Author Topic: 100 Series Conventional Brake Booster Swap  (Read 334 times)

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  • Offline Dusty Trails
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100 Series Conventional Brake Booster Swap
« on: Apr 19, 2020, 11:55:14 AM »
My new to me 1999 100 series had the dreaded fault codes for the master cylinder setup. Since it was a sub 200,000 mile rig I had my fingers crossed it wouldnt be and issue, but here i am.

If you are not familiar, the 100 series, as well as one or two camry and 4runner models (I'm told) use a mastercylinder, electronic brake booster/accumulator, ABS motor deal all in one unit. If you had a failing unit, and lets say, stopped by a dealership to have it fixed, they would most likely replace the entire unit with a new one for around 2200 dollars plus labor. Pretty spendy huh.
You can get master cylinder rebuild kits, a new accumulator, and a rebuilt ABS motor ( to fix the most common failure points, for around 700 dollars last i checked. Still too expensive for my pos land bruiser. In my opinion, the MC rebuild kit should be the first thing you do in case the other parts are working to hard to compensate for failing seals inside.

So my solution was to swap it for a conventional vacuum operated brake booster and the MC to fit it. Sky is the limit here when it comes to choices. My first though was to:

1. Use the original MC, block off unused ports and fit a booster to it. However the back side of the original mc protrudes a long ways and i think you'd end up with a really long, awkward unit with a lot of elongated push rods

2. swap in a after market MC and booster in from your favorite supplier (read big $)

3. find a cheap alternative from a similarly sized and weighted vehicle like a super duty, 3/4 ton chevy or the like and fab it up

4. swap a first gen tundra booster and MC as they were parred with this same engine and use a conventional booster.

5. Or what i did, which was to use what i had handy, the 95-1/2 year and older booster and MC.

(Pictures would be nice here but i guess i cant do that)

I had the large type, 95 and older, dual diaphragm booster sitting around for my 1st gen pickup, plus they are about 20 dollars from the local parts yard. These are the same unit that is used in the very similar size and weight, disk brake equipped front and rear 80 series, so i thought it was a good candidate.
The trick is the 100 series firewall stud pattern and the 80 series pattern (i will just refer to it as the 80 series from now on) is so close, with the 100 series being square to itself and the 80s a rectangular pattern less than a 1/8" away if you want it to be centered in line. Not wishing to modify the firewall, its brackets and definitely not wanting to disassemble the 80s booster to move the studs, i made an adapter plate. To speed things up, here is a step by step of what i did.

Get the large dual diaphragm booster with its vacuum line with its the inline check or residual valve (i forget which) in it, along with the 3 way bracket that the MC lines go to (front mc line to 3way, driver side of 3way to driver side front caliper, passenger side 3way to passenger side front caliper, rear most mc line to rear brakes)

~Cut a 3/8s inch square of mild steel.
~Trace both stud patterns onto it (the little gaskets between the MCs and the firewall are handy here to trace)
~Drill and tap the 100 series pattern to your preferred stud (i went with factory 8-1.25mm, about 2" long studs to reuse the factory nuts inside)
~Drill the 80 series booster stud pattern (they will be far to close to the 100 series pattern to fit a nut on at all) to maybe 8.5 or 9mm
~Cut a great big geezless whole in the center plate with what ever you have handy for the booster to slide through.
~Cut the booster studs flush with the back or firewall side of the plate and weld them in. You could weld the plate directly to the booster but i didnt want to put that much heat into such a thin, complicated part.
~Swap the push rods end from the 100 series onto the 80s booster (the pin whole is much smaller, same thread pitch however)
~Before you bolt in your new booster, gently manipulate the 100 series brake lines toward where they will hit the MC and the three way beneath it
~Bolt in the booster
~Install MC of your choice: i went with a 1-1/16 T100 master cylinder cause i had good luck with it on my rear disk swapped 4runner. However, i may swap it for the 80 MC with its residual valves and 1" bore, since the pedal feel is a bit long and requires a decent amount of force to bring the hefty 100 series to a stop.
~You need good vacuum pressure to run a booster, I found a already tapped, unused hole on the back on the Vbank and used a m12-1.25 5/16" 90degree barb with a swivel to connect to the booster
~Bleed brakes
~Remove the ABS box from under the steering wheel, just to the left of the brake pedal as you will not be needing it and it will start a siren as it believes you have no brakes at all.
~Watch for leaks, brake fluid or vacuum.
~You can pull the pesky ABS sensors that i believe run down to your wheels (where they get clogged with mud and fail or throw codes)
~TEST DRIVE IT SOMEWHERE SAFE and for the love of God if you think I am responsible for your safety after you modify a braking system you are either a level 1 scam artist or dumb.

Drive your sub $150 brake system and smile. No annoying ABS, parts compatibility between (in my case) my truck and the 100 series, and other than the 100 series brake lines to the MC being a little crazy in the bends it all looks very factory. Hope this helps someone. Cheers.
Yota with tires and stuff.


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