901 / 911 transmission GURUS, advice needed

[Norw911]

I need some advice from those of you who are really experienced with the 901 or 911 transmissions. The background is as follows: Due to a laborious squealing noise in both the 4th and 5th gears in my 1970 911 transmission, I decided a few months back to have a Porsche shop diagnose the cause. By listening to the transmission, they diagnosed it to be a bearing issue and subsequently was not too expensive to repair. The work commenced and the following parts were replaced:

901 301 035 13 Stop plate
999 053 025 00 Angular contact bearing
999052 016 00 Four point bearing
999 110 012 00 Bearing
999 110 008 00 Cylindrical-roller bearing
901 302 294 01 Thrust washer
901 300 916 00S Gasket set
Transmission oil Mobilube PTX 75W-90

According to the shop’s mechanics after the transmission was opened, the 4th and 5th gears were not visibly worn, i.e. “confirming” their initial diagnose to be a bearing issue.

But after reassembling the transmission, the 4th and 5th gears were as noisy as before. The shop therefore decided to open it again as it now was obvious to them that the noise was caused by the 4th and 5th gears themselves. The following parts were replaced (the gears sets are by the way extremely expensive):

904 302 921 10 Gear set
911 302 906 00 Gear set
901 301 191 01 Gasket
901 301 392 01 Gasket
999 201 470 00 Needle cage
901 111 193 00 Gasket
Transmission oil Mobilube PTX 75W-90

This time the 4th and 5th gears were noise free, but there was a new, strange, partly “rattling noise” coming from the transmission – definitely a noise that had not been there before. It was especially evident when cruising at 3500 – 4500 rpm (3rd and 4th gear) and when coasting from 4000 – 4500 rpm . After a discussion with the shop - they agreed that something was wrong and opened the transmission again (they actually opened it twice to get rid of the new noise. In total, they opened the transmission four times). The following parts were replaced during the last two attempts:

999 701 359 40 O-ring
901 332 297 00 Gasket
911 116 774 01 Leaf spring
911 116 743 01 Washer
996 117 999 Pressure spring
901 300 916 00S Gasket set
930 375 317 00 Hexagon-head bolt
999 059 027 00 Taper rolling bearing
Weltmeister Transmission Intermediate Plate
NOS ZF LSD
Transmission oil Mobilube PTX 75W-90
------
A PowerHaus II Reinforced Aluminum Side Cover was ordered but not installed due to arrival after attempt 4.
------

As seen above, a NOS ZF LSD was also installed – not as a measure to cure the new noise of course, but a rare opportunity that I couldn’t resist as the shop had one on the shelf. The LSD makes it’s own rattling noise in sharp, slow turns, but that is a totally different noise compared to the one described above.

After the 4th attempt I was back at the shop and they changed the transmission oil to see if that might have an impact. My observation of the oil was that is was very thin and I assumed that it should have been thicker due to it being transmission oil, the mechanic was also somewhat surprised by the thin oil. They store both the engine oil and transmission oil in separate large barrels, which could possibly be mixed up.

The shop by the way is an independent Porsche shop that deals mostly with 964s, 993s and 996s, occasionally G models, but not very experienced with pre ’72 911s and consequently not the 901 / 911 transmissions (as I realized too late in the process). They have not invested in the special tools for the 901 / 911 transmissions described in the Workshop Manual.

The verdict: The noise is still there and my questions to the experts on this Forum are:
Q1:Based on the above parts and the work involved, is it necessary to be vastly experienced with the 901 / 911 transmissions to get it right (?), or is it sufficient to be an experienced, general Porsche mechanic (as the mechanics in this case)?
Q 2: Again based on the parts replaced and the work involved, is it necessary to have any of the special Porsche tools described in the Workshop Manual to get it right or can the specific tools be substituted by others?

I have so far – relatively speaking, spent a fortune on the transmission. One issue is the current, new noise but an other concern is that there might be future, serious consequences if they haven’t got pinion depth, preload, backlash etc right. I am reluctant to have the shop open it again, even if there are not many alternatives to choose from in Norway, maybe in Sweden? My next step depends on your knowledge and advice.

Thanks.

[RPMClassic]

OK. A few issues and my best wishes for a healthy recovery!!

Use swepco tranny fluid - whatever is in there now, take it and drain it.

Its amazing that a shop would go into a tranny 4 times and not do a proper rebuild at any of those attempts. The armchair guess from here is that you have a faulty ball socket and retaining spring on the shift fork. However, lets stick to the facts as you know them - my guessing won't help.

However having a few 1970 boxes built for the racecar personally - I have learned a few things and wrtitten the checks for both bad work and incredibly great work!!

A NOS LSD requires different axle flanges than your stock ones. Otherwise the bearings are going to get wasted and the LSD will essentially become an open differential in the year ahead as it wears out. The backlash and preload need to be set correctly when you put this in, the billet intermediate and side cover only introduce more variables. These are MUST HAVE parts for big power cars and longevity in your box, but REQUIRE the correct tools. I can't believe that they kept upselling new parts without fixing the noise! What clutch/pp and flywheel are in there? All these bolts should be replaced + throw out bearing replaced. A proper box rebuild from a professional shop with all new gears,syncros,sliders + the billet parts can run up to 5-7k. For that $ it needs to be right!

There are only 3 core people in the country that do these boxes "spot on" in my opinion. I am sure there are others, but I found 3 that I have used and spent $$ with and am happy. Have the shop sort it out, PM me if I can give you any referrals that can help.

Good luck.

[Grady Clay]

WOW.

Welcome to the Forum.
You will find a lot of help here.
I’m sorry it is under such frustrating (and expensive) circumstances.

It might be useful to re-analyze the initial “…a laborious squealing noise in both the 4th and 5th gears…” if you can remember.

Was the noise related to engine speed or wheel speed?
Was the noise only in these gears or just most noticeable?
Was the noise more pronounced on acceleration or trailing throttle?
What happened when you pushed in the clutch?


901 301 035 13 Stop plate (clamps the intermediate plate bearings)
999 053 025 00 Angular contact bearing (4-piont, input shaft, intermediate plate)
999 052 016 00 Four point bearing (on pinion, intermediate plate)
999 110 012 00 Bearing (in case, pinion)
999 110 008 00 Cylindrical-roller bearing (in case, input shaft)
901 302 294 01 Thrust washer (adjoining free 3rd and fixed 4th on pinion)
901 300 916 00S Gasket set
Transmission oil Mobilube PTX 75W-90

These are the correct four bearings.

It is unusual to replace the clamping plate. This is the correct P/N listed in my ’71 manual. It uses a spacer between the clamping plate and the intermediate plate. I recall several versions of this clamping plate in ’70 models. The earliest 6-bolt clamping plate ‘70s didn’t have the spacer.

Replacing the clamping plate with the spare part on a non-spacer version and not adding a spacer would clamp the intermediate bearings tighter than spec and could move the pinion toward the differential – maybe.

Replacing the thrust washer (901 302 294 01) is very unusual. I think the only times we sold these washers was when a shop lost one.

Do you have the old parts?
If so, can you post some good images?

It might be useful to have the transmission oil tested. Real 75W90 is visibly pretty thick.

Let’s do this one step at a time.

Best,
Grady

[Geary]

Mobilube PTX is a synthetic oil, which is absolutely not suitable for early Porsche transmissions. The most easily obtained, high quality non-synthetic in your area would be Castrol LSX 90. Swepco would be cost prohibitive and unnecessary if the Castrol can be obtained.

I don't believe that output flanges will eat up side bearings, causing an LSD to become an open diff. But the mechanic should definitely check to certain there is adequate side clearance (flange should be able to move in & out a few thousandths after being torqued in place). If there is interference, the LSD will act like a spool. We see this quite often.

[RPMClassic]

Great info Grady. I only mention the flanges, because the LSD versions are longer and taller. I have both and the bearings became an issue with the wrong flanges installed.

