Master Cylinder leaking into Brake Booster

My 2005 SR5 Double cab 4 X 4 4.7 blessed me with a brake warning light a couple months back. I found the BF level at the low mark on the reservoir, so thinking my front pads may had worn enough to cause this, I added fluid. Same song about a month later, and then this past Friday, again with the low level. I popped the Vacuum host grommet out, stuck a tie wrap into the Booster and find about 1 1/2" of brake fluid indicated on the tie wrap. So I have acquired an education about this Master Cylinder. Learned it is a dual MC with basically 2 slaved together and the front MC, with the reservoir, providing braking for the front, and the slave unit, connecting to the front MC, and the Booster, providing the braking for the rear wheels. This must have been a disaster for Toyota because it was limited production. I learned on another forum that there is a seal failure in the secondary, or slave, MC that allows fluid to leak into the brake booster. I have been unable to find the complete MC, part 407207-0C010. It turns out that you will only get the front half which has the reservoir on top, even though the part diagram shows both the front & slave units are pictured in the diagram. You can get the complete assembly, part 47200-0C073 booster assembly, which includes the booster, both front and slave MC, and the reservoir. Prices are all over the place for this part from $850 up to $1500 from dealers. You can forget any chances from the parts houses as all you will get is the front part of the MC. I have the Booster assembly ordered for $875 and will be lucky to get it. I did read about one dear soul who took his and shipped to a rebuilder and his truck was down for a month. This is a disaster for Toyota as my 05 only has 91000 miles on the clock! Every parts house I tried, and I think I got most of them, only sell the front part of the dual MC.

 

Why not order an aftermarket booster and master cylinder? Post some pictures of yours.

 

Every aftermarket Master cylinder I have found, and I spent one day searching, will only get you the front part of the dual master cylinder, and the problem is the secondary part of the assembly that is leaking into the booster. This is basically two master cylinders bolted together. If anyone finds the complete master cylinder, minus the brake booster, please identify the source. I have a stock 2005 SR5 Double cab, 4x4, 4.7 V8 and the best photo can be viewed by searching on the booster assembly part number 47200-0C073

 

11-3300 master cylinder at O’Reilly

 

Ah ... you got the unobtanium MC on your truck that has screwed over so many members here. Your best bet is getting a rebuild kit. There are a few threads in this subforum about this, including one that had info on a rebuild kit. I can't seem to dredge them up.

1st case I heard about this was a member a couple years back who got stranded out on the road in the SW USA if memory serves. And he had an adventure getting a suitable replacement.

 

It's an odd one, but it's not the super rare one that goes with Vehicle Stability Control. That's what I assumed he had at first.

https://www.tundras.com/threads/is-this-a-common-option.102171/#post-2621015

 

That is correct. I do not have VSC on my truck and I have been uable to locate any rebuild kits. Toyota stopped selling them. Why sell a $40 rebuild kit when you can sell a $1000 complete booster assembly!

 

The full assembly is discontinued when I went to look up in a few places. You may be able to find a parts source out of the Middle East with it, but good luck finding in the USA.

https://parts.toyota.com/Toyota_2005_Tundra-47L-AT-4WD-Double-Cab-SR-5/Brakes-and-Suspension.html

There's the parts page for your truck. Not your exact truck, but your year/model/cab/engine/drivetrain/etc. You'd need to input your VIN To get closer.

Brake/MC is here: https://parts.toyota.com/a/Toyota_2...709171/BRAKE-MASTER-CYLINDER/841420-4702.html

There are 7 exploded pics with parts. It looks like the 2nd exploded below is for your specific truck. When I look at the MC itself, I see "47201" points to two parts. And I'm going to explain why the numbers are all over the f'n place for you. Anyway, here's the exploded.

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And here's why you're probably getting crazy numbers. There are TWO factory MCs for your make/model. Note the underlined text, and you'll know which is which, and why the absolute f'n crazy price diff (more info after this pic, keep scrolling):

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If you just need to replace the MC and the MC only, your part number is 472070C010.

When I add to cart at that link specifically, the part price is $450 at one dealership, and when I pick another dealership, it's only $370 (keep scrolling, more info).

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If you need to order from somewhere with free shipping and no tax at $354.95, this dealership will get you taken care of. Use coupon FREESHIP at checkout. https://parts.serratoyota.com/p/63552719/472070C010.html

 

That ^^ is, unless I'm misunderstanding the wall of text up there - if so, let me know.

It looks like they have the whole assembly too, $1200.

https://parts.serratoyota.com/p/Toy.../Power-Brake-Booster/63180877/470500C031.html

 

I wonder if he could make a normal booster and master cylinder work with a little modification.

 

Last comment: Is that intermediate unit even a serviceable part? It looks like it's just cast steel, with no seals inside.

 

After studying the crazy path of those hard brake lines, I don't think this would be an easy task.

