Rear shock maintenance

[Totti]

Had my rear shock serviced.

There should be 10 bar of gas, mine had 6. And the oil was in bad shape. Seems that Yamaha saved some money here also. 

 

Pretty different shock now. I advise that you have your rear shock serviced for the right amount of gas and decent oil, before doing anything else. Like changing the spring. 

[DT675]

Excellent advise! This seems to be an area often overlooked by many. Forks seem easy to do, the shock not so easy. How many miles/Km did you have on the bike at this service? 

 

I have to send out my track bike shock to get refreshed. I’m wondering if I should include the T7’s too. Mine has about 4K miles. 

[Totti]

About 23.000 km's and two years. By bike had rust inside the front forks. Yamaha replaced the inner parts to the forks and at the same time they serviced the rear shock. I changed a stiffer spring (90 Nm) before the service. Now when the shock is much better, maybe a 85 Nm spring would suite me better.

[williestreet]

Similar issue here, bike has only 3500km on it.

I wanted to get the shock revalved and took it out to a new suspension guy I decided to try.

We spoke about what issues I was having and what changes should be made.

 

I had removed the spring at home and I passed him  the shock.  He compressed it one time and said something was wrong with the pressure.

He checked the pressure before disassembly and it was at 80psi(5.5bar).  He usually uses 180psi(12.5bar) in KYB motocross shocks so this is where mine was set after service.

He didn't mention anything else was unusual, but low miles on the shock so I didn't expect the oil to be terrible yet.

 

All shocks I used when  I was club racing were serviced every year.

Street shocks always get done every 2nd year at the longest no matter the mileage.

 

So if you are having issues with the rear wallowing, there is a possibility it could be as simple as a low charge in the reservoir.

Just because your bike is a year old, consider when the shock might have been made.  Who knows the lead time from KYB to Yamaha to assembly and then the standard 6 months stuck on a ship outside Long Beach for the American customers.

[andy74rc]

From where do you check the shock pressure? Is it the allen bolt near the reservoir? There's nothing about it even on the workshop manual.

[williestreet]

58 minutes ago, andy74rc said:

From where do you check the shock pressure? Is it the allen bolt near the reservoir? There's nothing about it even on the workshop manual.

You can't check it at home with out special tools.

On the end of the reservoir you will see a small hole.  Our shocks use a needle type fitting inserted into this hole to recharge/pressurize the bladder after service.

Some shocks use a normal schrader valve which would make it easy, but unfortunately ours is setup differently.

 

You would need a suspension shop to reset the pressure if you want to have it checked.  If you have a good one nearby take the shock over and ask them to check/set the pressure to the proper pressure.  Better yet get a normal service done if you haven't had this done yet.

 

 

 

 

[andy74rc]

Thank you! I just changed spring. The bike is still at 0 km, pressing the shaft without spring everything seems in order although is of course impossible to be sure. So for now I'll put it back as it is.

(On a side note, as I'm going through the bike for a fair number of upgrades and mods, I have to say I found everything done properly. Even the swingarm shaft was with a proper coating of grease from the factory).

[Aburamla]

Very interesting topic!

I’d like to install the K-Tech shock absorber piston.

Does anybody know the exact amount of oil needed?

OEM shock pressure should be 10 bar and looking for that needle type to charge the bladder. Any specs?

Thank you to everyone who will help me

 

 

 

[Goody Boy]

On 1/16/2022 at 11:53 PM, Totti said:

Had my rear shock serviced.

There should be 10 bar of gas, mine had 6. And the oil was in bad shape. Seems that Yamaha saved some money here also. 

 

Pretty different shock now. I advise that you have your rear shock serviced for the right amount of gas and decent oil, before doing anything else. Like changing the spring. 

Same with mine. Had it serviced at 20k km at it was also at 6 bar. 

[williestreet]

21 hours ago, Aburamla said:

Very interesting topic!

I’d like to install the K-Tech shock absorber piston.

Does anybody know the exact amount of oil needed?

OEM shock pressure should be 10 bar and looking for that needle type to charge the bladder. Any specs?

Thank you to everyone who will help me

 

 

 

You will not find listed anywhere an  exact amount of oil. 

You need to fill and bleed it so there is no air remaining in the shock.  It takes however much it needs, but you could measure the shock body and calculate the approx volume.  My quick guess would be between 200--300ml, but you will waste/spill  some so you will need more.  A single 500 ml or 1 litre bottle of the proper weight oil will be more than enough.

 

I think most suspension shops these days are using a vacuum pump to fill and service their shocks these days.  It could certainly be done manually if you wish to do so, as I am sure some on here are servicing their shocks at home without a vacuum pump.

 

There are some very good service videos on YouTube showing the basic steps to service a shock, but there are also some very bad ones as well.

So look around and be sure you know the steps before you dive in.

Personally I have local suspension guy do mine.  He has a professional Vacuum pump setup that does a perfect job of getting all the air out.  Air left in the shock will allow cavitation and it is imperative to have it all removed.

 

If I was going to do mine at home I would change out the bladder cap from the needle style to a schrader valve type for easier servicing.

Search around for more info but the aftermarket sells replacement  bladder caps with schrader valves for the yz80 and most of the Japanese 80 mx bikes.  These are a direct fit for our shocks as well.

 

 

 

 

Edited March 24, 2023 by williestreet