[MBEngineering]

HI Norw911 was the diff out put flanges changed when the LSD was fitted, as the STD ones are shorter than the LSD ones, and have been known to jump splines in the diff, also IF the STD shafts have been fitted and the bolts tightened up you will have a solid diff untill the shaft desides to turn and then this happens,photo to follow

regards mike

[MBEngineering]

diff with wrong shafts fitted,



as you can see the swepco did not help!!!

regards mike

[Grady Clay]

Step 2,

“But after reassembling the transmission, the 4th and 5th gears were as noisy as before. The shop therefore decided to open it again as it now was obvious to them that the noise was caused by the 4th and 5th gears themselves. The following parts were replaced (the gears sets are by the way extremely expensive):

904 302 921 10 Gear set – very expensive new from Porsche
911 302 906 00 Gear set – very expensive new from Porsche
901 301 191 01 Gasket
901 301 392 01 Gasket
999 201 470 00 Needle cage – common replacement part
901 111 193 00 Gasket
Transmission oil Mobilube PTX 75W-90

This time the 4th and 5th gears were noise free,…

Since none of the bearing races under the free-gears, the bearings there hadn’t failed. This means the noise wasn’t from those bearings.
What did the old gears look like?
I’m concerned that the gears were OK and the changing noises is the changing mesh of the ring & pinion gears from all this changing of stuff.



“…but there was a new, strange, partly “rattling noise” coming from the transmission – definitely a noise that had not been there before. It was especially evident when cruising at 3500 – 4500 rpm (3rd and 4th gear) and when coasting from 4000 – 4500 rpm . After a discussion with the shop - they agreed that something was wrong and opened the transmission again (they actually opened it twice to get rid of the new noise. In total, they opened the transmission four times). The following parts were replaced during the last two attempts:

999 701 359 40 O-ring
901 332 297 00 Gasket
911 116 774 01 Leaf spring – clutch release arm part
911 116 743 01 Washer – clutch release arm part
996 117 999 Pressure spring
901 300 916 00S Gasket set
930 375 317 00 Hexagon-head bolt – these are the longer bolts for the ring gear on a ZF LSD.
999 059 027 00 Taper rolling bearing – for the differential
Weltmeister Transmission Intermediate Plate
NOS ZF LSD
Transmission oil Mobilube PTX 75W-90”


I agree with Pelican RPMClassic,

You cannot replace these parts without resetting the differential bearing pre-load, the pinion position and the R&P backlash. There should be spacers 901.332.065.xx used for this.

I agree with Pelican Geary

The incorrect axle flanges may not have end play. I have also seen them where the stretch bolt became (or was left) loose.

Replacing the first four bearings is something a reasonably competent Porsche mechanic should be able to do and requires only a few tools. Measuring and setting the R&P is something difficult (time consuming) even with lots of experience and all the tools.

To answer your question:
YES, you should now have someone with both the tools and experience look into this. One critical issue is to find someone who can identify the parts and recognize problems..

I would recommend you send it back to PAG but they may have the same issue with “experience.” Also, their policy seems to be replace everything possible with new. I’m sure there are long experienced techs who are currently doing this for 1970 vintage racers. Look in the UK and on the Continent. There are some here but shipping is prohibitive

Best,
Grady

If you want to discuss this off-line, feel free to contact me:
303-seven-five-six-7308 Mountain Daylight Time GMT-7
gradyclayathotmaildotcom.

[MBEngineering]

HI Norw911 from the info Grady has given you and assessed the prob' with the box, you should find some one with the diff setting tools , if you require any info to set up the diff get in touch and I will send any info you require. As a last resort I have all the tools for setting the diff for 901, 911, box's

regards mike

[Geary]

I believe the longer-shafted LSD output flanges were associated with the later 915. I don't think the issue of too short a flange existed with the earlier 901 LSD.... but I could easily be wrong.

[Grady Clay]

Mike,

Thanks for the great images.

This looks like a later differential than OE ’70, I can’t tell. Most of
my nice old stuff is in storage 20 years and coming out next year
for my son. Help me here.

What is this(green arrow 1)? It looks like the bevel gear that
drives the four spider gears.

