Jaguar XJ12 1981-89 Series III and XJS1982-89 OE 54405202 vacuum advance unit
Jaguar 5.3 ltr V12 HE distributor36DM12 41879
This isNOT the replacement JLM519
New OE type unit with the adjustablelimiter.
Lucas number 54405202 stamped 5 15 12limited as original to 5 12 8 spec.
Customer feed back always the same.Example;advanceunit has transformed my e type v12, 14mgp before just cheched it now21mpg unbelievable thanks very much if ever u need a reference for auk owner give them my no i will tell them how good your units are.54405202 Jaguar V12 vacuum advance.RegardsRob
All our products have a 2 yearwarranty.
30 day any reason return policy.
Any questions please ask beforeordering.
Disclaimer:Re-manufactured Lucas® distributor vacuum units by BritishVacuum Unit, which is not affiliated with ZF Friedrichshafen AG, theowner the US trademark for Lucas®.
It appears in the process of superseding part numbers, it was not realized the original 1981-89 Jaguar V12 H.E. 54405202 5 15 12 with the advance limiter, was set to 8 degrees advance.The 54402504 5 15 12 known as the JLM519 is set to code with 12 degrees advance.
The 54405202vacuum unit was the original equipment vacuum unit on the 1981-87XJ12 and 1982-89 XJS with #41879 36DM12 HE Distributor. The 54405202came stock on the cars when new and immediately superseded to theJLM519. Maybe because it cost less! The54405202 had a code of 5 15 12 but all the OE 54402502 units I\'vechecked, have been set to advance at 8 degrees. This unit has aadjustable advance limiter. With the ¼ lock nut lock loosened thelimiter stop is adjustable from 8 to 12 degrees.Thismakes sense to me because all the Jaguar guys I\'ve talked to, agreewith me, 8 degrees vacuum advance is enough for the Jaguar V12engines. Any more may cause pre-ignition. 8 degrees vacuum advance atthe distributor is an additional 16 degrees advance at the crankshaft above mechanical advance.12degrees vacuum advance as with the 54405204 seems to be to much forthis V12 engine! This may be why you hear of pre-ignition with theV12 engines and often hear timing needs to be turned back. Justturning back the timing is not the cure. This retards the much neededmechanical advance under load contributing to more heat, loss ofmileage and performance. What we don\'t want is more heat under thehood. TheV12 41879 distributor has8 to 10 degrees mechanical advance.Withinitial timing set at 12 degrees advance, total advance should bearound 28 to 32 degrees at the crank if mechanical advance isoperating properly.Withthe original 54405202 advancing 8 degrees, 16 degrees on top of thetotal mechanical advance at the crank would be just about the perfectcombination for a nice running engine. Note: this is very close to theearly 1960s XKE that had 8 degrees vacuum advance.Anotherreason I made the 54405202 is when a customer opens the package hewill see a part that looks like the part he is replacing. Customers like to feel they are receiving the original replacement parts. Theycan also reference the new unit with the old unit part number stampedon the old and new unit.
