915 Gear Synchro dimension (help a newbie)

Elektrobank · 11-02-2008, 03:25 AM

Hi All!

I'm new to This forum, and this is my first Post
I'm writing to all you from the busy city of Napoli and i'm looking for some measurements...

I'd like to know some dimensions:
outer diameter, when compressed in gear teeth and not and thickness of the Porsche 915 gear synchro, for all gears

if possible also the porsche part numbers for every synchro...

i lokked around older post with the magic "search button" but i find many nice info but no dimensions...

i need that measurements for my mechanic, he is not too practice with internet, i know that he is looking for some porsche 915 synchro to be modified in an older italian Alfar Romeo transaxle car

so please guys try to help me and my mech!

all you have a good beer and a nice trip around the city offered

Many Many Thanks in advance
Gianluca

RWebb · RWebb's Garage

welcome!

post your tranny ID - e.g. 915/xx

or at least the year of your tranny

Elektrobank · 11-03-2008, 02:27 PM

Quote:

Originally Posted by RWebb

welcome!

post your tranny ID - e.g. 915/xx

or at least the year of your tranny

Thank for your reply RWebb!

The trasmission type is and old racing AlfaRomeo Transaxle, during past years this transmission has been serviced with some porsche gear-synchro-ring but we don't know from what kind of porsche they come from (915 box is possible for the age of the car and parts used to race)....

at the moment only the first gear synchro is pulled off and measures 87,40mm (approx 3,44inch) uncompressed and... very worn

i can ask to pull off also the synchro from other gears if needed

Please let me know
Thanks
Gianluca

john walker's workshop · 11-03-2008, 03:51 PM

1st and 2nd 915 syncros are supposed to measure 86.20 to 86.54, installed. the inside of the retaining teeth also wear, which would increase the measurement.

356RS · 356RS's Garage

Welcome to the group Gianluca. I measured a first gear synchro ring not compressed and it comes out to 87.8mm and compressed on the gear its 86.3mm. The synchro is 7.9mm wide if you need that measurement. This is a used synchro ring. This is out of a 1975 with a type 915/40 box. Maybe a picture would help?

Grady Clay · 11-03-2008, 04:33 PM

Gianluca,

The Porsche patent syncros are VERY sensitive to the installed size you are looking for. Additionally they must be used with the Porsche sliding sleeve and the Porsche engagement dog ring splined onto the free gear. These are sufficiently sensitive that in some cases, simply turning over a slightly worn syncro can prevent proper shifting. Needless to say you must use the Porsche stops and bands Even the side clearance from the circlip is important.

There are two basic sizes: the 87.1 and 88.1 mm ones used on the 1st and 2nd gears of a 915 and the 78.0 mm ones used on the 3-4-5 gears of a 915 and all 901/911/914 gears. These are “free” dimensions with the syncro ring not installed on the gear.

Acceptable diameters for installed syncros are in the range of 86.20- 86.25 mm for the large 915 1-2 syncros. This is with the syncro ring bottomed under the engagement dogs and the side clearance between the syncro ring and the circlip. Porsche specifies 86.20 mm to 86.54 mm. Normal diameters are about 76.25-76.35 mm for all the others with Porsche specification 76.12 mm to 76.48 mm.

How is this Alfa retrofit accomplished? Does it use the Porsche hub for the sliding sleeve? How is it splined onto the shaft? How is the engagement dog ring attached to the free gear? Does the shift fork properly fit the sliding sleeve (side clearance spec is ? How much of the shift fork engages the circumference of the sliding sleeve? Porsche uses about 180º while some other manufacturers only use 30º or so.

Best,
Grady

Elektrobank · 11-04-2008, 09:34 AM

Quote:

Originally Posted by Grady Clay

Gianluca,

The Porsche patent syncros are VERY sensitive to the installed size you are looking for. Additionally they must be used with the Porsche sliding sleeve and the Porsche engagement dog ring splined onto the free gear. These are sufficiently sensitive that in some cases, simply turning over a slightly worn syncro can prevent proper shifting. Needless to say you must use the Porsche stops and bands Even the side clearance from the circlip is important.

Hallo Grady Clay, Thanks for your reply, i shot three pictures today,quality is poor but you will have an idea of what i have in my hands, better pictures will come today, i love to use an old reflex camera so is not fast as a digital camera...

http://i203.photobucket.com/albums/aa296/elektrobank2/Immag005.jpg
this is the first picture, the syncro is worn
http://i203.photobucket.com/albums/aa296/elektrobank2/Immag006.jpg
http://i203.photobucket.com/albums/aa296/elektrobank2/Immag007.jpg
here is the picture of the first gear the dog teeth is pressed in and is worn

Quote:

Originally Posted by Grady Clay

There are two basic sizes: the 87.1 and 88.1 mm ones used on the 1st and 2nd gears of a 915 and the 78.0 mm ones used on the 3-4-5 gears of a 915 and all 901/911/914 gears. These are “free” dimensions with the syncro ring not installed on the gear.