The (red arrow 2) seems to be a stripped single inner lamina.

Is this (purple arrow 3) damage from the axle flange?




An OE NOS ZF LSD like what Pelican Norw911 now has
doesn’t look like this – I don’t think. The images serve to
show the issue. I think it is important for us to document
all the LSD issues. PAG never looked over the
interchange among different models issue other than
appropriate spare parts for what they manufactured. That
wasn’t their place. There shouldn’t be any reason for problems.
Some blame PAG for not keeping up with “up-grades” as
opposed to just replacement parts. It has only been since
the internet (specifically Pelican and others) that this issue
became important. This all for another discussion.


Now we (collectively) need to help solve Norw911 set of issues.

Norw911, here already is a skilled service with MBEngineering in the UK.

I won’t claim to be a “world expert” but I know some small part
of this. I think the real value of this Pelican Forum is to
solve individual problems, commit that to Pelican Archives and
forever not have anyone not fully not knowledgeable of all the
details. This is a collective effort and I learn something every
day.

Best,
Grady


contiued


The issue of lube is serious.

First in this situation is: Was the lube totally wrong for a Porsche transmission?
Engine oil won’t work. Even some “transmission oils” are
inappropriate. This issue needs to be resolved so the
symptoms don’t complicate (or obscure) the progress to
a solution.

There is a lot of on-line discussion about transmission lubricant
for our Porsches. Even a simple search will show almost
overwhelming amount of discussion.

With our transmissions there are two conflicting requirements:

1) provide lubrication that prevents metal-to-metal contact.
This is what every differential lube focuses on.

2) Not provide too much “slippery” lubrication so the Porsche
patent synchronizing rings and ZF LSD clutches operate properly.

It is instructive to note that ours are transaxles, combining
the transmission and the differential.



I don’t think this thread should be hijacked to trans lube. Here,
the issue is the noises and the subsequent repair attempts.

There are many well intentioned Independent Shops and
PAG/PCNA Dealers that are not skilled (yet or again) with
these internal transmission issues. Addressing Norw911’s
situation can help solve his issues but also provide a resource
for others.

Best,
Grady

[MBEngineering]

HI Grady
What is this(green arrow 1)? It looks like the bevel gear that
drives the four spider gears.
this is the inside of the gear with the output shaft splines

The (red arrow 2) seems to be a stripped single inner lamina.

no this is just worn out oil in the diff looking very gray from the plates, as the diff has not been in bits for some time,

Is this (purple arrow 3) damage from the axle flange?

yes this is damage from the wrong shafts being fitted and the retaing bolt being tightened and locktighted in,

Do we know which gearbox (901 or 911) Norw911 has, if it is a 901 box then the out put shafts should be OK as Geary has commented on.

regards mike

[Geary]

Red arrow is that side's thrust washer. The internal splines on the discs can't be seen until going into the LSD

[Norw911]

Thank you all for great comments and info, this forum is an invaluable arena! To answer or comment some of your questions, Grady:
“Was the noise related to engine speed or wheel speed?” Wheel speed.
“Was the noise related to engine speed or wheel speed?” The noise was only in 4th and 5th gears.
“Was the noise more pronounced on acceleration or trailing throttle?” The noise was more pronounced on acceleration.
“What happened when you pushed in the clutch?” The noise was still there, but much less so.

The gears and other parts from the first and second attempts are still at the shop so I can unfortunately not take any pictures (yet).

Regarding the axle flanges, if I understand you correctly the longer ones are associated with the 915 transmission, i.e. that the standard ones are the correct one even with a LSD in a 911 transmission (mine is a 911/02, edit: 911/01)?

[MBEngineering]

HI Grady can you check the part No *********

999 701 359 40 O-ring
901 332 297 00 Gasket
911 116 774 01 Leaf spring
911 116 743 01 Washer
996 117 999 Pressure spring
901 300 916 00S Gasket set

930 375 317 00 Hexagon-head bolt****not for diff?? for mounting
on the gear box cross member on a 930??

