Overdrive fuse size for '54 Y block 239?

[JimNNN]

The one that's on the relay now is 30 amp, and has been there for years without a problem, but I don't know what the original fuse is specified to be...can't find it listed in the shop manual. I've got a new fuse box now with my rewiring job, and I want to know what the overdrive is supposed to be fused at.



Original overdrive - Borg Warner R10, I believe. 1954 Mainline 239 V-8.



It's 6 volt...but that shouldn't matter for fuses, right?



THANKS. - Jim

[dmsfrr]

Just assuming for discussion that the 6v '55 OD setup is similar or even the same... (?)
Page 245 of a '55 shop manual outlines a portion of the OD test procedure in paragraph "b." at the top of the page.

(paraphrased here)
Substituting an amp meter for the relay fuse should give an indication of 2 to 2.5 amps with a momentary higher reading during activation.

A 5, 7 or 10 amp fuse in the 6 volt circuit would be a 'safer' substitution than the existing 30 amp version. The 5 amp fuse might be a bit small if the current surge during activation causes it to blow too often, then try a 7 amp fuse.

Originally Posted by JimNNN

. . . .
It's 6 volt...but that shouldn't matter for fuses, right?

Yes it can, but not in your car if you're not changing the voltage of the electrical system.

In 6 to 12 volt converted cars that change will technically affect the preferred Current/Amperage values of fuses.
The Current/Amperage value of a fuse or circuit-breaker in a 6 volt circuit can usually be reduced by nearly half if that circuit is changed to 12 volt. (Ohm's Law)

"The fuses may need to be changed to values smaller than original or use the ones rated for the 56 and 57..."
(from this link)
https://www.ctci.org/gilsgarage/6to12.php
.

[JimNNN]

Thanks dmsfrr. I should mention, however, that since I made this post a couple of hours ago, I did find a wiring diagram in the 52-54 shop manual that says the OD relay is equipped in original form with a 30 amp fuse.



I should also say that I had been powering this circuit with a feed from my new fuse box (fused at 15 amps) since I completed rewiring my car a couple of weeks ago. I had this 15 amp fuse blow twice. The OD had never blown a fuse before with the original wiring, but I didn't now if the 30 amp fuse was right size, because I knew it had been replaced once before by a mechanic. It appears that 30 amp may be the correct size, though I may try a 20 amp first, and work up to 30 if I have continuing problems.



So the circuit will be double fused - one fuse at the fuse box and the original 30 a fuse mounted on the (original) relay. Will there be a problem with this? The original wiring was 14 gauge and I believe the new wiring is the same, but I will check.

In 6 to 12 volt converted cars that change will technically affect the preferred Current/Amperage values of fuses.
The Current/Amperage value of a fuse or circuit-breaker in a 6 volt circuit can usually be reduced by nearly half if that circuit is changed to 12 volt. (Ohm's Law)

Thanks a lot. I was wondering about that.

[zoegrant]

jimnnn…. The CASCO catalogue on page 51 recommends 30 Amp also....

[rotorwrench]

They were 30-amp. The fuse is to protect the wire circuit and 30-amp will protect a 10-gauge wire. A smaller fuse can be used as component protection device but in no case should a larger one be used.

[JimNNN]

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Thanks for the verification of that, guys.



It's interesting that the wiring diagram I found in the shop manual seems to show a 30 a fuse being used with a "#14" (14 gauge, I presume) wire, but the online sources seem to indicate, as rotorwrench said, a 30 a fuse is more appropriately used with a 10 ga. wire, depending on length.



What's up with that?