Triumphrat

jimmy bush · 04-18-2009, 09:29 PM

I must have gotten the wrong speedometer drive gear box. I put a new one on when I started the rebuild on my 68 T120 and after comparing what speed was registering to my 2006 T-100 ridden by my brother, I've have found the speedo reads 8 to 10 mph slow at 55 to 60 mph. Sh!!!

KADUTZ · 04-19-2009, 12:34 AM

What is the ratio of gearbox you used also what are the numbers on the face of your speedo. Ever think your speedo is correct and your brothers is off?

mark61120 · 04-19-2009, 05:03 AM

Do either of you have a satnav that give a speed reading?
Also, both your speedos may be out by 10%...

Mark

jimmy bush · 04-19-2009, 09:12 AM

The numbers on the speedometer are SSM 5001/06 1000. I dont know what ratio the gearbox is. When I ordered it I was just learning about Triumph and I ordered it from a guy that restores British bikes. I told him I needed the gear box for a '68' T120R.
I know all the motorcycles have a bit of generous error but I'm pretty sure the 68 is the one with the biggets error and it is a negative reading. On the freeway, I keep up with traffic and it is registering about 55mph. No way is that what reality is around here. I might believe it if it was reading 75 or 80mph.

jimmy bush · 06-19-2009, 01:39 PM

I pulled the "new" gearbox off and it has Ratio 15/12 stamped on the inner ring. The stripped gearbox that was on the bike when I bought it was a 15/12 but that doesn't necessarly mean it is the correct one. My shop manual calls for a 2/1 ratio in the general data section. The speedometer head is the correct one as per the parts manual. So does any body know how fast a '68' T120 should be going at 4,000 RPM?

GrandPaulZ · 06-19-2009, 01:58 PM

If you have the wrong ratio box, it will read about 30 when going 70, or 70 when going 30, depending on the wrong combo.

10% error is very typical, it gets worse as the meters deteriorate.

It can be dangerous on a tach, you think you'r spinning 5,000 and you're spining past red-line.

www.joellevinecompany.com is an excellent rebuilder.

GrandPaulZ · 06-19-2009, 02:04 PM

Jimmy, I'm trying to recall if you supplied me with the part number, or if I researched it, but my '68 parts book shows D637 (60-0637) which is what you received. Was it a Smiths or an aftermarket unit?

jimmy bush · 06-19-2009, 04:43 PM

It was an after market from JRC. The box was marked BG5330/168. If it would be off as much as you say, it must be my speedo head needing overhauled or lubed.

GrandPaulZ · 06-19-2009, 06:06 PM

I've sure not heard of the aftermarket speedo drives OR aftermarket Smiths replica speedos being off by even 10%...

mark61120 · 06-20-2009, 06:26 AM

Jimmy,
4000 rpm is about 60 mph.
Mark