Replacing bottom bracket on 1994 Cannondale R400

[BikeHouseDC]

I'm looking at a choice between two Shimano parts: SHIMANO ULTEGRA Press Fit Bottom Bracket 86.5 mm shell width OR
SHIMANO ULTEGRA Threaded Bottom Bracket 68/70 mm shell width. If you've replaced the bottom bracket on this old frame, I'd really appreciate knowing which to order. Thanks.

 

[Ajax Bay]

Almost certainly the BSA threaded 68mm BB. Pressfit is so this century.
I take it (from your question) you have not removed the current BB.
Square taper if it's the original crankset. You will need to measure the spindle to know which specific one to get. Shimano UN-300 BB is a branded option. But maybe you have H2 cranks?

 

[iluvmybike]

At that age of bike it is going to be a standard threaded bb. It may be a square taper - look for 4 flats, it may be octalink - looks round or it may be hollowtech - the latter is obvious if you look the crank you will see the outboard cups and you crankset fit is different - you will see this by looking at l/h crank where there will be only two allen head bolts. Different tools are needed for each. Be aware that You need to know which groupset is on there as on some of the older Ultegra or DA groupsets had octalink and these are not compatible with the newer octalink bbs as the splines are not the same depth. Photo would help us advise you better if you are stuck but I attach this link as you likely have either sq taper or octalink
https://www.parktool.com/blog/repair-help/crank-removal-and-installation-three-piece

 

[Milkfloat]

Page 23 I think http://vintagecannondale.com/year/1994/1994.pdf

 

[Ajax Bay]

We don't know whether the OP has the original crankset or a newer one. Without that info, we can offer no more, imho.

 

[rogerzilla]

Threaded and 68mm, if it's anything like my old M1000. You need to get the spindle length right, so take the old one out first. If it is original, you will need cup-and-cone BB tools few people have anymore, so it may be best to let a bike shop do it just this once. You can cope with a hammer, punch and large vice but it's best not to.

 

[Ajax Bay]

Won't be cup-and-cone for that make/model of Cannondale (1994). You/we don't know what crankset is currently installed. By implication from OP it's not ST, but that relies on OP's BB understanding (which I am inferring is low - given the advice asked for). OP has not yet been back to see our posts.