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improving dt250 monoshock suspension

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ive currently got my '79 dt250 apart,for engine rebuild,slight tuning and general tidy up,

starting to think about the rear suspension now,and wondering if a it250 shock could be made to work,never really been happy with stock shock,bit to stiff and not enough travel,about 5",

done some online research and it looks like pre '79 it250's had about 7" and after '79 about 10",before changing to a completely different set up in the '80's,

now if i could get 10" of rear wheel travel i'd be more than happy,realise new shock top mounting would be required,as the it shock is a few inches longer,but dont have a problem with that,

so anyone ever tried it,or know why it just wouldn't work,

very few it parts in uk,so would probably have to order from u.s,which gets pricey with shipping and import tax,so dont really want to order one on off chance it may work,

thanks for any help nick

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First, you need a semi correct length and travel. Too much travel can bust off your rear frame hoop or make your bike totally unridable.

Second, you need appropriate shock width to mate with your frame and your swinger.

Now, you seem to have done some research, but you seem to have ignored the other area where wheel travel comes from on a monoshock Yamaha: the swingarm.

Take a look, 1980 DT250:

bikepics-2255099-full.jpg

1981 IT250bikepics-2182073-full.jpg

The swingarms are totally different dimensionally.

I would suggest going for a mere 2" increase in travel using the earlier IT shock, but having it rebuilt first. There's builders of badass monoshock Yamahas in the UK, they can surely help

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I would suggesting looking on yamahaenduro.com for some information. I remember reading somewhere that someone wanted to or did use an it swingarm on the dt. It also increased the height about two inches from what I remember.

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the square section swinging arm does look very different,but the round section it swinging arms look a lot more similar to the dt,i appreciate dimensions could be very different,i have no idea,thats why i asked,

heres a pic to compare,

http://www.ebay.co.uk/itm/120685458608?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

Asking questions is how we all learn!:bonk:

Given that you want a travel increase to 10+ inches, you're gonna have to swap to the square section.

What are you planning on doing with the bike anyways? If you want to jump it, I'd suggest looking at something better suited and less likely to kick you over the bars.

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Asking questions is how we all learn!:bonk:

Given that you want a travel increase to 10+ inches, you're gonna have to swap to the square section.

What are you planning on doing with the bike anyways? If you want to jump it, I'd suggest looking at something better suited and less likely to kick you over the bars.

well from what ive been reading on the net,looks like '79-'80 had round section swinging arm and 10" of wheel travel,not saying i wont be happy with less than 10 ,7" of decent suspension would be a lot better than 5" of too firm suspension ,which is what ive got now,

the bike will only be used for riding trails,dont do jumps more than a couple of feet high these days ,my other trail bike an xr280,has much better suspension,which makes life so much better for my bad back and bad knees,but for some reason i like riding the dt better,really just trying to turn the dt into the best trail bike it can be,and dont think there's anything that can be done with the dt shock,so looking for alternatives,if you take a look at the '80 it swinging arm that i posted in the link,it dosen't look too different to the dt,but could well be totally different dimension wise,just wondering if its even an option

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You will run into trouble with increased rear suspension travel on the DT. It is due to

the distance between the Countershaft centerline and the Swingarm pivot. This causes

the chain tension to vary greatly between fully extended to fully compressed. If you make it right

at one point it is too loose at another point, causing problems keeping the chain on sprockets.

Shortly after the DT all bikes had their sprocket closer to the swingarm to handle the

increased suspension travel. Chain tensioners don't really work for the amount of slack

we are talking here.

The YZ and IT shocks are about 3-4 inches longer than the DT shock.

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The three dimensions you need are the pivot width, shock length and upper shock mounting width.

I recommend the aluminum unit over the tubular steel as a personal preference and a unsprung weight saving measure.

Beyond those dimensions, anything else can be fixed with spacers or new bearings.

