Installing the iBooster

The difficulty of installing the iBooster from a Tesla in your non-Tesla car van vary per model. In modern cars that already have an integrated master cilinder / vacuum booster setup and four disc brakes it might be a more or less a drop-in replacement. Often older cars require more modifications.

iBooster dimensions and bolt pattern

Nowadays there are two versions available of the iBooster by Bosch, GEN1 and GEN2. The GEN1 is typically found in the Tesla Model S and the GEN2 in the Tesla Model 3. Both master cilinders have a bore of 26 mm and the brake nuts used are M12x1 (tightening torque 16 Nm). It is a staged master cilinder connecting to the front and rear brakes (see below). In my setup the pedal travel resulted in a 15 cm3 brake fluid volume displacement. In the below sections you will find the differences between the two generations of iBoosters.

GEN1 iBooster

The GEN1 iBooster weighs 5 kg. The length of a Tesla Model S version from flange to the end of the reservoir is 32 cm. Center to top is 12,5 cm and to bottom is 9 cm. Overall width is 15,5 cm (center to ECU edge is 8,5 cm). The booster can be rotated to align the ECU either at the right or left hand side.

The bolt pitch for the mount is 72 mm and M8 bolts are used. A 3mm mild steel GEN1 Tesla iBooster weld adapter is available. Or fabricate your own.

Furthermore an iBooster GEN1 connector kit is available and ins and outs for wiring can be found in the “Wiring the Tesla iBooster” blogpost.

GEN1 iBooster mount pattern 1

For my 1967 Volvo Amazon I developed a mount using an old original master brake cilinder, some tube and the above weld adapter for installing the iBooster. Due to the weight of the brake booster I did add an additional mount at the front.

You can contact me if you need any custom solution like this.

GEN2 iBooster

The GEN2 iBooster weighs 5 kg and the length from flange to the end of the reservoir is 39 cm but to the end of the master brake cilinder only is 24 cm. Center to top is 10 cm and to bottom is 16 cm. Overall width is 19 cm but keep in mind the ECU orientation is a bit odd.

A connector kit is available from EVcreate and ins and outs for wiring can be found in the “Wiring the Tesla iBooster” blogpost.

GEN2 iBooster
Gen2 iBooster mount flange
Measurements taken from a Honda Accord Gen2 iBooster and validated.
Tesla Model 3 iBooster Gen2 flange
Measurements taken from a Tesla Model 3 Gen2 iBooster.
Flange Gen2 iBooster Peugeot and Citroen DS7
Measurements taken from a Peugeot 3008 Gen2 iBooster (also expexted to be valid for the Citroen DS7).

Push rod considerations

The iBooster as an onboard travel sensor. In failsafe mode (i.e. without correct CAN inputs from the car) the travel sensor is used to determine the level of assists. This is why the iBooster is so popular in stand-alone implementations. While studying an iBooster Gen1 I noticed that after enabling the iBooster with a 12V+ ignition signal (details in Wiring the Tesla iBooster) the iBooster starts calibrating.

When the calibration fails you will hear a rattling noise from the iBooster. This tends to happen when there is no pressure on the push rod. Once there is a slight pressure on the push rod (does not need to be depressed), calibration should be successful.

The noise could be a ‘sensor out of range’ issue and could perhaps also occur at the other end of the measuring range. So make sure the pedal leverage and thus maximum push rod travel matches the iBooster maximum travel.

Brake line size

Tesla and many other manufacturers who use the iBooster in their cars (see also Other iBooster donor vehicles) use large 6,25 mm brake line. In older cars 3/16″ or 4,75 mm is more common. While there are brake line nuts available that fit both the M12x1 thread in for example the Tesla master cilinder and are suitable for 4,75mm brake line, I would not recommend this. The seat is intended for a much bigger flare. You can for example use M12x1 to M10x1 reducers and from there use M10x1 brake nuts for 3/16″ or 4,57 or 5mm brake line.

