The best part about having a lift is finding new ways to keep your car on it. The original transmission went out and my car spent about 9 months on the lift while I gathered all the parts to repair and improve it to my liking. Drove it for all of a week until it was back on the lift for a plethora of suspension and chassis upgrades. That was another 9 months ago… Planned on having it back on all fours 2 weeks ago but, as luck would have it, I screwed up the brake booster while messing with it. In my typical fashion of "even if it doesn't break, dump a bunch of money into it until I have created a dealer tech's worst nightmare," I decided to install a Bosch ibooster from a 2019 Tesla model S.



This is ongoing and I'll be sure to document as much of the process as I remember to. I think I might be the first to do this to a G37, but certainly not in general. There is plenty of documentation for this swap into other vehicles.



So, first I needed to find the 'right' ibooster. Currently Bosch is on their second generation of ibooster. Off the top of my head, gen 2 can be found in Tesla Model 3 & Y, and Honda Accords. Gen 1 can be found in Tesla Model S & X, Chevy Malibu & Bolt, and some Honda CR-Vs. Just by looking at images of each, the gen 1 seemed to be the easiest to swap due to the mounting bolts being on a separate flange piece, rather than integrated into the housing like on the gen 2. I decided on a gen 1, and based on other people's experiences I went with one from a Tesla specifically since it was the one that presented the least amount of problems (for only $100 more than a Honda one on average! The programming on the Tesla one is more DIY friendly though).



I found this one on eBay, and got lucky by finding one that still had the connectors on it (getting the connectors separately will cost another $80-200 depending on whether they are pre wired or not).




Whether this would be a tight fit or not was not an issue for my angle grinder and novice welding skills. I'm happy to report this is looking like it's going to be relatively easy to get in.




The potential fitment issues I'm seeing are going to be the 3 brake lines running overhead of the booster, and the wiring harness below. The good thing is that parallel to the firewall the ibooster has a substantially smaller footprint than the stock one. Perpendicular to the firewall the ibooster and Tesla master cylinder (MC) is about 38mm longer than the stock combo. Here's some of the measurement I've taken so far.

Stock:



thickness without MC=131mm



MC(master cylinder) protrusion length=83mm



MC bore=25.5mm



MC fitting threads=12x1



MC line spacing=41mm



MC piston resting length=42mm



OAL=214



mounting bolt pitch=60x80mm



Firewall center bore diameter=62mm



protrusion into firewall center bore=8mm



Clevis pin diameter=8mm



Mounting surface to clevis pin(adjustable. each vehicle will be different)=127mm



ibooster:



thickness without MC=155mm



MC protrusion length=97mm



MC bore=25.5mm



MC line spacing=41mm



MC piston resting length=41mm



MC fitting threads=12x1



OAL=251



mounting bolt pitch=72x72mm



Firewall center bore diameter=62mm



protrusion into firewall center bore=6mm



Clevis pin diameter=11mm



Mounting surface to clevis pin(not adjustable)=110mm




The length of the ibooster will probably be the biggest hurdle to getting this in the car. I think it will probably fit if I move the lines from the MC to the ABS module out of the way. I'm also expecting I won't be able to use the plastic cover for the brake compartment. The inclination of the stock booster from the firewall might cause an issue with the hood being able to fully close on the ibooster reservoir. It looks like I might be able to transplant the reservoir from the stock MC onto the new one. If not I will probably need a remote reservoir.



The pushrod will need to be modified as well. I sheared off the clevis from the ibooster while seeing if it could be adjusted. It can't be so it was coming off anyway. I will probably end up cutting it down a little more and welding a stud that the stock clevis will thread onto.



Most of the critical dimensions of both MCs are about the same. The Tesla MC's extra length is from having a shorter portion on the inside of the booster and the first port is farther from the booster. It's looking like both have the same stroke and displacement per inch of travel (a bit worrisome considering the car this is from weighs 1000-1500lbs more than a G37). I'll be taking some more measurements, but it's looking like this swap might be easier than I initially thought. Of course, I'm still expecting there to be some level of issue with the ABS module.



When it was still in the Tesla, the ibooster used a combination of the built-in pedal position sensor and CANBUS signals. Luckily the ibooster can run in 'failsafe' mode where it only uses the pedal position sensor to determine braking assist. This makes wiring it up very straight forward. I used 10awg wire for the 40A hot & ground, 16awg for the 5A hot, and 18awg for the 5A switched. My pedal position sensor was still wired to the ibooster ECU but, if I needed to 20awg would probably be my go to.




Judging by pressing on the pushrod with my hand, I'm guesstimating about 7:1 assist ratio when the MC is filled with fluid. Current draw is about 5A although I suppose this is irrelevant since there's no resistance from any fluid yet.




I'm also going to need a new flange to mount this to the firewall. I've seen a lot of people cut their firewall and then weld in the correct bolt pattern. No way am I doing that!




Sent it off to my 3D printer for a prototype.




Looks like it's spot on! Once I confirm the fitment on the firewall, I'll be sending the design off to be laser cut or CNC'd from a billet. CNC service will probably cost a ton more but, I'd rather go this route to save me from having to weld two half inch pieces of steel together.​​

 

Update! The ibooster is almost a drop-in fit. The clearance between the bottom/front of the master cylinder and the body is about 1cm vs the 2-3 of the stock one. The reservoir doesn't seem to cause any issues when closing the hood, but the trim pieces will need to be trimmed. I might still try transplanting the stock reservoir on, but putting the cover piece on is a no-go. I could still try to do a remote reservoir, but the booster fits so far.






Looking at the pushrod a little closer, it does appear to be threaded, but the adjuster looks like it's riveted through the center in order to keep the clevis on. Still, I couldn't get it to budge, so I'll be cutting it about halfway then welding on an M10 stud in order to reuse the stock clevis.




The new flange is being machined now and should hopefully be here in about 2 weeks. I also needed to make some new brake lines from the MC to ABS module. I’ll also need to figure out where I'm going to relocate the MAP sensor.