 

The intermediate unit is a second master cylinder slaved to the primary. Again the primary brakes the front calipers, and the secondary brakes the rear drums. This truck is a 17 year old survivor, 91500 miles. I will not cabbage something together to make it work. It is 100% original, and will stay that way. I will buy the complete booster assembly if that is what it takes. Completely stupid and unnecessary for a $5.00 defective seal in the secondary MC.

 

Ok, so there definitely is a seal in the secondary?

Is it possible to find a compatible seal from another brake unit? Good hydraulic shops can help you find seals if they know the diameter and thickness of the seal, any other properties. I've had to do this with some more-difficult engine swaps back in the day.

 

I have a feeling that there are many more late model 05's and all of 06 that has this sleeping issue hiding in their Master Cylinders. Why has Toyota gone from a rebuild kit, no longer available, to a no longer available complete dual master cylinder, to a booster/MC assembly that sells for $1000

 

I have ordered a Booster/Master Cylinder assembly Part # 47200-0C073 If and when I receive the unit, I plan on doing a tear down on the secondary master cylinder, that connects to the booster, and posting photos for education of the forum. It appears Toyota only used this dual master configuration for a little over a year.

 

This member was in your boat. You may want to heed his process as advice on your path forward.

https://www.tundras.com/threads/im-at-my-wits-end-master-cylinder-issues.39933/page-5#post-2599135

Good luck to you.

 

Oh and while you're at it, you may want to read this whole thread from the beginning because it discusses your exact issue: https://www.tundras.com/threads/im-at-my-wits-end-master-cylinder-issues.39933/

 

The aftermarket part number for Cardone is 11-3300 sold by O'Reilly's and another rebuilder selling to Advance AP under the name Wearever, but both suppliers have 0 inventory.

 

Gotta have cores if you wanna rebuild parts

But these guys must be getting rebuild parts somewhere. Too bad nobody on Cardone works on here, else we might be able to get part numbers for it.

Could be interesting to search Google for that part number in quotes "11-3300" and "Cardone" along with the quoted phrases "gasket kit" or "rebuild kit". You may end up getting info you need for that. I'm locked into wiring up some new security lighting at home today, so don't have a ton of time to research.

 

After more research, it appears the mystery part between the Master Cylinder is in fact another, second MC that would provide some braking in the event of booster failure. Toyota also used this on the Sienna for 7 + years, so this is not a unique part. I am going to try and buy the one I had in my hand Friday that had brake fluid all over it, use the secondary master, from theirs, and bolt it onto the new Raybestos primary MC I have coming on Tuesday. I did see a listing on Ebay for just a secondary MC used for sale, listed under Siennas.

 

The company that sells a disc brake conversion kit & also sells a master cylinder for the disc conversion is https://sosperformance.com/ It was mentioned previously in this thread. It is about twice the price of the OEM booster/MC assembly. My OEM booster assembly is shipping today with a price of $850. The 11-3300 by cardone if found was $240. I have found some 7/8 bore MC kits but unknown if they would work in the second cylinder used on our 05 DC Tundras.

 

If you tinker with this, and find any of the kits work, you could go down in history on this forum as a hero for finding a solution to this problem!

 

Found this under "New Features" for 2004 Tundra Double cab: On double cab model with Brake Control System (ABS), a brake pressure conversion unit has been added between the brake booster and the master cylinder in order to provide the proper braking force when the
brake booster has no vacuum. I believe it ended with the 07 model
So Toyota calls this extra mystery piece between the Master cylinder & brake booster "a brake pressure conversion unit" The unicorn now has a name. I always thought my 05 DC was special!

 

There's already a detailed post here, or on TundraSolutions, or Youtube, that explains the failure and solution. It's an o-ring failure on a shaft internal to the unobtanium part, also know as the 3rd chamber. He included everything you need to know to replace the o-rings, location, sizes, etc. It truly is $12 of rings instead of a $900 new booster, but with something as critical as brakes, I decided to just purchase the entire unit from McGeorge Toyota, bolt it to the pedal, bleed the 4 corners and move on with life until it fails again in 10 years or 150k miles. Good luck.

 

I came up empty with my Google Fu on either the video or tech article on TS...

 

I looked through my old files and bookmarks with no luck, but as I said I just purchased a new unit. I think the solution I'm talking about was found on a Sienna forum. Here's a couple links to get anyone interested started. BTW, they refer to the unobtainium part as a "diameter converting unit".

Toyota Sienna Service Manual: Disassembly - Brake master cylinder - Brake control (tsienna.net)

Toyota Sienna Service Manual: Brake master cylinder - Brake control (tsienna.net)

 

The reference to a failed seal is correct. The post is Here: https://www.tundras.com/threads/im-at-my-wits-end-master-cylinder-issues.39933/page-4 post #109 and here is a photo of the seal in the MC between the booster and primary master: