T500 squidgy forks remedy?

[Mencie]

Hi all.

The forks on my '69 T500 are very soft, I haven't checked the fork oil quantity since I acquired her so I can only assume at this point the oil quantity and grade are correct.

Based on that assumption, are there any solutions to stiffening the front end? I think I read somewhere that preloading the springs with a spacer (washers) helps but had anyone tried different fork oil grades with success?

I have recently acquired a pair of NOS fork bottoms so will be stripping the forks to fit them so I want to try and nail the soft fork issue while I'm in there.

Any thoughts or advice are greatly appreciated.

[sbaugz]

Hi all.

The forks on my '69 T500 are very soft, I haven't checked the fork oil quantity since I acquired her so I can only assume at this point the oil quantity and grade are correct.

Based on that assumption, are there any solutions to stiffening the front end? I think I read somewhere that preloading the springs with a spacer (washers) helps but had anyone tried different fork oil grades with success?

I have recently acquired a pair of NOS fork bottoms so will be stripping the forks to fit them so I want to try and nail the soft fork issue while I'm in there.

Any thoughts or advice are greatly appreciated.

I have the same problem. Mine were just completely rebuilt and I have NOS fork springs on them. Still very soft and squishy. I used 15 weight fork oil, thinking it was going to make a difference, but it really didn't. After I get the bike running (once tank is back from painter), I may decide to add some preload washers. Will test drive it first before taking it back apart though.

[Alan H]

Soft fork (rebound) are usually because they don't have any oil in. Don't assume, check them!
I use 20w50 gearbox oil in the 550 and it stiffens them up just nice (as recommended by Eddie Crooks 'back then'!)

[ConnerVT]

Alan, don't compare the T500 and GT550 forks - They are completely different animals.

Here is a link to Cycle World's article on the T500/GT550/GT750 fork mods they tried: http://www.ozebook.com/compendium/suzi/ ... AtHome.pdf" onclick="window.open(this.href);return false;

[Vintageman]

ConnerVT. Good stuff

[Mencie]

Soft fork (rebound) are usually because they don't have any oil in. Don't assume, check them!
I use 20w50 gearbox oil in the 550 and it stiffens them up just nice (as recommended by Eddie Crooks 'back then'!)

Right, just drained the forks, one appears to have slightly less than the other, one had 215cc in it, the other nearer 205. I didn't stand there and wait for every last drop so the stated figure is likely in reality to be a tad higher.
I accept that specified levels are what we should adhere to, slightly less in one fork leg isn't going to make that much difference is it?

[Alan H]

If the forks are 'squidgy' I take that to mean they are bouncy - which suggests a lack of damping. If they are too soft as regards the springs being sad or weak, they thyy will have to be replaced or sorted depending on the weight of the rider and/or pillion passenger carried.

HOWEVER, my 1972 service manual gives lots of details for ALL models at that time and it says;
T500 R,J,K 220ml/0.46 US/0.39 imperial pint of either 10w/30 multigrade or ATF fluid.
It also remarks that the more oil in the forks the stiffer the suspension and the less oil the softer it becomes. Unfortunately if you put too much oil in you then run the risk of blowing the seals. - it doesn't mention that bit!

Now when I had my first GT550 back in '72, I called at Crooks Suzuki in Barrow in Furness to see what they had done with their production racer GT550 and was told to use 20w/50 oil in the forks as it gave better damping. Also tweaks to the ports and heads that were permissible at the time, take the centre stand off, get rid of the baffle padding and fit a 19" rear rim. Brakes were upgraded to Ferodo green linings.
The 550 could just about hold it's own with the Norton Commando, but struggled against the CB750 and a few other 750s at the time. That 200cc discrepancy took some working at so the GT550 racer wasn't carried on with. The GT380 was made into a water cooled 500 later by Barton Engineering, but Suzuki built the RGs and other 4 cylinder 500s so that quietly faded away too. Shame, they looked really good.

