Lotus Elan

Connecting a brake servo to a vacuum source

PostPost by: seight » Fri May 01, 2015 3:45 pm

Hi!
We have for several years been experience a brake pedal in my fathers 69 S4 Elan which feels really hard and requires a lot of effort to work properly (we are having trouble locking the brakes at the front on tarmac). We are now thinking about fitting a brake servo to make the brakes easier to use.
Where would we hook the brake servo up to get a vaccum source? Does any of you have a picture of an engine bay from a car fitted with a brake servo, which shows the vacuum hoses?

Thanks in advance

Tor
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PostPost by: Europatc » Fri May 01, 2015 11:28 pm

Welcome Tor.
The vacuum is via the inlet manifold. There is plenty of information and diagrams available on line. Do you not have a workshop manual?
good luck
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PostPost by: mbell » Sat May 02, 2015 12:56 am

Hi Tor,

Have you checked the size of the master being used on the car to make sure it is correct bore size?

There alot of different bore sizes available in the same style/fitment master cylinders so it may have been swapped out for a different sized one. I think it should be 7/10.

My +2 had a 7/8 on it which had very little movement and was very hard. I've swapped it for a 5/8 as the servo has been removed from my car. A smaller master is another option to trade pedal effort for pedal travel...
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PostPost by: seight » Sat May 02, 2015 7:52 pm

Europatc wrote:Welcome Tor.
The vacuum is via the inlet manifold. There is plenty of information and diagrams available on line. Do you not have a workshop manual?
good luck
Stuart


Thanks!
We have the original workshop manual, I checked the sections for engine, fuel system, and brakes. But I have not been able to find information or diagrams about where the vaccum connectors goes.
Pointers would be appreciated.

Tor
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PostPost by: seight » Sat May 02, 2015 7:56 pm

I did a quick check to see if I could find the size of the master cylinder, but couldn?t find it.
Is it on the underside of the master cylinder so that I need a mirror to see it?
I'll have a look again tomorrow, but any pointers is appreciated :)

Thanks

Tor
mbell wrote:Hi Tor,

Have you checked the size of the master being used on the car to make sure it is correct bore size?

There alot of different bore sizes available in the same style/fitment master cylinders so it may have been swapped out for a different sized one. I think it should be 7/10.

My +2 had a 7/8 on it which had very little movement and was very hard. I've swapped it for a 5/8 as the servo has been removed from my car. A smaller master is another option to trade pedal effort for pedal travel...
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PostPost by: types26/36 » Sat May 02, 2015 8:18 pm

Here is a pic of a couple of m/cyls that have the size shown but I have also seen them with the size on the underside and some with no size on at all.
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PostPost by: billwill » Sun May 03, 2015 11:41 pm

To answer your original question, the vacuum for the servo comes from a T pipe (items 9+10 ) in picture) screwed into the side of the front inlet manifold pipe of the cylinder head. One 'branch' of the T goes to the headlight lift system and the other to the brake servo. You should fit a non-return air valve in the feed to the servo (item 8 in picture).

Servo
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PostPost by: billwill » Sun May 03, 2015 11:57 pm

PS: Many of us have REMOVED our original brake servos, having found they were more trouble than they were worth.

see:
lotus-suspension-f42/seized-brakes-remove-the-servo-t33902.html
for example.
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PostPost by: seight » Mon May 04, 2015 10:25 pm

Thanks just what we have been looking for :)
billwill wrote:To answer your original question, the vacuum for the servo comes from a T pipe (items 9+10 ) in picture) screwed into the side of the front inlet manifold pipe of the cylinder head. One 'branch' of the T goes to the headlight lift system and the other to the brake servo. You should fit a non-return air valve in the feed to the servo (item 8 in picture).

Servo
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Headlights
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PostPost by: seight » Mon May 04, 2015 10:31 pm

That is indeed a consideration. It is just that we have been struggling with the poor brakes for years, not being able to find a solution. We have tried different pad material with no luck.
The size of the master cylinder will be considered.

Thanks
billwill wrote:PS: Many of us have REMOVED our original brake servos, having found they were more trouble than they were worth.

see:
lotus-suspension-f42/seized-brakes-remove-the-servo-t33902.html
for example.
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PostPost by: billwill » Tue May 05, 2015 12:09 am

seight wrote:Thanks just what we have been looking for :)


The parts diagrams are in the Wiki that Jeff our webmaster is preparing.
http://www.lotuselan.net/wiki/Lotus_Elan_Wiki
in the "Shop Floor" portion.

Click the "Wiki-COMING SOON" link near the top of forum pages.
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PostPost by: seight » Sun May 17, 2015 9:26 pm

For those of you that are running without a brake servo, what sort of brake pads do you use which still gives good braking and good brake feel?
If you have a good recommendation, we might try new pads if the master cylinder check out

Thanks

Tor
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PostPost by: rgh0 » Mon May 18, 2015 9:17 am

There are a number of high coefficient road usable pads including Ferodo DS2500 and EBC greenstuff. I have used both on my S4 with no servo when using on the road. When racing I use Hawk 9712 blue compound but this is extremely abrasive and causes excessive disk wear when cold and not suitable for road use due to this.

cheers
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PostPost by: seight » Tue May 19, 2015 5:42 pm

Thanks!
Then we have something to go by, I have successfully used Ferrode DS2500 in other cars previously :)

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