915 rebuild - how long to run in
02-01-2006, 05:40 AM
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915 rebuild - how long to run in
Ive just rebuilt my own 915. I did it because the syncro on 1 wouldnt let me in when rolling and she was popping out of 3rd and crunching on 4th.
on stripdown I found the gears to be OK, the syncros worn, I changed the sliding sleeve selector on 3/4th.
She's all back together and I find...
a) she wont let me into first when rolling, even when stopped I have to sometimes find 2nd then neutral, then clutch up/down then find first.
b) when moving from 1st to 2nd, I get a notch, then a crunch.
How long does it take for a new box to run in, I know the syncros need to wear a little, ive only done 20miles home from the shop and she is parked up over winter. Do these problems sound like a build error. I did the job myself so I know I did everything as right as possible.
Do we think it could be the 'tightness' of new bits that will ease up through use or should I bite the big one and pull it out again whilst she is laid up. Problem is, all I will find is new bits.
www.red964.com/html/dyndex.php
www.projectsonly.co.uk
on stripdown I found the gears to be OK, the syncros worn, I changed the sliding sleeve selector on 3/4th.
She's all back together and I find...
a) she wont let me into first when rolling, even when stopped I have to sometimes find 2nd then neutral, then clutch up/down then find first.
b) when moving from 1st to 2nd, I get a notch, then a crunch.
How long does it take for a new box to run in, I know the syncros need to wear a little, ive only done 20miles home from the shop and she is parked up over winter. Do these problems sound like a build error. I did the job myself so I know I did everything as right as possible.
Do we think it could be the 'tightness' of new bits that will ease up through use or should I bite the big one and pull it out again whilst she is laid up. Problem is, all I will find is new bits.
www.red964.com/html/dyndex.php
www.projectsonly.co.uk
02-02-2006, 04:32 PM
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hi
changed all syncros on 1-5, changed the 3/4 selector ring, kept the original 1/2 selector as it looked ok, but wear is v hard to detect on them. Did the dog rings on all of them.
1984 3.2 915
changed all syncros on 1-5, changed the 3/4 selector ring, kept the original 1/2 selector as it looked ok, but wear is v hard to detect on them. Did the dog rings on all of them.
1984 3.2 915
02-02-2006, 05:38 PM
#4
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OK, here's what's probably wrong.
1. NEVER replace a synchro ring without replacing the slider (selector). Those parts wear into one another and are not compatible with replacements.
2. Did you measure each assembled synchro per the factory manual?
3. Did you notice that the 1st gear is asymetrical, but 2nd is not. If you put the 1/2 slider in backwards you will have a very difficult situation in both 1st & 2nd.
4. When you assembled 1st gear did you put the brake band in on the correct side?
Pete
1. NEVER replace a synchro ring without replacing the slider (selector). Those parts wear into one another and are not compatible with replacements.
2. Did you measure each assembled synchro per the factory manual?
3. Did you notice that the 1st gear is asymetrical, but 2nd is not. If you put the 1/2 slider in backwards you will have a very difficult situation in both 1st & 2nd.
4. When you assembled 1st gear did you put the brake band in on the correct side?
Pete
02-03-2006, 05:04 PM
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Hi Peter
the honest answer is probably that I cant remember. I was working late in the workshop to do it after hrs. I was kind of left to it and followed the manuals with a tech friend watching over me.
1. Didnt do the selector, hindsight says I probably should.
2. all measured up ok
3. didnt notice and now you mention it, would it have been obvious if it was in the wrong way?
4. didnt notice?
assuming 3 and 4 are possible **** ups (but I was overseen and they didnt pick anything up).
would the problems I am having be typical of these mistakes or would the box just not work.
bear in mind the car/box does drive it just is a bit niggly?
If I had gotten 3 and 4 wrong would I just not be able to get the gears full stop?
www.projectsonly.co.uk
www.red964.com
the honest answer is probably that I cant remember. I was working late in the workshop to do it after hrs. I was kind of left to it and followed the manuals with a tech friend watching over me.
1. Didnt do the selector, hindsight says I probably should.
2. all measured up ok
3. didnt notice and now you mention it, would it have been obvious if it was in the wrong way?
4. didnt notice?
assuming 3 and 4 are possible **** ups (but I was overseen and they didnt pick anything up).
would the problems I am having be typical of these mistakes or would the box just not work.
bear in mind the car/box does drive it just is a bit niggly?