Eddie Crooks and his mechanic Frank Whiteway used to prep and race Suzukis very successfully then and since and are one of the longest established Suzuki dealers in the UK, so I still do what they said back then and it still works well today.
I mainly post what I know and do, but anyone has the option to take advice or not, I don't mind either way.
There's not a lot of difference between any of the forks regarding how they actually work and dampen rebound whether the forks have internal or external springs.

The file you linked to makes interesting reading, but remember that the bikes are now 40+ years old and the springs will certainly be softer! I don't find the forks underdamped on the downward stroke (when braking) but the slightly thicker 20w/50 gives a bit better control. I don't thrash about as much as I used to so really most of the changes suggested aren't necessary.
A good friend has just fitted a complete front end from a GT750J to his T500 and followed my advice and he's really chuffed with braking and front suspension now. The original twin leading shoe brake on the T500 was always marginal if you 'pressed on' a bit.

As I keep mentioning, anyone wants a free electronic copy of the manual, PM me your email address.

[tricky1962]

Squidgy forks could be lack of compression and rebound damping - thicker oil could help here although that link suggested most of the damping came from the oil seals, in which case new seals!
Softer springs are only a problem if the forks bottom out - so add some preload, unless the springs are going to get coil bound

Hook's law suggests springs don't soften on aging- your views may vary

I think we need a more accurate description than "squidgy"

[ConnerVT]

squidgy
adjective uk /ˈskwɪdʒ.i/ us /ˈskwɪdʒ.i/ UK informal
› ​soft and ​wet and ​changing ​shape ​easily when ​pressed

http://dictionary.cambridge.org/us/dict ... sh/squidgy

or possibly it is this:



(always glad to help)

[tz375]

I think that's a pretty good description.

The question is whether the springs are too soft (Spring rate or preload) or is it insufficient damping - or both.

I'd start by measuring sag and then I'd try the forks with 200ml of light oil and then drain that and try 200ml of 30wt fork oil to see if that's enough.

It is probable that damping is woeful by design and that springs are too soft to make for a plush ride. Stiffer springs or more preload are fairly easy to organize but other than oil viscosity I don't think there is much you can do if they are shuttle valve design. You may be able to silver solder the damping holes and re-drill to a different size or perhaps machine up new pistons with a different angle or clearance as they partially close off the oil holes - assuming that's how those forks work.

[Alan H]

If people want modern fork performance, they need modern forks.
These were only average 40 odd years ago when they were new.

[ConnerVT]

^ This

[Mencie]

Ok guys, I accept my description is not particularly err, descriptive!

The forks appear to compress excessively when braking or even dropping her off the center stand.

Simply pushing her into the garage and pulling the front brake on makes the forks compress a fair bit.

I guess I shouldn't compare her to my later GT500 but that never did it, more robust forks I guess.

Maybe I'm simply expecting too much for a bike of this age, I will put the correct amount of fresh oil in and review the situation..

[jabcb]

I used spacers to set the fork sag on a 71 T350 & used heavier oil. Was surprised at how much this improved the forks.

I think the T500 would benefit from softer springs with a good bit more preload.
The T500 has external springs which makes this more difficult to do.
Haven’t seen any info on a member trying this, but its in my project queue.


As Alan suggested, you can keep the retro look & get better brakes + suspension with a GT550J or GT750J front end.
A GS-series front end will give some additional gains. I have an 82 GS-series front end on a GT750M — its a good bit better than stock.

[Alan H]

A GS-series front end will give some additional gains. I have an 82 GS-series front end on a GT750M — its a good bit better than stock.

Now that's interesting. I only fitted a GS550 swing arm, alloy wheels and 3 discs to my GT550 (details HERE (clicky) but a pair of later forks as well?

Hmmm, how much work did that entail? I'll have to see if GS550 forks fit the GT550 frame - that should upset/annoy/dumfound the anoracks!