I'm at my wits end- Master Cylinder issues..

The Sequoia master cylinder from SOS doesn't use that special middle cylinder piece, instead there is a proprietary(?) cylinder/ adapter that replaces it and a different pushrod. In the picture below, you can see the black piece in front of the booster. This master cylinder is larger internally than the stock one, and I would guess that the cylinder piece is larger as well. Note that the larger internals are to accommodate the different rear brake setup I have. I can't tell you at all how this master cylinder performs with drums. The master cylinder is not stamped AISIN, which the OEM should be.

https://sosperformance.com/products...er-installation-kit-fits-rear-disc-conversion



I sold my stock MC to a fella that needed JUST that middle piece.

 

des2mtn - Thank you for this post. It definitely has some wheels turning inside my noggin. I noticed that the kit from SOS is intended for use with a rear disc conversion, and has a larger ID than the stock Tundra MC. I'm wondering if SOS offers a similar MC with 3/4" bore (same as stock) that would be more compatible with the stock rear drums. I plan to contact them and try to find out. I don't have any plans for converting to discs on the back.

This looks like a nice possibility for getting around the whole nightmare with the stock "middle piece" & MC assembly, since that assembly seems to be simply unobtainable right now. It would be sweet to just remove the "middle piece", "unicorn", "third-chamber", whatever we call it -- and just chuck it in the garbage and install a pre-engineered and tested replacement. Hmmmmmmmmmmm...........

Thanks!!
DsrtRat, aka Mac

 

More stuff to get the wheels turning in your head... Even though the Sequoia MC is 15/16", single diaphragm and made for discs, it can be fitted to a booster on a truck that has drum brakes. I honestly cannot tell you how or if it would stop correctly. I can tell you one of the other popular brake upgrades that people do on our trucks is a T-100 brake booster and MC upgrade. The T-100 has rear drums, but the booster it uses is double diaphragm and MC is 1" bore.

The AC truck's MC bore is something like 11/16" bore but does not have that center cylinder. Installing this on your truck would likely result in adverse affects.

Calling SOS might help, but they might try and steer you towards buying something more than trying to help you.

Not going to try and steer you towards any upgrades, but the T-100 upgrade alone is pretty cool. I believe it's @Thrussn that has a detailed writeup on here if you want to check that out. https://www.tundras.com/threads/t100-brake-booster-upgrade.86375/

 

Hi again,

• I traded brief e-mails with Tom at SOS. All he said is that they have not tested the Sequoia upgrade with rear drum brakes. I may go ahead and buy the kit from him and install it and see how it works. At the worst, it will act weird and I'll be back in the boat I'm in right now, which is twiddling my thumbs waiting on Toyota parts that may never come.
• 
  
• Pardon my ignorance, but what is the "AC truck" you refer to above?
• 
  
• The T-100 upgrade also sounds interesting. I will read up on it.
• 
  
• Am I correct that you installed the SOS upgrade in a Tundra? If so, how did the installation go? Fairly straightforward? What kind of plumbing did you have to do? I'll appreciate any insight you have. I'm a very good mechanic, have tons of tools and many years' experience, and not much of anything scares me. That said, I do want to end up with a robust installation that's going to work, be safe, and hold up well.

Cheers!

 

1. I'd say it's worth giving the MC a shot as you said. At best it could be an upgrade even?
2. AC refers to access cab. RC, regular cab, DC double cab.
3. Awesome!
4. Yes, I do have the SOS rear upgrade on my truck. Installation is fairly straight forward if you are mechanically inclined. From this discussion it seems like you are more than capable. The toughest part is that it requires you to press the wheel bearings and ABS tone ring, which needs to be done to a certain spec. I don't have a 20 ton press so I took the axles to a machine shop and paid them to do that part of the job. Timmy the Toolman has an excellent two-part series on Youtube for the complete axle seal and bearing job.

