In search of lower rpms, differential ??

Okay since we cannot just swap gears on the shafties I have another thought and er question.

Are all the rear diff's the same ratio?? meaning is the rear diff from a say 1100 the same ratio as a 650? or the seca's the same as the maxims?? If you think of cars usually the 4 banger jeeps get a lower ratio than the 6-cyls to help with acceleration. Soo if there is a different ratio from a different model bike in theory can I swap the diff and lower my highway70-75mph rpms down a bit with relative ease??

 

I believe they are all 32/11.

I know some of the XS1100 guys can swap out an old XS850 rear end to lower the rpm by a fair bit, but the rear ends are similar, and not the same design as the XJ's. This rear end might swap into an XJ1100 though.

 

hmm so are the splines just different for the rear wheel to slip on?? or different nolt pattern to the swing arm cause most i have seen have a simple 4 bolt to the swingarm. hmm for the price I see rear diff's going on ebay it could be a low cost swap to a solution. I don't get bad mileage by far but for those 95-100 mile run's down the freeway it would be nice to get the R's down at least into the mid 5k range. I know if I do 55mph on the two lanes around me I get way better mileage than 75ish.

 

I as well would like to lower my rpm's. I will keep an eye on this thread.

 

Anybody have a clue??? or where I can dig for this info? Might not do you alot of info to stay tuned Reaper if nothing comes of it.

 

Last night in someones sig they had a rear end swap mod that they had done.
I think I saw them posting in the mods section.
Maybe some help.

 

the plot thickens.........

 

It is early yet. Some one will stop by and tell us something .

 

I looked up the part #'s for the virago of the same year thinking that maybe a v twin cruiser may have a lower ratio nope same part number for the rear diff..

 

It's all ok because I love the sound ou all those rrrrrrrrrrrrrrrrrrrrrr's

 

This may have been what I saw in a sig.
Building my dream. Souping up grandpa's '82 XJ 650. Front & rear wheels and suspension from '79 XS11...which means dual disc up front and disc rear.
Sorry guys.

 

hi
I put a 1980 650 maxim engine in a 1981 750 seca frame while I was repairing the 750 engine. I can tell you there is a gear ratio difference. At 60mph in 4th gear the engine was turning 2100rpm. I had to go 80mph and faster to shift into 5th.

 

So the 650 has lower gearing in the tranny man thats alot of work and hoping to pull a whole gearset from a 5 yr diff bike. what are the R's with the 750? Thats a huge drop!!! I imagin being that far out of the power band the bike would be a slug. Thats over 4k difference from what mine runs...

 

So I checked the part number for a rear diff assy for the 81 seco 750 strange it comes back as the same part number again maybe the online fische is wrong or they are all pretty much the same on the xj's

 

To change the gear ratio significantly, you have to work on the primary reduction. I saw a post back in the spring where someone was going to try to cut some gears for the XJ 750. I believe he was a machinist in Vancouver, BC. Don't what he got accomplished. You might try and search and check it out.

 

that post is here...

http://xjbikes.com/Forums/viewtopic/t=7000.html

He should be in europe till september then he said he'd start working on it.

 

Hi, 85MaximXX
You are correct the seca was a slug with the maxim engine. The seca with the 750 engine ran about 4000 at 60mph.

 

Forgot to tell you that the seca has a 18" rear wheel and the maxim has a 16" rear. If you don't mind the different look you could try a seca rear wheel. This will lower your RPMs a little

 

It's not that I don't mind a different look But I just had(well in process and it's taking tooo long) the bike painted Yup even the wheels they turned out sweet too.

 

I would look at a pic of this new paint job