999 059 027 00 Taper rolling bearing
Weltmeister Transmission Intermediate Plate
NOS ZF LSD
Transmission oil Mobilube PTX 75W-90
------
looks like the diff was fitted with the S/H bolts and no lock tabs??, as the box is a 911/01 box I think the shafts are the size of the early 915, with that the diff could be a 915 and the wrong shafts(to short)be fitted, I will check when I get my 911/-- box back to me and I will drop the 915 diff in and check, I was told it fitted.

“Was the noise related to engine speed or wheel speed?” Wheel speed.

POSS; diff bearings,center case bearing, pinion bearings,CWP.

“Was the noise related to engine speed or wheel speed?” The noise was only in 4th and 5th gears.

POSS;as the 4th/5th gears are at the pinion end of the box we are back to the, center case bearing, pinion bearing or CWP.

“Was the noise more pronounced on acceleration or trailing throttle?” The noise was more pronounced on acceleration.

POSS;back to the pinion/diff area

“What happened when you pushed in the clutch?” The noise was still there, but much less so.

Was this when you where driving or stationary??
If you are driving, you have now taken the load off the transmission and the noise is less but still there??
If you are stationary it is on the input shaft bearings and loose gears only??

what do you Grady is this making any sense.

regards mike

[Norw911]

I have tried to investigate a little regarding the different LSDs that have been available for the 901 / 911 transmissions to clarify whether it is necessary to change the joint flanges or not in my 911/01. According to PET (Porsche Parts Catalog), there was initially a LSD with part number 904 332 053 00 (’65 – 69) that was in need of special LSD joint flanges. Then from April 1 1969, the LSD was changed, part number: 901 332 053 13. In the Workshop Manual it is stated that:

“ZF DISC TYPE LIMITED SLIP DIFFERENTIAL - 69 MODEL
G e n e r a l
From 1. April, 1969 on the ZF limited slip differential (strengthened version) has been supplied as a special option. It provides 50% locking effect. By modifying the sequence of inner and outer discs a locking effect of 75 % can be obtained for special competition purposes. The standard joint flange is now also used on the limited slip differential, but the expansion bolt has been modified"

“ZF DISC TYPE LIMITED SLIP DIFFERENTIAL PRODUCTION DATE AFTER 1 JULY 1969”
From 1 July 1969 on the optional ZF limited slip differential uses molybdenum coated inner discs.

When these inner discs are installed, the limited slip differential becomes quieter in operation and the level at which locking effect remains constant is increased.

The normal setting gives 40% locking effect. By changing the sequence of outer and inner discs, a locking effect of up to 80% can be obtained for competition purposes.

The molybdenum coated inner discs, part number 901.332.551.21/22/23, replace the plain inner discs, part number 901.332.551.11/12/13, and should be installed in the ’69 model’ limited slip differential if complaints are received.

Warning:
When subsequently installing molybdenum coated inner plates, the sequence of outer and inner plates changes. See pages SR 28i and SR 28k.”

According to the above information, the standard flanges should be used in my case. But what confuse me, is that the PET shows three (!) different joint flanges for transmissions up to model year 1971, one has part number 911 332 209 00, an other one 901 332 209 15 and the third one part number 901 332 209 21 (the last one pictured together with a LSD). So what is correct, should a 911/01 transmission with LSD use the standard flanges or not – and what is the correct part number? Or as MBEngineering mentioned, could it be that an early 915 LSD is fitted - or is that not possible, i.e. will not fit?

[Geary]

Mid '69-'71 911 uses the same diff as early 915 (w/ 7:31 R&P) and all 914 models. The diff does not change again until mid '75 (except for the "odd-ball" early '75 w/ mech speedo drive 8:31). The only way to know if the flanges and bolts fit properly is to install them and check for adequate flange-to-LSD body clearance.

The 904 LSD that you read about is of the "Early 901" type, which uses a much smaller (45 vs. 50mm) differential side bearing. The early '69 LSD was of very low production numbers (above info states April - June), thus the popularity of fitting the more plentiful 904 LSD with funky Nadella flanges to the Early 901 transmissions.

