Advice req'd:- shaft spline wear / measurements / possible fix 722.118 transmission - PeachParts Mercedes-Benz Forum

Stretch · #1 06-02-2011, 06:28 AM

G'day Folks,

I've got a slight problem with a 722.118 transmission - BUT BEFORE YOU THINK oh I don't know about transmissions please read on because I'm looking for help with splines.

Statement of the problem:-

The only noticeable worn part on my transmission is a splined shaft in the front planet housing.

You can see in the picture above that there is a slight ridge in the first set of splines => towards the roller bearing race in the middle of the hole.

It looks to me as though the front planet housing has been shimmying on these splines as both sides of the splines are worn. As I've said before only the splines in the front planet housing are worn. The splines on the intermediate shaft (that fits into this bit) are fine.

Here's a picture of the two parts fitted together

Now the situation that I'd like to avoid is this one:-

722.118 Transmission problems, stripped out splines!

Where the splines have sheared right out of the front plant housing

Stretch · #2 06-02-2011, 06:33 AM

I've measured the play in the splines to be 0.26 mm

I did this by fitting the intermediate shaft to the front plant gear housing and wiggled the fitting and measured with a DTI

The point of measurement (the DTI probe) was 50mm away from the centre of the housing, and the splines are 14mm away from the centre. The measurement at the DTI was 0.91mm

A bit of trig tells me that I've got a wiggle of 1 degree (edited value - offending trailing decimal fractions removed)

Stretch · #3 06-02-2011, 06:41 AM

I'm not sure why this happens. It seems as though the splines on the intermediate shaft are much tougher than those in the housing.

I had a look for similar things on the internet and came up with these possibilities (although they aren't directly concerned with transmissions perhaps there's something of interest?) from one source

http://www.franklin-electric.de/en/pdf/aid/AID_1_2007_E.pdf

Where is says

Reduced spline lifetime due to:
· Upthrusting conditions, i.e. pump operation at the very right hand side of the pump curve (large quantity, small
total head).
· Water hammering, high dynamic conditions in the pipe system.
· Frequent switching (on and off), such as with broken bladder in the pressure vessel.
Recommendation: Max. 20 per hour.
- Chattering relay contacts.
· Overpumping, possibly due to wrong pump selection, creating sudden changes in torque (pump discharge lar-
ger than well water supply).
· Motor back spin, resulting in increased shock loading on motor start-up (faulty pressure system, leaking check
valve).
· Excessive or insufficient revolutions (as a result of backspinning due to a leaking or missing check valve).
· Pump cavitation will shock load the splines and/or induce vibrations which may cause stripped spline or
accelerated spline/coupling wear (right selection of pump in accordance to suction conditions – NPSH).

Can anyone add any more possible reasons / information?

Stretch · #4 06-02-2011, 06:47 AM

I'm multi-tasking folks!

Solution 1)

Asking the dealer to get me a new part => They've asked the classic centre in Germany for a price

{I expect this to be mega bucks}

Solution 2)

Making a scale drawing of the part and asking someone to CNC mill a new bit for me.

The drawing is nearly finished (and I'll post here if anyone else wants it) but I need an educated guess for material sort - can anyone here help?

Solution 3)

Find a good second hand part

Hmmmmmmm always a problem area - I'll end up having to buy whole gear boxes which I don't really want as nobody seems to split them.

Solution 4)

Glue / shim material

This is the main area in which I'd like to ask advice (see next post)

Stretch · #5 06-02-2011, 06:54 AM

In this article

http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=ADA091861

The authors talk about coating splines with a second material to improve wear characteristics.

Perhaps I could do something similar with a glue and / or shim material.

I only need to add about 0.26mm of foreign material to stop these parts from shimmying.

Volvo seem to be putting loctite on their splined shafts (see http://volvospeed.com/vs_forum/topic/144258-loud-bang-from-s70-awd-when-backing-up/ for example) but I'm guessing that for the gap that I've got this would be too much.

I think loctite might be too brittle.

So finally the real question:-

Does anyone know of a glue that is ATF proof - rubberised - heat resistant and strong enough to hold and fill a gap of 0.26mm?

sjh · #6 06-02-2011, 12:08 PM

Quote:

Originally Posted by Army

I've measured the play in the splines to be 0.26 mm

I did this by fitting the intermediate shaft to the front plant gear housing and wiggled the fitting and measured with a DTI

The point of measurement (the DTI probe) was 50mm away from the center of the housing, and the splines are 14mm away from the center. The measurement at the DTI was 0.91mm

A bit of trig tells me that I've got a wiggle of 1.043 degrees

You can't take measurements with 2 place accuracy and then calculate 4 place accuracy. Assuming your logic/math is correct all you can say is your wiggle is 1.0 degree.

I don't know if that influences your actions but there is no validity to your last two stated digits and no decision should be based upon them.

Stretch · #7 06-02-2011, 12:13 PM

Quote:

Originally Posted by sjh

You can't take measurements with 2 place accuracy and then calculate 4 place accuracy. Assuming your logic/math is correct all you can say is your wiggle is 1.0 degree.

