 901 Transmission synchro help, Large brake band gap |
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| Driver174 |
 Feb 17 2021, 11:22 PM
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#1
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Member  Group: Members Posts: 120 Joined: 2-February 17 From: Nevada Member No.: 20,806 Region Association: None 
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I'm building up a core transmission with custom gear ratios. Most of the core trans pieces look really good, but I'm questioning the synchro assemblies; don't remember this large of a gap between brake bands and thrust blocks on previous transmissions.
Could this much gap be normal? It looks to be 1/8 - 5/32" gap on each brake band. Thanks, Jim  |
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| brant |
Feb 18 2021, 09:29 AM
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#2
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914 Wizard Group: Members Posts: 12,013 Joined: 30-December 02 From: Colorado Member No.: 47 Region Association: Rocky Mountains 
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There are different length of blocks and stops for 1st gear and early/late
I’m wondering if you have some short bands mixed in? |
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| oldie914 |
Feb 19 2021, 09:01 AM
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#3
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Member Group: Members Posts: 114 Joined: 2-May 10 From: Germany Member No.: 11,680 Region Association: None |
As far as I know, there are two versions of the 901/914 syncro blocks and bands. The earlier 901 version used longer bands and a shorter fixed block. The later version was used on the 914 and as far as I know on the 1970/71 911 transmission and 3rd through 5th gears on the 915 transmission.
The attached pictures show a 914 gear syncro on the left and a 901 syncro on the right. The approximate measurements for the short and long bands are also shown. That said, it looks like you have too much clearance between your bands and the blocks. There should be no clearance when you push the bands against the central ring..     [attachmentid=781732] Attached image(s) 
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| gtbarnes |
Jun 13 2025, 08:37 AM
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#4
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Newbie Group: Members Posts: 35 Joined: 9-July 13 From: nash,tn Member No.: 16,111 Region Association: South East States |
QUOTE(Driver174 @ Feb 17 2021, 09:22 PM)  I'm building up a core transmission with custom gear ratios. Most of the core trans pieces look really good, but I'm questioning the synchro assemblies; don't remember this large of a gap between brake bands and thrust blocks on previous transmissions. Could this much gap be normal? It looks to be 1/8 - 5/32" gap on each brake band. Thanks, Jim I know this is old, but just wanted to you to know somebody(me) noticed your zip tie trick there. I am going to try that today to get the new band & snap ring on without cussing... |
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