8 speed cassette on a 7 speed DA 7400 hub - possible?

I recently bought a pair of MA40 laced to some Dura Ace 7400 hubs. Hubs take a 7 speed cassette (BSC screw on thread according to the previous owner). My existing groupset has 8 speed STI shifters. Would it be possible to just put an 8 speed cassette on the hub? Apparently, it would simply be a case of tweating the derailleur cable to take the 8 speed (as it's a 7 speed derailleur) according to a few websites....I had a look on Sheldon, but it was either too late last night or I couldn't follow what he was saying....

Worst case scenario is I buy a new 8 speed derailleur, but that'll be cheaper than either a new set of wheels or a new set of STI shifters.

If anyone has any knowledge about this, sharing this knowledge would be greatly appreciated!

Some thing there aint right. Dura Ace 7400 hubs should be neither 7 speed (I don't think?) nor screw on.

I think they should be 8 speed which could be used with a 7 speed cassette if a spacer were fitted.

Obviously, if that's what you have then remove the 7 speed cassette, remove the spacer, fit an 8 speed cassette and Robert's your mother's brother.

However, if you have a 7 speed hub the freehub body will not be wide enough to fit an 8 speed cassette on. You could change the freehub to an 8 speed one but then you also have to respace the axle, if it's long enough, and re-dish the wheel slightly.

If you have a hub which takes a screw on freewheel then you could fit an 8 speed freewheel. They aren't common and they aren't exactly high quality but they do exist, probably only in mtb tooth counts though. No idea what would happen to the axle spacing.

"BSC screw on" could refer to a uniglide cassette rather than a screw on freewheel. Incase you are unaware, uniglide uses a screw-on small cog to hold the others on the freehub body rather than a lock ring. The final cog is female threaded, hyperglide lockrings are male threaded. For a while freehub bodies had both uniglide and hyperglide threadings and I think 7400 was out around this time. Not sure if you get 8 speed uniglide threaded freehubs or only 7speed though.

If you can post images of the hub and current cassette especially around the small end of cassette and axle area then it'll make diagnosis of what you need easier.

I have a 7400 screw-on freewheel. 7 speed. Uniglide.

8-speed is possible, but you'd need a freewheel with the correct spacing. There's a model made in the far East currently but I'm not sure if it is the Shimano 4.8mm spacing.

The nice quality Sachs/SRAM model (OOP) is for Campag 5mm spacing.

Are 7 speeds not enough?

I have a 7400 screw-on freewheel. 7 speed. Uniglide.

8-speed is possible, but you'd need a freewheel with the correct spacing. There's a model made in the far East currently but I'm not sure if it is the Shimano 4.8mm spacing.

The nice quality Sachs/SRAM model (OOP) is for Campag 5mm spacing.

Are 7 speeds not enough?

Uniglide ≠ screw on freewheel.

Uniglide is the last cog of the cassette being threaded and acting as the lockring.

I'm pretty sure that Uniglide was the presecessor to Shimano's Hyperglide system, whereby it used a twist-tooth cog design to improve shifting. Uniglide featured on both the earlier freewheels, and the later freehub cassettes. The cassettes had a screw on smallest ring rather than a lockring.

My bad. I thought Uniglide merely referred to the cassettes with the screw on small cog.

So in that case, sounds like the OP does have a screw on hub.

When I worked in Hellfrauds some of the bikes came with 8speed screw on freewheels. I'm pretty sure they were all equipped with grip shifters, some of those being Sram so spacing might be an issue.

Thanks gents. I'll stick some photos up when they arrive - hopefully this weekend.

the issue surrounds the fact that the STI shifters are 8 speed. Will these work freely on a 7 speed cassette? Other option is to try and swap them with someone here for 7 speed ones....

Your comments are greatly appreciated tho!

I'd consider swapping the shifter for a 7-speed model if I were you. You can use any 7-speed block then.

Another alternative would be to re-space a 7-speed block using different spacers.

Thanks gents. I'll stick some photos up when they arrive - hopefully this weekend.

the issue surrounds the fact that the STI shifters are 8 speed. Will these work freely on a 7 speed cassette? Other option is to try and swap them with someone here for 7 speed ones....

Your comments are greatly appreciated tho!

Not as stock no.

