Fork oil change opinions wanted


Information and questions on GL1100 Goldwings (1980-1983)
Post Reply
johnny42
Posts: 129
Joined: Sun Apr 18, 2010 11:15 pm
Location: Lancaster, NY
Motorcycle: sold: 1983 GL1100I Interstate (original owner)
2018 Royal Enfield Himalayan
2020 Goldwing Tour 6sp

Fork oil change opinions wanted

Post by johnny42 »



I'm going to flush and replace my fork oil (1983 Interstate). I have Progressive Suspension springs. I plan on draining, flushing and replacing using the drain bolt and air valves. I saw a Youtube video where a guy uses "diesel treat" to flush/clean the forks, then uses Marvel Mystery Oil for a second flush/clean then fills the forks with oil. He says the diesel treat does a good job cleaning out the crap. The MMO cleans but also keeps the rubber bits soft and pliable.

I've researched this topic on this site and flushing is good. Using the air valves is also doable.

First question: does anyone see any problem with using these 2 liquids to flush/clean/lube before filling with fork oil/ATF?

Second question: I think Prog. Susp. suggests 15 wt. oil. I only weigh 145 pounds and ride solo. Honda calls for ATF in the forks. Looking for suggestions.


User avatar
WingAdmin
Site Admin
Posts: 22232
Joined: Fri Oct 03, 2008 4:16 pm
Location: Strongsville, OH
Motorcycle: 2000 GL1500 SE
1982 GL1100A Aspencade (sold)
1989 PC800 (sold)
1998 XV250 Virago (sold)
2012 Suzuki Burgman 400 (wife's!)
2007 Aspen Sentry Trailer

Re: Fork oil change opinions wanted

Post by WingAdmin »

johnny42 wrote: Wed Apr 15, 2020 10:54 pm I'm going to flush and replace my fork oil (1983 Interstate). I have Progressive Suspension springs. I plan on draining, flushing and replacing using the drain bolt and air valves. I saw a Youtube video where a guy uses "diesel treat" to flush/clean the forks, then uses Marvel Mystery Oil for a second flush/clean then fills the forks with oil. He says the diesel treat does a good job cleaning out the crap. The MMO cleans but also keeps the rubber bits soft and pliable.

I've researched this topic on this site and flushing is good. Using the air valves is also doable.

First question: does anyone see any problem with using these 2 liquids to flush/clean/lube before filling with fork oil/ATF?

Second question: I think Prog. Susp. suggests 15 wt. oil. I only weigh 145 pounds and ride solo. Honda calls for ATF in the forks. Looking for suggestions.
Any decent flush that doesn't leave residue should work. Personally I used brake cleaner, it is a good solvent, cleans out everything, and it's volatile, so it evaporates leaving nothing behind.

ATF is about equivalent to 10 weight oil. I think 15 might be a bit firm for you with the load you're looking to put on it. I'd go with ATF or 10 weight fork oil.
johnny42
Posts: 129
Joined: Sun Apr 18, 2010 11:15 pm
Location: Lancaster, NY
Motorcycle: sold: 1983 GL1100I Interstate (original owner)
2018 Royal Enfield Himalayan
2020 Goldwing Tour 6sp

Re: Fork oil change opinions wanted

Post by johnny42 »

I ended up doing what I said. The drained fluid was like thick mud and black. I found an old bottle of PJ1 Fork oil 20wt in my stuff so that's what was in there with the Progressive Suspension Springs. I put back Valvoline ATF Type F.

I measured the old fluid at 8 oz. I don't remember when I last did them but at that time I did remove the fork caps and would have used the measuring method described by Prog Suspension.

So (and I could not find this answer anywhere nor would Prog Susp tell me) it seems like the Prog Susp springs displace quite a bit more real estate in the fork tubes. Instead of the 9.1 the manual specifies, I put in 8 oz.

I'll ride with that for a while and if they don't bottom out, I should be good. I'm pretty confident they are not overfilled. And yes, the ride quality is better!!!
User avatar
WingAdmin
Site Admin
Posts: 22232
Joined: Fri Oct 03, 2008 4:16 pm
Location: Strongsville, OH
Motorcycle: 2000 GL1500 SE
1982 GL1100A Aspencade (sold)
1989 PC800 (sold)
1998 XV250 Virago (sold)
2012 Suzuki Burgman 400 (wife's!)
2007 Aspen Sentry Trailer

Re: Fork oil change opinions wanted

Post by WingAdmin »

johnny42 wrote: Fri May 01, 2020 8:54 am I ended up doing what I said. The drained fluid was like thick mud and black. I found an old bottle of PJ1 Fork oil 20wt in my stuff so that's what was in there with the Progressive Suspension Springs. I put back Valvoline ATF Type F.

I measured the old fluid at 8 oz. I don't remember when I last did them but at that time I did remove the fork caps and would have used the measuring method described by Prog Suspension.

So (and I could not find this answer anywhere nor would Prog Susp tell me) it seems like the Prog Susp springs displace quite a bit more real estate in the fork tubes. Instead of the 9.1 the manual specifies, I put in 8 oz.

I'll ride with that for a while and if they don't bottom out, I should be good. I'm pretty confident they are not overfilled. And yes, the ride quality is better!!!
Yes, the progressive springs do displace more oil, particularly if installed with the narrow end down.
User avatar
julimike54
Posts: 604
Joined: Sun Feb 01, 2015 12:21 pm
Location: Euless, Texas
Motorcycle: 1986 GL1200A original owner
2016 HD FLTRU

Re: Fork oil change opinions wanted

Post by julimike54 »

Progressive instructions state to measure fluid level (max. 5.5" from top of fork, no spring installed), anything below that they show 'safe'. I'd suggest the 'level' method unless you completely rebuilt the forks, cause how much might have been retained in the forks. The 20wt oil is Progressives recommendation for a GL1200.

Progressive install instructions
download/file.php?id=34232
download/file.php?id=34163


Image
Riding anything is a good day!
Mike
Post Reply