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Brando
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915 failure diagnosis gurus opinion
Ok, first ill give symtoms of my drama.
In second gear nearing full throttle right after right hand sweeper 40mph I get a bang, and push in the clutch. Engine is normal idling up and down fine. Clutch feels normal but gear is in second stuck and won't move. Let out clutch and have what feels like the clutch is stuck in but is released. Won't move from second gear but is not in a gear. Coasts like clutch is pushed in. Won't engage anything but second gear position but no gears engage. Now my engine/car is a 1977 911 with 915/61 gearbox mated to a 1977 930 engine running .8bar boost. I just installed a center force clutch a month ago and all seemed great for 1500 miles or more since clutch change till tonight. Have had the engine trash mated for over a year and wonder if I've been hard on the box. I don't drag race launch. But love to pull hard in most gears eeeek! I hope I didn't damage the case. I coasted all the way downhill to home 2 miles and into the garage with no trouble there. Any thoughts?
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Turbo powa! 1977 911s. it's cool |
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ROW '78 911 Targa
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Start simple, check the shift coupler under the cover in the back seat didn't self destruct.
Then I'd hope it was the clutch cable , then the release bearing or fork, then, clutch failure, then tranny internals .
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Dennis Euro 1978 SC Targa, SSI's, Dansk 2/1, PMO ITBs, Electric A/C Need a New Wiring Harness? PM or e-mail me. Search for "harnesses" in the classifieds. |
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Brando
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Thanks. I'm going to drop again to check these. (Coupler looks fine). And I'll certainly report back. I realize its hard with so many things that could be wrong. Hope it's the clutch as its brand new.
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Turbo powa! 1977 911s. it's cool |
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Registered
Join Date: Apr 2010
Location: New Orleans, LA
Posts: 1,493
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I would look under the trans at the clutch cable and external clutch mechanism. there're good photos of how it should look in the tech section of host site. look under floorboard where cable connects to pedal.
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1982 911SC, Mocal oil cooler, Bilsteins, Carrera tensioners, backdated heat, factory short shift, Seine gate shift, turbo tie rods, pop off. 2005 Mercedes-Benz C230 kompressor sport 6-speed (daily driver) |
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Registered
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Exploded second gear and bent/jammed the shift linkages?
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Steve Sapere aude 1983 3.4L 911SC turbo. Sold |
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Brando
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Is this possible? If so then yeah makes sense.
I've been trying to imagine a scenario where the clutch might be an issue and can't. But I'm no expert. I really only heard the one bang and then nothing. No clattering or anything. |
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Schleprock
Join Date: Sep 2000
Location: Frankfort IL USA
Posts: 16,639
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Agree with Steve. If 2nd gear comes apart and jams, you're in neutral all the time. Sure, when you work the clutch you should hear some ruckus because with the clutch engaged it is spinning the input shaft. But if it banged out of second, then the free gear is not engaging the dogs and no power can be applied. Clutch engagement can still spin the input shaft because w/out the free gear engaged, it's free to spin on the shaft.
Any time you hear a bang, you're going to want to open the trans. Especially with jammed linkage. Considerable torque from a turbo motor is hard on a 915. Especially in the lower gears like st & 2nd with their greater torque multiplication.
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Kevin L '86 Carrera "Larry" |
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Brando
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Thanks that's good info. I've felt I've been on borrowed time since adding boost to this car over a year ago. I don't want to pay for a 930 trans swap yet though. Maybe I will just save up for it.
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Registered
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One of the things I found that surprised me when I rebuilt my tranny last year was how loose the main shaft bearing race was in the main case (front MS bearing) not just the typical loose pinion race in the final drive housing. It was not noticeably loose when I had the tranny apart to replace 1st and 2nd synchro's but the metal in the case was severely egged out now several years after the turbo conversion. This suggests to me that the MS and PS can walk apart under severe torque placing more stress further out on the teeth of the gears where there is less strength. I wonder if this is a major contributor to failure in high torque motors.
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Steve Sapere aude 1983 3.4L 911SC turbo. Sold |
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gearhead
Join Date: Nov 2007
Location: Loverland, CO
Posts: 23,555
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Now that the gearbox has cooled down, have you attempted to pull it out of gear? If you haven't you should try to, and see if it will now shift through the other gears.
Also, when you have a chance, drain the gearbox and pull the plate off the bottom of it that carries the selector fingers. You might have broken a finger. Regards, Matt
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1974 914 Bumble Bee 2009 Outback XT 2008 Cayman S shop test Mule 1996 WRX V-limited 450/1000 |
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Crotchety Old Bastard
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Verify coupler is properly adjusted and omega spring did not snap. If you haven't beat on the tranny it should hold up.
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Brando
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I literally coasted the car two miles(seriously) home and into the garage last night, got out like normal, walked into the house and got ready for bed and went to bed(after posting). Woke up, got kids to school, and went to work. Haven't even looked at it other than last night I looked briefly into the coupler area and had a glance at the omega spring from an upside down position using my iphone flash light. So tonight will be telling.
If in fact the coupler is the culprit, or some other item of simple remedy, I still think it's time to look at the situation. I want to feel like I can drive this car across country and there is no reason a car like this should not do that. So I intend to make sure it would be able to do that whatever that means. I understand thats a pricey statement but I love this car.
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Turbo powa! 1977 911s. it's cool |
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Brando
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Quote:
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Turbo powa! 1977 911s. it's cool |
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Registered
Join Date: May 2008
Posts: 2,948
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Read my 915 Tutorial and some of it will start to make sense!
Welcome to Red Line Porsche Wiki - Porsche Wiki Scroll the left side of page, click on "915" under "Page tags," and the site will take you to the 9-part Tutorial. Enjoy!
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Keep the Shiny Side UP! Pete Z. |
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Schleprock
Join Date: Sep 2000
Location: Frankfort IL USA
Posts: 16,639
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Yes indeed. You won't find a better step-by-step tutorial to walk you thru the rebuild of a 915 from beginning to end.
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Kevin L '86 Carrera "Larry" |
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Registered
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They are really not difficult to do some of the basic repairs on if you are very careful and have a few of the necessary tools. Pete has a wonderful tutorial/wiki and there are several older threads available that really step you through the process as well. It is a very educational and rewarding project.
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Steve Sapere aude 1983 3.4L 911SC turbo. Sold |
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Brando
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Well the coupler is fine. And the omega spring is ok too. The clutch isn't perfectly adjusted but its very functional ad far as the cable is concerned. I'm going to have to drop it guys. I just had it out a little over a month ago too.
And to be honest I'm leaning toward doing a 930 trans swap. What exactly are the particulars required there? Obviously I'd love the 76-77 930 short bell but I need to stay realistic so let's focus on the late model 930 trans swap? Any one know what's exactly needed parts wise and mod wise?
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Turbo powa! 1977 911s. it's cool |
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Banned
Join Date: Nov 2007
Location: Rockwall, Texas
Posts: 8,559
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Hey Brando - I imagine that the liberal use of JB Weld will solve your transmission problem!
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Brando
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Quote:
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I am curious, though, where the real differences are in strength and durability between the 915 and 930/G50. I see a lot of loose bearing races in the 915's that don't seem to be a problem for the others. Is this one of the principle failure modes? Does the WEVO insert fix this and increase torque capacity or are there other weaknesses? How much improvement in torque capacity do you get with all of the 915 strengthening mods and how close does it get you to a 930 equivalence?
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Steve Sapere aude 1983 3.4L 911SC turbo. Sold Last edited by sjf911; 03-22-2013 at 06:44 AM.. |
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