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Mushy brakes  Rating:  Rating
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 Posted: 01-05-2011 12:00 am
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mcguan.2
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About a week ago, my brakes started getting really mushy and the pedal was going down to the floor on some stops.  I put it up on the jack and bled the brakes, but the problem just came back.  I bled 'em again, and they were fine until about two minutes into the test drive.

I don't appear to be leaking any fluid.  It's particularly noticeable when the car is running a little rough after a cold start.  Any thoughts?

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 Posted: 01-05-2011 12:05 am
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JodyKerr
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Take a serious look at the master cylinder/brake booster as well as the inside of your firewall/carpet. I'll hazard a guess that the MC is leaking into the brake booster (thus not seeing it).

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 Posted: 01-05-2011 02:03 am
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Jensen Healey
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Good call Jody. I had the same problem.

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 Posted: 01-05-2011 06:11 pm
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mcguan.2
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Thanks for the tip.  It *does* appear that there is seepage between the MC and the booster, but not a lot, so it wasn't too noticeable.  In your experience, did that mean the MC was shot?  Or, what would be my next move?

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 Posted: 01-05-2011 06:25 pm
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JodyKerr
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I'd rebuild the MC.

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 Posted: 01-14-2011 03:26 am
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pbahr
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I've had a similar problem in the past.  Rebuild the MC first.  I'm certain that's your problem, as you don't have leakage at the wheels.

YELODOG

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 Posted: 01-18-2011 02:56 am
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mcguan.2
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I pulled the master cylinder and it looks like the bore is pretty corroded, so I'm thinking of getting a new or rebuilt one from Delta or the Club Store. While I'm at it, I'd like to replace the brake hoses with SS versions.

A question: Since I'm doing all this, I'll be bleeding out the old brake fluid and putting in Castrol LMA Dot4 (I don't know what was in there already). As such, any thoughts on how I'd know when I bled enough out (maybe a volume capacity?). I figure I can easily catch and measure the fluid as I'm bleeding the brakes.

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 Posted: 01-18-2011 03:16 am
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CarlosThe Jacker
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The old fluid will probably be a darker color, you should be able to tell when the new fluid comes out. ATE used to make the same fluid in two colors so it was easy to tell.

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 Posted: 01-18-2011 03:38 am
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JodyKerr
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Do you have the Jensen Healey MC or are you already running a TR6 MC?

And I've started converting everything to DOT5. So far I'm a big fan, and am not missing having to change out brake fluid every couple years or risking my paint job being stripped when there's a leak.

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 Posted: 01-18-2011 04:11 am
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pbahr
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Jody,

Now you've opened a can-of-worms - using DOT-5 silicone fluid.  I'm certain that the both of us are going to get blasted ! ! ! !

I've run DOT-5 in the JH for 15+ years (and my 911 as well), including lots of track time on both and swear by it.  I've done the research, and the rubber compounds used 25 years ago are compatible with silicone fluid.  Of course, the today manufacturers can always change the compound, and might do so as long as it is compatible with the DOT-3,4.

Well, I did have to rebuild my MC a couple of years ago, but really can't blame that on the silicone, because I think the rubber would fail in much less than a year if it was not compatible.

YELODOG

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 Posted: 01-18-2011 02:15 pm
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Brett Gibson JH5 20497
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Well blast it Pete, wish I had put in silicone when I painted the engine compartment, now I have a few paint / brakefluid bubbles to show for not doing it. lesson learned.

Brett

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 Posted: 01-18-2011 05:04 pm
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pbahr
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Please heed the warning:

"Of course, the today manufacturers can always change the compound, and might do so as long as it is compatible with the DOT-3,4."

Pete

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 Posted: 01-19-2011 03:04 am
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mcguan.2
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Jody,  I have a Jensen Healey MC, at least according to one of the old posts on the forum.

Also, take it easy on me here, fellas.  All this talk of different brake fluids is starting to freak me out.

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 Posted: 01-19-2011 03:17 am
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JodyKerr
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Ok, in regards to Master Cylinders.

You're not going to be ale to buy a new MC. You can either rebuild the one you have or convert to a TR6 Master Cylinder. There's no functional difference, but if you're trying to keep the car original it's a consideration. (on the off chance you decide to go with the TR6 MC, can I have your old one? :)

And on to brake fluid.

Don't fret too much about the brake fluid. Basically you can either stick with DOT3/4 or go to DOT5. The reason I went to DOT5 instead is that it does not absorb moisture like DOT3/4 does. If you are properly maintaining a car that uses DOT3/4 you should be flushing your brakes every two years to remove absorbed moisture. The other reason I went with DOT5 is that it is not harmful to paint. I've seen too many paint jobs ruined by leaky brakes.

 

Jody

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 Posted: 01-19-2011 04:14 am
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CarlosThe Jacker
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When you convert to Dot 5 is there anything special to do, or just bleed the old out thoroughly?

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 Posted: 01-19-2011 04:25 am
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JodyKerr
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Nothing super special. The last conversion I did was on my mum's Spitfire. I had the MC and PDWA off the car at the time. From there I opened the bleeder valves, put rags securely over them, and then used a low pressure setting (~15-20psi) with an air nozzle to blow out the lines.

Then you add the DOT5, and start bleeding the system. The fluid I happened to buy was purple, so it was pretty easy to see when the last bits of the DOT3/4 were out and the DOT5 was all the way through. If by chance there's a little left over in the lines it's no big deal.

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 Posted: 01-19-2011 05:50 am
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pbahr
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When I did YELODOG, it had been in a garage for 10 years and all the brake lines/components were frozen or gunked up.

I opened all the joints, soaked and flushed the glycol out of all the lines with methyl/ethyl alchol.   Then used air pressure to fully clear an dry the lines.

YELODOG

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 Posted: 01-19-2011 10:54 pm
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CarlosThe Jacker
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Thanks Jody and Pete, thinking of going over in my modern Honda next bleed, soounds like it will last longer. Not sure what my prospective JH will have in it, probably 4.

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 Posted: 01-20-2011 12:33 am
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JodyKerr
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You need to double check on the Honda.

You have to be sure that the ABS system can handle DOT5.

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 Posted: 01-20-2011 06:26 pm
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mcguan.2
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Thanks for the help, Jody. I'm not especially concerned with keeping my car original, so the TR6 should work for me. Sure, you can have my old one. Contact me at my username@gmail.

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