Brake Master cylinder

HENRY BURMEISTER

MEMBER
2008 TOYOTA SIENNA
3.5L
V6
4WD
AUTOMATIC
200,000 MILES

Replaced master cylinder about 3 years ago because brake pedal was going down too far before engaging. Got somewhat better after replacement but never got back to where it was when we first bought van. Recently noticed pedal going even further to floor before engaging. If I pump them, she holds nicely and pedal comes up 2-3 inches and does not fade. Recently cleaned out all fluid from reservoir and thoroughly bled all brake lines. No leaks. Also recently replaced rear disk brakes, three years old but were not wearing evenly, so also replaced calibers. Re-bled system. Pedal at same low level considering replacing master cylinder again since your description of problem seemed to align with pumping and faulty seals in unit. Also considered replacing Brake Booster, since I replaced master cylinder three years ago and did not seem to totally correct problem, although booster seems to be engaged when I step on brake when performing booster test. Any thoughts on the matter? Thanks, Henry Burmeister

4 Replies

KENW1

MECHANIC
213 POSTS

Hi Henry,

It does sound like the master cylinder is leaking internally from the first to second piston. The multiple pumps and pedal coming up would confirm this. Air can also do this. I would replace it and be very sure to bench bleed it before install. The guide below explains it in a little more detail.

https://www.2carpros.com/articles/how-to-replace-a-brake-master-cylinder

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Monday, December 28th, 2020 AT 12:22 PM

HENRY BURMEISTER

MEMBER
3 POSTS

Thank you very much. Appreciate the timely response.
Have a blessed day and a Happy/Safe New Year!

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Tuesday, December 29th, 2020 AT 4:46 AM

HENRY BURMEISTER

MEMBER
3 POSTS

Based on your reply I was ready to pull Master Brake Cylinder from 2008 Toyota Sienna when I noticed that there appears to be two parts to the master cylinder. The portion between the front and the Brake Booster has a bleeder valve on top. I decided to bleed that first since air in the line could be causing a problem. After bleeding the brake pedal it did come up a bit, but not all the way to the top. I've decided to replace the master cylinder based on the observation that it could be leaking from the first to the second piston. When I go to any Toyota dealer website they show the front piece separately as the "Master Cylinder". On any dealers website parts diagram they show the second half attached to the brake booster. The parts technicians at the dealers confirm that it comes with the new booster. I've also checked on line and at Advance Auto and they all sell the front portion but do not show the back piece attached to booster as show on Toyota diagram. The online part warehouses sell the booster separately, but none show that second half. The technicians at Toyota parts say I need to purchase booster from them to get the middle part. Of course the booster from Toyota will cost between $800.00 and $1,000.00 depending on which dealer I order it from. Are you familiar with the Master Cylinder on the Sienna and the second piece behind it attached to booster? If so, is it part of master cylinder or booster? Any other suggestion where I can find the center portion or am I stuck going to dealer? Thanks again, Henry Burmeister.

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Monday, January 4th, 2021 AT 4:24 PM

KASEKENNY

MECHANIC
18,907 POSTS

If your issue is that the brakes are dropping and it is the master cylinder then you do not need to replace the entire unit. You need to replace the master cylinder which is shown in the picture below. I show you can get these for less then a $100.00.

Here is a guide that will help with this issue:

https://www.2carpros.com/articles/brake-pedal-goes-to-the-floor

Below you will find the attached info for this. Let us know what questions you have. Thanks

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