need help from the transmission gurus

[cab66]

my 5speed 901 trans. is rattling in all gears but first I have replaced all the linkage bushings incl. shifter bushings, springs and stop plate but that did not help. If I put it into 2nd and disconnect the linkage from transmission and start driving the rattle is still there! could it be something within 1st gear since it is the only one that doesn't rattle
Any help is much appreciated

Peter from Denmark

[kodioneill]

Check the engine and trans mounts they may be collapsed or broken.

[Grady Clay]

Peter,
First, WELCOME to Pelican
You will find a lot of help here.



I can see you have been dealing with this since at least March.

To clear up a few things:
Yes, you have the ‘simplified’ differential.
No, that isn’t causing your rattle. When that fails, there is no warning, just catastrophe.

Yes, the throttle rod has several (3, I think) plastic guide bushings in the tunnel.
There is not a ‘guide tube’ except where the rod exits the rear of the tunnel and that is only to hold the rubber boot.
If those bushings are missing, there is a very annoying rattle.
I would eliminate this possibility first.
While dealing with this, carefully bend the sheet metal of the tunnel near the front throttle bell-crank (at the pedal assembly) to ensure adequate clearance.

Did this noise appear after the transmission syncros and new clutch?
How much of the clutch/flywheel were replaced?
Was the flywheel taken off the crankshaft?
If so, was it reinstalled with a new ‘gland nut’ and properly torqued? (A loose flywheel can make an annoying rattle as it ruins the crankshaft.)

Is the rattle load dependent? Does it increase or diminish on acceleration or trailing throttle (compression deceleration)?
Are you sure it goes away in first gear?

Does the rattle change when you operate the clutch?

Have you confirmed the engine is bolted tight to the transmission?
How many rubber blocks (4 or 6) in your engine mount? Are they in good condition? (Good, you installed the 911 transmission mount.)
Is all your engine tin in place and properly secure? The rear pan is not touching the muffler?
Air filters on tight?
Engine fan not failing?


We will solve this!

How about posting some pictures?
Enjoy

Best,
Grady

[cab66]

Hi Kodioneill & Grady,thank you very much for your replies!
The trans.mount is in good condition and all 4 engine mounts are new.
I put in 3 new throttle cable bushings but that didn't change anything.
All clutch parts are new, the flywheel has been resurfaced and the gland nut is new and torqued to specs.
The rattle is not load nor rpm dependent and I am 100 percent sure that it isn't rattling in 1st. there have always been some rattle but I feel it has gotten worse. I also have noticed that it doesen't go out of 1st as smooth as the other gears.
sheet metal,aircleaners and fan is all ok.

By the way I had a rolling road session the other day to have the solexes jetted and tuned,it made 134 hp & 200nm.
not to bad for a little(ish) 4 banger me think
Grady I'll see if I can upload some pics.

Thanks again Peter

[cab66]

[70S Targa Guy]

With Grady on your side and saying, "We will solve this!" needless to say you are in good hands! I just subscribed to this thread.

Just a thought and a quick diagnosis suggestion because I find these noises/rattles are difficult to pinpoint while driving the car....perhaps you can take the car to your favorite garage/mechanic, sit in the driver's seat & lift the car up on a hydraulic lift (not on jack stands). Start the car and go through the gears to simulate real time driving conditions when this rattle has occured previous. At the same time, have a friend or mechanic underneath the car listening carefully trying to locate the annoying rattle.

BTW, stunning & absolutely gorgeous 912! Please, more pics from all sides and some interior shots of this beauty!.

[Grady Clay]

Peter,

Remove the rear tunnel/shifter cover.
Slide the passenger seat out and take someone for a ride.
Have them use a stethoscope to try and isolate the rattle location.
They can push & pull of things to see if the rattle changes.

Are the CV joint bolts tight?
Is the rear deck lid drip pan secure?
Are the rear quarter window latches tight (tighten the knob when closed or open)?

See if lightly applying the parking brake changes the rattle.
See if the rear brake dust shields are loose.

Thinking again of the rear pan, there is a bracket between the pan and muffler that helps support the pan.
Is it in place and tight?


What parts were replaced in the transmission?

How is your clutch adjustment?
Do you have to push the clutch to the floorboard for the reverse to not clash?
Many times a clutch that is not fully releasing will make it hard to come out of a gear.
This can also be due to the clutch disc splines not free on the input shaft splines.
Also, new 1st gear syncro and 1-R sliding sleeve can be difficult to engage and sometimes disengage.

Before I absolutely commit your transmission to having a ‘simplified’ differential, what is the type number (stamped on the bottom rib under the differential area)?
It should be of the form: 902/xx or 901/xx.

Great looking 1968 912 USA coupe.
More pictures please.
Your biggest challenge will be to keep it dry and in a low humidity environment in order to slow the rust.
My 1968 911 USA coupe is surviving (now 43+ years) due to the high altitude and very low humidity.

Best,
Grady

[cab66]

Good idea lifting the car and driving it in gears,I had my father shifting while I was under the car.
The result was: no unusual noises in 1st, rattle in neutral and rest of gears appearing from front of transmission, probably from inside nose cone but I am not 100% sure as the sound spreads throughout the case.
Checked for loose nuts and bolts while I was under the car but found nothing wrong.
The rattle/chatter do seem to stop when the clutch is depressed but only when in neutral!
Grady it's a 902/02 with a ZA 5th gear.
Yes rust is always a big problem here in cold and rainy Denmark, so one of my first projects was to give it a good shot of wax oil !
Thanks for the nice comments about the car.

[cab66]

[cab66]

I'm about to remove engine and transmission, so I can have a look at that 1st gear to see if I can find out what causes that rattle.
Any suggestions about what to look for?