2005 DC Master cylinder/booster alternatives?

[MoCoNative]

I had noticed the brakes feeling weak on my 2005 Double Cab for a bit now. I only drive it occasionally, but its primary use is towing the camper with the fam. A few times now quick stops with the camper were alot longer than I felt they should be. Now I know everyone says the brakes on these trucks were pretty lack luster, and they probably are, but this is beyond just extra weight pushing you further than you think. The notion got driven home over the weekend when some quick traffic stops were almost collisions.

I read mulitple pages on some of the Tundra forums about master cylinder failure. The truck is in very good shape, 166K miles, but it has probably sat too much, which can be a detriment to hydraulic systems. Most guys talked about a soft or sinking pedal, poor braking. Most had experienced a loss of brake fluid, that seems to be going into the booster. I have noticed a very small drop in fluid level that has had me curious. No external leaks are evident.

The complication is that on the 1st Gen Double Cab trucks, and apparently on a few years of Sienna, Toyota added this secondary master cylinder piece called a "brake pressure conversion unit" that is supposed to assist braking efforts during the loss of vacuum, or brake booster failure. I have attached a picture of the new unit from Toyota. The Tundra guys were calling it the unicorn piece. New and rebuilt master cylinders are readily available, but they are only the forward part of the cylinder. This extra piece mounts between the master and booster and is filled with brake fluid off the back of the master. It appears the rear brake circuit passes through it. No one really knew how it worked. I'm starting to wonder if booster vacuum has some effect on it, and the lack off lets a primary piston within it activate the rear brakes. It is a smaller bore, which would make more pressure without assistance. The problem is, this extra piece of the master is not rebuildable, or able to be purchased separately. It fails and lets the master leak fluid in the booster. The only solution is to replace the entire master cylinder combo at $850 plus.

I fear I'm headed down that road, need to try and dip the booster and look for fluid, maybe try a bleed, it has felt to me like the rear brakes are not doing alot, so this all makes sense.

Some guys have put T100 master cylinders and boosters on these trucks with mixed results. The pedal designs are different, so leverage is different and the master bore sizes are different. I don't know if the bigger master from the T100 is really the right approach to this. The regular and access cab Tundras used a different booster and master combo. They did not have this extra doohicky on the master. What I don't know is if the pedal bucket and firewall design is identical between the two truck bodies. The double cab is unique, basically a seqouia front half. I looked at Sequoia master booster combos, they are different too. The exisitng booster appears to not accept any other type of master cylinder, it is unique to the unicorn piece.

Has anyone used a normal master/booster combo from other tundras in place of this special limited master/booster combo? The master bore size differs slightly, 3/4 on the special unit, 13/16 on a normal tundra master. I'm assuming that should not have a significant difference. The special unit is below, a normal Tundra master combo below that. These double cabs have a very short booster rod it seems.

Also, forgot to add, the proper master/booster part, 47200-0C073, may or may not be discontinued. I haven't called around but the Toyota parts sites keep showing a price, but then says unavailable, manufacturer shortage, discontinued, that sort of language, so maybe conversion is the only answer.

 

[MoCoNative]

Son and I bled all the brakes and the special bleeder on the master. I'm pretty sure master is suspect at this point. Seems to pump up okay but if you hold it you can shove on down sometimes, especially with the engine running. On road testing if you kind of do a pump and quick jiggle of the pedal and such it may hold and the brakes bite good and hard. Other times you can jam on it quick and the pedal goes way low. This can be reproduced just sitting too. Sometimes you get a hard pedal, or if you stab it quick and hard you go way towards the floor. Did not find evidence of any fluid in booster.

Anyone try a regular Tundra booster/master combo in these?

I see similar year Tacoma uses the stubby style Aisin master like the original one, minus the extra chamber, but the booster pedal rod is very long. There does not seem to be much interchangeability of the boosters. I have looked and looked at pictures on rock auto and such. Some bolt on with a straight bolt pattern, some are slanted one way or the other. Not sure what the assist is on all the different boosters obviously. Wish they were all more interchangeable like the old Toyota brake systems, but they all differ on bolt patterns, pedal rod length and internal master rod lengths, without a bunch in your hand, kind of hard to tell.

 

[MoCoNative]

Well, surprised I didn't get any more input on this. Hopefully by the end of the weekend I will have regular Tundra booster/master swapped in place of the semi unicorn booster/master and still have functioning brakes. The braking issue remains the same, good most times you hit the pedal, but if you stab it hard and fast, like a panic stop, they just don't work right. I'll report if this works properly.

 

[Mitya]

I'll report if this works properly

Hi there. Any news?

 

[MoCoNative]

Man, I went on vacation last summer and forgot all about this thread. Took the truck and trailer to the Black Hills of SD and back no issues.

