Bigboy Torsion Spring Upgrade - '08 RMK 155

[PGPete]

I'd like to put heavier springs on my '08 RMK 155. I see that other big guys are getting .405/77 degree springs for their sleds. I just want to do a sanity check to see that they will fit on my machine before I place an order. I did try and search the forum to get an answer but I haven't seen anyone specifically talk about RMKs, and I'm not sure if there is a difference between models. The part numbers that I'm considering are 7041940-067 & 7041941-067. I gather that you can also buy them as a matched set p/n 2900098. My only concern is that when they list compatible sleds for these part numbers, my year and model aren’t on the list… Can someone please let me know if these are the right parts or am I missing something?
Thanks in advance,

 

[4Z]

Ftxmotorsports.com. Talk to Curt

 

[ripalip2]

go with the 375/47 springs , i have the same machine as you and weight 260 lbs.with gear , took all the sag out with a nice ride. 79 and 80 on the part numbers, talk with mike at pierres or kurt at fastrax

 

[diamonddave]

Below are the springs almost evrybody has went with on 2007-2010 RMK's, Dragons, and Shifts with track length of 155" - 163".

The .405's are too stiff.

These springs definately help and will fit your 08 RMK 155.

As for the part number having the springs sold as a set for a better price than seperate, we haven't been able to get our hands on that. Maybe now, they are actually available.

Curt at Fastrax has these in stock.

7042079-067 Spring, Torsion, LH, STD [.375/47 °]
7042080-067 Spring, Torsion, RH, STD [.375/47 °]

 

[PGPete]

Thanks for the replies...

I'm easily pushing 280lbs with all my gear - and then I usually carry spare gas and a bit of gear on my tunnel. So are you still thinking that the .375/47 will be adequate?

 

[donbrown]

Thanks for the replies...

I'm easily pushing 280lbs with all my gear - and then I usually carry spare gas and a bit of gear on my tunnel. So are you still thinking that the .375/47 will be adequate?

Did you already turn the spring tensioner to the stiffest position?

 

[snowmobile6]

I am too considering this upgrade. I am about 200 lbs in gear and carry spare gas with the adjustment block on the stiffest setting im just not happy with how much my sled sags. would this be the right way to go?

 

[MORSNO]

Get the .375/47 for a great ride and more than enough spring tension. I've also tried the .375/77's, they were no improvement over stock for me. The .405 can be made to fit, but they are not made for a RMK skid, they are for a 2-up trail sled. Curt at Fastrax has been doing the .375/47 upgrade for years. He also is the guy who recommended relocating my rear swing arm 5/8" back. The relocation will help remove excessive sag, but will still allow the suspension to work throughout its full travel. I'm 6'3" 250 and have my pretension adjuster on the light or middle setting with this setup depending on the days ride.

7042079-067 Spring, Torsion, LH, STD [.375/47 °]
7042080-067 Spring, Torsion, RH, STD [.375/47 °]

 

[tahoermk]

springs

There is also a .359/ 47 deg spring that I got from Curt at Fast Trax 253-848-0908. I run the .359 on his suggestion, I weigh 225 with gear, carry gas, and ride these on the low and middle setting. It solves the sag issue and rides so much better. The #s for .359/47Deg springs are:
7042068-067 and 7042069-067. Call Curt like others have suggested, he has both the .375 and .359 in stock, and will help you decide what is best for you, he's super helpful.

 

[PGPete]

Thanks very much for all the helpful suggestions. I'll call Curt before proceeding. Sounds like he's the guy...
Cheers,

 

[94fordguy]

.375/47* are perfect for the RMK... I'm 240 + gear and carry 2 large tunnel bags on my sled and they have enough spring tension to them to return the sled to max extension when you step off, but not so stiff that your not utilizing the suspension effectively. And that's on the softest pre-load setting too

 

[151Viper]

I am also running the .375 - 47 springs and they are perfect. I am also 240 plus gear. My dealership also told me they would not fit but I ignored them and ordered them anyways. They fit perfectly.

 

[gerrman]

There is also a .359/ 47 deg spring that I got from Curt at Fast Trax 253-848-0908. I run the .359 on his suggestion, I weigh 225 with gear, carry gas, and ride these on the low and middle setting. It solves the sag issue and rides so much better. The #s for .359/47Deg springs are:
7042068-067 and 7042069-067. Call Curt like others have suggested, he has both the .375 and .359 in stock, and will help you decide what is best for you, he's super helpful.

I have tried both the .375/47* and .359/.47* and liked the .359/47* springs better. I go 250 all in. Had an Exit X0 rear shock though. Probably comes down to personal choice/feel as well. If you could only buy one, the .375/47* would probably be the best choice. Good luck on your choice.

 

[snowmobile6]

Anybody tried the .375/77?

http://www.polarispartshouse.com/oemparts/a/pol/503ec307f8700222b848f2c7/suspension-torque-arm-rear

 

[94fordguy]

The 77* does not give you the increase in pre-load that the 47* offers. The 47* is important for decreasing the 'dead spot' in the suspension, after that, the thicker spring material increases the ride height/quality.

 

[MORSNO]

Anybody tried the .375/77?

http://www.polarispartshouse.com/oemparts/a/pol/503ec307f8700222b848f2c7/suspension-torque-arm-rear

Yes, not much if anything in gain over stock. The 47's have a tremendous gain in ride performance. They offer a smooth ride throughout their travel and yet can handle heavier rider weight without feeling like a pogo stick.

 

[Repsol83]

did the 375 / 47 springs come on any sleds stock?

 

[GKR]

Another vote for the .375/47 springs. Done it on a few sleds, guys are all 190-260lbs and it works great for all weights. The 47 degree preload is the key to the sag issue, after that the spring rate is the same as stock. The 77 degree preload does not deal with the sag issue, the .405 will be stiffer all the way thru the suspension travel but sag will still occur, maybe less that the lighter spring but not what you want if you just want to get rid of the sag.They did come stock on a sled but can't remember which, older model around the late 90's I think. They are not very expensive at the dealer. The part numbers are in the above posts.

 

[diamonddave]

The 47' is key for eliminating the sag. The 47' provides the "necessary" pre-load in the upper 50% of the spring travel. I weigh 215-220lbs. and carry 4 water's and 12lbs of tools in my tunnel bag and they have always been on the lightest setting. Even my wife runs these same springs on her 09 660 and she's about 60-70lbs lighter than me.




7042079-067 Spring, Torsion, LH, STD [.375/47 °]
7042080-067 Spring, Torsion, RH, STD [.375/47 °]

 

[q-bert]

You guys are talking rmk's, but for swb 09 800? (std 359s 12.5)

I have same problem... Sled is staying down even whit out
me sitting.....(come up 1'')
195lbs

Thanks