Testing the Tesla iBooster power brakes

iBooster connector kitUpdate: I opened a webshop for EV conversion parts and now offer a complete iBooster connector kit

In October I finished my power brakes 2.0 by having the Tesla iBooster ready to be mounted. At the same time I did have a lot of questions. What if it is too strong? Or not enough? Or the wheels lock up too soon? Does it need to be a diagonal split or can it also be front/rear? What are the characteristics of the main brake cylinder?

Let’s do some research.

The Tesla main brake cylinder on the iBooster is a dual type and the nuts are different compared to my Volvo.

Tesla dubbele HRC

So first I sourced these for 4,75mm or 3/16″ brake line.

The master cylinder bore probably is different.

Volvo en Tesla HRC naast elkaar

Measuring = knowing!

There are all kinds of tools to do calculations on the brakes such as this one on brakepower.com but perhaps doing some measurements is the most effective way to gain insights in the braking system. So first I got myself a brake pressure tester.


And measured the brake pressure of our daily driver Volvo Amazon. Without brake boost I reached 100 bar and with assistance up to 140 bar.

Remdruk Amazon

But that is based on “as hard as I could” pedal force. The electric Volvo Amazon wagon is from 30-06-1967 so there is no requirement for pedal force.

Pedaalkrachteis RDW

There is a general deceleration requirement of 3,8 m/s2.

Next to pressure, also the volume is an interesting parameter. This is determined by master cylinder bore and pedal travel. So I created a test setup to measure the displacement of brake fluid.

Vloeistof verplaatsing test Volvo HRC

I found a displacement of 11 cm3. In the end I could have calculated that since the master cylinder bore of 22,2 mm is known.

For the Tesla master cilinder I made some brake lines.

Remleiding felsen

And also measured the displacement.

Vloeistof verplaatsing test Tesla HRC

This is different for both outlets. Together they do 15 cm3 and I found a bore of 26 mm. That is different from the Volvo Amazon. So I will need more pedal force for the same pressure and will have more displacement. Will this be a problem?

I tried to do a pressure test, but since the pedal force is not know that does not add much value.

Drukmeters aan Tesla HRC

Is measuring knowing?

Making is knowing!

I wanted to know whether my plan works out on forehand and not being surprised once the electric Volvo is painted and drives for the first time. So it’s time for some real world testing!

Ruimte maken in Amazon

I decided to install the Tesla iBooster in our daily driver Amazon. I did have to sort out how to wire it all up and make a temporary wiring harness.

Bedrading Tesla iBooster uitvogelen

And after making some brake lines it was in place. I used the Wagner split also known as pseudo split like Volvo also did for the Amazon MY 1967 and 1968 for the US market. A dual master cilinder with a front/rear split. Only difference is that Volvo only used brake assistance on the front circuit.

Tesla iBooster in Volvo Amazon

And then it’s also about measuring again. The iBooster draws up to 15 Amps when in use.

iBooster 14 ampere

And a brake test in our driveway:

Eerste iBooster remtest

A deceleration of 0,9G so 8,8 m/s2, not bad, but a very sloppy brake pedal feel. Probably still some air in the system. My regular Eezibleed tools did not fit so I had to be creative.

Plieger stop


Ventiel autoservice Twello

Yes, that is going to fit!

Stop past op remvloeistofreservoir

So after putting these two together:

Stop en ventiel voor ontluchten

Hold it into place, add 1 bar of air pressure and ready to bleed the brakes.


Pedal feel was much better already and the pressure is OK, a little low though.

Drukmeting iBooster

The next question was: is it similar to the original brake pressure or not? After all measuring = knowing. I bought a old and used pedal force tester.


That allows me to really compare. Time for another test, this time with 500N of pedal force like required for modern passenger cars.

Drukmeting iBooster on off en pedaaldruk

With the brake booster switched off I had a deceleration of 0,5G so 5 m/s2. That is slightly below the lowest value for modern cars but above the minimum value of 3,8 m/s2 applicable to my car. With the iBooster switched on I reach 1G so 9,8 m/s2 and thus exceed the requirement for modern cars. Pedal feel was still a bit sloppy so I decided to bleed the system once more and it improved.

So I did a testdrive to my garage and my mechanic did a test.

Remmentest Amazon

Conclusion: brakes are good!

Did a test myself too. Maximum achievable deceleration on a dry road is 1,22G so 12 m/s2 while only requiring 300 N fo pedal force. For a more direct response a higher point where you feel pressure on the brake pedal would be nice.

I designed a cap to make the bleeding process a little easier.

3D getekende dop

And had it 3D printed an it fits well.

3D geprinte dop met ontluchting

It’s not perfect yet, so some tuning is needed, but it got too cold to work on it.

Amazon in de sneeuw

Next to the mechanical side, there also is an electrical challenge. I got a flat battery.


I added a Brake Residual Valve. Such a valve is needed if you have drum brakes in the back and discs in the front. It was integrated in the original master brake cilinder, but since a Tesla has 4 discs, that master cilinder does not have it. Therefore I need to add this external one.

Wilwood 10psi restdrukventiel
I will also add a adjustable proportioning valve. What a difference such a small valve makes! This is the brake pedal feel I was looking for.

I also checked the electrical part. Probably the battery was drained by the radio, not the iBooster. It only draws 1,2 mA when not in use.

Stroomverbruik 12mA

So soon, I’ll convert the brakes of our daily driver Amazon to normal.

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OldVolvo is a classic Volvo hobby blog by Lars Rengersen.

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