Brake Servo / Booster

[Simon_P]

Hi All,

Does anyone know which other cars use the same servo or who it was made by?

Has anyone taken one to bits?

In particular I am trying to work out how the pressure is applied proportionally to the pedal effort - so a cross section would be good. I'm trying to find a diagram for our particular servo.

Thanks for any help
Simon

[Simon_P]

Maybe someone has a picture of one out of the car?

[wayne]

I can help with the pics. Not sure of how you would seperate the 2 halves?
They look to be crimped together.

Attached pdf may help explain the operation

DSC06929.JPG

DSC06927.JPG

brake05.zip

[Brit-Car-Nut]

I don't know if this will help, but here is an overview of the operation:

http://www.autoshop101.com/forms/brake05.pdf

This is more engineering oriented:

http://ode.engin.umich.edu/publications ... -96-12.pdf

Sorry, I just saw Wayne sent the first file in zip form.

[Simon_P]

Thanks, Wayne, John,

I've read and looked and done the tests all seems ok. But when I apply the brake I get the initial assistance and then it sort of runs out of assistance at about half pedal pressure.

From my new/limited understanding, I'm guessing that I don't have full vacuum - anyone any ideas?

It will be a week or so before I can get a vac gauge to test it with.

Thanks,

Simon

[Brit-Car-Nut]

Is it possible your sliders are frozen and you experience the motion of the single caliper piston moving until it runs out of travel and then the caliper doesn't slide giving you 50% of the stopping power? No increase in pressure will move the caliper so you don't get much more braking regardless of how hard you press the brake pedal.

I am just guessing. Please describe exactly what you are feeling/what is happening.

The vacuum check valve could also be bad. They are quite common and I don't believe anything makes them unique. You might try another one. Part # A100J6017F is still a good number at Lotus. It is GBP3.07 so certainly affordable to get one for a test. You should also check the grommet where the vacuum line goes into the booster. If it is leaking, all sorts of issues can occur. Again, the gromets are fairly universal. The Lotus # has gone obsolete, but later MGB, Jag Fords and everyone else uses vacuum assist and they all have an entrance grommet.

[Simon_P]

Hi John,

I've been addressing this issue on and off for a number of years. I have now decided to go through each component in the system.

When I first got the car I read here that I needed greenstuff pads and disks and new sliders - money spent - Hopeless!

I changed the calllipers for Elise AP 2 piston type a couple of years ago - better - eliminated the callipers/sliders as the issue.

I will try to describe further-
upside down in the footwell looking at the servo and pressing the pedal...
1 initial pedal movement takes up slack
2 further movement activates servo (as described in the notes posted)
3 further movement takes up slack in pistons etc until resistance is felt
4 pressure makes smaller movement as brake force is applied - servo follows and gives assistance
5 further pressure results in the inner shaft moving a short distance relative to outer shaft then a "metallic" click and does not provide additional servo assistance - Condition as described in the notes as no Vacuum.

The brakes work ok but after say, half effort I do not get additional servo assistance.

If I do the tests described the servo checks out ok.

If I apply the pedal quickly the movement with servo assistance is shorter
If I apply the pedal very gradually I can get greater movement/pressure
If I apply max pressure with the engine off, then start and tickover, I get the greatest movement.

The feeling is as you describe for the locking sliders, and that was what i thought the problem was. I believe that others may have the same problem as even after brake upgrades they are still not confident in the brakes.

Any help would be gratefully received!

Thanks,

Simon

[Brit-Car-Nut]

More info please: What year/VIN is the car? There were several variations of brake pressure regulators and line designs. Is your's a UK , ROW or FED car? They are a bit different between the versions.

Where are you in the UK? (I am assuming again). I have a used booster currently in Southampton (still installed in a body I purchased) but soon to move to Notts. If that is at all convenient, you are welcome to "borrow" if as long as you can remove it. My mate in Notts might be able to find the time to pull it for me, but if you can do it, it would be easier for me to offer it.

Didn't the early brake system use a pressure valve for the fronts as well as the rears? I remember there were 3 used in some models. Is it possible you have issues in that system?

I will do some conjuring.

[Simon_P]

The car is an S2
I'm in the UK - St Albans

Interesting that you mention the valves - I get a slight pull to the left (front) and the rear left disk hasn't polished-up as much as the left has after having them skimmed.

Thanks for the offer - I believe that the manual instructions start "remove dashboard" so I would like to do a bit more testing first.

[Brit-Car-Nut]

The car is an S2
I'm in the UK - St Albans

Interesting that you mention the valves - I get a slight pull to the left (front) and the rear left disk hasn't polished-up as much as the left has after having them skimmed.

Thanks for the offer - I believe that the manual instructions start "remove dashboard" so I would like to do a bit more testing first.

Pulling and different disk appearance suggests brake line issues or, in the rear, pressure valve issues too. There is a write-up on rebuilding the pressure valves on LEC. Remember to use o-rings that are impervious to brake fluid. It also can indicate that you have some suspension issues like "tired" bushes at the Raft and lower wishbones or possible ball joint issues. It is certainly a good idea to check everything carefully.

Before getting too deep into it, try replacing the check valve. They don't like backfiring and don't last forever. Maybe you get enough vacuum over time to let the booster work at the beginning but the line (valve) is restricted and you are using up the available vacuum faster than the valve is letting it past. I know it sounds odd as vacuum is a negative pressure, but I think you get my drift.

The S2, like the FED did away with the extra pressure valve, so I believe you have lines that go directly from the Brake Master Cylinder to each caliper in the front.

Check each line for clear passage. If you are still using the original fabric hoses, check to see if any are breaking down internally. They will slowly close up and pressing on the brake will get pressure to the cylinders, but the pressure doesn't abate quickly after releasing the pedal. That gives one side an advantage but also heats that side since the pistons never completely pull back.

