Lotus Elan and Lotus Elan Plus 2 Forums

Update on my servo. I just separated the vacuum chamber & found that the diaphragm had a large split in it, so one problem solved. I also found what I think is engine oil in this area which I have no idea where it could have come from. The other explanation is that it is brake fluid, I am using a synthetic fluid. Whatever it is this appears to have attacked the rubber of the diaphragm thereby causing the failure. I will disassemble the rest of the servo in the next few days to see if one of the seals has failed.

saildrive2001 wrote:The other explanation is that it is brake fluid, I am using a synthetic fluid.

You don't mean silicone fluid do you ? My rebuilt servo came with a warning not to use that. Synthetic dot 4 is what I use with no issues.

Sorry for the error, yes I mean synthetic DOT4 fluid.

Keith
That answers a lot of things I have never seen a split diagphram before and silicone fluid is definitely a no no in the classic car world. Silicone is a poor lubricant

I'll take a picture of the diaphragm & post it later. I am now sure that the fluid is brake fluid & as I said originally & then repeated I am using synthetic DOT 4 fluid.

Here are two photos of the diaphragm, one shows the split & the other the distortion of it due to the fluid attacking it. The area where the brake fluid has been sitting is quite soft & gummy.

Saildrive
It certainly looks like a solvent of some kind has attacked it. More like dissolved than torn.

I think that's a better description, it really is like it has been dissolved by brake fluid. The unit was rebuilt in 2013 & I have put on about 10,000 miles since then.

The destruction of servo diaphragms is often due to the failure of the vacuum check valve either in the pipe or at the actual servo vacuum connection.
As you cruise along or decelerate with a nice vacuum inside the servo and manifold it’s fine however, when you then accelerate the vacuum inside the manifold is lost so the built up vacuum inside the servo pulls air AND FUEL from the manifold into the unit.. resulting in what you now see!
Used to be, new servo? Change the check valve or no warranty!

Hello Keith,

I'm late to this I know, apologies for that. It sounds like the last post has hit the nail on the head, fuel or oil has rotted the diaphragm which is veg oil complaint but not mineral (engine oil) or fuel (particularly with the high Ethanol content of modern fuels). Just a final word of advice, even thought your car only does small mileage (same for most if us!), it is still important to change your brake fluid every 2 years, longer than that and it will absorb more water than is good for it, resulting in low boiling point and high chance of corroding master, slave, caliper piston and servo bores. Its a commonly overlooked point, but even a car sat with only a few miles per year still needs the same brake fluid change cycle as one doing 20k per year.

Regards, Jonathan

Hi Jonathan,
No problem with the later reply, it's winter here so no driving the Elan for a few more months. I have shipped the valve block to J & L in the UK. I will post what they find with the valve block assembly. There is no question that the diaphragm was attacked by the brake fluid. There was absolutely no smell or evidence that gasoline or oil had entered the chamber. The one way valve in the servo works correctly & there is no evidence in it or the hose to show any oil or fuel leak. In Canada we can still buy gasoline without any ethanol in it which is what I use. I did flush the brake fluid a couple or more years ago but I must admit I don't do it religiously every two years.

Here is an update on my servo problem. I sent the valve block back to J L Spares in Lancashire & they found that the piston was the wrong size & rebuilt it with the correct size one. The local rebuilder also added an additional return spring in the vacuum can that is not standard. The only explanation I have for these two errors are.
1 I took to them a MK1 servo & the MK2 that they rebuilt, they said the MK1 was not able to be rebuilt. I can only assume they maybe got the the two pistons mixed up.
2 I had an intermittent problem where the brakes would lock on when stopped. I returned it to them 3 times to try to solve the problem & each time they said when they bench tested the unit that it worked fine. I think that they thought the problem was the piston & diaphragm not returning fully, so they added another spring to stop what they thought might be the problem.
I have used the car four times since getting it back on the road & the brakes are better than they ever were after the rebuild by the local shop. They are as they should be.
The shop here in Ontario is a locally recognized rebuilder of all automotive hydraulic systems.