So I've been doing some research on the internet and found out about a guy who swapped in some rear disc brakes from a Corolla into his Prius. Those of you with some mechanical inclination, how difficult do you think this would be? I imagine most of the parts would be quite compatible, if not completely. Any thoughts? Now before anyone answers I want to make it clear that I want mechanical and technical answers. I DO NOT want any crap about how the rear drums are sufficient and how the regenerative system does most of the braking and so on. If that is all you are going to post don't waste your time and more importantly my time. :angry: I would be doing this simply becasue I could. Now, if you have something useful to post, I would be most appreciative.
yeah, it's definitely possible. costly though- can see the cost hitting upwards of 1500 because of the number of parts you'll have to replace.
okay, our movie is over. here's what he came up with that may need to be replaced. rotors calipers backing plate possibly bearing hub unit- if the offset difference changes brake lines- currently too short currently hard line, would need to go to flex line from a tech's perspective, if you have all the parts right there it shouldn't be TOO difficult. it may even turn out to be fairly easy. please report back when you do this and let us all know how it went! he's interested to hear about it. BTW, he said he did just hear that the TMPS sensors are in the wheels in the 06s. first car they've applied this to. thanks for bringing that up earlier.
Guys, this is something that I would NOT do especially for those that have active handling. I too would LOVE to have rear disk brakes just as the European cars do however let’s not forget that the computer that controls the VSC/active handling would have to be changed or re-programmed. The software algorithms that control the individually braking at each wheel would be substantially different on a rear disk brake vehicle vs. one that has rear drums. I am not saying that it is impossible but probably not financially feasible if you want to do it correctly. Thanks!! Brian BT Tech 305-652-3115
very true. good point, brian. the computer programming would definitely not match up to the disc brakes. thanks for reining in the excitement. damn.
Okay, instead of using corolla pieces why don't you just use European prius pieces and just re-flash like a UK prius or something. I was trying to figure this out as well. I see great minds want to accomplish similar things...
Hello Chris.. Sure, one can go out and get all of the parts from Germany or England to convert the rear drums to disks but we would still have to get the traction control computer as well. Generally, this computer is usually referred to as a BCM (Body Control Module) and does not usually have "flashable" ROM. The PCM (Powertrain Control Module) is what controls the engine and is OBDII compliant meaning that this IS flashable by the dealer using specialized equipment. The BCM and the PCM are 2 totally different computers. I do not have a complete working knowledge of all of the computers that the Prius uses but I am sure that there are more than just a "few"!! To make this conversion work you would have to get the European BCM and then hope that all of the inter-connects are pin to pin compatible and it is a "plug and play rather than plug and pray operation". IMO all of this work just to get rear disks is not worth the effort and expense. I will be the FIRST one to admit that the Prius SHOULD have come with rear disk brakes but honestly, the car actually brakes extremely well and I have never had an issue with fade or a lack of braking performance yet with this car. Thanks!! Brian BT Tech 305-652-3115
The computer thing is what I was worried about. ON a car with no fancy gizmos it would be pretty easy. Throw in VSC and a TCS, and that's where it's over my head. I know enough about mechanical stuff (or as my wife says, enough to get in trouble), but when you throw inproprietary ECM's and such, that's where I'll draw the line. As there is so much gadgetry that could potentially go wrong, I do think I'll hold off on this indefinitely. Maybe.
Yeah, sounds like my low-key modification approach is out as well. Like you said though, I don't drive our Prius hard enough to induce brake-fade anyway. . . . If anyone takes this on and makes it work, I would love to read about it.
Someone already did this about a year ago. Guess info may have gotton lost in the server changes. They got the disks from the European version.
Regarding problems with the Skid ECU (that's what does the braking), that all depends if the ECU learns about the braking dynamics of each wheel, or is statically coded. I would assume the latter, though there may be a static table to start with, much like the ECM (engine module) dynamically adjusts fuel volume based on sensor input. It does start with table values, which is why E85 will work, but will eventually trigger an error; the deviation is too far out from the calculated estimates. I would suspect it is dynamically determined, since brake characteristics change over time. Tires wear out, as do pads and shoes, not to mention the brake shoe adjustment deviations. After all, the car can tell what the individual wheel speeds are, so there is a closed loop feedback to work from. If you can afford the time, and can make the change reversable, give it a try. Do some controlled testing before relying on it.
I also believe that it would be a dynamic system, as vehicle loads change too. Having a single driver is different from having 5 passengers and some luggage (or any combination thereof). The braking and VSC performance would have to be different.
I too would expect that the breaking application would be dynamic and not necessarly pre-programmed based upon the type of brake system. It shouldn't be too hard to find out if the ECM or BCM part number is different for US vs JP cars. If the part number is identical then the computer(s) should not be a problem.
Can I ask a silly (and possibly obvious) question at this point? Why is it that the US cars dont have disks on the rear when it seems all the other countries in the world have them? Add Australia to the list, they are there. uA
In a car with "regular" brakes, you might also have to change out or adjust the proportioning valve, in order to balance the braking force of the front and rear brake systems. Discs usually require more pressure to activate than drums, to the balance would change. Not sure if this is all done in software in the Prius, making the above academic. IF VSC/ABS works merely by sensing yaw angle and wheel rotation (or lack of it), then it may already be self-adjusting to the greater rear braking force that discs may give under some conditions. If it is hard-coded, how would it adapt to brake fade, wear, or other changes over time? Damn, we need a complete theory of operation on this car!
The alleged reason they didn't put disks on the U.S. version is two fold. One and probably the major reason is cost, they wanted to keep their costs down so they could offer the car at a lower retail price. The second reason is they feel since we drive at slower speeds than in Europe that we didn't need the extra braking capacity afforded by all wheel disk brakes. There are probably other reasons but these are probably the tow most prominent.