[MBEngineering]

HI Norw911 the diff you have in has the late bearings in as a 915,

"999 059 027 00 Taper rolling bearing – for the differential"

this part No' is for the 911/915 box diff bearings, from this I would say you have a late diff and short shafts??

Flange list;
915 man' 4bolt/2 dowel, length into diff=56mm, total length=99mm, shaft dia'35mm.

915 LSD 4bolt/2 dowel, length into diff=61mm, total length=103mm, shaft dia'35mm.

911 man' 4bolt/2 dowel, length int diff=56mm total length=105mm, shaft dia'35mm.
901 man' 4bolt/2dowel, length into diff=56mm total length=105mm, shaft dia' 34mm.
925 4bolt/2 dowel, length into diff=61mm, total length=110mm, shaft dia'35mm.
915 man' 6bolt small cv, length into diff=56mm, total length=99mm, shaft dia'35mm.

I would drop one off your drive shafts off and pull the output shaft from the box and check the length of the shaft into the diff and the depth in the diff it's self, from inside the oil seal to the inner plate in the diff, if you look on Grady's photo with the arrows on, from the GREEN 1 to the PURPLE 3, should be ??(61mm??).

regards mike

[Norw911]

I finally found time to get under the car and pulled out the drive shaft, and MB Engineering’s assumption was right, the drive shaft’s length into the diff is 56mm, the splines’ length = 15mm:



As seen from the photo below, the spline length inside the differential = 20 mm:



Based on this, I assume that we can conclude that the drive flanges are not suited for the LSD diff. MBEngineering, RPMClassic, Geary, Grady or other – any comments?

There is no reason to believe that the shop has used the 12 longer ring gear bolts designed for a limited-slip differential either (as the LSD bolts are not in the invoice, nor are the old bolts in the used parts box).

According to the Work Shop manual and the PET the stretch (elastic) bolts are different in the LSD compared to the non LSD differential, they have not been changed either.

Summing up the comments from the previous posts:

Possible change of pinion position due to possible use of wrong parts:
Grady C: “It is unusual to replace the clamping plate. This is the correct P/N listed in my ’71 manual. It uses a spacer between the clamping plate and the intermediate plate. I recall several versions of this clamping plate in ’70 models. The earliest 6-bolt clamping plate ‘70s didn’t have the spacer. Replacing the clamping plate with the spare part on a non-spacer version and not adding a spacer would clamp the intermediate bearings tighter than spec and could move the pinion toward the differential – maybe.”

Shop lost part – reason for adding it to the invoice?
Grady C:“Replacing the thrust washer (901 302 294 01) is very unusual. I think the only times we sold these washers was when a shop lost one.”

Inappropriate transmission oil:
Geary:
“Mobilube PTX is a synthetic oil, which is absolutely not suitable for early Porsche transmissions.”

Even worse, motor oil instead of transmission oil:
Norw911:
“My observation of the oil was that is was very thin and I assumed that it should have been thicker due to it being transmission oil, the mechanic was also somewhat surprised by the thin oil. They store both the engine oil and transmission oil in separate large barrels, which could possibly be mixed up. ”
Grady C.: “Real 75W90 is visibly pretty thick.”

Possible unnecessary replacement of 4th and 5th gears:
Grady: “I’m concerned that the gears were OK and the changing noises is the changing mesh of the ring & pinion gears from all this changing of stuff.”

Shop owner claimed that resetting pinion position was not needed:
Grady: “I agree with Pelican RPMClassic, You cannot replace these parts without resetting the differential bearing pre-load, the pinion position and the R&P backlash. There should be spacers 901.332.065.xx used for this.”


Etc…..

Any additional comments?

[MBEngineering]

HI Norw911 the diff looks damaged on the bottom photo, just under the oil seal, could you please take the depth from the bottom of the splines to the top of the diff,(under the oil seal) where it looks damaged/rub-ed from the out-put shaft , it should be the length of your shaft to under the shoulder on the top photo where the MM are, if thay are to short then the shafts will damage the diff as in the photos before, is there no billing for diff bolts at all or lock tabs on the paper work??

regards mike