Changing the fork oil in my 1982 Suzuki GS450T

[Shelby]

Hey gang,
Square in the middle of replacing my fork oil and I'm having one heck of a time determining what model GS450T I have! The manual shows a pretty big difference in oil amount between the TZ and the TXZ. The TZ will take 125mm and the TXZ will take 208mm.
I would've just measured the amount that I drained out of each fork except there was hardly 2oz of jet black crude.
(by the way, depressing those dumbass metal caps and digging out the metal ring that locks in the caps was a bitch doing it myself. I had to have my 70+ year old father with his "old man strength" come over and help

I have the VIN of: JS1GL52A0C2102989
I only have the old glue from the sticker opposite of where I found the VIN. I'll go look for an engine and frame number when I get back home this evening.

Modifications from stock are as follows:
Changed handlebars.
No airbox.
Changed mufflers.

Here's a couple pictures if that'll help.

[Shelby]

Another pic
20190505_152522.jpg

[Nessism]

The amount of oil isn't overly important. You just need to have enough to cover the damper rods. Try compressing the forks after removing the springs and then fill up the oil to within 6" of the top of the tubes. 10 weight fork oil is a good choice unless you weigh over 200 lbs, in which case 15 weight may be better.

[Shelby]

Ed, thank you for the info!
I'll go with the 15w fork oil because I weigh 170lbs and my father likes to "test ride it for safety" for me and he's just over 200lbs. LoL he rides my bike so hard, but babies his L model. Now that I think about it, maybe it's because I jetted mine and his is stock. Oh well.
Also, oiling to 6" from the top when compressed falls right in the middle between what the manual calls for between the TZ and TXZ, so that's what I'll do for sure.

Thank you once again!
I'm off to get my hands dirty!

[Nessism]

Pumping the forks a couple of times to get the air out of the damper rods before measuring may be a good idea.

[grcamna2]

15 wt. Is what works best and recommended by the book.I used 5 ozs. In each leg on my 450txz after completely pumping out all the old oil.

[LAB3]

Looks to me like you have the txz based on the fact you have wire wheels, the seat looks to be off an L. If your fork tubes don't have an air fitting at the top, it confirms that it is in fact a txz. The fork oil should be 143cc or 4.8oz. I'm 190lbs and pack about 100lbs of gear and am using 15w oil, seems to work just fine whether running loaded or unloaded. Last winter I put a 2" spacer in each leg to stiffen it up a bit which made a big difference in how it rides and handles.

[LAB3]

BTW, the parts fische is indespensible for finding the right parts and if you haven't already downloaded the manual, do it.

https://www.babbittsonline.com/oemparts/l/suz/50d3f2caf8700230d8b4bf8c/1982-gs450tx-parts

[Shelby]

Ed, grcamna2, LAB3, thank you all for the valuable info! I plan to apply what I've learned in my TXZ tomorrow.

[bwringer]

The amount of oil in the forks is entirely irrelevant other than making sure you buy enough.

The level of the oil is the only thing that matters. It's most important to make sure the levels in each leg are the same. The levels in each leg must be identical within 1mm.

The actual level is somewhat secondary. If you have a specific spec for your bike use that. If not, on most streetbikes with about 4 inches (100mm) of travel, 140mm to 150mm is the usual universal number. 6 inches is about 150mm, close enough.

Fork oil levels are measured with the fork leg removed and held vertical, fork springs removed, and the forks collapsed all the way. Dump in some amount of oil a bit more than what's needed, pump the forks slowly several times to work out any air bubbles, then slurp out the excess oil with a measured piece of tubing attached to a syringe.

Google "fork oil level tool" to see the idea; you can make one yourself easily enough. Tubing by itself usually isn't stiff or stable enough, so I attach a piece of coat hanger wire to a large syringe from a farm store, then zip-tie the tubing to that.

[Brendan W]

H
I would've just measured the amount that I drained out of each fork except there was hardly 2oz of jet black crude.

More than likely there is some crud sitting at the bottom of the tubes.
I would plan another change out fairly soon and keep going until the oil drains cleaner.
For this flush time you could use a mix of 10W40 and ATF. 3:1 is about the 15W mark give or take depending on the spec of the ATF
I run that mix all the time. Too tight to buy proper fork oil