FITTING A VACUUM RESEVOIR IN THE BRAKE SYSTEM

[John McCormack]

I've been told by a reliable source that installing a brake vacuum reservoir between the booster an engine will make a significant improvement to the PI TR6 brakes.

Any advice or experience of this modification?

[Coops]

Hi, this is always going to be a useful mod if you tend to use your brakes frequently,for example going down a long hill or towing a heavy trailer. It’s rewarding to fit a vacuum gauge so you can see what’s going on. In earlier years trucks would have servo brakes which also incorporated a low vacuum warning light or buzzer. The main things you need to be sure are sorted properly are the piping and the one way valve  you will need on the vacuum pipe from the inlet manifold. At the moment, you have one where the vacuum pipe connects to the servo. That can stay, but without the other,the vacuum created in the manifold every time you let your foot off the throttle will simply rush back and forth. There’s a lot to be said for having a separate pump creating the vacuum, either belt driven as on some older diesel cars or the electrical option I often see here in the forum, usually Audi sourced, I don’t know if that’s used to run central locking or more? I hope this helps! Regards Alan.

[Mike C]

47 minutes ago, John McCormack said:

I've been told by a reliable source that installing a brake vacuum reservoir between the booster an engine will make a significant improvement to the PI TR6 brakes.

Any advice or experience of this modification?

I don't expect it would make much difference, given that vacuum is stored in the booster and every time you take your foot off the throttle to brake you turn the engine's inlet manifold into a giant vacuum pump.

[BlueTR3A-5EKT]

Triumph fitted a vacuum reservoir to the big PI estate cars.   The tank can be found on Jaguar too.   Pt no C24910.

[Waldi]

Hi John,

As Mike says: with throttle closed when braking you have the maximum vacuum available.

Unless the reservoir provides an instant large volume, I can only see disadvantages:

- Longer line, more resistance. It should be really large capacity, also the lines.

-Additional potential for leaks.

-Space required.

-Added complexity.

The Volvo servo upgrade is the way to go, also on RHD cars.

Just my 2 cts.

Waldi

[Andy Moltu]

There are some alternators with vacuum pumps that can give a relatively deeper vacuum than the manifold

This can be a consideration using some hot cams that don't give as much manifold depression than standard.

[Z320]

Hi,

I did some measurements years ago and I remember being off the pedal the vacuum is 0 bar / 100%.

My car is a TR4A with SU HS6 carbs, means it has air throttles, I don’t know how the PI works, Google tells me TR6‘s have them too.

A vacuum container was for example fitted at my dads MB /7 and my own MB W123 and MB 190 2.5 Turbo

because they had diesel engines - and diesel engines have no air throttle and can not produce any vacuum.

For this an engine driven vacuum pump and vacuum container was fitted,

also for the vacuum driven features which have to work while the engine was off.

For example the door openers and light (angle) regulator.

Also the brake servo was still working with the engine off for 4-5 brakes - but it was risky to trust on this!

In my opinion a vacuum container makes no sense on a car with air trottle

if no other vacuum driven features are fitted in the car.

Others may know better and tell different.

Ciao, Marco

Edited July 19, 2022 by Z320

[stuart]

11 hours ago, Andy Moltu said:

There are some alternators with vacuum pumps that can give a relatively deeper vacuum than the manifold

This can be a consideration using some hot cams that don't give as much manifold depression than standard.

Unfortunately they also require an oil feed which does then complicate it further.

Stuart.

[Andy Moltu]

Not all require plumbing into the oil system, think one of the Vauxhall Corsa alternators doesn’t need an oil feed. 

There was a thread on this a couple of years ago and I cannot find it.

[Z320]

Google tells it it fitted on Opel / Vauxhall Diesel engines only.

Why is this the case, please? 

Edited July 19, 2022 by Z320

[stuart]

12 minutes ago, Z320 said:

Google tells it it fitted on Opel / Vauxhall Diesel engines only.

Why is this the case, please? 

Cheap?

Stuart.

[Z320]

Really cheap is the vacuum from the inlet manifold,

if there would only be one on Diesel engines.

[Mike C]

11 hours ago, Z320 said:

Really cheap is the vacuum from the inlet manifold,

if there would only be one on Diesel engines.

But the inlet vacuum wouldn't do much for the Diesel's power output.

[Z320]

Sometimes I‘m very tired…..