If you're looking at the SOS kit, I would take a look at the front caliper 14WA upgrade too, as most of your braking force is applied in the front. The 14WA upgrade requires 17" wheels or larger -- I have 16" wheels so that is not an option for me, which is one reason I did the SOS kit. Here's the thread with info on doing the 14WA install: https://www.tundras.com/threads/2000-2006-tundra-big-brake-upgrade-kit-14wa-calipers.61231/

Anyways, here's a quote from myself on another thread with more info on my experience with the SOS kit which should answer other questions you may have:

 

Well, duh!! A brain is a terrible thing to waste! AC / RC / DC. Didn't even think about that. Thanks for jostling my brain a little. Thanks also for all the valuable info, links, etc. Most helpful!

Mac

 

If the upgrade brake proportioning is off when you try it, you can tune the rear brakes by swapping to different wheel cylinders. A smaller diameter one like for a Tacoma decreases the rear braking. Also, adjusting the LSPV does the same thing. So you will have some ability to tune your setup.

 

Main take away Mac is that DC is top dog and AC/RC are the runts

 

Hey guys ---

Dbiittle - Thanks for the input. I had already thought about tweaking the LSPV a little if the front-to-rear balance seems off after the upgrade. We'll see how it goes. I have a fairly heavy camper on my truck, probably close to 1500 Lbs. fully loaded and ready to go. I installed airbags on the rear to help out with the weight, along with an on-board compressor to control them. Pretty nice setup, and I'm very pleased with it. The LSPV is supposed to work by adjusting the proportioning in response to load, by changing the valve setting when the rear end squats under load. However, with the airbags, when the truck squats under load, I "un-squat" it using the airbags. This pretty much nullifies the effectiveness of the LSPV. However, I can make semi-permanent changes by changing the positioning of the valve. Again, we'll see how it goes.

BubbaW --- I'm quite happy with my DC, though the long wheelbase took a little getting used to at first - I used to have a 4-runner, then a Tacoma Xtra-Cab, which I still have and it has almost 300K miles. Just like the Eveready bunny - it just keeps on truckin'. But, I'm sure the folks with access cabs and regular cabs are happy with them too. I've always felt like everything has a purpose and serves some good, and if the owner is happy with it, that's all that counts. With our DC / camper setup, it's always just me and my wife, or more often, it's just me solo. I removed the rear seats early in the game, which removed probably 100 Lbs. of weight, and provides a lot of open space in the rear for camera gear, solar panel, and other stuff. Works out pretty good. If I had it to do over, and IF money was not an object, I might have removed the bed and replaced it with an aluminum flatbed tray, and bought a flatbed camper instead of the regular truck-bed version. I've seen some examples of this setup on the internet, and it looks pretty slick (also pretty expensive). But, I'm happy enough with what I've got.

Thanks to all,
Mac

 

Hey guys, I thought I would update you on my status on the MC part. I spent hours and hours on Monday (I was basically useless at work) calling several dealerships with no luck. I was about to give up when I decided to reach out to one more company called, Monster Discount parts that was referred to me by my mechanic. I emailed them on the availability of the MC, part number 47200-0C073. Within 10 minutes, I got a response and they said they didnt have any in stock but according to their records, Headquarter Toyota located in FL had one in stock. I immediately called them and sure enough they had it. I was able to pay over the phone and over night the part which arrived this morning. I say all this to provide hope to anyone that is still looking. I have a feeling there might be more out there but it may require lots of emails and phone calls to dealerships all over the US. Please stay the course and dont give up if you are in need of the part. I want to thank everyone that provided all their thoughts and inputs on this debacle. I will keep my eyes and ears open and if anything comes up, I will be sure to pass it along.

 

ikr, I'd rather have a slightly smaller cab so my bed looks bigger. The inverse on the DC is like having a dick-do, only swap belly with cab...

I need all the help I can get making mine look as big as the ones RCLB are rockin.

 

Man this thread just won't die. Every time I see it I get PTSD when thinking about my own brake issues.

 

TitanKeeper84:

Wow, glad to hear you were finally able to beat one of these things out of the bushes!! Please let us know how the installation and bleeding go. BTW, here is a link to a video about our favorite part, that I've watched a few times:

https://www.youtube.com/watch?v=V1Q83GDmplY Starting at about 15:56, he talks about bleeding the "Unicorn". I've looked at the relevant section in the TSM, and the video replicates it pretty accurately. The process seems a little peculiar, but apparently it works.