Brake fluid reservoirs

Sometimes it is really tight so the original brake fluid reservoir does not fit. The reservoirs on many cars such as the Tesla Model X, Model 3 and Volkswagen have odd shapes anyway.

There are two interesting alternatives that I know of:

Honda CR-V

This is what I referred to as the ‘remote reservoir’.

used remote brake fluid reservoir

Model year I filtered on is 2007 – 2012.

Most of the time using the part number for the master cilinder 0204y24357 results in usable hits.

The small reservoir fits into the Gen1 and Gen2 master cilinder so you don’t need the actual Honda master. Do make sure the rubbers and locking pin are included.

The connector for the brake fluid level sensor is the Sumitomo HX040 series.

Remote reservoir brake fluid sensor connector

Keying is tricky. The correct one is 6189-0891

Mini / BMW

And sometimes you just want a compact reservoir. The reservoir is for example found on the BMW F40 and the Mini F56.

Compact brake fluid reservoir from a Mini or BMW.

Shown on a Gen 2 iBooster (from a Tesla Model 3)

Compact brake fluid reservoir on Gen 1 iBooster

Shown on a Gen 1 iBooster (from a Volkswagen)

Found when searching on part number 0204794060.

Brake fluid sensor connector of the compact reservoir I don’t know anymore.

iBooster in cars with rear drum brakes

When installing an iBooster in a car that originally has rear drum brakes often some more modifications are needed. Master brake cilinders for cars with (rear) drum brakes have an internal residual valve. Master brake cilinders for cars with four discs don’t or one with less pressure. Therefore adding an inline 10 lb residual valve is recommended.

It prevents the drum brake springs to retract the brake shoes all the way back and thus reduces pedal travel and improves brake pedal response feel. Both position A and B in the below diagram are valid for the residual valve.

Brake layout schematic with residual valve and proportioning valve

The above diagram also shows the Wilwood combination proportioning valve (260-11179). It features a knob that allows you to adjust (reduce) the rear brake pressure. This helps in fine-tuning your brakes as most stopping power should come from the front wheels.

The Wilwood combination proportioning valve (260-11179) also features a 1/8-27 NPT port and by default holds a brake light switch. However the port can also be used to hold a pressure transducer (via an adapter).

Wilwood proportioning valve 260 11179 with pressure transducer
Wilwood 260 11179 drawing

In many controllers or vehicle control units, the signal from the brake pressure transducer can be used to activate regenerative braking when hydraulic braking is used.

Wrap up installing an iBooster

In conclusion I prefer the GEN1 iBooster due to the more convenient dimensions and brake fluid reservoir orientation. However given the number of Model 3’s currently being produced by Tesla the GEN2 might become more easily available. Looking forward to hearing your implementation stories in the comments.

Thoughts on special implementations

In case you do not have room for implementing the iBooster in line with the brake pedal push rod you could consider a hydraulic master/slave remote setup. This typically applies to cars with a remote vacuum booster or no booster at all. Or if you need to create space for battery boxes.

Blog series on power brakes

  1. Vacuum assisted power brakes
  2. Electric power brakes
  3. Installing the iBooster
  4. Wiring the Tesla iBooster
  5. Performance test of the Tesla iBooster
  6. CAN control of the iBooster
  7. Other iBooster donor vehicles

23 thoughts on “Installing the iBooster”

  1. Thanks for the information, I was wondering what bore Bosch master cylinder was on the Tesla. I recently discovered the 2018 and up Honda Accord also used the Bosch iBooster Gen 2.

    Do you have a measurement of the mounting studs the master cylinder uses? I am looking into being able to use a whole Wilwood brake set up with master cylinder

  2. The iBooster master cylinder uses a M12x1 6.25 mm line DIN/ISO/bubble flare? The M12x1 to M10x1 reducers you have interface by bubble flare on both the male and female sides? I believe the brake lines on my car that go from the master cylinder to the ABS pump are M10x1 4.75mm SAE/double/inverted flare. So I am thinking I need M12x1 to M10x1 reducers with bubble on the male master cylinder side and double/inverted flare on the brake line female side.

