New Superdream problem - bit of a bodge?

[McCabe-Thiele (Ted)]

Earlier this week I cleaned up the Superdream rear swing arm, the bushes are pretty good so after degreasing with Bilt-Hambler  stuff I did a final petrol wash to remove some of the unusually thick underseal like layer that was on the right underside  of the arm where the brake steady arm fits.
I brushed my petrol along the part where the brake steady arm bracet fits, it looked like a layer of underseal. After scraping it off it revealed a hole in the underside of the swing arm. Yes it could have been road tar but I'm making excuses.

Not the end of the world, I found a good looking replacement that was listed as suitable for the CB 400 A/T/N & Hondamatics.
As there was no part number listed I rang up the firm to make sure it was correct. I was assured that the models listed all shared the same swing arm.

Part arrived today it's in fabulous NOS looking A1 condition - but. Its not quite the same, different bracket placement for the chain guard fitting plus its just over an inch longer as well so the chain will not be long enough methinks. So I'll probably be driving over to Newcastle-under Lyme next week to see if I can do a swop. Bu**er I knew it was going to well.

TBH I'm not keen on having it welded unless there are no other options.

[Johnny4428]

That’s a real bummer that Ted. Does it have drain holes Ted? Maybe just a little corrosion around that.
Need to get back in touch with the person that assured you that the replacement  swing arm was the same as yours.😡

[McCabe-Thiele (Ted)]

I heard a dry rattle when I removed the swing arm. I tipped a pile of rust out of the rat hole.

[andy120t]

Have you checked part numbers on CMSNL? I had a quick look in my phone at a Supredream and a 400A and the part number seems the same ,( but I might not be looking at the correct ones for your bike). If they are though, your new one could be from a totally different (ie - the wrong) model.

[Bryanj]

Ted, i know its stating the obvious but could the one you took off be the wrong one?

[McCabe-Thiele (Ted)]

That thought occured to me last night Bryan, it might sound an odd thing to say but the swing arm somehow looked like the oldest part on the bike and the guard was really bad on the inside. I'm going to look at the CSML site to see if I can work out the correct location of the chain guard bracket. I've posted on the two SD  sites but they are not as quick to respond like on here. I'll pop a couple of photos later.

[McCabe-Thiele (Ted)]

Here you can see the difference, the one in the foreground is the replacement, the replacement fits the frame mounting.

I'm researching the frame numbers, my Honda parts manual shows 52110-413-010ZA, I can't find a part number on CSML.







.
side by side by Macabe Thiele, on Flickr

[Orcade-Ian]

Ted,
I just got a mate up here with a '79 400 SD (unmolested, low mileage) to brave the sleet showers to go and measure his.  Swing arm pivot centre to rear end of wheel slot is 558mm.

Ian

[McCabe-Thiele (Ted)]

Ted,
I just got a mate up here with a '79 400 SD (unmolested, low mileage) to brave the sleet showers to go and measure his.  Swing arm pivot centre to rear end of wheel slot is 558mm.

Ian

Thanks Ian, my old swing arm is 530 from center of pivot to the end of the fork itself (enclosed slot not open ended).
The replacement unit is 550, That extra 8 mm is probably the diagonal meased from the shaft on the alloy plate.

[Orcade-Ian]

Yes Ted,
Not too easy to get an accurate measurement with all the other bits in the way, it was only for a guide but it would appear that your better replacement is at least the right length.  I wonder if any of your earlier pics before stripdown show the rear shockers at a different angle nearer the vertical from other web pics? 
I'm sure I can persuade him to measure the guard bracket positions when he gets time!
Ian

[K2-K6]

Quite often a later iteration of bikes will utilise a longer swing arm, it's an easy way of calming down a chassis if there's been any observation of sharp handling or instability noted by press report or internal R&D development.

There's some possibility that the short one could just be incorrect in this case, and worthy of further investigation to establish if that's the case.

This engine is quite grunty in 400 capacity and fairly potent for a twin 4 stroke of that era. The geometry being quite high in overall mass position vs 400 four layout, these will wheely quite easily,  especially two up  which a longer arm will mitigate.

The four is generally a lower down weight/mass and highly unlikely to lift the front on power, in my experience.

[AshimotoK0]

I wonder if it's from a CM400T or CM auto Ted?

[Bryanj]

Ted, the silver lable on the new one suggests to me its from a US model

[McCabe-Thiele (Ted)]

At the moment I'm being advised to keep what I have bought on the SD site,  ones as good as the one I have are very hard to find. I'm advised it will lower the back wheel a tad if I can live with that.

I'm minded to run over to D&K and see if they have anything closer to mine or go for a chain guard that will fit, TBH I'm in a quandry as to the way forwards. Then there is the potential chain issue, that said there is a fair overlap between the two wheel adjustment slots so the chain might be good. Presumably chains can be bought by the number of links.

I saw a swing arm  on ebay for a 250 (same part) that was advertised as in good condition. I asked to see a photo of the underside that was not in the listing - it had two rot holes near the brake arm bracket similar to mine.

[Bryanj]

Ted, just buy an extra long chain and cut it down to suit