What do you use in place of "Delco Shock Absorber Fluid" these days? I drained and flushed the shocks on my 48 and they seem to work fine but after driving for awhile I seem to be getting some tire bounce. I used hydraulic jack oil and don't know if the oil is becoming aerated.

 

Wow big difference from jack oil. The stuff that came out didn't seem that viscous but it was 70 years old.

 

Hydraulic jack oil has an antifoaming additive. Some people use motorcycle front fork oil also.

 

Or ATF it's anti foaming also. I would be leery of anything thicker than 20 wt. I could see bad things happening with anything as thick as STP. That oil has to move through tiny valves to work.... Tedd

 

Tedd, thanks for that update. I will go back and delete my original post since it has some bad info. I have never fooled with these shocks so what I posted was some pad hearsay.

 

Confirming what has already been stated regarding motorcycle fork oil. Motorcycle fork oil (cruisers/baggers/bobbers) standard weight is generally 5. Happy medium is a 7. Most often no one goes above a 10. AMSOIL sells both #5 & #10 motorcycle fork oils. H-D refers to their fork oil as “E” (just as a general statement) which I think is ~7. Can’t recall exactly. I ride an Indian and use AMSOIL #5.

 

Wouldn't they have used ATF back then? I would think motorcycle back shock oil would be better than fork oil but I really do not know these vintage shocks at all.

 

Try contacting:

https://dansshocks.com/

Dan rebuiids spiral shocks for the HOBBY from 1953-1982 per his website, but he could have a good recommendation for hydralic oil for your '48 shocks. He rebuilt the shocks on my 442 so I know he is legit.

Good luck~

 

Motorcycle fork oil is the answer. Out of five grades on the shelf at my local motorcycle shop, I chose one in the middle. I reuse a empty floor jack oil container with the pointed spout. Be sure to leave about 1/8" air space for expansion, and first clean off the surface where the pipe plug is located so no junk falls into fluid chamber. What a huge difference in rebound, jounce, road noise judder handling etc etc. Also no leaks suggesting compatibility with existing seals. - Good luck

 

I fully agree about the fork oil for bikes, over the years I have tried mixes of engine oil and STP to really high viscosity and it will for sure give you a stiff absorber but bike oil is the way to go.
If you have leaky absorbers STP+oil might be a way to minimize leakage.