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TR4/4A TR4A Vacuum Advance Question

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Stinger

Stinger

Jedi Hopeful
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Our TR4A's distributor is marked 40795 25D. It has a vacuum advance unit that has a screw in vacuum line. We ordered one from one of the big three going by their catalog and they sent one with the push on vacuum line. What is the correct configuration for our car and could their catalog be wrong?? Thanks
 
Correct is push on.
 
ISTR that 40795A uses a vacuum advance marked 2-6-3 and that it has a metal vacuum line with threaded connector. Should be screw on for the 4A but I could have it backwards. The advance curve is different for the push on advance units used on earlier TR4s.

Here's the parts list for the 40794A for the TR4A:
<span style="font-style: italic">D25 # 40795, lower control plate is a 54412154 or 10 degrees which gives 20 degrees max. advance, the vacuum advance unit is 54413565 (2-6-3), springs # 54411614 and weights 54413073,</span>
 
2-6-3 is the most important spec. So either push on or screw on function the same.
 
Should be a footnote somewhere that the replacements are supplied with push-on connections.
 
You can use a short piece of rubber vacuum hose to couple the original metal to the advance, I think you can just slide the nut back and leave it on the original pipe (vs cutting the pipe). Make sure it's vacuum hose and will not collapse with vacuum.
 
All TR4/4A's originally had push on vacuum advances.

Fit the vacuum they sent, and just cut the screw fitting off the end of your vacuum pipe, and fit a rubber coupling. It was push on at the carby end too, whether Strombergs or SU's are fitted.

The screw on type vacuum advance hasn't been available for many years.

Regards,

Viv.
 
My 65 4A had the screw on connector, and I know that this is the original configuration.

One option is to return the new one, and have Jeff at Advanced Distributors rebuild your original distributor. That was my choice and the car has never run better....believe this is also least expensive alternative, and you know that it has been set up, re-curved, and tested by an expert. Good Luck
 
And all three TR4/4A engines I've worked on have had thread connectors. Perhaps this was a US market vs UK market difference.
 
Threaded connector here as well on my first 1966 TR4A. I'll have to go check my second one...

Scott
 
That's odd, as the push on Vacuum Advance unit was introduced during TR3A production on Dizzy part 40698, model DM2P4 for 83mm engines, and part 40735 model DM2P4 for the optional 86mm engines.

Later TR3A's delivered here had push on Vacuums, as did TR4/4A's.

I can't see why LHD cars would be different, so that's yet another TR mystery.

Viv.
 
As late as 1967 (last year I checked), the Lucas catalog still showed some vacuum advance units with threaded instead of push-on connectors. I thought perhaps that might be the difference between the 40795 and 40795A dizzys, but it does not appear so.
 
I checked this evening and both of my TR4A's have threaded connectors (1966 and 1967). My TR4 factory workshop manual also shows threaded connectors in all the photos of the distributor (same for the Bentley).

I'd definitely say that it was standard since we have 9 cases here with screw-on connectors and it would be hard to believe they all had distributors replaced.

Scott
 
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