View Full Version : TR6 TR6 Brake Issue

12-15-2009, 08:08 PM
I just upgraded my brake lines to stainless steel Goodrich lines and also used synthetic fluid. Took it for a test drive and now it feels like the booster is not working. The pedal is nice and hard, but makes a slight "poof" sound when I depress it and there is very little braking power. I did a hard brake test and the thing barely stopped.
Anybody experience brake booster failure after doing the upgrade I did? Also, what exactly does a failed brake booster feel like? Comments, criticism, etc welcome!

12-15-2009, 08:31 PM
Here's something you can try to determine if the brake booster is functioning: With engine running and foot firmly on brake pedal, turn engine off. If no downward movement of brake pedal is felt when engine stops (or a feeling of the pedal becoming more firm), it's usually pretty good sign that there is no vacuum assist.

12-17-2009, 12:47 AM
A better test is to apply and release the brakes several times with the engine off, then start the engine while you press on the brake pedal. If the booster is working, the pedal will sink slightly once the engine starts.

The booster doesn't touch the fluid; so it shouldn't be affected by changing lines & fluid. Sounds to me more like there is something else wrong, since it shouldn't be all that hard to lock the wheels even without the booster. Could the pads & rotors have gotten contaminated while you were bleeding the new lines?

12-17-2009, 12:49 AM
Another thought, was the MC disturbed or replaced during the process? Sometimes the pushrod needs to be adjusted or replaced to accommodate differences.

12-17-2009, 09:16 PM
Could the pressure differential valve shifting cause these brake problems?

12-18-2009, 12:14 AM
Could the pressure differential valve shifting cause these brake problems? Not unless it is clogged somehow. It never "shuts off" the flow of brake fluid, and in fact is not a valve at all. It only senses pressure differential, and closes a switch if the differential is high enough to move the piston.

12-18-2009, 03:46 AM
I have the very same problem Zach. If I put too much pressure on the brakes, there's a "PFFFT!" and braking power goes way down and I have to quickly let up and reapply. I can do this at a stand-still and I notice that after the PFFFT the engine revs a little higher and I hear a hiss if I keep the pedal depressed, so I'm convinced it has something to do with the vacuum assist, but I have yet to resolve it. But I haven't really been trying too hard to resolve it yet. I'll share any discoveries with you as I make them.

12-18-2009, 10:31 AM
sounds like a tear or hole in the rubber bellows inside the booster. if you have one of those hand held vacuum pump you can pull a vacuum on the port that goes to the manifold and if it wont hold your booster is bad


12-27-2009, 11:41 PM
Thanks for all the replies guys! I got busy over the holidays and forgot about this thread. I think I may have determined the problem. I went out to the garage two days after I first drove it and discovered that the brake fluid had all leaked out from the right front. I inspected the caliper and its totally blown, so that I believe is the problem.
I have a rebuild kit on the way for both front calipers, so we'll see how that goes. Ironically, I know what caused this too. A few months ago, I did a few laps at the local racetrack in the TR. On the way home, the right front bearing disintegrated on the freeway, so I lost the brakes and the front hub was literally warped from the heat, though I did manage to get it safely off of a VERY busy freeway.
I installed a new hub and bearings and had the rotor resurfaced and was back on the road. A few months later, the right brake line went, so in went the braided lines. And now the caliper goes. Guess I should have checked everything more thoroughly...