The distance between cogs differs between 7 and 8 speed. As Rodabod says though, you could respace the 7 cogs with 8 speed spacers and then just not use one of the clicks on the shifter. An 8speed cassette will cost ypu a lot less than an 8speed STI, infact you could probably pick one up for free if it's got worn out cogs and just salvage the spacers from it.

The only issue with re-spacing is that the easy-to-find cassette spacers are not the same as those used in freewheels. The 7400 freewheel body is larger in size than a freehub body IIRC. For that reason, I'd maybe just get a spare shifter.

The only issue with re-spacing is that the easy-to-find cassette spacers are not the same as those used in freewheels. The 7400 freewheel body is larger in size than a freehub body IIRC. For that reason, I'd maybe just get a spare shifter.

Ah yes, I was forgetting that we were talking about freewheels as opposed to cassettes.

Or you could get on the hunt for a Regina extra 8 speed freewheel.. I have one but it's going nowhere!

It is possible to get an 8 speed screw for freewheel hub I have seen them on e-bay but I would not recommend this course of action. This is because one of the reasons Shimano went to free hubs i.e. the ratchet mechanism in the hub was that a weakness of 7 speed screw on freewheels was that the distance between the bearings and the frame was too big. This meant 7 speed freewheels hubs often get broken axles. However you will find that an 8 speed changer will work for 7 speed jus minus one gear stop

Zebs

Gents, thank you very much for your comments. they are greatly appreciated. as you will have noticed, no doubt, i'm a complete novice when it comes to the more mechanical bits. I think it may be wise to just use it without using all the 'clicks' until i find a 7 speed STI replacement.

Alas, my rush into picking up a good looking pair of wheels has come to bite me in the ass. I'll keep you updated on the situation. cheers again!

Well, from one end of the block to the other, you'll be 6 shifts X 0.2mm short = 1.2mm short. Might just be fine as has already been suggested.

If you wait around, you should be able to get a 7400 freewheel. Otherwise try and get something else nice. Just avoid any shitty Tourney stuff!

8 speed shifter on a 7 speed block will probably work fine in the workstand, under load, not so much.

Oh that is the reason I have so many problems with my 8 speed shifter and 7 speed block - Not works fine and has for years

Zebra, check out Sheldon's ideas on alternative cable routing to get around the spacing issues - http://sheldonbrown.com/derailer-adjustment.html#alternate. I've used it before and it does work with a bit of experimentation.

Sorry but the myth around 8 speed screw on (& for that matter 7 speed) is just that, a myth. Maybe one or two people spoke about this & then it propagates like all failures. Yes the bearings are too far out in an ideal world however does anyone know of someone whose axle snapped because they were using an 8 speed screw on???
I used a Sachs 8 speed for years on a Mavic 501 hub, I've been around 95-100kg in that time so not exactly flyweight, never had issues with it at all even with loads.
The only thing you might want to check though is the spacing on the Sachs & other 8 speed freewheels (unless you get a cheap shimano MTB type)

Additionally unless the axle on your 7400 hub is 130mm at the rear (7 speeds were generally 126mm) then you would likely struggle to get an 8 speed freewheel and clear the inside of the chainstay with the chain as an 8 speed cassette is wider than a 9 speed in any case.
As mechnaical Advantage mentions above, the 7400 hubs came in varying types.
Screw on - shimano 'road' freewheels only went up to 7 speed though 7 & 8 speed mtb were/are plentiful..cheap 8 speed here for example
http://www.amazon.co.uk/13-28-Speed-Shimano-Compatible-Freewheel/dp/B0045EQR68
Uniglide only- 6/7/8 speed 'cassettes' the beaings are contained within the freehub body as per modern cassettes, screw down last cog so no lockring as such.
UG/HG hybrid, these allowed the use of UG cassettes and std 7/8/9 and even 10 speed cassettes
Hyperglide only, these latter models removed the end hreading on the freehub body.

I've bent rear axles with 7/8 freewheels, but never snapped one.

The SRAM/Sachs 8 speed block has Campag spacing (I have one right here). You can make it a 7 speed block just by losing the little ring.

I kind of remember the bikes with 8speed freehweels coming back to Hellfrauds pretty regularly because the freewheel mechanism shat the bed but don't remember many axle problems.

I've had to replace 3 broken axles for friends with this kind of freewheel (one 7, two 8 if my memory serves me). None of them is a lardy arse. Common feature was that they all rode down a hill with sleeping policemen and some of the roads are pretty shoddy around here (Devon). I was really surprised first time, now it feels commonplace.