T3 '82 model vacuum leak in brake booster

[brujef]

only an issue when you push the brake pedal - no leak until then. web points to faulty seal / corrosion b/w booster and master cylinder or booster diaphragm holed. 
it does not seem that hard to remove the booster to check - but is there a way around having to disconnect the hyd lines from the master cylinder, i really dont want to bleed the system as its not required ATM and a real pain.
any tips / pointers for this issue would be appreciated.
i see new boosters are available if that is required, has anyone had luck with re sealing the junction b/w the booster and master cylinder?
thanks, Bruce

[Andy.]

only an issue when you push the brake pedal - no leak until then. web points to faulty seal / corrosion b/w booster and master cylinder or booster diaphragm holed. 
it does not seem that hard to remove the booster to check - but is there a way around having to disconnect the hyd lines from the master cylinder, i really dont want to bleed the system as its not required ATM and a real pain.
any tips / pointers for this issue would be appreciated.
i see new boosters are available if that is required, has anyone had luck with re sealing the junction b/w the booster and master cylinder?
thanks, Bruce

Just curious when you say there is a vacuum leak? Normally that would wither affect the engine running (runs lean if the booster or vacuum lines have a big leak), or you need to apply a higher than normal pedal pressure (booster not doing it's job).
When you say it only leaks when you brake, that would be normal as there is a balance across the diaphragm until you brake. What are the symptoms though?

The boosters are tricky to get our (I assume it's under the dash like late T3's??). And unfortunately, yes, the master cylinder needs to come out also. They are not that bad to bleed, pulling the booster out is a bigger job!

Yes if it's an old original booster they can certainly get corrosion that affects them operating (not necessarily leak though). The diaphragm themselves are often good. I've re-built a few Bay window boosters and not needed to replace the diaphragm. The master cylinder bolts to the booster, so there's normally just a gasket there. (I've re-built Bay window and late T3 brakes, not an '82 but expect they would be similar).

As for tips, I'd certainly check all the vacuum lines from the engine to the booster, especially connections and the non-return valve before pulling the booster out. These are more likely to fail.

[brujef]

Just curious when you say there is a vacuum leak? Normally that would wither affect the engine running (runs lean if the booster or vacuum lines have a big leak), or you need to apply a higher than normal pedal pressure (booster not doing it's job).
When you say it only leaks when you brake, that would be normal as there is a balance across the diaphragm until you brake. What are the symptoms though?

The boosters are tricky to get our (I assume it's under the dash like late T3's??). And unfortunately, yes, the master cylinder needs to come out also. They are not that bad to bleed, pulling the booster out is a bigger job!

Yes if it's an old original booster they can certainly get corrosion that affects them operating (not necessarily leak though). The diaphragm themselves are often good. I've re-built a few Bay window boosters and not needed to replace the diaphragm. The master cylinder bolts to the booster, so there's normally just a gasket there. (I've re-built Bay window and late T3 brakes, not an '82 but expect they would be similar).

As for tips, I'd certainly check all the vacuum lines from the engine to the booster, especially connections and the non-return valve before pulling the booster out. These are more likely to fail.

Hi Andy - thanks for your input
its an electric conversion Kombi so any issues with the infernal combustion motor and vacuum are eliminated.  i do remember the old petrol (ugh) motor running a bit rough with the brakes on, it was not an issue as the van was obtained solely for the EV conversion and with all the noise you could not hear a vacuum leak. 
there is a 12V elec vacuum pump. it runs to create vacuum and then auto switches off once adequate vacuum reached. it will not run again until the brakes are used and then it will not turn off and you can hear the vacuum sucking under the dash somewhere. once you release the pedal and the vacuum created it (pump) turns off again. also the brakes are not that effective.
this makes me think the lines are fine as there is no leak until you activate the brakes, but I will check the non return valve before going further.  is that in the engine bay or right on the booster?
first stage is to remove the dash and watch it all with the brake pedal pressed and see if the vacuum leak is obvious. 
any other input would be appreciated.
thanks, Bruce

[Andy.]

Ah, I do remember reading your great post. So you're the modern world now and just need electric brakes  (or regenerative braking!)
I forget you had the electric conversion.
It does sound like the leak is at the booster, but still worth checking the hose etc are all good. The check valve is normally just forward of the engine, but with the 12V pump, it may have it's own built in? Is the pump still in the engine bay, or up the front?
As you have already researched it could just be the gasket where the master cylinder bolts to the booster. You'd need to remove the master cylinder, but if the leak is there you could do that without removing the booster itself.
I guess you have the advantage to run the pump with the brakes on and go looking for the leak!

Removing the booster is a little tricky, and assuming it's the same as late T3's you can (just) access and remove with the dash pod etc removed.

If you are delving that far, and have not had the brakes out before, new seals in the master cylinder is well worth the effort. The linkages between the brake pedal and master cylinder are also prone to wear and worth checking while you're in there.

[brujef]

yes, the new world of no infernal combustion engines! I had to buy some fossil fuel the other day (1st time this year) and it was horrifying - really expensive and smelly etc. + it did not last that long too..... 
it does have regen braking (why waste all that energy into your brakes when it can re charge the battery - free power), but you still use the service brakes occasionally .

The vacuum pump is in the engine bay. I will check all the hoses, but the way it only leaks when you press the pedal makes me think the hoses must be fine. 
ill pull off the dash, run the vacuum pump and see if the leak is apparent, hopefully its just the seal b/w the booster and m/cylinder, point noted re re building the m/cylinder if its removed - may as well do it. 
ill also check the link b/w the pedal and booster. 
thanks for the advice.

[Andy.]

Sounds like a good plan, hope you can find it!

Nice to have regenerative braking. It's not free, you just don't throw all your kinetic energy away..
It will be interesting to see what if anything that does to the gear box life. I assume you have a lot more engine braking than a stock engine, even compared to a diesel.

[brujef]

the braking is greater than engine braking, the gearbox seems up to it but lets see - time will tell. if it breaks the gearbox / diff itll be time to go full tesla with no gears

[AC-T3]

if it breaks the gearbox / diff it'll be time to go full Tesla with no gears .

Will be sad to hear if this happens, but then a T3 with a T3 (Tesla 3) is ...... oooohhhhh.

[brujef]

So i have spent the morning on it (wasnt that hard to get out) and it is the booster leaking - problem is where to find a new 1? any ideas. mick motors and just kampers dont have them.
its an ATe unit that does not appear to be openable to replace the diaphragm.

interestingly there was no seal b/w the m/cyl and the booster. i put 1 in but it made no difference....

[brujef]

you tube shows a BMW e30 booster fitting with some minor mods

https://www.youtube.com/watch?v=JhBI1QJoMTo

No idea what he's saying, but it seems straightforward........any ideas anyone?

BTW, whats with those conical headed bolts under the dash into the bracing brackets? some sort of security feature? My 4" grinder with a cutting disk gave them a nice slot for a screwdriver to fit into. 

replaced with nice hex head bolts. what a weird feature