broken transmission, any ideas?

[brittbolen]

So I went out for my usual saturday morning drive except instead of getting home tired and with a giant grin, I got home without my car.

I pulled up to an interesection with 64 west down in Apex (just west of NC55, Green Level Church Road, you'll know the spot by my characteristic oil stains) I put it into first to pull out onto 64W and nothing happened, I gave it gas and nothing happened, all I heard was a sound that can best be described as bolts, glass and rocks being shaken in a milk jug. I pulled half out of the lane (best I could do!) tried to go in second and the same thing happened. So I cut it off right there. Luckily I could roll back down the road a bit and get out of traffic, and then a guy stopped and we pushed it off to the side and out of the way.

This was about 10:45 this morning. My ride got to my by 12:15, but I didn't get a tow truck until 2:30. At least the people down here are very helpful, I had 2 police officers stop and check on me and lots of other people asked if they could help. One guy, however, just wanted to know what year my car was, I guess he was trying to find out which ones to avoid

Anyhow, from my description any idea what might have happened? I already had the car towed to my mechanic, hopefully he can get me fixed in time for the NC pelican drive!

What does a good used 901 transmission cost these days?

thanks,

Britt, porscheless for now...

[Bill Verburg]

Are your half shafts still in place?

[brittbolen]

I should have looked under the car more, I had enough time waiting for the tow truck! I don't remember anything looking out of place when I stopped the car and gave it a quick look.

Britt

[Grady Clay]

Britt,

Sorry to hear of your distress.

Yes, searching out a replacement may be in order.

The two weak points of a 901/911 transmission are:
The strength of the cantilevered input shaft for 1st gear.
The “Simplified differential” in ’68-’70.

There is not much to be done about the input shaft except don’t stress it with excessive standing starts.

There are still a few cars that have the original “Simplified differential” that haven’t had the update differential shaft block parts to replace the axle flange stretch bolts with the teat on the end.

If you need to find another trans, this Forum has some experts to coach you.

Best,
Grady

[john walker's workshop]

diferential, mainshaft, or cv joint. hope for the joint.

[brittbolen]

Grady, thanks for the info, if you have the time, I wouldn't mind some more explaination on that 1st gear weakness. All I know about how transmissions work came from howstuffworks.com so I'm a little lost on what you mean about 1st. Is it that having first gear all the way out at the end of the transmission is inherantly weak?

When I pushed the car off the road, and when the tow truck pulled it onto the bed, I didn't hear any noises. That would seem to eliminate the differential and the cv joint, right?

Britt

[Zeke]

Originally posted by brittbolen


When I pushed the car off the road, and when the tow truck pulled it onto the bed, I didn't hear any noises. That would seem to eliminate the differential and the cv joint, right?

Britt

CV joint anyway. It would flop around and bang. That is unless it came loose the wheel end. But, from your description, I don't think it was the axle anyway. When you put it in 2nd for another go, if the axle had come off, it would have made a hellacious banging not like bits in a jar as you mentioned.

I'll bet it's internal. There's a 901 in the For Sale BBS right now.Here

[Grady Clay]

Britt,

First the input shaft.

The input shaft is the long shaft that connects the clutch into the transmission.
It supports “Gear I” of the gear pairs and first and reverse
are cantilevered off the end of the shaft.

In late ’67 Porsche “reinforced” the input shaft by enlarging
the threads that hold 1st gear I in place.

Here are some images to orient you:
"
"
(C) Dr. Ing. h.c. F. Porsche A.G.

Below is a view of the 1st gear I in place with the nut torqued and pinned.
Note that 1st gear II is not yet in place.
"
"
(C) Dr. Ing. h.c. F. Porsche A.G.

Below is a cross-section diagram of the input shaft.
The two arrows at the left indicate the weak points.
Between the arrows are the splines for first gear.
"
"
(C) Dr. Ing. h.c. F. Porsche A.G.

Below is a image of the input shaft.
"
"
(C) Dr. Ing. h.c. F. Porsche A.G.


Now to the "simplified" differential that was introduced in '68.
The term simplified refered to the fact it had fewer parts
and was less expansive to manufacture.

In the diagram below, note the teats on the ends of the
two streach bolts (directly in the center of the diagram.)
Those two little teats were what kept the differential gear shaft in place.
When they wore off from vibration of the shaft, all hell breaks loose.
The shaft slides out of the differential while driving.
This can actually saw the transmission in half.
"
"
(C) Dr. Ing. h.c. F. Porsche A.G.

Below is the exploded (apt expression) diagram of the original simplified differential.
There is an error in the diagram.
It doesn't show the teat on the #14 streach bolt in the uppre left.
Both streach bolts had the teat.
"
"
(C) Dr. Ing. h.c. F. Porsche A.G.


Below is the diagram of Porsche's fix to the failures.
They added #3 Block and #1 roll pin.
The streach bolts no longer had teats.
On most transmissions, #5 and #6 had to be changed to fit the additional parts.
"

(C) Dr. Ing. h.c. F. Porsche A.G.


#@&%!!! I can't get the other images to load correctly.
I'll post again.




John Walker is correct. Another possibility is the failure of a CV joint.
Below is a Lobro axle from a '67-'68.
When it fails, it forces tha balls out of the CV and into
the boot and area between the CV and axle flange.
This is easy and inexpensive to fix.



Another possibility is your axle came loose at the outboard end.
That sounds awful aslo.

Good luck,

Best
Grady

edited for spelling 12:11 9/05/04 G

[john walker's workshop]

i've seen plenty of cv joints break and not make a lot of noise. start the car and put it in gear and look at the axles. see if anything is turning. for instance, one of the joints may be turning and the axle beyond it is not.

