 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: 4,840 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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Replies(1 - 4)
| mepstein |
Oct 28 2025, 06:54 PM
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#2
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914-6 GT in waiting Group: Members Posts: 20,189 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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#3
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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: 4,840 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: 5,955 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. Ron is the only one that I know of that installed the mechanical drive option. He hasn’t checked in for awhile.. @RON S.
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