FZR 400 3tj-1 rear shock

[MikeD400]

Hey there KBer's!

Ive got a bit of a problem with the rear shock on my bike its too soft but its on the tallest preload stack im 100kgs and get over 50% sag when i sit on the bike and it just generally feels soft and when im two up with my wife (65kgs) its bottums out on bumps that arent even that harsh.

Questions is! Is this shock serviceable? Does it just need pulling apart and new oil putting in? Does it need a stronger spring?

Any advise would be muchly apreciated, note im a full time push bike mechanic and have serviced many types of suspension forks and rear air shocks and coil shocks i was just wondering if anyone could advise me to have a go or not before i go ahead and go threw the big drama of taking it out.

Cheers! Mike!

[NinjaNanna]

Sounds like you need a stiffer spring. May take some measurements and do some googling to see if any other models will fit. Either that or I wonder if a spring place could reset it for you?

[Paul in NZ]

I'm afraid those rear shocks were not much chop even when new and I dont think they are rebuildable. Replacement ones can cost as much as the bikes worth - sorry...

[Robert Taylor]

Hey there KBer's!

Ive got a bit of a problem with the rear shock on my bike its too soft but its on the tallest preload stack im 100kgs and get over 50% sag when i sit on the bike and it just generally feels soft and when im two up with my wife (65kgs) its bottums out on bumps that arent even that harsh.

Questions is! Is this shock serviceable? Does it just need pulling apart and new oil putting in? Does it need a stronger spring?

Any advise would be muchly apreciated, note im a full time push bike mechanic and have serviced many types of suspension forks and rear air shocks and coil shocks i was just wondering if anyone could advise me to have a go or not before i go ahead and go threw the big drama of taking it out.

Cheers! Mike!

The shock in that bike is rebuildable but having said that the shim stack / piston is not that sophisticated. From memory though we can do something with it to stop it ( hydraulically ) blowing through its stroke
It 110% needs a stiffer spring to suit your body mass, without that rectified it is NEVER going to work properly. Ohlins springs are closest to fitting a lot of those particular shocks, the fitting dimensions are very similiar, usually without recourse to needing machining of centralising / distance spacers.
With the increase in spring rate required it will also require more ( internal ) high speed rebound damping to control the extra spring force at near to full closed distance.
We ( CKT ) are the only company that in NZ has genuine rebuild parts left in stock for these older Yamahas.

[MikeD400]

The shock in that bike is rebuildable but having said that the shim stack / piston is not that sophisticated. From memory though we can do something with it to stop it ( hydraulically ) blowing through its stroke
It 110% needs a stiffer spring to suit your body mass, without that rectified it is NEVER going to work properly. Ohlins springs are closest to fitting a lot of those particular shocks, the fitting dimensions are very similiar, usually without recourse to needing machining of centralising / distance spacers.
With the increase in spring rate required it will also require more ( internal ) high speed rebound damping to control the extra spring force at near to full closed distance.
We ( CKT ) are the only company that in NZ has genuine rebuild parts left in stock for these older Yamahas.

Awesome post thanks! Seeing as your so knowlegable on this topic would you have any idea as to what a rebuild and a heavier spring would cost?

Cheers Mike!

[Paul in NZ]

Roberts a bit more than 'knowledgable' .... Hes a fully fledged Guru

[nzspokes]

The shock in that bike is rebuildable but having said that the shim stack / piston is not that sophisticated. From memory though we can do something with it to stop it ( hydraulically ) blowing through its stroke
It 110% needs a stiffer spring to suit your body mass, without that rectified it is NEVER going to work properly. Ohlins springs are closest to fitting a lot of those particular shocks, the fitting dimensions are very similiar, usually without recourse to needing machining of centralising / distance spacers.
With the increase in spring rate required it will also require more ( internal ) high speed rebound damping to control the extra spring force at near to full closed distance.
We ( CKT ) are the only company that in NZ has genuine rebuild parts left in stock for these older Yamahas.

Do they use an IFP? Would you increase the pressure in that? as well as better oil and shim stack change.

[Robert Taylor]

Do they use an IFP? Would you increase the pressure in that? as well as better oil and shim stack change.

IFP meaning? Freon cell?

Yes shim stack improvements but first and foremost its undersprung

In such shocks the gas pressure is set a bar or so above the point at which it would otherwise cavitate. Gas pressure is NOT and should not used as a means of ''increasing'' shock hold up. It increases seal friction enormously. The aim of good shock design is to have the function so well pressure balanced that the gas pressure can be lowered significantly. Eg Ohlins TTX36 run at 5 bar gas pressure, whereas most single tube shocks run at anything between 10 to 20 bar