 915 /916 mechanical speedo drive, 915 /916 mechanical speedo drive |
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| rgalla9146 |
 Oct 28 2025, 04:58 PM
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#1
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Advanced Member  Group: Members Posts: 4,839 Joined: 23-November 05 From: Paramus NJ Member No.: 5,176 Region Association: None 
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Anyone here have a running driving Martin Bott 915 / 916 conversion with mechanical speedo drive ?
My car is up and driving but my mechanical speedo shows 120 mph when GPS says 60. I've tried other 914 speedos and even borrowed a '72-'73 911 speedo to see if that was the difference. It wasn't. A well known instrument restorer suggested the difference I was seeing was outside the range of normal adjustment. I'm trying to stay with 914 era parts. Anyone ? |
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| mepstein |
Oct 28 2025, 06:54 PM
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#2
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914-6 GT in waiting Group: Members Posts: 20,188 Joined: 19-September 09 From: Landenberg, PA/Wilmington, DE Member No.: 10,825 Region Association: MidAtlantic Region
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Can you substitute a 914 drive and try it.
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| Maltese Falcon |
Oct 29 2025, 05:07 AM
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914 Guru Group: Members Posts: 5,116 Joined: 14-September 04 From: Mulholland SoCal Member No.: 2,755 Region Association: None  |
See if California Motorsports (Lake Havasu) has a different 915 drive gear for the problem .
Marty |
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| rgalla9146 |
Oct 29 2025, 06:53 AM
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#4
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Advanced Member Group: Members Posts: 4,839 Joined: 23-November 05 From: Paramus NJ Member No.: 5,176 Region Association: None
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QUOTE(mepstein @ Oct 28 2025, 08:54 PM)  Can you substitute a 914 drive and try it. Mark as you know in a 911 chassis the speedo cable is driven straight forward into the tunnel A Bott 916 rear cover is arranged just like a 914 with a 90 degree bevel gear on the rear of the pinion shaft, then another 90 degree adapter on the outside of the trans (1:1) forward to the cable. That is how mine is assembled. I think the difference lies with the gear ratio machined onto the tip of the 915 pinion shaft. Any chance you can count the number of teeth on a 915 pinion shaft speedo gear ? If not, I can probably get it from a trans shop...Patrick Motorsport ? Or someone here ? |
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| Steve |
Oct 29 2025, 08:09 AM
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#5
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914 Guru Group: Members Posts: 5,952 Joined: 14-June 03 From: Laguna Niguel, CA Member No.: 822 Region Association: Southern California
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Did you try reaching out to Martin? It does sound like a trans gear issue. You can also try James at PMS. He built my MB 916 trans, but mine is an electric speedo. Also check the MB ad in the members vendor section for 914world members that bought the mechanical speedo option.
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