GSXR400 - tonne of suspension issues

[yamahaggis88]

Shit, been a while since i've been on here

Hoping someone can answer a few questions for me, just got my bike going again after just over a year of it lying round the back of the house in bits. Since day one it hasn't felt right, the rear's always felt too stiff and the front far too soft. The guy that done the work on my bike (1985 GSX-R400, btw) tried softening up the rear a little by releasing a tiny, and i mean tiny bit of pressure from the reservoir on the rear shock thinking someone may have put air in it, it hasn't worked and now the rebound is really slow... I cant feel the rear end of the bike at all and it hates bumps. He's wound the preload adjusters up on the front a little but to no avail, got a feeling it may just be a case of changing to heavier fork oil, there's no leaks or anything, but the bike is basically bottomed out under braking even at low speeds and feels pretty unsettled. Fronts not too much of a worry but the rear is, is there a remedy for this? No rebound clicker on the shock and the spring isn't preload adjustable...

Also, since day one at decent speeds the back end of the bike seems to want to weave from side to side, travelling in a straight line. Is my setup anything to do with this? Rear wheel is straight, no play in bearings, chain correctly tensioned, bars not bent etc. Any ideas? Shit scary considering I have little riding experience at the moment... Not inspiring much confidence in me to want to learn either

EDIT: weaving isn't constant, only seems to happen now and again, sometimes after cornering, sometimes on straights with no explanation.

[tigertim20]

try eating more pies.
if that doesnt work
try eating less pies?

Sorry. Im sure someone helpfull will be along shortly

[yamahaggis88]

try eating more pies.
if that doesnt work
try eating less pies?

Sorry. Im sure someone helpfull will be along shortly

Mate, if i carry on the way I am with pies, i'll be in a 6 foot hole in a nice plot somewhere before im 30

Surely won't help my vat-of-treacle-like rebound issue either

[kiwi cowboy]

Shit, been a while since i've been on here

Hoping someone can answer a few questions for me, just got my bike going again after just over a year of it lying round the back of the house in bits. Since day one it hasn't felt right, the rear's always felt too stiff and the front far too soft. The guy that done the work on my bike (1985 GSX-R400, btw) tried softening up the rear a little by releasing a tiny, and i mean tiny bit of pressure from the reservoir on the rear shock thinking someone may have put air in it, it hasn't worked and now the rebound is really slow... I cant feel the rear end of the bike at all and it hates bumps. He's wound the preload adjusters up on the front a little but to no avail, got a feeling it may just be a case of changing to heavier fork oil, there's no leaks or anything, but the bike is basically bottomed out under braking even at low speeds and feels pretty unsettled. Fronts not too much of a worry but the rear is, is there a remedy for this? No rebound clicker on the shock and the spring isn't preload adjustable...

Also, since day one at decent speeds the back end of the bike seems to want to weave from side to side, travelling in a straight line. Is my setup anything to do with this? Rear wheel is straight, no play in bearings, chain correctly tensioned, bars not bent etc. Any ideas? Shit scary considering I have little riding experience at the moment... Not inspiring much confidence in me to want to learn either

EDIT: weaving isn't constant, only seems to happen now and again, sometimes after cornering, sometimes on straights with no explanation.

First question is - is it an 85 or 86 model gsxr?.
I only ask as you say it is an 85 but you have an 86 according to your profile.
Sounds to me like your rear ir buggered and when was the last time you changed the fork oil?.
Has the rear shock got an eye both ends or eye top and forked bottom?.

[Robert Taylor]

Shit, been a while since i've been on here

Hoping someone can answer a few questions for me, just got my bike going again after just over a year of it lying round the back of the house in bits. Since day one it hasn't felt right, the rear's always felt too stiff and the front far too soft. The guy that done the work on my bike (1985 GSX-R400, btw) tried softening up the rear a little by releasing a tiny, and i mean tiny bit of pressure from the reservoir on the rear shock thinking someone may have put air in it, it hasn't worked and now the rebound is really slow... I cant feel the rear end of the bike at all and it hates bumps. He's wound the preload adjusters up on the front a little but to no avail, got a feeling it may just be a case of changing to heavier fork oil, there's no leaks or anything, but the bike is basically bottomed out under braking even at low speeds and feels pretty unsettled. Fronts not too much of a worry but the rear is, is there a remedy for this? No rebound clicker on the shock and the spring isn't preload adjustable...

Also, since day one at decent speeds the back end of the bike seems to want to weave from side to side, travelling in a straight line. Is my setup anything to do with this? Rear wheel is straight, no play in bearings, chain correctly tensioned, bars not bent etc. Any ideas? Shit scary considering I have little riding experience at the moment... Not inspiring much confidence in me to want to learn either

EDIT: weaving isn't constant, only seems to happen now and again, sometimes after cornering, sometimes on straights with no explanation.

