I am installing an Audiovox cruise control (Rostra) in my 64 MK2 3.8 MOD. I need a vacuum source for the servo. The instructions advise against putting a "T" in the vacuum line for the brake servo. Can anyone give me an idea on what I should do about a vacuum connection?

Thanks.

Lin

 

Does it matter, the brake servo has its reservoir _ should be plenty of vacuum ?
How big is the port on the cruise control, if it's small it won't matter.

Plus the fact there is no other vacuum port on the manifold anyway _ not that I can remember.
I just bolted mine back on, and the only one is for the brake servo.

 

I don't know why the instructions with the kit say to not use the vacuum line for the brake servo.
Lin

 

Hook it up with a "T" and if it work, great, if it doesn't you'll have to make your own port.
1/8 pipe thread fitting works well, if you don't mind making a small hole in the manifold. Probably at the other end somewhere, but you will have to be carful of the water jacket _ that would be the tricky part.

Best just use a "T"...
In a moderen car where there is no reservoir, it may be an issue.
They also may be just covering the liability issue of someone messing with the brake system on a car.

 

I will give it a try, but it will be a while before I can test it.
Lin

 

My '60 has a vacuum line coming off the carbs that does the vacuum advance for the distributor- not sure what the '64 used...
That could be an option though.

 

Probably not a good idea there, as a vacuum change in that area will effect the carb directly.
That vacuum port is there intentionally to effect the vacuum advance in the distributor directly as the butter valves are opened and closed.
If the cruise control port was fed off of that area, the vacuum advance would not work properly.

 

As Mike Eck pointed out to me when I was wondering about using the carb vacuum port, that port has no vacuum at idle. I really hate to violate the directions that came with the cruise control, but I guess that I will.

Lin

 

Lin, I assume the reason for not tapping the brake vacuum reservoir is safety (and lawyers) - thinking the cruise will require the greatest vacuum for open throttle, when manifold vacuum is lowest - possibility of drawing from the reservoir? As Jeff notes it's hard to imagine exceeding that tank's capacity to drive the cruise servo. Is the motor assembled yet? Even if so it's simple enough to pull the intake manifold and add a tap if you're concerned - nothing wrong with doing it right.

 

Hi,

I know this thread is a month old now so the OP has probably installed the system already, however, if not it occurred to me that the S-Type uses vacuum for the heater valve and scuttle vent.

When I restored one years ago I remember that it has a small tank under the n/s wing for this which was connected to the larger tank under the o/s wing (note that i'm in the UK so this will be the other way around in the USA).

If I remember correctly the small tank served the scuttle vent and heater valve. Might be possible to use the same system and components for the OP purpose.

Hope this is of help.

 

That would probably work well, but the OP has a Mark 2 and unfortunately the scuttle vent is not vacuum operated on a Mark 2.
Do you have an S-Type, where is the vacuum port on the intake manifold tapped off of for the scuttle ?

 

Thanks for the responses. I have now discovered that Rostra makes an electronic servo/controller that does not require vacuum, so I am now going that route.
Lin

 

I see that the OP has replied and has found another way to achieve this, for reference I was suggesting that the OP could use the S-Type setup on their MK2.

Having looked at the SNG barratt website to remind myself it appears that the S-Type has T Piece in the line, please see below link.

SNG Barratt - The Ultimate Jaguar Parts Specialist

This then feeds a little reservor under the wing on the other side from the servo which can be seen here.

SNG Barratt - The Ultimate Jaguar Parts Specialist

If it was good enough for Jaguar to install a T Piece then it should be good enough for us!