For a chuckle, check out the clip below. It's Cardone's reply to an e-mail I sent them, asking whether or not they still rebuild MCs. Check it out!

Customer Cardone.com

7:17 AM (3 hours ago)

to me, Customer


Good Morning Paul,

Master cylinders are obsolete now- no rebuild.

Have a great day!

Thanks.

Aneeta
Customer Service Representative | Cardone Industries
800-777-4780​

 

@DsrtRat thanks for the video. I was actually watching the video last night. I will keep you posted on how it goes. I plan on installing it this Saturday.

This is very frustrating about the mc rebuild. I was hoping when this whole "back-order" ordeal dies down that companies like Cardone would start rebuilding master cylinders again. Hopefully other companies will step up or at least provide rebuild kits.

Does this mean, once the MC goes out sell your truck?

 

There is a Toyota parts guy on Facebook "Joe Joe".

Not sure if he's on here but on Facebook he's the OE parts god. Cheapest around and best service.

 

@DsrtRat

Just curious why not go the SOS disc brake route instead of messing with stuff that may or may not work? The way I see it, you go the full disc brake conversion have a MC that is available and all new brake parts in the rear that are obtainable in the future. And the cost is the same.

Also that toyota mechanic I linked is in Utah so may be worth chatting with him to see what he has tried (I know he found a way around the unicorn part)

 

Hi,

Valid question. To be honest, the main reason I don't do the rear disc conversion is money. For the stuff I use my truck for, i.e. back-country, off-road camping, having dynamite braking performance just isn't a big-ticket item to me. I'd love to do the conversion, but it just isn't a priority for me. That said, getting my brakes to an operational and safe state IS a priority. I have ordered the SOS MC upgrade kit, and it should be here next week. I have high hopes that it will get me back on the road soon. If it doesn't meet expectations, I'm only out $300 or so, and will start pursuing other possibilities, though the "possibilities" are rapidly running out.

 

My hunch is you will be over biased on the rear brakes with the sequoia mc and your drums, but you’ll be able to turn down the LSPV to compensate.

 

Makes sense! And if it works you just saved a bunch of us. Luckily mine still works fine, but I've "budgeted" the disc brake conversion if it ever did.

 

One thing I'm not sure if I mentioned - the internal push-rod that it comes with is adjustable. You will likely have to do a little trial and error with how far it's screwed in. I think one of the ports is on the opposite side too, but the SOS kit comes with an extension line you can hand bend.

Be careful with your first test drive, maybe don't go too far or bring a few tools. If you have the push rod adjusted too far out, it will cause your rear brakes to lockup and not release the pressure. If this happens on a test drive, you can let a little fluid out of the bleeders to relieve the pressure, then make it back home slowly while trying not to use the brakes.

 

https://www.tundras.com/members/des2mtn.48721/
Again, point well taken and good advice - thank you. One of the first things I will do when installing the kit is to try & get the pushrod where it needs to be right off the bat, and get my pedal freeplay within range. And, you're right - in reality, both pressure ports are on the opposite (left) side from the stock MC. SOS includes Qty. 2 straight, 3/16 X 12" lines for making the connections. I'll bend those to fit as required. The first test drive will be up & down the dirt road that I live on, and no point on that road is more than a 5-minute walk from my house. Shouldn't be a problem, but I definitely like your proactive approach of carrying tools. I always do anyway, but thanks for mentioning it.

HERE'S A QUESTION, for everyone viewing this thread: we've talked a lot about the infamous and much-maligned "Unicorn" or "third chamber". Does anyone know what its function is? What does the dang thing do? I assume that it was Toyota's attempt to fix some kind of problem on the pre-2004 trucks. Does it tweak the front-to-rear proportioning in response to pedal pressure, or something along that line? I always like to know the whys & wherefores of stuff I'm working on. I'd love to hear everyone's input on that.

Best to all,
Mac

 

I'm by no means a master mechanic, but always happy to share what I've learned in my journey. Especially if it's something dangerous like your brakes potentially locking up!

