Brake servo cylinder

[LanciaFin]

Hello,

Anyone familiar with the internals of the servo cylinder? When I dismantled mine, I didn't pay much attention to the location of parts, thinking that I have all the parts books and manuals anyway. Well, that turned out to be a mistake, because the pictures are not that accurate... Didn't make the same mistake with the master cylinder, though. My question is, that which spring is for the front circuit and which for the rear one?
https://onedrive.live.com/redir?resid=5 ... hoto%2cjpg
On the master cylinder the stronger spring (thicker wire) was on the front circuit, maybe it's the same with the servo cylinder?

Any suggestions how to remove the brass inserts from the pistons? 30+ years of sitting unused seems to have them stuck quite dearly. Valve are behind them, so they must be removed.

Regards,
-Miika

[grifo63]

Hi Miika, I can't help you so much because when I'd dismount the servo I didn't note the difference but also I didn't mix parts ; I've checked on the brake manual drawings and I can't see any difference in size but in the spare part manual springs codes are different also for first series. Anyhow also to me make sense that the stronger is for front brakes section.

About brass insert it's strange, I did'n find any difficulties to remove them; may be you have to sink for a while the servo into strong solvent, in order to remove any dirt, and then try again. Of course, after, I would reccomed to replace all rubber gaskets.

[bmw8890]

Miika,

I rebuilt my servo unit about two years ago and in the initial build I had several issues that I had to address to get the system to work properly and one was reversing the same springs. From my memory and taking a look at the attached servo cross section the strong spring is installed in the rear circuit chamber. The rear circuit push rod is held open by a light spring (small blue circle) and when brake pedal pressure is applied to the circuit it overcomes the light spring sealing the rear circuit port valve. So the heavy spring (large blue circle) allows the light spring to bottom out and also reduces the fluid pressure for the rear circuit.

Another issue I had was with the master cylinder check valve springs being too weak so I was not getting a good seal thus not enough fluid pressure going to the servo circuit.

Make sure you have no vacuum leaks particularly around the vacuum end cover gasket or the brakes will tend to stay on after you release the brake pedal. I used a RTV sealant on both sides of the gasket to correct the vacuum leak issue.

Make sure you soak the assembly in a light penetrating oil to avoid corrosion to the aluminum parts.

Once I addressed all the issues the car braking system was as good as todays cars

Brian

[FL30]

Hi Miika,

i do not have a dismantled servo at hand, but you should consider the following thoughts.

Both springs have to push back the pistons of the corresponding circuit upon release of the pedal. The first spring is retained against the front end plug of the servo (rear circuit), the second, weaker, spring is supported against the rear circuit assemby, pushing the front circuit components back.

I´d say that it it makes more sense to put them this way. If you put them the other way round, the strong spring could prevent the weak one from full expansion, at least theoretically.

What do you think?

Best regards

Hubert

[LanciaFin]

Hello everybody,

Thank you for your suggestions. Unless further information appears, I'll follow Brian's advice, and try with the stronger spring in the rear circuit. If it doesn't seem to work, it's not that bad to get the cylinder apart, as it is quite easily accessible.

It will take its time to get the results, though. I'm just slowly assembling the car after a complete rebuild, and the wheel cylinders are still waiting for restoration from their corroded state.

Regards,
-Miika

[bmw8890]

Miika,

Make sure the rear circuit slave cylinder is installed passed the threaded stop (circled in blue). This prevents the strong spring from acting on the small rear rod spring in the static assembled position.

Brian

[LanciaFin]

Brian,

Thank you for this advice! I'm quite sure that this could have gone unnoticed from me.

Regards,

-Miika

[bmw8890]

Miika,

When you get a new seal kit make sure the cylinder piston rod seal ID is the correct size for the piston rod before you install into the servo housing. My kit had a seal for a larger piston rod OD and I did not discover the leak until I went thru a lot of brake fluid creating a big mess. You will not be able to detect the leak right away because the brake fluid leaks into the slarge vacuum chamber.

Brian

[flavia1800]

Hi Mika,

a good help to get the brake servo cylinder mounted correctly (and other parts as well) is to visit the restaurationflavia.over-blog.com/ It's a very well documented,, logicially explained and easy to understand. Really worth to visit when you get stuck.

regards Gunther

[LanciaFin]

Ok, things are going well and I'm putting the parts back together. The brass inserts in pistons came out after soaking overnight in penetrating oil. Not really much rust, just dried brake fluid and other junk.

Time for the next question: To get the servo piston to resting position for adjustment, a bracket 8053055 should be installed after taking the lid off, according to the repair manual. Unfortunately I dont have this 8053055 - which basically seems to be like the lid with a hole in the middle - so other means will have to be used. Is there some known trick to do this with home tooling, or should I make a copy of this factory tool 8053055?

Regards,
-Miika