Hi guys, I am looking at a 1974 Jaguar XJ12 that has had a 350 GM transmission with a lock up converter and a brand new 350 GM V8 engine installed because of a blown 12 for $ 4,250.00. The shop with the car is selling it with a mechanics title because the owner could not pay for the new engine to be installed. I am looking for a daily driver that I can use while my 26 Model T is in the garage and this came to my attention.


Problem #1:
The shop is telling me that rust is getting up to the carb and shutting down the engine - they have installed 2 filters in line besides the original. The shop said you can open the filler cap and see the rust - but when they drained the tanks they did not get any rust. They said for me to be able to drive the car I need to pull the tanks and clean or replace them.
QUESTION #1: What all is involved in pulling the tanks?


Problem #2:
The horn does not work on the steering column so they installed an accessory horn button, but the state they are in will not let them title it on the road because accessory horn buttons are illegal - so no tag.
QUESTION 2: What are common problems with the horn buttons that would cause this?


QUESTION #3:
What the heck is a "lock up converter", we never had one of those on our old 88 jag sedan that I recall?



Thanks in advance…

Travis E. Towle
785-408-3409 cell
Topeka, Kansas

 

QUESTION #1: What all is involved in pulling the tanks?

• Remove rear 1/4 bumpers, (probably have to take whole bumper off)
• Remove rear silencer boxes
• remove rear 1/4 panels
• remove round cover plates at rear of rear wheel arches
• remove fuel filler caps complete
• drain tanks at drain plugs
• disconnect fuel pump wiring
• disconnect fuel pipes
• undo tank bolts
• lower tank to ground.

QUESTION 2: What are common problems with the horn buttons that would cause this?

I can't answer this as I've never had the problem, but suspect the upper steering column will need removing to inspect and correct connections.

QUESTION #3:
What the heck is a "lock up converter", we never had one of those on our old 88 jag sedan that I recall?

It is a lock-up clutch on the torque converter so all slip is eliminated once the car is in cruise, to improve fuel consumption. Modern Jaguars now have it too, like mine.

 

The tanks....removal is easier than is sounds but removing the rear 1/4 panel screws is a real pain. There are many multi-step tank sealing treatments which convert the rust then seal the tank with an epoxy like sealant. But you have to be creative in getting any scale out. Some people use pea gravel, ball bearings or shot and shake the tank, if you do make sure you inert the tank with exhaust fumes. Since your car is already heavily modified you could ditch the side tanks and install a 12-15 gallon fuel cell in the unusable space right behind back seat. You could drop some weight and move some to the center of the car and improve the Jag's already great balance. You might as well replace the fuel lines too, they can rust too.

The horn...I've seen the contact brush ring at the base of the column fall apart. If this is the case you'll need a new column. A column from a 80's series 3 will fit and is an improved design. You might get lucky and just have a band ground or bad contact on the brush ring. This will be very easy to observe with the column valence removed. Could be a bad horn, horn relay wiring....start with a test light. Connect the test light clamp to a 12v source and the test lite point on the ground brush. Press the horn and the test light should shine.

The trans....A Turbo Hydomatic 350C transmission is one of my favorites of the era. Some built TH350's have harsh engagement but this is considered normal if not too severe. The lockup is great and will let the torque converter lock and have no slip. It's almost a 4th gear and is great for highway cruise and efficiency. No slip mean less heat and less heat is less wasted energy and longer transmission life. The question is what controls the lockup. The trans should only lock up above about 35 MPH and under light load and whenever the break pedal is not depressed. B&M has a device that is adjustable and does the speed and pedal logic. You can accomplish the load logic with a vacuum switch or skip it. The lock up may need be hooked up or some transmission shops rewire the valve body to always be locked up in 3rd gear. I'd consider that an impediment to driveability and the wrong approach. Make sure the lockup operates properly and the transmission cooler lines are not looped.