What effect does grease between the leaves of a pre-50 spring have please?
Besides stopping them squeaking.
If the springs are really pre-1950’s, the grease will help them slide against each other easier and help stop the squeaking.
This means springs from the pre-1950’s, not a vehicle from pre-1950’s.
Since the mid 1950’s or so leaf springs have been made from SAE 5160 High Alloy Spring Steel. And this type steel does not like petroleum based products.
Greasing between the leaves will have a detrimental effect on SAE 5160 High Alloy Spring Steel and the springs will prematurely fail.
So be sure of what steel the springs are made of.
Please remember, looks alone will not tell you how old those springs are.
Often we encounter problems when the springs look original (look like they’ve never been off the car) and they are not.
If you took a new set of springs and left them in your yard exposed to the elements for a couple of years, they would look like they’re from the 50’s.
Looking old, and actually being old can be two very different things.
If you are not the original owner, and/or the vehicle ever been modified, there is a good chance the springs have been replaced in the last 50+ years.