Nope. That's PN# 54021. In the images below, this would be the peach and baby blue parts.

This is the Montero/Montero Sport BMC.


The sensor float assembly is the peach colored rectangle.


This is the 3000GT VR4 BMC.


The sensor float assembly is the baby blue colored rectangle.


This is the 'cup' thing that sits inside. It just sits there loosely. It falls right out if you turn it upside down. There's space between it an the sensor float - the two are not connected.


This is the reservoir with the 'cup' installed. If you look closely at the slots around the outside edge, you'll see that their screened off from below.


Mystery part of the month.

I spent a bunch of time yesterday surfing. I can't find another image anywhere of this, or even an approximation in some other manufacturer's BMC. No explanations, not even a mention on any other forum. I've never seen anything like this in any other Mitsu BMC.

I checked and it doesn't appear to be in the 1" 3000GT BMC, either. Only the VR4 1 1/16" BMC.

The only purpose I can see for this is to prevent sucking air into the BMC and lines under very hard cornering conditions and/or to keep the sensor float from signaling low fluid level under the same conditions. Like I said above, its a loose fit so its not like those screens are going to keep any crud smaller than a BB out of the lower half of the bowl.

Edward

Every Gen 2 I've ever owned has that screen, they seem to fit reasonably tight on the ones I've had.

Thanks Toasty. Weird. I've gone through half a dozen OEM Gen 1 Sport BMCs over the years and none of them have it. My '03 still has the original - doesn't have it. My little '97 was replaced four years ago with an OEM new - not rebuilt - BMC, it doesn't either. I've replaced the big Sport's three or four times over the years. One aftermarket from Napa and 2-3 OEM new units from Mitsu. I know for certain the aftermarket didn't and none of the OEM ones have had it either.

Do you have any idea what its for? The 3G BMC is definitely not reasonably tight. Its not even kinda snug. If you flip it on its side more than 90 degrees it just slides out. Its not so loose that it rattles around but ....

I'm taking the big Sport in tomorrow morning. The tech is going to do a brake pressure test (front/rear) on the existing system, swap in the 3G BMC, and then do another pressure test. I want a benchmark and an 'after' reading before/if I start messing with an adjustable proportioning valve.

Stock readings are in the FSMs. Be interesting to see what he comes back with. I've started paying more attention to the difference between my '97 & '99 with the 15/16" BMC and my '03 with the 1". There is DEFINITELY a difference. Both the Gen 1s had the brake system completely gone through in the last three weeks and the '03 flushed, bled etc. last year. Brake performance feels the same, but the Gen 1s have a much firmer, higher pedal. The '03 feels more like my big Sport, with a little more pedal travel and a little 'squishyier'. Takes less pressure on the pedal to haul down the Gen 1s compared to the '03. The behavior is about what I now expect based on the reading I've done.

Edward

Maybe the Sports didn't come with the little baffle or whatever? I've noticed over the years that the Montero parts are slightly different than their Sport contemporaries even parts that look exactly the same. For example the Montero vs it's identical Sport steering wheel is slightly different internally and a lot of pieces on the Montero are more "finished" than on the sport. The trucks are built in the same plant but I maybe the Sport parts come from Thailand where the Triton is built?

Talked to the Mitsu tech: No, never seen them on the Sports. Yes, seen them on the VR4, No, not on the 'regular' 3G. Hit and miss on the Montero. Says they're there to keep the 'crud' out of the brake system. Also said they need to be removed to do a brake flush. He thinks I may be (partially) correct about that being kind of an anti-slosh/baffle device to help prevent getting air in the brake system.

Maybe. I don't know. As far as I know at this point, Nabco is the manufacturer for all the OEM BMCs for Mitsu. Cars, trucks, SUVs, etc. If there's a difference in the Montero BMC vs the Sport BMC, I can't find it.

I'm more curious about what its really for then what it comes in. The tech wheels a truggy and he's run into the same problem of sucking air on the trail. He uses the same solution I do to try to mitigate the problem - over fill the BMC. Not exactly the best idea. I looked at the BMC again last night. Unless fluid flows through those screens freer than it looks like it would, it looks like it'll keep fluid contained over the ports irrespective of how much bouncing even if the fluid level drops to between full and add. How much help it would be when you stand the vehicle on its butt is questionable but it probably wouldn't hurt. I'd just be happy to not have to do a brake bleed 1-2 times a year.

Edward

Brake master cylinder trivia. From what I've learned, this makes sense. As the volume of the caliper increases, the diameter of the BMC piston increases to feed the larger volume calipers.

Front DSMTalk: "From what I've learned the brake master cylinder on the RS, GS, and GS-T have 15/16" bore (single piston calipers), GSX and base/non VR4 3kgt have 1" bore (two piston calipers), and the VR4 3kgt have an 1 1/16" (four piston calipers)."

Edward

I'm running the stock Mighty Max master cylinder with my SAS (4 piston Toyota calipers front and 1 piston Montero calipers rear) interestingly the first gen MM Master cylinder was the same size bore and looked to be about the same stroke as the stock Hilux MC. Works like I think it should. How much wiggle room do we have?

Do you know what the Mighty Max cylinder bore size is? I thought I ran across that a week ago and it was 15/16" like the '90s Montero and Sport. Curious, 'cause I think I saw that the bore on the BMC for the 4 piston Toy calipers is 1". The 1 piston Mitsu calipers uses the 15/16" BMC.