The rears have the same possibilities although twice as many hoses to fail.

If you are using braides hoses, they can fail too so check for slow pressure return.

To "quick check" for a hose failure, with the car off the ground and the wheel removed, have someone apply full brakes and then release them. Quickly check that you can spin the disk by hand. They should all be about the same difficulty, so do the apply /release process for each corner. None should be very hard to spin the disk.

[Simon_P]

John,

Thanks for the reply.

Front suspension checked and rebuilt; no handling issues, new top ball joints (old ones weren't worn - I couldn't get the bolts out)
Rear Calipers rebuilt, hoses checked, The rear brake pipework is one of the few parts of the elan that I have not had to bits

Fluid changed regularly, brakes bled (and bled, and bled)- good pedal. All wheels move freely - no brake drag

My thoughts are
1. That the valves need looking at / rebuilding or
2. That I have some air trapped on one side that I can't detect as the valve isolates it when the pedal has enough feel - am I clutching at straws? The pedal is very good

I've had the car 10 years and there has been no change, always a very slight pull to the left under hard braking - most people probably wouldn't notice but I'm really fussy about things like that. I had expected that it was the old calipers... but it wasn't!

But first back to the servo
Is A100J6017J the correct no. for the non-return valve (you wouldn't have posted it if it wasn't!) for £3 I'll change it anyway and buy a spare - £20 is what I have been looking at for a suitable part - I'll change the hose as well - the grommet looked ok but I will change it if I can find a suitable replacement. The manifold end of the hose is held on by an oversize jubilee clip I will cut the end off the pipe and put a new clip on in the meantime.

I need to check all of the other take-offs from the plenum but will do this when I have a vac guage and have identified all of them!

[Brit-Car-Nut]

Have fun. Let us know what you turn up.

Sorry: A100J6017F (NOT J) is the inline check valve for the booster vacuum line.

[Simon_P]

Wow! I wouldn't normally have questioned the number and haven't checked.

I will do - likely to be slow progress though

[Brit-Car-Nut]

The part number system at Lotus is exasperating. The easiest way to get your part is to use the middle portion as the part number, 100J6017 is what you would lookup. That will get you ALL of the variations which usually show the supercessions. Then you follow the list to find your part. Sometimes it gets a bit tricky as they change a design or the compound of a something like a bushing and give it a new prefix but keep the old prefix active. Some bushings around the raft and the front inner rear arm bushing are examples of multiple versions of a part number all still being active. Then, they love to mark the differences with a slap of paint. GM had nothing to do with helping that system! It doesn't help that I am a bit dyslexic and with 3 letters mixed in, I sometimes swap the middle and end letters.

Sorry to not have verified the number. I fixed it in the original post as well.

[Simon_P]

Ok - here is an update.

Rear callipers taken to bits and rebuilt - OSR had one slider that was stuck appears to be the reason the disk didn't clean-up
Proportioning valves taken to bits checked rebuilt - easy enough following the wiki - nothing wrong there, didn't need to change the 'O' Rings - on the 2/15 valves the larger 'O'ring is 8.8mm id
Removed Master cylinder - took to bits - easy enough following notes in the M/C thread - nothing wrong there.
Bled brakes went for a drive - not much improvement.


Notes for removing Master cylinder (RHD)
Remove the reservoir first to give access - no need to move the PAS reservoir or the wheel arch liner.
When removing the level sensor - the little black cap flies off and disappears to the depths of the engine bay - you have the reservoir in on hand and a screwdriver in the other put a piece of tape over it to stop it flying away.
The off-side nut is accessible, but much easier is 2ft of 1/4" drive socket extension bars, threaded under the PAS reservoir (straight on to it)
The Near-side nut and pipe connections are either with a spanner in front of you, or right arm across the back of the plenum (as for the oil filter change) full reach, and very uncomfortable.

[Brit-Car-Nut]

Simon: Sounds like you have removed a lot of possibilities from the list of causes. Did you ever get the check-Valve for the booster? I know it is over 2 hours away, but there is still a used booster in Notts, near Doncaster. The body is reasonably stripped, but not as much as the last one. If you are interested, I can provide some pictures. Just PM me. The booster is yours for the taking.

[RayD]

...

The "Notes for removing Master cylinder (RHD)" have been added to the Wiki

Ray

[Simon_P]

Ray,
Thanks, I would have taken some photos, but I was too busy looking for the little black cap - Could have saved myself an hour, by reading the federal M/C wiki "Pry off the black plastic cap. Be careful it pops right off. - I still haven't found mine. It is only available by purchasing a new reservoir. "

Brit-car-nut,
Yes, I replaced the non-return valve - Stratton Motor company had it in stock and it was only about £7 delivered. When I took the old one off there was a good hiss of air as I released the vacuum, so I don't think there was much wrong with it. I replaced the hose from the valve to the plenum and put a new jubilee clip on - No noticeable change.

I will replace the other hose to the servo - should have done it while I had the M/C off as access was easy - too busy looking for the bloody little black cap... with a torch... at 1am

Since my last post I have bled the brakes to death...callipers off... rubber mallet... Twice! a noticeable improvement to overall feel - less tendency to lock up the left front first, I even locked-up the right front which was a surprise. I think that is down to lots of bleeding through the M/C in particular - I have put about 4 litres of fluid through! But I still get the feeling of lack of braking assistance after about half pedal pressure.

After rebuilding everything I am back to looking at servo vacuum. According to elanscan I get 0.33 bar (absolute) manifold pressure at idle. So now I need to rig up a gauge to the servo line.

I also need to sort-out the O/S handbrake self adjust, as the piston is coming further back than it needs to.

Any ideas?

Simon