whats wrong with this mount ????

[kodioneill]

checking for clutch judder i pulled the two transmission mounts. as you can see the bolt barely sticks out of the mount. about 5 threads. is the bolt to short or is the mount to long? also the washer is bent. the mount also seems to be very low on the bushing sleeve. this is a 1982 sc 140,000 miles. i know someone changed the clutch before.

[kodioneill]

someones got to know. how can the tranny mount bolt only thread in, 4.5 or so threads????? as you can see the bolt measures 68 mm. seems short to me. yet it's a special bolt. well anyway, ordered 4 sport mounts and new bolts.

[Oh Haha]

Looks like the person "shaped" the end to get it thread a bit easier or line up with the hole. Hard to tell in the pic but the rubber doesn't look that bad. You will see a difference in the sport mounts.

[rattlsnak]

those look just like any ive seen, and about the same length.

[boyt911sc]

Originally Posted by kodioneill

someones got to know. how can the tranny mount bolt only thread in, 4.5 or so threads????? as you can see the bolt measures 68 mm. seems short to me. yet it's a special bolt. well anyway, ordered 4 sport mounts and new bolts.

kodioneil,

After seeing the pictures, my first reaction was it got to be longer than that. So I went out to the garage and picked up the box containing my trans mounts and bolts. Lo and behold!!! Mine look exactly like yours!!!!! They must be really that short in the first place and you got company.

Tony

[RWebb]

Originally Posted by Oh Haha

Looks like the person "shaped" the end to get it thread a bit easier or line up with the hole. Hard to tell in the pic but the rubber doesn't look that bad. You will see a difference in the sport mounts.

those bolts are shaped like that by the factory

they are not cheap

[jorian]

The rubber part crushes a bit when the bolt is torqued down, so you get more purchase on the threads.

[Oh Haha]

Originally Posted by RWebb

those bolts are shaped like that by the factory

they are not cheap

I found my old ones and they look the same. guess it's been a while since I've seen them.

[BK911]

According to my machine design professor, only the first 3 threads of a bolt do any work. Can anybody verify this?

[kodioneill]

one reason is that there was a super thick lock washer on the bolt. i compared them to some old trans. bolts and like the previous poster said the bolt looked ground down to a sharper taper than normal. probably some mechanic down the line tapered them to help get them started.

[boyt911sc]

Originally Posted by BK911

According to my machine design professor, only the first 3 threads of a bolt do any work. Can anybody verify this?

BK911,

Depending on the size or pitch of the thread, I've been told that four (4) threads are sufficient to overcome the stress or shear the bolt/nut. Most nuts have 4 to 5 threads on them. Anyone familiar with 'Strength of Materials'? Please share your knowledge with us? Thanks.

Tony

[T77911S]

what about the clutch chatter? ive got some too.
hot spots of flywheel? or broken springs on disk?

[equality72521]

The rule I've always heard is if the shank of the bolt is 1/4" wide then you need to thread in 1/4". If it is 3/8" wide then thread in 3/8" deep and so on with all sizes.

[Gunter]

Originally Posted by BK911

According to my machine design professor, only the first 3 threads of a bolt do any work. Can anybody verify this?

Depends a little on pitch and size.
Anymore than 4-5 threads will not add any additional tensil strength to the bolt.

The bolts for the transmission have a lead designed by Porsche to help you find the hole.
Torque is ~58 ft-lbs and if you go more you'll be very sorry meaning you'll strip the thread in the body!

I grind a small lead on the longer bolts for the engine mount as well.
And I use Anti-seize on them.
If you haven't taken the engine out for a long time, these bolts will rust solid resulting in doing damage to the crossmember; it'll bend/break the ends.

[kodioneill]

Originally Posted by T77911S

what about the clutch chatter? ive got some too.
hot spots of flywheel? or broken springs on disk?

my four motor mounts were collapsed and bottomed out. i'm 100% sure that this is the reason for the judder.

[T77911S]

i had a 72 karman ghia in high school and after. all the time i had it, it had clutch chatter. just before i sold it, i was jacking the car, at the motor of course, and just happened to notice the tranny was lifting off the mount and hitting on the body or bracket, cant remember for sure. anyway, i replaced the motor mounts and it fixed the chatter and i sold it. all those years and that was the problem. everytime i jack up the 911 at the motor i think about that car.