'66 1800S tacho glass cracks

[laptoprob]

Anyone know of a way to fill or eliminate the cracks in the plastic 'glass' of the 1800S tachos? Or anyone with a spare 'glass'? I am very happy the tacho finally works, but now I can hardly see the hand.

[Derek UK]

I've seen posts on the Yahoo 1800 forum, I see you've posted there too, that suggest that applying a light clear oil until the cracks fill improves things a lot. Johnson's Baby Oil? This would be similar to using resin for windscreen damage. I wouldn't think it's a long term fix though.

[Burdekin]

Would a windscreen repair kit work http://www.ebay.co.uk/itm/CAR-WINDSC...#ht_3059wt_725 YouTube has vids showing how it's done.

[Ron Kwas]

Rob;

That crazing is not really repairable because it is not only a surface phenomenon, but extends through the plastic (and although Derek"s idea will work conceptually, but I don't think it's usable here...sorry!...oil is just too unpredictable, and uncontrollable, because with its low surface tension will tend to continue to creep...to who knows where, not to mention unknown materials compatibility between plastic and oil and oil will be a magnet for dust and dirt...forever). The resin systems used for filling windshield cracks are stable once the resin sets...they do however require a vacuum to assure ingress into the crack...alos difficult if not impossible to achieve here...

...the tach on my 1800 had been vandalized with much worse results, so I had to replace the entire transparent face...I removed the tach for dash board, unbent the chrome edge to allow disassembly, then replaced the broken face with a piece of polycarbonate (1/4" thick or thereabouts if I recall)...yes it is flat which the original is not...it's slightly conical, and yes it has no paint-filled numbers from the back side which the original has but it still looks a lot better...I look at the angle of the needle anyway, and I know 4000RPM is at the vertical...

I suggest you keep a look up for a dead tach to serve as a donor...these are quite common as the germanium transistors, electrolytic capacitors and calibration potentiometer inside all fail with age, so these can be picked up on e-pay inexpensively...then you get to make one from two...and if you are so lucky to have one with functional innards, I strongly suggest you you perform a preventative maintenance on it when its apart. See: http://www.sw-em.com/service%20notes.htm#Gauges and http://www.sw-em.com/Smith%27s%20Tachometer.htm

Cheers from Connecticut

[laptoprob]

Thank you all. I can try to get some thin liquid into the cracks. Indeed maybe a thin oil. The plastic is somewhat ruined anyway, so until I can get a replacement part this might just work.

The electronics are all tested and replaced when necessary.

Thanks for your replies.

cheers, Rob

[laptoprob]

Full marks to Derek!

Baby oil does work indeed! Brilliant! It takes some time to get into the cracks though, it's not instantly.

cheers, Rob

Originally Posted by Derek UK

I've seen posts on the Yahoo 1800 forum, I see you've posted there too, that suggest that applying a light clear oil until the cracks fill improves things a lot. Johnson's Baby Oil? This would be similar to using resin for windscreen damage. I wouldn't think it's a long term fix though.