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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?

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).

Jensen Healey
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Good call Jody. I had the same problem.

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?

JodyKerr
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I'd rebuild the MC.

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

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.

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.

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.

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

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

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

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.

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

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?

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.

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

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.

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.

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.

mcguan.2
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Jody,

Any particular brand of DOT 5 fluid I should use?  Also, what's the capacity of the system, i.e. how much should I buy?

JodyKerr
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no particular brand, I've used a couple different ones. I don't remember the fluid capacity of the brakes. I buy stuff in volume because of the number of cars I work on. Accounting for bleeding, I'd hazard 2 bottles should be sufficient.

Greg Fletcher
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Just my 2 cents and based on my specific experience- rebuilding, reboring, resleeving (in brass, stainless, it doesn't seem to matter) or or whatever else you can do to an old master cylinder is a fool's errand. I've done them all multiple times over the years and they have ALL ended with what I can only describe as premature failure and money not well spent. This failure rate varies from less than 1 minute to less than one year of normal driving. On three completely different occasions (using different rebuilt master cylinders), this resulted in catastrophic brake failure meaning I had no brakes to stop the car. This is not a fun feeling and I would recommend you keep the brake system up to scratch and keep it safe by avoiding rebuild masters. Again, your mileage may vary, this is simply my experience with the brake system on the Jensen Healey that an owner is well ahead in installing a new master cylinder. A master cylinder on any vehicle should always be considered a consumable item.

mcguan.2
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OK, so I installed the new master cylinder (the TR6 model) and changed over the brake fluid to DOT 5.  However, I'm still getting a little bit of leakage right behind the MC, where it meets the booster.  Did I miss some sort of O-ring or something?  It did seem a little weird how the two just seem to "go together" without any sort of seal. 

Brett Gibson JH5 20497
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No seal there, sounds like your new master cylinder is leaking.

Brett

Greg Fletcher
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These Lucas units have old school rubber based seals inside and are designed to use mineral based fluids. I don't recommend the use of synthetic brake fluid in a JH system for this reason.

mcguan.2
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Greg, understood, but wouldn't it be strange for a brand new MC (purchased from the club store) to start leaking within minutes of installing?  I completed this whole project yesterday, and literally as soon as I took the JH for a test drive, the MC started leaking out the back.  To me, that would seem more like a faulty piece of equipment than a seal failure due to using a synthetic fluid. 

Has anyone else had anything like this happen?

LambandAndy
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Are you sure that fluid from your old master cylinder didn't leak into the brake booster and that is what you are now seeing leaking out?

Andy

Greg Fletcher
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It shouldn't leak, some people can get it to work with DOT 5 and have no problems, but putting in the fluid recommended by the manufacturer is usually a safe bet. Take a look at the box or the instructions that came with the unit. They usually say what fluid is required, some actually say DOT 5 with void the warranty- it depends on the brand. I would try draining the system, replacing with DOT 3 or 4 and do a complete flushing and see how it works.

JodyKerr
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How much is "a little"?

And what colour is it?

purple = dot5, dirty/brown = old fluid.

mcguan.2
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It's really hard to tell what color the fluid is because it's not coming out in copious amounts, just seeping out. I've been driving it around to see if it was doing as you suggested and just coming back out from the booster side (from the previous MC failure) and it's still coming. It does not appear to be dirty fluid, though, which suggests that it is the new fluid.

I put a white napkin under the booster, but like I said, it just seems to be in such small amounts that it's "clear" if anything. I thought that if it was just residual coming out of the booster, that it would stop after a few drives, but that doesn't seem to be the case. I'm trying to strategize my next move. If I have time tomorrow, I might do as Greg suggested and just empty it all out and try again with DOT 4.



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