Lucas distributor vacuum advance units

1948-1989

Lucas DVX, DMBZ6, DM2P4, 22D, 25D, 35D, 45D, 36D, 47D

We stock many more not listed.

$89.95 ea.

Below is our list of all the original proper vacuum unit part numbers and advance codes originally installed on you vehicle when new.

The O.E. Part number represents the unit type “Hex or cup chamber, link type, threaded or hose fitting and operating advance code.

Unit s are not interchangeable unless they have the same code. A hose unit may take the place of a threaded line unit or vice versa, but a unit with the wrong code will effect how the engine runs and may cause damage. Always order units by referring to the O.E. distributor number to assure you receive the proper O.E. unit.

Operation of the distributor vacuum advance unit.

Vacuum units are not interchangeable unless they carry the same identification number, as each unit is made up to suit a particular engine. Additional control of the spark timing is brought about by the vacuum unit. As the unit is connected to the engine intake manifold, its operation depends on the vacuum  present in the manifold.  The vacuum effect varies with the engine load. The vacuum unit produces additional advance when the engine revs are high, but mainly when the load is light. At full throttle when the engine is pulling hard the vacuum unit becomes wholly or partly inoperative. The general effect of the vacuum unit is to increase the liveliness or performance of the engine and enhance a noticeable improvement in fuel economy. Proper vacuum advance function depends on a tight vacuum line. Failure due to cracked, chafed pipes or loose unions, result in vacuum advance unit failure to operate!

 Many units checked for code operating specs are found defected.

Most vacuum gauges are calibrated in inches of mercury. The Mityvac vacuum pump can be use to check fairly accurate movement. 1- Check for the correct unit. Units are not interchangeable. 2 - Check the unit holds vacuum. If the unit leaks, it needs replacing. 3 - Check for proper movement. Most over looked, effecting performance, mileage and cooling. The vacuum units operates within the range indicated by the 3 digit code next to the part number. Example; the code 5 12 8 indicates, the unit starts to advance at 5 mercury "vacuum", will reach full advance at 12 mercury "vacuum", with 8 degrees total distributor ignition advance / 16 degrees spark advance at the crank. Units that no longer hold vacuum are obviously bad. It seems most people are under the impression that if the unit holds vacuum, it's considered in good operating condition. This assumption is wrong! Not obvious is a majority of original units are dry, stiff or plugged with condensed fuel vapor restricting proper movement and many operate well above the coded range. This renders the unit inoperable with very little benefit, if any at all. Replacing an original unit with a fresh new unit, often has a significant improvement in overall performance, mileage, cooling and often for much less that expensive engine modifications.

 Disclaimer:Re-manufactured Lucas® distributor vacuum units by British Vacuum Unit, which is not affiliated with ZF Friedrichshafen AG, the owner the US trademark for Lucas®.

 For the first time in 60 plus years "British Vacuum Unit" is the only manufacturer in the world of
early original type hex chamber distributor vacuum units.
Accurate in detail & operation, made for specific vehicles and part number.

State the original unit part number you need with your contact information.

All shaft units supplied with the full 4 pc micro-adjuster kits.

"micro-adjuster parts have not been available for years!"

We can manufacture any unit you request, such as our

special 1971-76 TR6 vacuum advance. "Not retard"

Takes the place of the original retard unit and delivers the performance of the 1960s.

All DVX 2 stud and DM units with "large vacuum cap" can be ordered by code.

Many early Lucas units were manufactured with only the code for ID.

Let us know the unit type and 3 digit code stamped on your brass or aluminum cap.

We have all coded units in stock.

Understanding the Distributor Vacuum Unit

Used to control fuel efficiency, running temperature and power when not under load. Old vacuum diaphragms are most likely dried out and stiff, coated with gummed up fuel vapor or leaking. A loss of significant performance!

The “mechanical advance distributor” is totally different from the “vacuum advance distributor”.  The mechanical advance distributor controls ignition for performance under load and is usually installed on high performance engines.  The vacuum advance distributor is used on most vehicles to enhance performance when not under load.  Once up to cruising speeds and/or steady RPMs, the vacuum safely advances ignition to enhance mileage, power and running temperature.  The vacuum unit is most often overlooked and because of its age should be checked during regular tune-ups. Ignition timing is greatly affected by any worn or loose linkage to the point plate from the vacuum unit.  Frozen or leaky diaphragms are easy to check by installing a vacuum pump or a simple vacuum hose to the unit and create vacuum.  The point plate should move with a good operating unit.  If the unit needs constant vacuum or has no movement at all the unit is in need of replacement. 

Replacing a worn out vacuum unit will usually result in a noticeable increase in power and performance. Note that when you simply disconnect the vacuum unit, it fixes nothing.  The mechanical advance on a vacuum advance distributor is calibrated for under load conditions only.  You lose peak performance the other 95% of the time you are not under acceleration. 

Vacuum units are unique to the vehicle.  The code shows the specification of vacuum advance.  Example; 7-18-12 code indicates 7 lbs of vacuum, the amount of vacuum the unit starts to advance, 18 indicates the lbs of vacuum at full advance and the 12 is the degrees the unit advances.  If you are assuming this makes little difference, consider the distributor turns half the speed of the crankshaft.  This amounts to a total loss of 24 degrees of ignition timing when not under load.

  British Vacuum Unit stocks vacuum units for all British vehicles 1950 through 1970. Manufactured to original

 appearance and exceeds OEM specs.

Any units not stocked can be built.

State year, vehicle type, model, engine size.

To build any unit by request, we need to know the type: hex chamber or cup,

 spring or pin link, part number and code.

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