You and Roman both determined that it only comes with the whole booster assembly, 47200-0C073. Looking that number up on Toyota's website shows it only fits double cabs, so something about the booster's construction, similar to the master cylinder bore, must be different (probably to accommodate the added weight of the double cabs). Maybe there's more stroke that's needed, hence the unicorn chamber? Again, just theorizing here.

So I am re-reading the brake bleeding procedure again from the factory service manual and I'm looking at the differences between the master cylinder bleeding procedure between the double cabs and access cabs.

Here's the procedure for a double cab like you and I have. It talks about utilizing that bleeder valve while bleeding the master cylinder:



Here's the procedure for bleeding an 2005-2006 access cab master cylinder. This is how I bled my SOS master cylinder.

 

Veeeeerrrrry interesting! Thanks yet again. I hadn't realized that the AC & RC don't even have the unicorn. Those models are irrelevant to me, so I had never paid it any attention.

Good thing I've got long legs & arms, so I can simultaneously press & hold the pedal AND stick a finger in the MC port! (ha ha just kidding)!

 

Yeah, it was a feature added to 04 DC w/ABS.



1st Gen Tundras New Features Chronology | Toyota Tundra Forum

 

Nice find, Bubba. Seems like my theory about the stroke may hold some water. It sounds like the main time you'll wish you had that piece is if the booster fails or you loose vacuum from the engine.

 

BubbaW / Des2Mtn-

Great catch. Good info to know. Thanks for following up and running my question to ground. And Des2Mtn, about your comment regarding pushrod length, possibility of lockup if it's too long, etc. --- I've located the setting tool, somewhat resembling an H-shaped depth mic, that's used to measure the depth to the MC pushrod receptacle, and then transfer that exact measurement to the booster pushrod. Looks like it works pretty slick, and eliminates any guesswork when installing the MC. I'll check O'Reilly to see if they have one as a loaner. If not, I'll buy one - they are $50 or less, and undoubtedly worth the investment. Anything to avoid nasty surprises on the first drive.

Thanks again. This forum really is a valuable source of knowledge and experience. I'm really enjoying the back-&-forth with all you guys.

Mac

 

Once you become the guru, can we all bring out trucks to you to bypass the unicorn?

 

Well, not too sure I'll every be the guru. I just want to be enough of a guru to get my truck back in operation, and then I will be heading out to parts unknown to catch up on some long overdue travel and camping. You probably couldn't afford to have me work on your truck, anyway. I'm not sure what my hourly rate would be, but to get me to leave my retirement and starting working again, it would have to be astronomical! I've found that I REALLY like not working. Sometimes I wonder why I devoted my entire lifetime to a dead-end pursuit like WORKING! What was I thinking??!!

 

Folks,

Quick update on 4/1/22, April Fool's Day! I installed the SOS Sequoia MC upgrade kit. The installation was pretty straightforward. Only problem was that the reservoir of the Sequoia MC had a slight leak - fluid dripped out of the port where the level sensor goes. I went ahead and completed the installation, bled the system, and took it for a preliminary test drive. Pretty uneventful, I would say. The pedal felt nice and solid, and no surprises like grabbing brakes, pulls to one side or the other, etc. The front-to-rear balance actually felt pretty good. My truck has a camper on it that weighs approx. 1200 Lbs, so without that it's possible that the rear bias might be a little aggressive. I'll probably never find out, as I never remove the camper. I'll learn more as I drive it, and will pass along any new impressions or experiences.

The folks at SOS very promptly sent me a replacement for the leaky Sequoia MC, and I plan to install it tomorrow (Saturday 4/2). Hopefully that will finally put the cap on this very frustrating saga. Frankly, I'm tired of dealing with it.

Ironically enough, the 47200-0C073 assembly that I had ordered over Amazon finally showed up yesterday, after being "lost in space" for a solid month. I'm sending it back, and plan to stick with the Sequoia MC upgrade. If any of you are still looking for the stock booster/MC/third chamber assembly, Daytona Toyota will be receiving one from me sometime late next week.

Cheers to all -------