What size tires are your running? I think Danny's running 37"s. I've been meaning to ask him how the brakes work on his Sport SAS.

"How much wiggle room do we have?" What do you mean?

Edward

It's a 15/16" and i'm running 35x13.5 Toyo M/T which are really heavy. It stops really well that's what I meant by wiggle room, how much will a 16th hurt my performance vs piston size, amount of calipers/pistons as well as the other variables like brake booster size and pedal leverage?
Like my booster is half the size of the original Hilux booster and I was seriously worried about this but I cannot fit a larger booster (physically impossible) but fortunately for me it works perfectly and there's really no noticeable difference in braking feel from the donor rig. What's your take? Luck?

The 1 1/16" BMC is installed in my '97 SAS'd Sport. That one runs the Chevy K10 callipers front and Exploder late '90s/early '00s callipers rear with Powerslot rotors and Hawk 'green' pads all the way around.

Everything installed as expected. Just a simple bolt in replacement for the OEM 15/16" BMC. The only thing of note was making sure to install the 'filter cup' right side up. It has a top and bottom and apparently it came to me installed up side down which was why the fit was so loose. Having the Mitsu tool to adjust the booster push rod made the tech's life significantly easier. Another tool I'm not going to be without in the future is a brake pressure test set for testing brake pressure at the callipers and BMC. Its already proved to be a very useful tool.

I liked how my brakes were before with the OEM 15/16" BMC. The only real complaint I had was how much force it took to hold on a hill and that they had a VERY slight tendency to bleed down while sitting with a foot on the pedal. The latter seemed to be almost entirely due to the brakes not being bled completely or correctly - or both. The former was a real PITA if I had to sit for 20-30 minutes on the trail but thankfully that was a fairly rare occurrence. Otherwise, there was never an issue with stopping. The only complaint of others driving it was how squishy the pedal was and how much travel there was.

All of that is now gone. The feel is so close to an OEM Gen 1 Sport that if I hadn't been driving both my stock '97 and '99 for the last few days - both of which have had the entire brake system run through in the last three weeks - I don't know if I'd be able to tell any difference between the three.

The new BMC set up is more sensitive to foot pressure than the old set up but its absolutely rock solid stable and predictable. There is absolutely NO leak down. I tested that sitting in a drive-through for 20 minutes. Hill hold is fantastic! It isn't necessary to actually press on the pedal. Just the pressure of resting my foot on the pedal is sufficient.

I did a couple hard 'highway' stops from 55-60 MPH. I didn't attempt a 'panic' stop, first because I don't lock up the brakes in lifted modified vehicles, but mostly because we have a LOT of crud on the roads since the last snow. Too much gravel and sand on the roads for it to be safe.

Anyway, brake performance is as good if not better than it was with the 15/16" BMC. Its hard to tell, but its definitely not worse and it takes less pressure on the pedal to brake the same distance. That's great - thatÆs the one thing I was afraid of changing since the bigger BMC bore produces less pressure and I wasn't going to tinker with the pedal ratio.

Front/rear pressure wasn't great with the 15/16" BMC. I had them do a steady, moderately heavy pedal press, not a panic stop so pressures are not maximum, but they are consistent. Something like 750/600 F/R with the stock OEM BMC. This isn't terribly accurate - I was primarily interested in getting the rear pressure as I already knew the front wouldn't be an accurate reading. The new BMC came in at about 1100/700 F/R. This is an accurate reading for both F & R.

Roughly the proportioning percentage F/R should be around 60/40 loaded and 70/30 unloaded +/-. The new 1 1/16" BMC with the OEM '97 Sport non-ABS valve and the above callipers/pads produces almost a 60/40 split - like 61/39. That's good with a heavy load in the cargo area - I normally have 500-600 lbs of gear in the back - but bad if the vehicle is empty. Empty should be more like 70/30 with about 550 psi in the rear, +/- a little depending on the pad/rotor combination. Figure with my rotors/pads 550 should be pretty dang close. That'll send another 150 psi to the front which will actually improve the front braking a noticeable bit more.

So, the big '97 will stay on the OEM valve until it becomes strictly a DD. When that happens, all the gear comes out and goes in the new '99 and I'll change out the OEM proportioning valve for the Wilwood and set the pressure ratios to what I talked about above. The '99 will get a Wilwood when I pull the ABS here shortly and I'll set it to the 'loaded' values since it'll have a cargo bay full of gear all the time once its finished.

I'm a LOT less concerned with whether this set up will work with 37"s now. I think the most I'll have to do - if I have to do anything - is switch to a little more aggressive pad. I don't want to because I REALLY like the Hawk 'green' pads, but since the '99 won't be a DD I expect I'll live.

So, right now I'm ecstatic! This BMC is as close to a perfect match to the callipers I'm using as I can expect. Between the 1-ton steering last spring and this, its like driving a different vehicle. Now, if the 3G BMC wasn't so insanely expensive!


1997 Montero Sport OEM Brake Master Cylinder






1997 Montero Sport w/ 3000GT VR4 Brake Master Cylinder








The booster hose is in a different location between the 'OEM' (stock 3.0L) pictures and the '3G' (transplanted 3.5L) pictures. One more minor difference between the 3.0L and 3.5L.

Edward