The first thing you need to establish is the condition of the swingarm bearings and the shock linkage bearings. Given that the bike is a full 2 and a half decades old and that manufacturers are not noted for being generous with assembly grease the chances of partial seizure in these components is high. Similarly successive owners are usually just as guilty of neglecting maintenance of such items.
The shock itself could also be failing. Whichever way to look at it this bike is currently a danger to you but also other road users.
Filling the forks with heavier oil is an old wives tail and will slow down the rebound too much, always a big contributor to crashing. They are ''soft'' in the front for several reasons, as follows;

1) The rear is semi locked up and all action is happening on the front because that is the only thing that will move!

2) The damper rod top hat piston rings are likely very worn and not sealing concentrically meaning there is uncontrolled bleed . That in turn makes the forks softer in action

3 ) Like many bikes of its type and vintage its severely undersprung in the front end.

Oil viscosity selection in the front end of damper rod type forks is first second and last all about achieving correct rebound return speed. Dont let anyone else tell you any different because they are very wrong, wrong, wrong. Dive and ride height control is ( simplistically without adding modern enhancements such as Race Tech emulators ) about suitable spring rate and preload, also secondary trapped air spring compression ratio. Air spring is tuned by varying oil level.
The reduction in internal ( nitrogen only ) gas pressure inside the rear shock is still likely to be significant as even a ''hiss'' of removal is significant with a very low gas volume at high pressure.

[F5 Dave]

An old girlfriend had a Gasaxe 400 of that vintage (actually it's still in her garage) & it had soft fork springs even for her 60kgs. They were aimed at the Jap market & came over here with little changes.

Many years back I remember the local suspension chap telling me a story about how he rebuilt & revalved a CR500 shock. The owner came back in complaining it was still way too hard, so he softened the com valving again. Owner comes back again.

Hmm, bring in the bike.

Sure enough, take the shock out & the wheel swingarm didn't move.

[ducatilover]

I'd be reading what Robert Taylor says. He's the man.

[yamahaggis88]

A good read indeed

Sorry, it is an 86, was a typo, netbook keyboards are tiny, but i digress...

Any idea how long it would take a shop to have a look at the swingarm and linkage bearings? As well as pull the forks down for a look? I have no time to do it myself, and frankly none of the confidence to pull my bike apart to that extent yet either. Just trying to work out labour costs, that's all, it'll be up for sale shortly, but I'd rather sell it legal and safe rather than something some unsuspecting bugger's gonna take for a ride and kill themselves on...

If the rear shock needs replacing, rather than going to an OEM unit which i imagine would be nigh-on impossible to find, is it simply a case of finding a shock with the same eye-to-eye center length, diameter etc?

Sorry for the million questions, and thanks for all your input

[Robert Taylor]

A good read indeed

Sorry, it is an 86, was a typo, netbook keyboards are tiny, but i digress...

Any idea how long it would take a shop to have a look at the swingarm and linkage bearings? As well as pull the forks down for a look? I have no time to do it myself, and frankly none of the confidence to pull my bike apart to that extent yet either. Just trying to work out labour costs, that's all, it'll be up for sale shortly, but I'd rather sell it legal and safe rather than something some unsuspecting bugger's gonna take for a ride and kill themselves on...

If the rear shock needs replacing, rather than going to an OEM unit which i imagine would be nigh-on impossible to find, is it simply a case of finding a shock with the same eye-to-eye center length, diameter etc?

Sorry for the million questions, and thanks for all your input

Reference the fitting of a replacement shock its much much more than finding one that fits in. The spring rate and preload has to be suitable for the motion ratio that is imparted to it by the linkage and the leverage of the swingarm, weight of the bike, engine torque applied etc. As for the internal piston and valving calibration. Again it has to match the motion ratio imparted to it as damping is velocity sensitive, also the high speed rebound damping has to be matched to the spring rate.
I wonder aloud how many riders have been injured or killed because an unsuitable shock has been fitted.

[yamahaggis88]

Reference the fitting of a replacement shock its much much more than finding one that fits in. The spring rate and preload has to be suitable for the motion ratio that is imparted to it by the linkage and the leverage of the swingarm, weight of the bike, engine torque applied etc. As for the internal piston and valving calibration. Again it has to match the motion ratio imparted to it as damping is velocity sensitive, also the high speed rebound damping has to be matched to the spring rate.
I wonder aloud how many riders have been injured or killed because an unsuitable shock has been fitted.

I had a feeling it wouldn't be that simple... Went for a quick ride to a mates tonight and managed to get a better look at what the arse of the bike's actually doing (at a standstill at least). It seems the shock isn't as stiff to compress as it was when I picked it up on tuesday, and the rebound, while still slow, is a little quicker, will still get it looked at when I can find time to book it in somewhere, as it seems this is one of those problems that will only get much worse/more expensive the longer it's left...

Also learnt that riding in the pissing rain with no wet weather gear is absolute shite!