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The brake Master Cylinder

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This series is divided into seven sections:
Part 1 - Why it goes bad and what it feels like (and why your pedal goes to the floor)
Part 2 - Removal and replacement
Part 3 - How to bench-bleed the new Master Cylinder
Part 4 - What the Master Cylinder looks like inside
Part 5 - How the Master Cylinder works, and why the pushrod needs to be set correctly
Part 6 - How to check the pushrod freeplay (a link to the bottom of Part 2)
Part 7 - How to adjust the pushrod freeplay
Note: All pictures can be clicked on for LARGER versions!

PART 7: How to adjust the pushrod freeplay

I don't think Honda really wants you messing with pushrod adjustment. Otherwise why would they have made it so cryptic?


What it looks like and where the adjustments are:

Honda factory-spec pushrod adjustment
To the left is how Honda wants you to adjust the pushrod: Booster OFF the car, and with one of those famous "Special Service Tools" that nobody ever has, including a lot of dealers.
This is WAY more trouble than it's worth, especially since it's easy to do it with the booster in place. You just have to modify a few tools.

Take a good look at the booster diagram at the upper left, then the ones below.


Adjustment points       Complete assembly

This should enable you to make sense of the photographs below.

"Star locknut" The "Star locknut" was a bit of a puzzle at first, until I discovered it was just a 12-pointed 14mm hex, like the closed end of an ordinary combination wrench.

We will modify one 14mm and one 17mm combination wrench in our quest to adjust the pushrod on this Integra. Your car may have different sizes, so check first.



Getting at the pushrod adjustment:

Knee bolster removed The first thing we need to do is remove the knee bolster. This is an invaluable step that allows people larger than a chihuahua to perform this procedure. For general details on how to do this, click here to go to a Main Relay page that requires the same thing.

View of linkage, where adjustments are
I've crawled under the dash, camera pointing straight up. Damn, it's snug under there...

The "Star locknut" has already been loosened here. I did that before thinking I ought to take a pic first.  Do NOT allow the Adjusting Nut to rotate while it's free of the "star locknut"!

The booster is at the top of the photo while the pedal is at the bottom.


To summarize, we need to:


The actual adjustment procedure and tools needed:

We need tools before we start. The problem is that the "Star locknut" will NOT take any sort of open-ended wrench I know of, and I discovered that, as you work, open-end wrenches keep trying to fall out of place on you. For this reason I want a "claw" shape, like a brake flare wrench. More likely to stay put as I fiddle around.

Four tools will be needed:
With the wrenches, I had to modify them so I could get them to be thin enough, be the right angle to get around the pedals, and to stay on when I wasn't actually holding them. A grinder, a Dremel, and a torch were needed.

Closed ends opened up with grinder First thing was to grind off a slot in the tops of the closed ends of the wrenches. The slot was made just large enough to pass the pushrod. I want it to hook on once it's on the nut, so it is less likely to fall down.

Since the pushrod is connected at both ends, you can't just slip the wrench over the end unless you take everything apart first; you have to treat it like a hydraulic brake line.

Faces ground off
Next I ground the 17mm wrench head down evenly back and front. I took it down to a thickness of 5mm, or 3/16". The faces were left square, with no chamfering. You'll need as much bearing surface as possible for that skinny Adjusting Nut.

The 14mm wrench was ground flat only on the back face, the one that meets the Adjusting Nut. The "Star locknut" is similarly skinny, and the chamfer that's normally put on wrenches takes too much away from a secure hold on the locknut, making it prone to slippage.



Side view of wrenches
Since space is very tight between the firewall and the pedals, the angle of the wrenches needed altering.  Heating the wrenches cherry-red with a propane torch and pulling them to the angle you see was enough. My daughter enjoyed watching this part, especially when I dunked the red-hot wrenches in water to cool them.

See how skinny the 17mm's head is? It's now no thicker than the wrench's  shaft. Took some grinding, too. The metal wrenches are made of is pretty hard.

Wrenches together
This is what the wrenches will look like once you have them in place on the nuts.

The 17mm will go closest to the booster (the left side in this photo)


Wrenches hanging - one view
Wrenches in place, hanging Bad angles and very limited space meant I had to rotate some photos after the fact so things would be recognizable. Sometimes it was not possible to look through the viewfinder or even the camera's rear screen, so I had to guess where the camera was aimed (thank goodness for digital cameras!).

Here the wrenches are in place on the Adjusting Nut and the "Star locknut". To loosen them, you need to place the wrenches more-or-less as shown, use one hand to press them in place over the nuts, then use the other hand to squeeze them together, like you were closing a pair of pliers. There's no room for any other approach. And you must keep them fully-seated on the nuts or they will slip.

You must use both wrenches. If you don't, you'll rotate the entire assembly, changing the pedal height. This is how you keep the Adjusting Nut from rotating.

I put a dab of Wite-Out on the bottom of the pushrod so I could tell if it rotates on me. You don't want it to rotate just yet.


Loosening pedal height locknut
Once you've got the Adjusting Nut and the "Star locknut" free, you can loosen the pedal height locknut with a regular 12mm wrench. Just crack it loose. It does not need to be turned any more than that for now. Make sure the pushrod has not turned. Turn it and the Adjusting Nut back to their original positions if they move.


Turning pushrod The pedal height adjusting nut (opposite its locknut) is welded to the back of the clevis, which is pinned to the pedal arm. If you use the 17mm wrench to keep the Adjusting Nut from rotating while you turn the pushrod with a pair of pliers, the distance between the pedal height nut and the Adjusting Nut will not change, so the pedal height will be unchanged even as the free play changes. The locknuts themselves will not alter any clearances.

By the way, this photo was posed, and I forgot to put the 17mm wrench back for the picture. Don't rotate the pushrod until you secure the Adjusting Nut! If you can reach it, you can just use a finger to hold the Adjusting Nut still.

I discovered that one turn of the pushrod was worth approximately 6mm at the pedal. I ended up turning the rod clockwise 1.5 turns, which removed about 8mm of free play at the pedal.

The screw thread goes the usual direction:
Clockwise (in towards the booster) REDUCES free play.
Counterclockwise (out away from the booster) INCREASES free play.


All done!
Now you can snug up the locknuts (making sure the rod does not rotate) and check your pedal freeplay. If it's less than 5mm but still present, you're fine.  Make sure the locknuts are all good and tight and put the knee bolster back. If a test drive sees the brakes lock on again, the free play is still insufficient. You've done something wrong. Start over.

And when you've done it right, WHAT a difference! My brake pedal was transformed after I set the free play to what ended up being 2mm. You wouldn't think 8mm would make much of a difference, but to your foot, which has become accustomed to a certain feel, it's a world of difference. My pedal now feels better than that on my wife's Tercel, which is only 6 years old and has been the beneficiary of the same sort of maintenance that my '91 Integra has been given (as long as we've had it, anyway).