that the larger tires make extra work for the brakes and D2's aren't known for good brakes to begin with. In pictures the calipers don't look that different between the P38 and the D2 but I have never held them side by side.

Not sure where you're getting the 45mm vs 48mm but D2 and P38a both have used the same front calipers at some point whether it be STC1915 or STC1916 or STC1917.

The parts listings are way too confusing for these vehicles. I see the P38 and D2 interchange on some sites and not others, some use a different part number for the 2004 D2, some of the rebuild kits only fit through 2002, etc. I think I found where the bust is. Based on the TRW catalog, the diesel D2 may have been fitted with front calipers with 45mm diameter pistons while the petrol D2's and the P38's had 48mm pistons. The spec sheet I saw for the D2 calipers must have been from the diesel one and not necessarily been correct for all D2 calipers. That kinda sucks because I was hoping it would be a quick way to add another 14% of clamping force on the pads.


I'm just really unhappy with the brakes on this rig. To me, any vehicle should have brakes powerful enough to lock up the wheels on wet pavement. With ABS, there is no concern for loss of control in panic stops so why not. My company truck is a Ford F250 crew cab super duty and the brakes in that behemoth even with 1,500 lbs. in the bed make the D2 look like it's fitted with a set of cantilever brakes with old shoes.

Well there was a brake switch for the 03-04 D2s, but now all parts superseded to 1 part number for both. I agree, it is very confusing.

I hear you though, they leave something to be desired. I go from my S60R with brembo 4 pistons all the way around to the rover and just weep a bit.

I recall someone mentioning that there's a difference between the 99-02 and 0304 DII calipers, but was never able to find out/verify what.

As near as I can tell, the change between 2002 and 2003 was from the caliper having the word "Lucas" cast into it to having "TRW" cast into it.


I checked the specs on calipers from other Land Rover vehicles and the fronts use the same 48mm diameter pistons on the LR3, Range Rover and Range Rover Sport. The Range Rover Sport SC uses Brembo calipers but they won't fit inside a 16 inch wheel. Overfinch used to offer an upgrade kit for the P38 but I believe that only worked with 18 inch wheels and it is no longer available and was outrageously priced anyway.


The trick will be finding a caliper with slightly larger diameter pistons that can be adapted so that the stock master cylinder moves enough fluid to activate it without going to the end of its travel.

I hope you will continue to look into this because its very interesting and I'd love to upgrade my brakes further! I read somewhere that the late 03/04 models received slightly improved brakes over the early D2 models. Think I read that in this book: You and Your Land Rover Discovery: Buying, Enjoying, Maintaining, Modifying by Dave Pollard | Barnes & Noble

Right now I'm using the basic brake rebuild kit from AB to get me through the winter, but I plan on upgrading to the slotted/drilled rotors and ceramic pads in the spring. That combined with the SS brake lines I expect my braking might improve? Or will it be the same?

Keep us posted if you find anything.

Clamping force will be the same, perhaps a bit better with the new brake lines. Ceramic pads and slotted/drilled rotors really just let heat escape quicker, which is only a problem at a track or with tons of downhill braking.

I think you've hit the nail squarely. Often upgraded pads are great for performance on the track but for intermittent braking on many road vehicles they don't generate sufficient heat fast enough to 'bite', coupled with crossed drilled and slotted discs which dissipate heat, the heat generated is never sufficient. In racing where there is constant heavy breaking one tries to reduce brake temperatures and effect cooling whereas the reverse is applicable on the public highway (consider how often one breaks on an out of town highway - not often). My guess is the ceramic pads are too hard for the application whereas softer pads would probably work better. This is probably why the front ABS won't activate as there is insufficient heat to lock the front brakes and the fronts do by far the most work in any vehicle.

If one extrapolates this to the end, think of the F1 cars and MotoGP bikes with carbon/ceramic brakes, under normal road and town use they would probably be incapable of out braking a peddle cycle.

The Akebono ceramic pads I installed are the same ones everyone seems to install on these trucks. They are not a race pad. They are likely very similar in composition to the OEM ceramic pads on most new cars so they don't require high heat to bite. My F250 has ceramic pads all around and the brakes are amazing.


Regarding the rotors, slots and dimples (or holes) primarily allow the gases generated across the face of the pad to escape which can help with braking. During braking the pads get hot and any organic matter in them (like what is binding the pad together) turns into a gas. Any gas between the pad and the rotor surface reduces the amount of contact because you are just compressing the gas. The venting of rotors is the main source of cooling, not slots and dimples. You don't really pick up much surface area with the slots and dimples. Of course, if you sweep out the hot gases before the heat is transferred into the rotor then you will improve cooling indirectly.


I realize that typically such measures are of greater benefit on a performance car but I went with the better rotors to try and get these brakes to work as best as they could. I don't agree that the setup I'm using has reduced my braking power. It stops better than it did with the OEM pads (clamping DBA rotors) it had on it when I bought it, but I would like better.