[brittbolen]

Thanks Grady, this is very helpful. So one possible failure would be the input shaft just breaking off? Why couldn't/didn't porsche put some sort of bearing in the rear of the transmission housing to support 1st gear and the end of the input shaft?

General 901 question, the input shaft runs in the bottom of the transmission with the output shaft and differention above it, right? Are all the gears on the input shaft fixed, with all the gear selectors on the output shaft? From the photos it doesn't look that way.

Looking through my records the previous previous owner had the transmission overhauled in December of '88, approx. 16,000 miles ago. 4 new syncro rings and 1 sleeve. The invoice was written on my 10th brithday. This makes me feel both old and young!

Britt

[Grady Clay]

Britt,

To answer your first question, all we can do is to speculate
on Porsche engineer’s ideas and motives.
To support the transmission shafts in three bearings would have added
a lot of cost to a transmission design that was just an extension of
the prior types all the way back to pre-36 HP VW.
The 901 wasn’t done with a blank piece of paper and unlimited budget.
It is a great transmission and, with care, can handle engines
up to 2.8 liters and 250 HP in my lame opinion.

Your second question; no, all the gears are not fixed in
the sense that they are cut on the shafts.
Only 2nd Gear I is cut on the input shaft.
All the other “fixed” gears are splined onto the shafts.
The 1st and 3rd gear are splined on the input shaft,
4th and 5th Gear are splined onto the pinion shaft.
The mating gears are free to rotate on needle bearings on the opposite shaft.
An exception to the above is the 904 input shaft has a
splined fixed second gear in place of being cut on the shaft.
It is a very elegant transmission.
You can re-gear the individual ratios to your heart’s content (and pocketbook)

Here is a good cross section diagram.

"
"
(C) 1966 Dr. Ing. h.c. F. Porsche A.G.

Best,
Grady

[brittbolen]

And the problem was the CV! It came loose and was put back on and it was undamaged.

Thats where the good news ends...

After he fixed the cv, chuck noticed the engine was running loud and rough on the right side. So he pulled the valve cover off. And my #4 rocker shaft is broken. And 5&6 are installed incorrectly.

So he's pulling the motor.

Joy!

Britt

[Jess]

Britt,

Better grab your car!

No need to pull the motor to replace rockers or shafts. You're about to get the shaft!

Jess

[Jim Sims]

"No need to pull the motor to replace rockers or shafts."

If the shafts were installed incorrectly there is a good chance the motor DOES have to be pulled. Damn hard to get the rocker shaft bolt wrenches in place if the shafts were installed incorrectly - bolts facing the wrong way.

Jim

[Randy Webb]

Ask him to look around _really carefully_ at both the engine and the stuff in the engine compartment while he's got it out. Somebody screwed the car up once -- and might have done it more than once. Also a good time to clean up the comp. and maybe replace some wear items. An engine drop is neither expensive nor difficult, so you aren't in bad trouble. Glad to hear it was "just" the CVs.

Be sure to check the torque on all CV bolts (4 x 4 or 6).

[Grady Clay]

Britt,

Ya Hoo! That is an easy fix. Was it inboard or outboard?
Well, you got an education in Porsche trivia.

I would inspect all the CV bolts and replace all the locking washers. That can be a one-at-a-time DIY. Cheep insurance.

While the engine is out, there are a few “while you are there” issues you might consider.

Jess,
I wouldn’t jump to that conclusion, yet. If some hack installed the rockers wrong, what else needs attending? It is far easier to find and fix those issues on the engine stand than in the car. Besides, a ’70E engine is incredibly easy to R&R.
Britt, keep us up to date.

Best,
Grady

[brittbolen]

Went out to have a look-see after work today.

Chuck checked both CVs and said the one that didn't come off was loose so he tightened up both of them, don't know if he replaced the locking washers. What other stuff should I have him check? I asked him to check clutch see how that looks, and to replace the old horse hair sound pad.

Chuck showed me the broken shaft, it had worked it's way into the head such that it just broke and the rocker arm was all wobbling about. (#4 cylinder, upper arm, thats intake, right?)

I posted a while back about this, I guess I should have been more concerned! He also showed me that the other two shafts were not centered, and were going to suffer the same fate. He said he'd check all 12, and try to just recenter them if possible.

I checked my receipt pile and the engine rebuild from '88 lists 6 rocker arms and 3 rocker shafts. I looked at it again and it's like they only rebuilt one side of the engine, I wonder why... anybody want me to post the parts list from the receipt and theorize on why they rebuilt it that way? Come to think of it I'm pretty sure the PO still lives in Morgantown...

Britt

[brittbolen]

oh yeah, my cam tower oil leak was due to the rocker arm shaft being broken, and oil was leaking out around that. Chuck's going to put in the newer arm which has a small integrated oil seal...

Britt

[john walker's workshop]

small integrated oil seal on the rocker arm?? there are flat o-ring seals that are used in the shaft grooves. maybe that's what you're getting. when the shafts get loose and beat around in their bore in the cam tower, the bore can get so bad that a new tower is necessary. first clue, other than scoring, is the shaft won't expand enough so it stops turning in the bore as it's tightened.

[brittbolen]

John Walker was onto something. My mechanic said the bore for that rocker arm shaft is ruined and that I need a new cam tower.

Any ideas what a fair price on a cam tower for a 2.2L engine would be?

I'm going to go out and look at the motor, is there anything else that my mechanic should be looking for while doing this sort of work?

thanks,

Britt