Spacer width question 8 speed cassette on 7 freehub

[The utility cyclist]

So fixing up a bike for a friend, cleaned up the cassette (Shimano 7 speed) and it skips like crazy in the bottom 3 or 4 sprockets, chain is a relatively new 8 speed SRAM that isn't stretched in the slightest so presume the previous owner just put a new chain on to try resolve the problem and why they in the end gave it to a charity to sell on.
I've an 8 speed cassette that's not seen much use so would like to use that (using the 7 speed spacers), however will the bottom two sprockets with the fixed spacer be okay shifting wise or not?

[mattsccm]

If the free hub was originally a 7 speeder then an 8 speed cassette won't fit. Quite possibly you could leave a sprocket out but in theory the spacing is different and thus wrong.
You can put 7 on an 8 speed freehub with a spacer.

[rjb]

I think the original poster is going to dismantle the cassette, to reuse the 7 speed spacers. He will need to lose a sprocket and the top 2 cogs ie the smallest should be ok as a pair. But you may be better off losing the smallest sprocket and keeping the rest. Loosing a sprocket from the middle of the cassette may affect the shifting performance as the ramps on the sprockets will not line up. To dismantle the cassette may involve grinding/drilling/filing the heads off the pins which hold it together. These will not be needed as the lock ring will hold it all together.

[cycleruk]

So fixing up a bike for a friend, cleaned up the cassette (Shimano 7 speed) and it skips like crazy in the bottom 3 or 4 sprockets, chain is a relatively new 8 speed SRAM that isn't stretched in the slightest so presume the previous owner just put a new chain on to try resolve the problem and why they in the end gave it to a charity to sell on.
I've an 8 speed cassette that's not seen much use so would like to use that (using the 7 speed spacers), however will the bottom two sprockets with the fixed spacer be okay shifting wise or not?

When you say the "bottom 2 sprockets - do you mean the smallest ones ?
Presuming you do, and as there is only 0.2mm difference between 7 & 8 speed spacing, I would expect no problems.
Spacing for 7 speed = 5.0mm and 8 speed = 4.8mm.

[The utility cyclist]

When you say the "bottom 2 sprockets - do you mean the smallest ones ?
Presuming you do, and as there is only 0.2mm difference between 7 & 8 speed spacing, I would expect no problems.
Spacing for 7 speed = 5.0mm and 8 speed = 4.8mm.

Yes, the two smallest sprockets have the integrated spacer and as the 4 smallest are skipping my question was pertaining to the spacing of those two which you answered thanks.
I took the 15t out of a 13-26 so with a 42/34/24 & 13/14/17/19/21/24/26 it now has a 24"-85" gear range which fine for intended use.

Mattsccm, was just dismantling an 8 to use the sprockets + spacers from the 7 but you can fit an 8 on a 7 with the correct spacers IIRC

RJB, no fettling/grinding aside from using a 2mm Ak key to remove the pins off the shimano and prising the Suntour sprockets off the even narrower pins that don't have a head to them, was hardly any effort at all and probably could have pulled them apart with my fingers tbh.

Just got to get out and test now
thanks all for responses

[Brucey]

you will usually be fine if you just delete one sprocket from the 8s cassette and use the 8s spacing.

In fact this setup can work better than a 7s cassette if the rear mech is a bit baggy; the 7s mech ought to slightly overshift on an 8s cluster and this usually helps the shift along. The maximum error is only about 0.3mm anyway.

cheers

[The utility cyclist]

it worked perfectly with the 7 speed spacers and a Sedis chain I decided to use instead of the 8 speed SRAM

[fastpedaller]

it worked perfectly with the 7 speed spacers and a Sedis chain I decided to use instead of the 8 speed SRAM

Is the Sedis a very old chain? - I thought they hadn't been made for years!

[hamster]

And Sedis became SRAM anyway, so in all likelihood an identical chain design.

[The utility cyclist]

And Sedis became SRAM anyway, so in all likelihood an identical chain design.

Yeah, the sedis is from the 6 speed era but as you say the design with the flared inner and bushless is the same (as are all modern chains), it's a bog std black sedisport but still probably better than most, black looks better than the silver SRAM anyway.

I kept back a few lightly used D.I.D. and Sedisport chains in case they came in handy and I still use suntour 6 speed freewheels anyways which I have a lovely top end silver Sedis chain to match to it, runs lush
As a side note Sedis still make chains in France but for industrial use only, SRAM were knocking their bike chains out in Portugal apparently whereas the rest of SRAM is based in Taiwan.

it worked perfectly with the 7 speed spacers and a Sedis chain I decided to use instead of the 8 speed SRAM

Is the Sedis a very old chain? - I thought they hadn't been made for years!

The Sedis brand name was to become Sachs-Sedis, Sachs a German company buying them out, then it became SRAM. Production of the Sedis/SACHS chains in France stopped some years ago but as above SRAM chains are still made in Portugal i think. It wouldn't surprise me if the old Sedis worked with 8 speed, certainly some online sellers sell them as 5/6/7/8 speed chains. A NOS Sedisport can be as much as £40 and to think they were not much more than what i got for my weekly delivery round back in 1982!