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CFD CFD is offline
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Noisy gearbox - '76 930

Experiencing the following symptoms - noisy/growling gearbox under load. More noticeable in higher gears. Oil level is correct although I do suspect the car had been driven at some stage with low gearbox oil - to what extent I don't know. Put the car in fourth gear at low revs and accelerate and the harshness is very pronounced. No trouble with gear selection, all four gears and reverse engage smoothly every time - driving and while stopped. How noisy are these gearboxes in people experience? In my opinion this harsh roughness/growling is excessive.

Thanks...

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'76 911 Turbo
Old 04-25-2012, 02:58 PM
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They aren't loud. These cars really don't do well at low revs and have lame power there. What rpm's are you talking about?
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76 930
Old 04-25-2012, 04:04 PM
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agreed my gearbox is not loud
Old 04-25-2012, 04:11 PM
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Quote:
Originally Posted by Les Paul View Post
They aren't loud. These cars really don't do well at low revs and have lame power there. What rpm's are you talking about?
Ok, thanks for that. Down as low as 2000rpm - so the car still pulls away fine - certainly wouldnt be winning any drag races, but I wouldnt have expected a rough harshness (not a vibration) from the 'box under these circumstances. Obviously under normal driving conditions one wouldnt have the car in 4th gear at this rpm, but the noise it there under all driving circumstances, but very pronounced when the gearbox is loaded.

Indicative of needle cage / shaft bearing issues perhaps?
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Old 04-25-2012, 04:34 PM
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Hard to say what the grinding is but I would be concerned with a pronounced grinding sound from the transmission. If it is indeed from inside the transmission, I would suspect that the pinion/ring gear has lost its back-lash clearance due to race creep. Needle bearings more or less stay put and only have to be checked once you press on new dog teeth - if the box has been rebuilt before. If it has, perhaps they torqued the pinion/main-shaft nuts with an impact wrench, hardly enough forward torque for those bolts. One other thing to check is the rear wheel bearings. They can also make that type of grinding sound.
Old 04-25-2012, 05:11 PM
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Um, mines loud to '77. It's more of a wine though not grinding and it ishifts fine.

Big Buttt though, I received this car from the untimely death of my brother and the trans was empty with the drain and fill plugs in! My fault for not checling it, so I'm sure I took a few years off it.
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Old 04-25-2012, 05:44 PM
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Do you have stock sound proofing, carpet etc...? I don't have, so every gear has it's own sound, improved by WEVO mounts. I can tell you which gear is in just from sound

If stock, it's only little, but compared to modern cars, newbies think always of failure
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Old 04-26-2012, 12:44 AM
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Thanks guys.....in my opinion this noise is certainly (to me) not normal transmission whine/noise and in my experience is a bit much to ignore - as zcorker says. Its not a wheel bearing noise, as while the car is rear wheel drive and acceleration/load may have some change on a wheel bearing rumble, certainly not to this extent, plus the simple test of pushing in the clutch eliminates the noise completely, so its definitely in the gearbox.

When I got the car I did an inspection in the workshop and discovered basically an identical situation to jly535 - both plugs in and no oil in the gearbox!! Cause eventually traced to the vent facing the wrong way!! The previous owner wasn't aware and as the car was driven very little over the last few years, wasn't in a position to say how long or many many miles may have been covered in this condition. I only have experience of 915 boxes prior to this, so before coming to any conclusions I thought you guys might have some insight on noise levels.

profighter - yes, all stock sound proofing is in place....I wouldn't describe myself as a newbie.....but this is the first 930 gearbox I have had on the bench

So from the info above I would conclude I do have excessive noise, and I had more or less decided to strip it as I wouldn't be happy to leave it.....that in itself is only time on the bench. As we can do the work inhouse if it does need a rebuild then thats not a problem - I have priced up all the replacement bearings. I have already had the engine out and did the "while I am in there" jobs that needed doing as well as some bodywork to take care of rust so no surprises left on the car....
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Old 04-26-2012, 06:46 AM
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Your description sounds like worn bearings especially since it ran low on oil.
The OEM two piece roller bearings are ridiculously expensive from porsche.

They are standard size standard clearance bearings so you can take them to a bearing supply store and they will measure them and sell new ones just as good as what porsche will sell you for around half the price.

For the gasket set the usual Victor Reinze packaged gasket sets have dropped in quality and sometimes they even include some wrong ones in a sealed package.

Wrightwood Racing gasket sets are higher quality but I don't know where to get them. I'd start with calling EBS - engine builder supply Porsche Racing Parts : Engine Performance Parts : Brake Parts : Used Porsche 356 : 911 : 912 : 914 : 944 : Porsche Boxster Parts : EBS Racing Inc.
Old 04-26-2012, 07:21 AM
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Agreed JFairman - much appreciated....so I will proceed with stripdown.

Good point on the bearings....I have done this before when rebuilding older engines from the 20's and 30's and have been able to source hard to find / expensive bearings at lower cost - engineering place not far from here has been able to source them every time. Mostly they end up coming from you guys over there...
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Old 04-26-2012, 01:13 PM
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Those bearings are expensive even as aftermarket products. The original FAG bearings are one-off aerospace quality, through hardened rollers and races and if you can find them, are even more ridiculously expensive. I've checked with major bearing companies and come up empty handed with proper interference diameters, so it does not seem likely that you can just go out and get duplicates on the cheap. You can, however, re-bore, sleeve and then match the race OD with proper ANSI standards. That's only the outer race. Next is the inner race, another altogether different problem with proper interference requirements.
Old 04-26-2012, 07:45 PM
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Generally speaking, if the noise is consistent throughout the rpm range, tranny shifts fine, and noise grows louder with gear selection 1-4, with it being loudest it 4th.

I would highly suspect the input shaft bearing as the main culprit.

As the gears stack up in the tranny {front of car to rear} 1st is closest to the driver, 4th is closest to the engine. 4th gear puts the most load of all the gears, on the input shaft bearing.

My .02 worth.

Mark
Old 04-27-2012, 02:33 PM
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Hello

This seems to be a worn MainShaft bearing..

I rebuilt my geerbox last month for the same problem






Old 05-20-2012, 01:37 AM
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Seems to be? That road needs to be re-paved. Be aware that FAG no longer makes some of the vital bearings in the Porsche transmissions. There are fakes out there. They are cheap. They will not last long. And the will look as above in your post sooner if not later. Get the bearings from the Porsche dealer network. Here is an updated pinion roller from Porsche...direct from Germany.

Old 05-20-2012, 05:50 AM
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Thats certainly a bit of wear there alright!! Gearbox coming out in a couple of weeks, so see then exactly what condition its in.

I agree on getting the right quality bearings - saving a few hundred euro on a rebuild is certainly false economy if they are going to cause problems in the not too distant future. Do it once and do it right comes to mind....

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Old 05-25-2012, 03:37 PM
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