Brake Tech-- a big DUH

JeffYoung

JeffYoung

New member
Here is something I learned over the last few weeks.

We've redone all of the brake lines on the TR8 and Jensen over the last few months. Nice stainless ones on the TR8, too.

But, despite that and despite a residual valve in the rear line to help with pedal feel, the first stroke on the brake pedal on both cars was always soft. We bled the brakes endlessly to no avail, and just figured it was more old car crap.

Wrong. A few weeks ago, Ron noticed that on both cars, the lines in places were higher than the master cylider. Big duh there. THis of course allowed the fluid to drain back towards the M/C, creating space in the lines. We fixed the Jensen before the driveshaft disaster and voila, instant firm pedal feel.

So, if rerouting your own brake lines, make sure they follow a downward path from the M/C. Or at least that is my experience.
 
Good call. The other issue that hurts the initial pedal stroke is sometimes rotors that have runout, or loose bearings, which result in the pads being "slapped" back a bit. Usually it's minor, but it can become an issue.
 
Good call. The other issue that hurts the initial pedal stroke is sometimes rotors that have runout, or loose bearings, which result in the pads being "slapped" back a bit. Usually it's minor, but it can become an issue.
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Newbe mech. but getting better. How do you check rotor runout (bearings are tight)? I am having issues with my brakes, new master, was going to replace calipers and power booster. Thanks.

(Double post - duh)
 
Get a run out gauge, pretty cheap I think. It bolts to the hub, you turn the rotor and it reads runout. Harbor Frieght has them I think.
 
I'd want to bolt it to something like the upright or caliper, and then you can yank the disc around to see if the bearings are loose as well.

If the bearings are loose, you can tell by yanking the rotor at the 12 and 6 positions and tring to move it in and out, then at the 9 and 3. It can even be felt on the ground with tires on sometimes.

If the discs are warped, it will show up when you rotate them as the runout guage will pulse. Warped discs are oftne easy to feel thru the pedal as well. Stainless steel brake lines help the feel.
 
You'll probably have better luck at the tool counter if you refer to this tool as a Dial Indicator and Magnetic Base.

If you ask for a runout gauge the 19 year old clerk is probably just going to give you a dumb look. :wacko:
 
i had a customer put on his own pad before a track day and some how he bent a pad witch became a big return spring,caused a low pedal. it was had to find. i havenot seen it happen before or since,(15 years) but it could happen. food for thought.

I will keep the brake line location in mind from now on, thanks!

lael
 
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