I agree with Wessi, excellent answer. I am looking into new springs purely for restorations. Surface rust should not affect spring rate but age will. Major rust will also. If you are looking for a better ride and /or better handling, then I suggest buying better shocks. With member Silo 7 making new internal parts for the Thermal Flows, I wanted to find springs to make the restorations complete. I don't expect the new springs to make them any better. New chrome plating does not restore an old spring, it just makes it look better IF the surface is smooth to start with. Severely rusted and pitted springs will eventually break no matter what " coating" is applied to them.

Have you looked at these springs?  They don't give any dimensions so I'm not sure of length or circumfrence...

Replacement springs

have you tried evaporust?

I put very rusted set of DT1E springs that i thought were gone in a ziplock bag for a few days with this weird stuff and they came out 95% clean

Mace6772,

If you just HAVE to have the original Thero-Flow shocks (which were removed from ALL the bikes I saw as soon as they got home from the Shop (they didn't work very well, to say the least...), then continue.  If you are open to other routes, here is a site form Red Wing shocks (NOS).  I have the 'hammerhead' Red Wing shocks on the RT-3, and have been thrilled with them--but they are seen VERY infrequently these days!

Hammer

NOS NEW Red Wing Shocks XL250 XL350 R5 H1 H2 TS400 TS250 DT1 RT1 GT750 Z1 13" Buy It Now

 

No, I don't HAVE to have them. I just wanted to locate replacements for the FULL RESTO crowd. Looking to boost my meager COVID income. Also think that 2021 small batch chrome will look better than new 1975 mass produced chrome. 

To airbornesilva:Top of spring is smaller I.D. than bottom. Spring O.D. is larger than original TF spring. Would not work on stock TF body. Not a viable replacement.

To msavitt: You are lucky to have a pair that could be " saved". I have never tried EV. I am looking for repro springs because the useable supply is drying up. parts-traders is selling repro springs for the Pre-TF bikes. Measurements show the springs are smaller in all dimensions than TF springs.                                                                                                                                                                                                     P.S.: There is currently a set of new NOS Thermal Flow shocks on EB. They are priced at $ 499.oo + $125.oo shipping from Singapore. Hmmm...    I have a brand new pair too. Well my shipping will be cheaper.                                                                                                                                 

I was skeptical of evaporust and didn't use it with dt360 resto, which was aesthetically a pretty clean machine. My DT1E on the other hand was crusty and rusty and beaten to hell. I thought for sure evaporust couldn't help, I was wrong this crap is magic. Key i found is a through cleaning in BBQ lighter fluid then soak in evaporust. Come back in a day and brush with plastic bristles and soak another day if needed.   Once 250 is done I am going to kerplunck some 360 bolts and fittings 

if finding new vs cleaning is your thing that's cool, I am sharing so others who doubted that moderately rusted parts can be saved. 

  Evaporust