Triumph Repair/1968 Triumph Spitfire Brake Line Fittings
QUESTION: We are restoring a 1968 Triumph Spitfire Mk III. In doing so, we are replacing all the brake lines. However, we've ran into a problem area. One of the lines from the master cylinder to the PDWA valve and from the PDWA valve to the front? brakes has larger thread on the fittings than that of the standard brake lines (3/8" thread). The brake line is 3/16". We've gone to several auto parts stores to fine these fitting, or adapters with the proper thread, without success. What size threads are used, and do you know of a source from which to obtain the fittings?
ANSWER: Hi Jim,
I was working in the dealership in 68 and it was about that time or early 70's when BLM started to make all British cars metric brake lines. I don't think they were Witworth or BSF as that was only on the much older cars. But I do remember some metric stuff showing up on all the British cars back then. Moss Motors makes a statement that metric started later from chassis # CC81079 on up on the TR-6 cars. Plus you have the problem that anything on the car could have been changed as it is 44 years old.
First try some metric nuts on the line fittings to see if that was the problem. keep in mind that there are three different thread pitch sizes for each size metric bolt size. Only two sizes in US bolt sizes. If that don't work, get a tread gauge and measure the threads to see what size it really is.
Carefully measure the size of the threaded part of the fitting and the line size and the thread pitch and call Moss Motors to see if they have them. 1-800-667-7872
---------- FOLLOW-UP ----------
Thanks for the response. The OD of the fitting mics up as 0.422 inches. that would convert to 10.7 mm. If it was metric, I would guess 11 mm. However. that's an odd size. We did try the "standard" metric sizes at the autoparts stores but without success. Short of finding the proper fitting, I suppose I could cut off the old nuts and reuse. If it was just my PDWA valve, I would eliminate it. but, the master cylinder has the same thread so I need at least one.
I run into the same problem often as I restore British cars and I found an assortment of bleeder valves at an auto parts store a long time ago so I don't remember the store. I use it often to gauge size of master cylinder holes and wheel cylinder and caliper holes for thread size. I just try a bunch of bleeders in the hole until I find one that fits right and then I just measure that bleeder valve threads to ID what line fitting it takes.
When I have a line fitting it is easy to just try different nuts on the fitting until you find one that fits it to ID it. The trouble with the metrics is that they have three different thread pitches for each size nut so you need a big assortment of nuts to find the right size.
Your .422" and 10.7 mm is also very close to what a 7/16" is. You didn't tell me what the threads per inch was so I would just take a 7/16" fine and course thread nut and see if either fits it. If they don't fit good then go to a bolt & nut company and try all three metric 11 mm nuts on the fitting. Most bolt companies sell thread gauges that have US on one end and metric on the other end and they are not very expensive. I have to use one all the time because all of the old British car have all three sizes of bolts and nuts on them. BSF, US and Metric all on the same car. 80 to 90% of all British sports cars were made for the US market so that is why ever since the MGA in 1956 most of the bolts and nuts are US. But even on those cars there are Witworth nuts in some places. Then in the late 60's and early 70's they started putting some of the brake lines in Metric. Then you add the problem that some mechanic or owner of the car changes parts so in the 40+ years of the car's life there is no telling what is on the car. So you need to be able to measure thread pitch and sizes.
I don't have much trouble with that now because I keep my bleeder valve assortment and I have a good metric nut and bolt assortment and a coupe of thread gauges. And I get to use them often.