So a regular cab or access cab Tundra master and booster will bolt in. I had to trim the pushrod on the pedal side of the booster about 5/8 of an inch to match the original pedal height and length of the factory booster rod. Also had to reuse the clevis from the double cab booster, as the donor was to narrow to slip over the brake pedal arm. Reuse the aluminum spacer between the booster and firewall.

The brake lines will need to be adapted. I also modified the "tee" below the master to bolt on like it did before. The tee is offset on the DC, but centered on the other boosters. I cut the tee off the bracket and added a little bit of metal to offset it and welded it all back together using the donor tee mount bracket. The brake line origianlly attached to the tee going over to the ABS controller is the front curcuit as I recall. A generic metric tee could be used here and allowed to float if you didn't want to mess with the bracket. The other brake line is now floating in space by the master. To adapt this I used the same technique SOS does on their master swaps, a metric line union and a short brake line to the correct port on the master. I reused one of the lines that came on the donor master that went to the tee for this purpose and made a custom line from master to tee, as the distance had increased. Not shown in my pictures is the little bracket I later made to support the splice point with a bracket that clamps to the forward part of the master. Thought it would protect twisting the line off if a guy got into it or set something on it. There may be enough line to bend and bring it over if you are good at manipulating lines like that and not kinking them.

I bought a few of the proper 10x1.5 nuts for the lines, but had some on the donor master to use too. Hardest part of the swap was laying under the dash and getting at the booster nuts and getting my worn out flaring tools to hold the brake line and make a double flare. A short metric brake line could be ordered on-line and solve that whole custom double flaring issue. I bought regular merican brake line at NAPA and had to modify it with the needed metric nuts.

Brakes feel much better, they seem more linear, the stock booster seemed to be weak then hit hard, maybe it had been failing for a while, or that stepped master body does more of an instantaneous application of pressure. Either way I like them better, they feel more like my T100 and FJ60 brakes with the linear foot pressure to brake pressure feel. Newer cars feel more vague on the brake pressure.

 

[pineapple15]

Great thread, thanks for the right up. Have diagnosed a similar issue on my tundra to also be a failed master - the booster is full of brake fluid.

I am wondering if you have the access/reg cab setup part numbers? I am having trouble finding them.

I have ordered a new double cab master (47200-0C073) but want to compare price to do the ac/reg cab setup instead like you have.

 

[MoCoNative]

The reg/ac cab master is no longer available from Toyota at least time I checked, they were discontinued. Only option is aftermarket. If you just want to go back with stock than what you ordered is the full deal and the only way to repair the failed intermediate booster part. The forward section is available aftermarket, but does not repair the little cylinder between it and the booster, which is what fails and fills the booster. To get the other style master is cheaper, but you also have to change the booster and re-work the lines. Plus as said above, no longer available from Toyota. I just converted mine due to availability of the correct part and the fact it will fail again. Now I can just replace the master more easily.

 

[styran]

The reg/ac cab master is no longer available from Toyota at least time I checked, they were discontinued. Only option is aftermarket. If you just want to go back with stock than what you ordered is the full deal and the only way to repair the failed intermediate booster part. The forward section is available aftermarket, but does not repair the little cylinder between it and the booster, which is what fails and fills the booster. To get the other style master is cheaper, but you also have to change the booster and re-work the lines. Plus as said above, no longer available from Toyota. I just converted mine due to availability of the correct part and the fact it will fail again. Now I can just replace the master more easily.

Say you had a RC/AC booster failed on the truck, this part is discontinued.
From reading your post above, I understand you are saying that the obtainable brake master cylinder/booster assembly from the double cab models ($$$) will bolt on to an RC/AC model? Or are you saying something else?

 

[MoCoNative]

The RC/AC model brake master cylinder is not available brand new from Toyota, but is available new from aftermarket suppliers. That is unfortunate, but the aftermarket parts are probably fine for this application, I would preferably get the Beck/Arnley part if I needed it. The booster is also not available new from Toyota. A used one is probably a safe gamble from a wrecker or ebay. There is also aftermarket available and rebuilt. I don't have any personal experience with any of those brands/suppliers.

The master and booster from the DC is completely different as far as bolt pattern between the master and booster. If you swap in the RC/AC combo, you have to do the whole combo, only common bolt pattern is the booster to firewall. The next hurdle is the brake lines come at the two combos from different sides, so they have to be modified to reach the master. I would not pay the $1K for the DC master booster combo for a regular Tundra. It doesn't make sense, they cannot be repaired and you have to do a bunch of extra mods when you can buy new aftermarket for less than $300 dollars and be on the road for many years to come. The used OEM combo I got has been fine for that matter. If you only have a failed booster, that is all that needs replaced/sourced from a RC/AC.