Lotus Elan

Mixed silicone and mineral brake fluid together by accident

PostPost by: berni29 » Fri Jul 08, 2005 10:05 pm


I have just bought (another) +2. On the test drive there was an illuminated red light on the dashboard with "fail" next to it. Before driving home I checked the brake fluid, and sure enough, there was hardly any in the cylinder. So I filled it with mineral DOT 4. It turns out that the car had silicone fluid in it, and had had for 18 months. The leak was found (braided hose) and fixed. I have bled more mineral fluid through the system but cannot get a hard pedal. During the hose change the master cylinder ran dry.

I am wondering if my helper was not pusing the pedal down fast enough to get the air out. Is that possible?

Any suggestions appreciated.

Racing green +2s with green tints. See it at:

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PostPost by: 1964 S1 » Sat Jul 09, 2005 1:53 am

Hello Berni, how many +2's? I too have a soft pedal in my '69 but still very driveable. A leak on a braided hose? At the end of the hose? We've got to stop your inventory growth and get you on the road ! Which hose was leaking... You found a Lotus with an illuminating "FAIL" light? Disconnect it !
Helper pushing fast enough? You need a slow pusher with slow deliberate pushes to the floor and holding the pedal down... How many plus twos do you have? ...
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PostPost by: type26owner » Sat Jul 09, 2005 3:08 pm

The DOT4 stuff I think is a glycol based fluid. It should be densier then the silicone and it's okay to flush the system in this direction. The silicone should float to the top and since the bleed screws on the calipers are also at the top the silicone will get flushed out. The silicone fliud is great stuff as long as you never get it really hot. The stuff becomes extremely compressible then and even though there is no air in the system it's quite possible to push the brake pedal all the way to the floor and have no brakes at ALL.

If the clutch has been filled with the silicone fluid you're in trouble and don't know it yet. Apparently the seal in the slave cylinder is a silicone one. Silicone fluid is the only solvent for the silicone seals and it will attack it slowly. After about a year the slave cylinder will fail due to the seal turning into the consistancy of chewing gum.

Go buy a set of one-way check valve bleeders for the calipers and the clutch slave cylinder for a few quid. You can do the bleeding by yourself then. Only downside with that method is you can't see the bubbles coming out of the bleed tube.
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PostPost by: Rob_LaMoreaux » Sun Jul 10, 2005 1:09 pm

You may have gotten some air into the master cylinder and that is why the pedal doesn't want to go hard. Probably the best way to deal with this would be to use a power bleeder like the ones that look like a garden sprayer reservoir/pump chamber.

Otherwise you may need to bench bleed the reservoir to get the air out of the master cylinder.

I'd probably go with the power bleeder method so I was sure to get a lot of new fluid through to clean out the silicon.[/quote]
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PostPost by: type36lotus » Mon Jul 11, 2005 1:42 am

What Keith say is goodness. I installed these on my brakes and clutch. Makes life so easy. I now change my brake and clutch fluid annually, instead of almost never. The brand I bought were called Speed Bleeders. I used SB3824 3/8 - 24 the long ones for the brakes, I think the clutch was the same except you can use the short ones there.
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PostPost by: berni29 » Mon Jul 11, 2005 3:49 am

Many thanks for the replies.

I have looked the up Speed Bleeders and they look really good. I will get a set of those. I did bleed the brakes again this weekend and have a pretty good pedal now. I think that I am OK with the clutch because the fluid looks a bit gungy. I will be bleeding that next.

The reason that I have so many plus 2 bits is that I crashed my original one, but shortly before that had bought a complete (26,000 mile but derelict) one with the intention of restoring it, then I learnt about painting fibreglass and couldn't face it, then I saw a JPS that needed a chassis, halfway through that I saw this green plus 2 that had been rebuilt and that I could drive straight away. Plus in the middle I bought a galvanised (complete) rolling chassis. Now I have to do something about it all. I love driving a plus 2 again though.

I have already sold the excess engines, except for the JPS, which is complete.

All the best
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PostPost by: carrierdave » Wed Jul 13, 2005 8:16 pm

Hi Berni,
I too have the rather strange cork float device in my master cylinder ? I think I have got it too work but generally I just ignore it if it comes on.
When I changed my master cylinder I had problems with bleeding the system, I would get all of the air out of the calipers but still had a soft peddle. I think I then read a posting that Keith commented in ? It spoke about bench bleeding of the master cylinder. It also went on to talk about sticking a large heavy weight on the brake pedal over night.

This basically applied continuous pressure to the master cylinder in the hope that the air bubbles would get squeezed out. The first time I tried it I was amazed at the results. I also find that you need to push the pedal down slowly, you get a far better bleed off from the caliper.


PS. I must give you a call about those wheels.
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PostPost by: Si_130/5 » Thu Jul 14, 2005 11:05 am

"I also find that you need to push the pedal down slowly, you get a far better bleed off from the calliper."

Thanks carrierdave and 1964 S1 for your vindication,

Simon (berni29's slow pushing bleeder) :)
Last edited by Si_130/5 on Tue Jan 17, 2006 11:08 pm, edited 1 time in total.
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PostPost by: DJThom » Tue Jan 17, 2006 10:14 pm

When you get a chance, I would suggest taking your calipers apart, cleaning everything and putting them back together with the fluid of your choice.

Several years ago, my dad flushed his XKE brakes with silicone. As one of the above posts indicates, the silicone fluid floats. The result is some mineral fluid sitting at the bottom of your calipers that never gets flushed out and that collects moisture. The result several years later: new pistons and slieves all round.
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PostPost by: Dave-M » Tue Jan 17, 2006 10:58 pm

"Go buy a set of one-way check valve bleeders for the calipers and the clutch slave cylinder for a few quid."
Kieth, Is aCalifornian Quid the same as a British Quid?
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PostPost by: elansprint71 » Wed Jan 18, 2006 11:55 pm

........dismantle the car, sell the parts on eBay, double your investment, buy a two seater!

You may have to do this twice to get into the Elan +0 market at the moment, though. :P

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PostPost by: bengalcharlie » Thu Jan 19, 2006 4:04 am

Why would you do that Pete?
the plus two is a very underrated but fantastic sports car and in my opinion a more balanced a prettier car than the baby elan and cheaper so plusses all around!



PS One day they may be even rarer than the baby elan due to people wrecking these beauties for parts!
up goes the value!
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