Steel synchro for 71A / 71B gearbox

[krizza]

Gday guys,

Just finished pulling down my FS5C71B (71A??) 5 speed due to a very crunchy second gear only to find that it doesn't use Borg Warner type synchros as I expected(I had already bought a kit with these in preparation for the rebuild), instead it has the Porsche style steel servo synchros. I can see that all other gears look good, but second gear synchro is very polished and stuffed.

My mistake as I thought the C was for Close ratio and W was for Wide, apparently it denotes the type of synchro used.

My searches have come to nought as these appear to be NLA, so hoping someone has one on hand or a broken box that I could rob a 3rd or 4th gear synchro from as a replacement.

Hoping someone can help as I was hoping to keep the standard CR box instead of doing a 71C swap.

Cheers,

Kris

[C.A.R.]

Give SW Motorsport - Stew should be able to supply you with the Steel Bulk rings.

But FWIW it's not worth rebuilding it with the bulk rings, as any heavy handed sifting will prematurely wear out the bulk rings.
I just convert the CR 260Z box to brass syncro rings - they last far, far longer and it makes for a much smoother, faster gearshift.

[HS30-H]

3 hours ago, krizza said:

Just finished pulling down my FS5C71B (71A??) 5 speed due to a very crunchy second gear only to find that it doesn't use Borg Warner type synchros as I expected(I had already bought a kit with these in preparation for the rebuild), instead it has the Porsche style steel servo synchros. I can see that all other gears look good, but second gear synchro is very polished and stuffed.

My mistake as I thought the C was for Close ratio and W was for Wide, apparently it denotes the type of synchro used.

 

The 'C=Close, W=Wide' thing is only a useful mnemonic. In practice it is mostly true, but the C and W actually denote Synchro type, as you have found.

But why were you surprised to find your FS5C71B uses the Servo-patent, Porsche type, steel synchros? That's correct for the type. 

There's a lot of bad information and data floating around out there, and when it comes to gearboxes a lot of it emanates from the USA. They get confused because they never saw a factory 5-speed on an S30-series Z until the 280Z turned up. Most of the time they are talking about S130-series transmissions and Warner-patent synchros, whereas most other markets got Servo type synchros from the beginning of production (with the FS5C71-A and then the FS5C71-B). They also talk about 'close' and 'wide' ratios when both would be considered 'wide' in other markets.

The fact is that the Servo type steel synchros were thought to be too 'sporty' in nature for the north American market (its all about the nature of the shift, with the Servo type requiring a deliberate and positive action by the driver) so they were given what was considered a more easy to use, less effort required, Warner type.   

[krizza]

Thanks for the feedback guys. I have contacted SW Motorsport to see if Stew is able to help source a replacement synchro ring, and am waiting to hear back. If anyone is wrecking a gearbox and has a good condition steel synchro I would still be keen in case I can't track down a new one.

HS30-H, I was surprised as I didn't realise the C and W denoted the type of synchro and I thought that B boxes onwards used the BW type synchros. You are right about the misinformation on the web though, but you live and you learn!

[krizza]

All sorted now! I managed to track down 4 new baulk rings today locally, so the rebuild can progress.

Big thanks to Martin Falconer at TuneRight. Really helpful, nice guy.

Edited November 26, 2019 by krizza