Brake Servo Rebuild?

[Rob_LaMoreaux]

I think by dead weight he meant hydraulic dead-weight in the brake
system. I have driven a the same model of car with working and
nonworking vaccum boost and a non-assisted model. The worst was the
non-working vaccum boost which was three times more effort than the
non-assisted model. The working vaccum boost was just slightly less
effort than the non-assist model. Of course this was with a modern
vaccum assist unit that is between the pedal and the master cylinder,
but it seems to me that it would be the same with any boost. The extra
effort is to move the vaccume diaphram and springs to get the boosted
side to move, in addition to having less hydraulic effort from the
master cylinder diameter.

Robert D. LaMoreaux
BT Electronics LLC
22700 Heslip Dr.
NoVI, MI 48375
Main Phone:(248)-348-6560
Direct Phone:(248)-348-6504
Fax:(248)-348-6558
Email:***@***.***
Alternate Email:***@***.***

[gobw2]

UH- OH LET ME REPHRASE THAT what I meant was the force required to move
the servo guts. like I said - no experience with elan type, but on USA
ford, (GM usa uses same system) the diaphragm and stuff inside has to be
moved thru it's normal travel to actuate brakes, as it is between pedal
pushrod and master cyl pushrod. Not only did one have to actuate the
master cyl piston, one had to actuate all the stuff in the servo that
vacuum would actuate on a working one. It was impossible to brake hard
with that inoperable thing in there. Once got it out, could lock
wheels. Not as nice as with power unit, but safe and operable. George
On Thu, 28 Sep 2000 15:13:20 +0100 "Sean Murray" <***@***.***>
writes:

[ddddumas]

Don't know about Kevlar pads, but generally both racing brake pads and racing
tires don't work so well on the street because they both have to be heated-up
considerably before they work well. This can be dangerous if you're not
expecting it.

Paul Garrett
'66 S2

["fred23"]

Sean said:

"I would welcome any suggestions how to get an improvement here."



I notice that the brake pad part number changed when they went to power
brakes. I strongly suspect that they went to a compound with a lower
coefficient of friction. I believe good results can be obtained by changing
to a pad that is used by non power brakes, either Lotus or Triumph. After
all, much heavier cars than Lotus work OK without power brakes.

Fred McDonald

["David Comeau"]

--- In ***@***.***, Steve Heath <heathste@r...> wrote:



Steve & Lotus Elan list

The small diameter girling servos (elan) are 2:1 boost.
The large diameter girling servos (+2) are 3:1 boost.
The boost on a dual servo system system is no greater because there
are 2 servos. There are 2 because of the federally mandated brake
failsafe system have to seperately function on their own in case of a
failure of either half.

David Comeau
Co founder NELLI
Lotus Ltd
Pittsburg LOG 19??
Brake Servo Tech Seminar Instructor

[yanni]

Hi to all

The actuation of the brake pedal raises the engine idle from the normal 850rpm to 1200-1500rpm.
At the beginning, I thought it was due to a brillant 'anti-stall' conception, but I feel that the suction I hear when I brake causes the mixture to be modified in the manifold, and subsequently increases the revs. I don't like the idea that a servo could temporary modify the settings of my carbs.
Anyone has an idea of what is happenning, and if this reaction is normal. Could this be a contribution to burn my valve seats ?

Yann
S4/SE 4500219

[kstrutt1]

Yann,
I would sugest your servo is shot, from memory (someone correct me if I am
wrong)the servo should not flow air under braking, under no load the servo has
vacum both sides of the diaphram (therefore equal pressure and no assist)when
you apply the brakes air (at atmospheric pressure) is let into one side of the
diaphram giving assist, when you release the brake pedal the atmospheric port
is shut and both sides of the diaphram linked again(ie no pressure differental
and no asist), the air in then sucked back into the inlet manifold via the one
way valve until full vacum is achieved. I would guess either the valves or
diaphram are damaged in your unit.
When I re-built the unit in my +2 I was able to buy all the components from
Norton Classic Servo's in the UK(01494 563254), they specilise in parts and
re-builds for Girling and lockheed servos.

Kevin

[Rob_LaMoreaux]

It sounds like your carbs are a little rich at idle, and the servo(s)
are leaking air when the brakes are pressed. This leans out the mixture
and the idle goes up. And yes this could easily contribute to burnt
valve seats (too lean a mixture).

Robert D. LaMoreaux
BT Electronics LLC
22700 Heslip Dr.
NoVI, MI 48375
Main Phone:(248)-348-6560
Direct Phone:(248)-348-6504
Fax:(248)-348-6558
Email:***@***.***
Alternate Email:***@***.***

[Frank Howard]

First, burnt valve seats are usually caused by not enough valve clearance.
Second, you have a leak in your servo and it needs to be removed or rebuilt.
Your fuel mixture is not suspect. Hope this helps.

Frank Howard
Minneapolis, U.S.A.
71 Elan S4 SE
74 Europa TC Special

[Rob_LaMoreaux]

Thanks for correcting me. I'm going to need to learn all this when I
start my new job in a couple of weeks since I will be designing
powertrain test equipment including Combustion Analysis systems, and
engine test cells.

Rob LaMoreaux
Ann Arbor, MI 48108
Phone: (734)-971-5583
Work phone:(248)-348-6504
Work Fax:(248)-348-6558
Email:***@***.***
Work Email:***@***.***
Too many Hobbies, Too little Time, and way too much work.
1969 Lotus Elan...It's not a restoration, it's a never-ending adventure.

[lotocone]

Valves can definitly become burnt by too lean a mixture. I am an experienced valve burner. (bad front frame x-member/vacuum resevoir on S2 - burned #1 valve till it split!)


Ken Claiborne
26/4396
50/0118N
So California

["David Comeau"]

--- In ***@***.***, "Yann DELCAN" <yann.delcan1@l...> wrote:


the
mixture to be modified in the manifold, and subsequently increases
the
revs. I don't like the idea that a servo could temporary modify the
settings of my carbs.


1 A "good" servo sits normally with vacuum on both sides of the
diaphragm. No air should be passing thru the check valve to the
engine
manifold.

2. When the brake is depressed, air is supposed to enter throught
the air control (T valve) one side of the vacuum pod and press until
the "called for" pressure is satisfied (over simplified). This is the
hiss you hear. However, at this point NO air should be passing to the
engine, and NO idle increase should occur (in a good servo).

3. Upon reduction(or elimination) of "called for" hydraulic pressure
the air valve opens to allow the engine to reestablish the vacuum.
Only at this point should the additional air influence the running
performance of the engine. This would be normal.

4. A continuous cronic leak could burn a valve, but only the
occasional brake use should not.

5. The servo is only getting vacuumed at light throttle settings,
like
16-20" mercury, WOT (4-10" mercury) will not remove the air and
charge
the servo with the vacuum.

So the way you've described your problem , I would say No it is not
normal

hope this helps
Dave