  3. Hi, looking for dimensions if that’s okay. On the Gen1 iBooster, the standard firewall mounting flange seems to be a separate part which itself is mounted to the iBooster body with two bolts. Do you know whether this is the correct interpretation (i.e. can the flange be removed by un-doing those two screws without the booster falling apart in other ways), and if so, what is the bolt spacing and type of those two bolts? Any chance of a photo of the flange removed?


  4. On the prop valve diagram above it shows that the rear outlet on the master cylinder is for the front brakes and the forward outlet is for the rear brakes. Just confirming that’s accurate?

    • Thanks for checking. It’s an example, not intended as accurate for your setup or any setup.
      As fase as I know there is no consensus on what outlet should be connected to what brakes.
      Especially since many vehicles use a dual / triangle system.

  5. Lars, I’m putting a gen 1 booster in the car I’m building in my garage. I plumbed the brake lines to the proportioning valve, and then the abs pump, then the disk brakes. I have the car on jack stands without the wheels rotating. When I press the pedal, I get a pulsating from the ibooster at about half stroke and more. Could you offer suggestions on what to change? Thank you.

    • What a cool car!
      Myself I’ve only experienced this pulsation at IDLE but I’ve heard more occasions of the same issue during or at the end of the pedal travel. My current understanding is that this may be some kind of ‘pedal travel sensor out of range’ issue.
      If you press the brakes a second time quickly after the first time, is the pedal then higher up and does the pulsation then disappear?
      If you have drum brakes (at the back), have you added a residual pressure valve? Otherwise too much brake fluid displacement might be needed (to first bring the brake pads to the drums since these are pulled back by the springs without such a valve).

  6. Lars, I watched the video and I was double checking that I had the wiring of the 26 pin Bosch connector on the ibooster ECU hooked up correctly. I have an extra 22 gauge black wire on position 15 that doesn’t show up in the online searches. I’m curious to know if this is preventing the startup calibration, because initiating 12v on pin 20 doesn’t do anything different audibly, and I get boost without it. I may have to see if the Honda guys know about how that wire is used. It will be interesting to see their response when I tell them my car has a CRV booster, but it isn’t a CRV.

    • Hi Dan,
      I’ve done some research. Unfortunately I cannot find a wiring diagram of a 2018 (ish) CR-V with an iBooster. Apparently there also is another type of electric brake booster used in the Honda CRV in those model years. What I learned from how this one is wired it is woken up when someone opens the drivers door. So you can perhaps try the following:
      – Power the iBooster with 12V but not the ignition input
      – After that connect that mystery wire to ground and see what happens (perhaps / hope it does the calibration)
      – After that power the ignition input
      My theory is that if for some reason (ie missing that door open signal or pedal pressed at idle already) the iBooster cannot do the calibration it may assume a default value and that does not match with your installation and thus you get the ‘out of range’ shuttering.

      What you could also try is to disconnect your brake pedal and put slight pressure on the rod like in my video. Perhaps the idle pedal position is wrong. But I’d first test the above with that mystery wire.

      • Hi Lars,

        I also have a Gen1 ibooster out of a CRV – looking to fit it into a 1973 VW Bus Type 2. :Like Dan above there is an extra small black wire. When I power the unit up, I get a clicking of the pinion/pushrod assembly. I’ve tried slight and major pressure on the pushrod – but still clicking. I also experimented with grounding the small black wire (as suspected door signal) but no difference (suspect this may be a ground for the CAN system). My best guess is that the position sensor is faulty OR the calibration is extremely sensitive to pushrod positioning.

        • Maybe in that case the sensor is faulty. Next to door open, I’ve also seen extra wires for brake light. But can indeed also be a CAN ground if they use isolated transceivers.
          ps. Do not try to adjust the sensor. I did and it looks like it solves the issue but in the end it was on the edge of triggering braking so no good.

  7. Wonderful site!
    Can you tell me the size of Gen2 Booster from center (push rod) to the right? I want to install an V6 engine in my car instead of an R6. I am missing space there. Thanks!


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