Lotus Elan

Elan Plus 2 Twin Circuit Brakes

PostPost by: nigelfletcher » Wed Nov 12, 2003 1:24 pm

Hello All. A sad story.....

I own British Elan +2 which I crashed after total brake failure. I have traced the fault to a dodgy seal in the master cylinder. It happened totally out of the blue whilst I was travelling downhill (typical).

In order to prevent this happening again I'm in the process of installing a twin circuit braking system, loosely based around the federal setup. I've sourced a new old stock federal master cylinder which will bolt straight in, and I'm also renewing all the brake lines and unions to cope with the change. However I'm a bit unsure as to what to do with servo assistance. My current plan is to attempt to run without a servo and see what it's like, but I was also thinking of copying the Triumph GT6 setup and only adding a servo to the front brakes. Does anyone have any experience of this kind of change? I don't really want to go down the route of two servo's that the full federal setup uses because it's expensive, and seems a little over the top. Any ideas....?

Nigel Fletcher
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PostPost by: Ramsden » Wed Nov 12, 2003 4:52 pm

Nigel,

I own a late plus 2 which which has a dual circuit system using a single servo. I have only recently acquired the car and have no idea whether the setup is original.

The system uses the standard single circuit master which feeds, via a length of copper brake line to the back of a single lockheed servo located on the opposite side of the engine bay. This in turn activates a dual circuit master cylinder. Only the single circuit system has the plastic reservoir tank.

Thinking about it, this system would not help you in the event of a faliure of the single circuit master cylinder.

Does anyone else have a similar setup?

Simon
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PostPost by: patrics » Tue Nov 18, 2003 11:11 pm

Hi Nigel,
Its not a good idea or save to use a single hydraulic servo with a dual circuit master cylinder.
On the standard set up the hydraulic pressure is the same for both front and rear brakes. If you connected a servo to the fronts only then this would reduce the rear pressure by half i.e. if front pressure was 40 bar then rear pressure would be 20 bar - assuming a 2:1 ratio.
The overall effect of this would be very early front brake lock.
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Steve
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PostPost by: 1964 S1 » Sat Nov 22, 2003 2:18 am

I've got a federal booster assisted 1969 +2 which stops quicker than I've ever needed but has brief vacuum faults if the car has sat for more than a couple of days. (Pedal soft, needs pumping on the first few stops.) If you can figure out an actual dual brake line system without any power assist that's what I'd recommend. The boosters are nice but unless you're either driving very hard or not paying attention, I personally don't think they're necessary. Keeping the rotors, calipers and pads in top working order without power assist will make a +2 stop quicker than most cars on the road today...
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PostPost by: nigelfletcher » Mon Nov 24, 2003 8:20 am

Thanks Guys,

I think I'm going to go ahead with an un servo'd (boosted) dual circuit braking system. The federal master cylinder I have has a 60:40 split for the front/rear brake lines. If I then feel that the brakes are too hard (and/or my right leg too weak) I'll add two small servo's rather than one big one to the front. When I've done this I post up my thoughts and results.

Cheers

Nigel
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PostPost by: patrics » Tue Nov 25, 2003 9:30 pm

Hi Nigel, didn't mention it last time but you need a small diameter master cylinder (0.7") to keep the pedal efforts down.
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Steve
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