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got someone to measure up a '80 it swinging arm for me,the dimensions that make up the triangle of shock mount,pivot and wheel spindle are the same as the dt,thought they looked similar,the tubes of the swinging arm take slightly different routes between those points,but they are geometricly the same,so this says to me the it shock should work,when the swinging arm swings,it will be putting the same force on the shock with the dt arm,as with the it arm,

disconnected my shock and swung it down so there was 10 1/2" between tyre and underside of mudguard,10" travel with it shock,then measured 27 1/2" ,length between centres of it shock,from shock mount on swinging arm to point on frame where new mount hole needs to be,its just over 2" above original mounting position,

all looks pretty simple,wont even have to swap swinging arms,will have to modify airbox a bit , to gain a bit of clearance,and will make bike a bit taller,but still lower than my xr,im 6' anyhow so thats not an issue,

something to keep me busy over winter months

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got the it250 shock back from being serviced today,threw it on and took a picture,

http://025.jpg

http://i1117.photobucket.com/albums/k599/nickxjr/023-2.jpg[/img]"]http://023-2.jpg

after a bounce in the back yard ,i think its going to work pretty good,

over the winter ive also fitted a bigger tank,this ones off a cg125 12litres,the dt tank is about 8litres and would be drained in about 50 miles,

made up the single seat,

made the sidepanels,they're not my best work,but they'll do for now,

fitted some nice big footpegs

fitted the front end from a xr250,that i happened to have lying around,

and drilled some boyeson boost ports,all ready for a shakedown run now,but i'm just about to start a 7 day run of 12 hour shifts,so thats gonna have to wait a few days,

once ive ironed out any bugs i'll try my hand at a bit of porting,ive got 5 or 6 barrells lying around,and 2 spare bottom ends,

Edited by paint it black

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Wow that swing arm is at a much different angle that the stock setup. I wonder if you'll run into problems because that bike has to be sitting at least another 4 inches higher in the back. The actuating lever on the back brake looks to be at an awkward angle too. Is that where it has to be to compensate for the extra travel and height.

Got a big enough tire on the back of that thing? haha.

I hope it works out for you okay for you.

What forks and triple trees are you running?

Edited by 79yamdt

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the brake isnt actually connected up in that pic,it will sit in its more regular position when it is,

the front end is all from a '88 xr250,

could have mounted the top of the shock further towards the headstock,which would have lessened the swingarm angle,but that would have made the wheel hit the mudguard when it bottoms out,could have raised the mudguard,but should be fine as it is,sinks about 3" when i sit on it,seat is a couple of inches lower than my xr,feels about right

the tyre is a mitas c02,actually street legal, 120 18

Edited by paint it black

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Huh I'm surprised a tire like that is street legal, that front one isn't is it? How much modification did it take to get the front end on the bike? I have a '78 400 and 250 right now so I might try that swap. Disk brakes are always a good thing.

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the xr stem is too short for the dt headstock,you cant get the nut on the top,i tapped the inside of the stem and screwed a large bolt into it ,to hold it in place,then messed around with different bearings and spacers,not really a straightforward job,easiest way would have been to press out the dt stem and fit it to the xr yoke,but i dont have access to a press,

both tyres are street legal,in uk anyway,but they are scary on the road

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Doesn't sound too easy then. I do like the front end on that bike though, it has to be a major upgrade over the stock setup. Yeah the back one kinda looks like it could be street legal but the front looks like a straight dirt tire. I like your side panels too. What did you make those out of? I'm missing the side covers on mine and don't wanna pay 40 bucks for one for a beater bike.

Edited by 79yamdt

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front tyre is a michelin enduro comp iv ,street legal in uk ,i would think in the u.s too,the pairing of the michelin front and mitas rear is very popular over here,

sidepanels i made up from some sheet steel ,made a cardboard template,then copied it in steel,they could be better,

ive got the original panels,but they wouldnt work with the bigger tank,

i left all the original mountings in place,so i can put the original tank and panels back if i want,but think the extra range is going to be too useful to go back to the stock tank,

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