87.40is the dimension of the uncompressed ring and 85.4mm-85.5mm when pressed in...

Quote:

Originally Posted by Grady Clay

Acceptable diameters for installed syncros are in the range of 86.20- 86.25 mm for the large 915 1-2 syncros. This is with the syncro ring bottomed under the engagement dogs and the side clearance between the syncro ring and the circlip. Porsche specifies 86.20 mm to 86.54 mm. Normal diameters are about 76.25-76.35 mm for all the others with Porsche specification 76.12 mm to 76.48 mm.

many usefoul info!
so my compressed diameter is too little? what will happen if i can press in this syncro? too much stiffness during engaging?(if engages...)
premature wear of the forks?

Quote:

Originally Posted by Grady Clay

How is this Alfa retrofit accomplished? Does it use the Porsche hub for the sliding sleeve? How is it splined onto the shaft? How is the engagement dog ring attached to the free gear? Does the shift fork properly fit the sliding sleeve (side clearance spec is ? How much of the shift fork engages the circumference of the sliding sleeve? Porsche uses about 180º while some other manufacturers only use 30º or so.

Best,
Grady

the mech. states that was used all porsche parts, forks, gears and many other parts,so, in his mind will be more or less easy find parts in "porsche areas"
today you will see some better pictures of all sliders and shifter

i try to find the synchroin two porsche official spare parts here in napoli but it is difficult (always looking for a chassis number...if you don't have a chassis number you buy at your own risk...is crazy)

Elektrobank · 11-04-2008, 09:41 AM

Quote:

Originally Posted by 356RS

Welcome to the group Gianluca. I measured a first gear synchro ring not compressed and it comes out to 87.8mm and compressed on the gear its 86.3mm. The synchro is 7.9mm wide if you need that measurement. This is a used synchro ring. This is out of a 1975 with a type 915/40 box. Maybe a picture would help?

The measures that you have looks to be approximately the same... thickness of synchro in my hand also is 7.9 and uncompressed diameter is the same
a picture? if you have one... why not?

thanks!

356RS · 356RS's Garage

Gianluca, Your first gear assembly looks just like a 915/44 & 915/61 type. The anchor block and thrust block with brake band look exactly the same. Interesting............

Grady Clay · 11-04-2008, 01:07 PM

Gianluca,

The image looking at the gear lying flat, the engagement dog teeth appear to be ‘down inside’ a recess in the side of the gear. Is this so? Is this just a shadow? If the dog teeth are in a recess, the sliding sleeve will not fully engage the dog teeth. This will tend to ‘pop out of gear.’

The ends of the engagement dog teeth appear badly worn but that just may be the poor image. If worn, they need to be replaced with new.

Is the engagement teeth ring only attached with a key (yellow) or is this only the notch for the stop?

Looking forward to better images.

Best,
Grady

ChrisBennet · ChrisBennet's Garage

Quote:

Originally Posted by Grady Clay

How is this Alfa retrofit accomplished?

Alfa licensed the Porsche synchros at some point so perhaps it wasn't a retrofit at all?
-Chris

Grady Clay · 11-04-2008, 04:24 PM

Chris,

That would be great.
Simply replacing OE Porsche parts is MUCH easier than trying to fix something cobbled up.

Lets see what better images show.

Best,
Grady

Elektrobank · 11-06-2008, 09:52 AM

Quote:

Originally Posted by Grady Clay

Gianluca,
Looking forward to better images.

Best,
Grady

new pics....
also for 2nd and 3rd gear...

Peter Zimmermann · 11-06-2008, 10:09 AM

Quote:

Originally Posted by Grady Clay

These are sufficiently sensitive that in some cases, simply turning over a slightly worn syncro can prevent proper shifting.

No hijack intended, I just want to say thank you to Grady. I've been telling people to never "flip" synchros for 35 years, and have been seriously flamed for it. This is the only time that I've ever read where a fellow professional feels the same. Thank you, Grady!

Grady Clay · 11-06-2008, 10:22 AM

Well … clearly you need all four syncros, engagement dog tooth rings on the free gears and both sliding sleeves. I would also replace all the stops and bands. I’m surprised that it stayed in gear.

This appears as if there was amazing abuse or the clutch wasn’t releasing – or both.