If I had gotten 3 and 4 wrong would I just not be able to get the gears full stop?
www.projectsonly.co.uk
www.red964.com
02-03-2006, 05:33 PM
#6
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The difference with the 1st & 2nd gear sides of the 1/2 slider is obvious - unfortunately you have to know that it's there! Doing transmission work requires above average organization, an extra dash of cleanliness, and a lot of looking & measuring. When I do a 915 it feels fully broken in at the end of a 5-mile test drive (city traffic & freeway). Regarding your 3/4, I'm not sure what you're saying. Is it also not shifting correctly in those speeds? The fork setup is tricky until you figure out how and why it's done the way it is. If they're not adjusted using the holding plate, with the shaft nuts torqued, you will definitely have trouble.
Pete
Pete
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02-04-2006, 02:42 PM
#8
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Good luck with it; I'm pretty sure that you installed the 1/2 slider backwards. When you take it back apart you'll see the asymetrical dog teeth on 1, and you'll have to match those to the asymetrical side of the slider.
Pete
Pete
02-07-2006, 02:27 PM
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Hi Peter
Thanks for your advice to date. please forgive my 'noggin' level questions ive dont most things on the car so far, built 2 964 engines but the gearbox was my first attempt.
I cant remember if I changed the 1st/2nd slider or the 3rd/4th slider. Because of the problems before I stripped it, logic would indicate that I would be most likely to change the 1-2 slider since that was the one I had difficulty with, its highly likely it will have shown wear. 3rd/4th never gave a problem and the box was rebuilt about 50k miles before it so I think the 3-4th was fine.
so, assuming I put a new slider on 1-2, and possibly got it in backwards can you explain in plain man in the street terms to me to explain
a) Would the slider being in the wrong way completely block selection of first or just make it difficult, if just tricky - in what phase of selection ie, as the brake bands slowed the syncro or regardless - just the inability to mesh and lock. The symptom I have is a resistance to lock select the gear, if I go back to neutral, dib the clutch then try again, it will sometimes find it. It will do this when moving or when stationary. Do the dog teeth and ring teeth clash (when gear is stopped), if so why can I get the gear at all.
b)When you say the slider is sided with syncronous and async teeth, can you explain a little I just cant picture it.
I know my questions wont help me, only stripping it will provide the answers but your replies might make me sleep better at night until then.
thanks for your time
----
www.salenca.com - "death to your website long live your content"
www.red964.com
www.projectsonly.co.uk
Thanks for your advice to date. please forgive my 'noggin' level questions ive dont most things on the car so far, built 2 964 engines but the gearbox was my first attempt.
I cant remember if I changed the 1st/2nd slider or the 3rd/4th slider. Because of the problems before I stripped it, logic would indicate that I would be most likely to change the 1-2 slider since that was the one I had difficulty with, its highly likely it will have shown wear. 3rd/4th never gave a problem and the box was rebuilt about 50k miles before it so I think the 3-4th was fine.
so, assuming I put a new slider on 1-2, and possibly got it in backwards can you explain in plain man in the street terms to me to explain
a) Would the slider being in the wrong way completely block selection of first or just make it difficult, if just tricky - in what phase of selection ie, as the brake bands slowed the syncro or regardless - just the inability to mesh and lock. The symptom I have is a resistance to lock select the gear, if I go back to neutral, dib the clutch then try again, it will sometimes find it. It will do this when moving or when stationary. Do the dog teeth and ring teeth clash (when gear is stopped), if so why can I get the gear at all.
b)When you say the slider is sided with syncronous and async teeth, can you explain a little I just cant picture it.
I know my questions wont help me, only stripping it will provide the answers but your replies might make me sleep better at night until then.
thanks for your time
----
www.salenca.com - "death to your website long live your content"
www.red964.com
www.projectsonly.co.uk
02-07-2006, 06:30 PM
#10
Rennlist Member
OK, we're talking about the ring of small teeth that you press the synchro ring into. That ring on 1st speed will have teeth that are offset when you look at them straight on. If you look at the side of a very simple house, you will see the roof extend up and in from each vertical wall, forming an upside down "V". That is what the "symetrical" description of 2nd gear's teeth means - each tooth is machined in a symetrical way. On 1st gear's "asymetrical" teeth one side of the roof will extend up and in until that line is directly over the other wall, and then drop down vertically to the other wall, forming a "Z" turned sideways with one leg removed. Many backyard storage sheds have roofs like this. The slider (selector) has a ring of inner teeth that match the teeth on 1st gear and on 2nd gear, which just happen to have the same outside diameter. That makes it possible to direct the slider's symetrical teeth toward 1st gear's asymetrical teeth, which produces a very bad marriage - almost as bad as putting a square peg in a round hole! I can't answer your question regarding driveability, the transmissions that I've repaired following work done by others just come out and apart, I can tell there is a problem in the parking lot and don't bother to drive the car. Again, good luck with it.
Pete
Pete
02-08-2006, 03:11 PM
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