I would still make sure that first gear sliding sleeve completely engages before it hits the side of the free gear. There should be clearance to the gear when fully engaged.

It is interesting that the 1 & 2 free gears are on the input shaft and the 3 & 4 free gears are on the pinion shaft. Just the opposite from Porsche.

Best,
Grady

Grady Clay · 11-06-2008, 10:53 AM

Peter,

No hijack. This is appropriate in this discussion.

So everyone understands what we are talking about:
There are two wear places on the syncro ring – the side that goes under the sliding sleeve and the side that goes under the dog teeth on the free gear. The side that contacts the sliding sleeve gets much greater wear than the side toward the gear.

It is possible (and very tempting) to simply swap (‘flip’) the syncro ring around to put the less worn side toward the sliding sleeve. This extends the useful life of the syncro ring without buying a new part.

The problem arises with a worn syncro ring. The more worn part is now under the engagement dogs on the free gear. This allows the center diameter of the installed syncro ring to be larger than the specified maximum diameter (86.54 mm or 76.48 mm depending on gear). In fact even being at the large end of the specification range becomes a problem when a new sliding sleeve is installed and used engagement dogs are still on the free gear.

What happens is the larger than ideal diameter of the installed syncro ring provides too much resistance when the sliding sleeve moves over it when attempting to engage the gear. To the driver it feels as if it won’t go into gear without unreasonable force on the lever. To some it will feel as if it is in gear. When they let the clutch out without the dogs engaged, the syncro and sliding sleeve take huge abuse – sorta like trying to put it in gear without the clutch disengaged.

Have I ‘flipped’ syncros – you bet. With a ‘like new’ transmission, flipping the syncros can give extended life. You must exercise caution and see that the installed diameter remains at the low end of the specified range and you still use the used sliding sleeve.

For the fastest and best shifting you can select the ‘right’ combination of used and worn (not worn out) parts. This can be significantly better functioning than all new parts. Those are the syncro ring, sliding sleeve and engagement dog ring. The downside is this won’t last as long as all new parts.

The most significant things for long syncro life are driver shifting technique and fully disengaging the clutch.

Best,
Grady

Peter Zimmermann · 11-06-2008, 12:11 PM

Quote:

Originally Posted by Grady Clay

Peter,

No hijack. This is appropriate in this discussion.

Hi Grady:

My post above (#14) was really geared to long life and maximum durability (that's the way that I think, and what I always felt was having my customer's best interest at heart).

That said, I agree 100% with you that used pieces that are thoughtfully assembled can be made to produce a very quick-shifting, reliable trans for the short term - one that often feels "broken in" before it's put in the car.

Cheers!

Elektrobank · 11-06-2008, 02:13 PM

Quote:

Originally Posted by Grady Clay

Well … clearly you need all four syncros, engagement dog tooth rings on the free gears and both sliding sleeves. I would also replace all the stops and bands. I’m surprised that it stayed in gear.

I'll tell the mech to pull out other syncro and will let you know the diameters... hope to find something here that will fit... do you think it's possible?

Quote:

Originally Posted by Grady Clay

This appears as if there was amazing abuse or the clutch wasn’t releasing – or both.

yes... clutch wasn't releasing completely but only half... the clutch bearing was not working properly and the releasing fork worn out...

2nd gear crunches always and 3th was stiff and slow during shifting and sometimes first gear did not engage well, sometimes pops put of gear

Quote:

Originally Posted by Grady Clay

I would still make sure that first gear sliding sleeve completely engages before it hits the side of the free gear. There should be clearance to the gear when fully engaged.

if my memory is good, when the slider engages the first gear there is no contact between the slider and gear (thanks to the recess in the gear i think)

what kind of measurement is needed to look for some porsche spare part?

Quote:

Originally Posted by Grady Clay

It is interesting that the 1 & 2 free gears are on the input shaft and the 3 & 4 free gears are on the pinion shaft. Just the opposite from Porsche.

Best,
Grady

Many many thanks for all your help
Gianluca

Elektrobank · 11-07-2008, 04:55 AM

The other worn syncro measures 87.40mm uncompressed at the larger point, as you all can see in the picture it has a double diameter.... the smaller part that is under the dog tooth measures 85,4mm uncompressed and thickness is 7.50mm

http://i203.photobucket.com/albums/aa296/elektrobank2/IMG_7764.jpg

the dog tooth is pressed in gear like the first gear and has 39 teeth

Grady Clay · 11-07-2008, 05:24 AM

Re:
http://i203.photobucket.com/albums/aa296/elektrobank2/IMG_7764.jpg
IMG_7764

Does anyone recognize this?

Best,
Grady