I don't know if that influences your actions but there is no validity to the the your last two stated digits and no decision should be based upon them.

Good point - I'm not particularly worried about the angle of wiggle - I wanted to try and gauge how big the average gap on the splined shaft is when assembled.

I'll edit out the offending numbers - thanks!

Stretch · #8 06-02-2011, 02:14 PM

I've been looking at the set up of the gear box and how virtually everything that does something is on this intermediate shaft. Take a look at the following parts picture I've made from screen shots (it isn't great quality):-

There is a lot of stuff that fits between the ends of the intermediate shaft

Now I can feel and see that both ends of this shaft wiggle. I guess it isn't surprising that they do as there are 3 brake bands operating on drums and two internal-drum clutches operating within the length of this shaft.

Unfortunately the ATSG manual doesn't specify any limits of play on the ring gear (part 592 in the first picture) and the fitment to the intermediate shaft.

I must confess - sorry layback40 - that I'm still leaning towards using some Loctite epoxy on the shaft splines. I think any play in the system will be taken up by the loose end at the other end of the intermediate shaft. But before I do so I'm going to do some calculations to see if the epoxy is going to be elastic enough for the gap I've got.

To be continued...

barry123400 · #9 06-02-2011, 05:53 PM

The epoxy does not sound to me like a good solution if there is a real problem. I would try to find a guy that has rebuilt tens of thousands of automatic transmissions over the years and talk to him.

Experience does count in this area I believe. If you could just get your hands on a blown simular transmission and check it's wear in that area is another option. Might be common for all I know.

No wear evident just use the parts in the junk transmission. Overall it should work out cheaper than buying new parts. Especially if the new fit tollerance is not much better than what you have.

At one time with mercedes transmissions you loose bolted them up and then centered them prior to torquing the bolts down. Mercedes got away from that eventually. In those days the drive system seemed super smooth. I believe they paid a lot more attention to the quality of manufacture of those vintage cars.

If you can identify the part numbers a stocking non mercedes transmission parts house may have it. Some of those transmission parts suppliers are huge. The part may only be a fraction of mercedes in house parts costwise.

Stretch · #10 06-02-2011, 09:01 AM

Mini - update

A search on the internet gave this pdf

http://www.henkel.com.br/brb/content_data/SM_UK_211205.pdf

layback40 · #11 06-02-2011, 09:36 AM

Looking at the spline misfit, it makes one suspicious that there is a very slight miss alignment through the transmission.
Often splines are used to allow for such unless they have an interference fit.

Use of some material to fill the gap generally does not work as the filler is softer than the parent metal. In your case, the shaft is harder than the damaged spline. Using some loctite product will not last long & then bits will float around & maybe block a control valve.
Probably some thing in the planetary is not perfect & the misalignment has shown on the spline.

You cant make everything rigid as there must be room for expansion & contraction, misalignment and end float movement.

As to what to do, if it was me, I would probably rub the sharp edges off & put it back together. I am a firm believer that unless its broken, dont try & fix it.

We have an old scraper here with a 6 speed Allison trans, some of its splines are much worse than yours & it has done many thousands of hours since it was last in pieces. There are no flex disks in the drive line either & it has a lock up on its torque converter so the splines in the trans get a beating.

Did the car have trans problems before you disassembled it ?
Was there clunking on power off/on ?
It would appear that the trans has probably spent much of its life changing between the intermediate gears & not much time in 4th.

Given the relative low mileage of your car, I wonder what has been going on to cause this & the other issues that you have uncovered.

As to our friend with the trans that has lost its splines, it must have been running bad for many 10's k miles to get like that.

Stretch · #12 06-02-2011, 10:11 AM

Quote:

Originally Posted by layback40

Looking at the spline misfit, it makes one suspicious that there is a very slight miss alignment through the transmission.
Often splines are used to allow for such unless they have an interference fit.

Use of some material to fill the gap generally does not work as the filler is softer than the parent metal. In your case, the shaft is harder than the damaged spline. Using some loctite product will not last long & then bits will float around & maybe block a control valve.
Probably some thing in the planetary is not perfect & the misalignment has shown on the spline.

You cant make everything rigid as there must be room for expansion & contraction, misalignment and end float movement.

As to what to do, if it was me, I would probably rub the sharp edges off & put it back together. I am a firm believer that unless its broken, dont try & fix it.

We have an old scraper here with a 6 speed Allison trans, some of its splines are much worse than yours & it has done many thousands of hours since it was last in pieces. There are no flex disks in the drive line either & it has a lock up on its torque converter so the splines in the trans get a beating.

Did the car have trans problems before you disassembled it ?
Was there clunking on power off/on ?
It would appear that the trans has probably spent much of its life changing between the intermediate gears & not much time in 4th.

Given the relative low mileage of your car, I wonder what has been going on to cause this & the other issues that you have uncovered.

As to our friend with the trans that has lost its splines, it must have been running bad for many 10's k miles to get like that.

Ah ha - thanks for that layback40 - Solution 5 is now on the board.

Answers to your questions (in order of appearance)

Did the transmission have problems before I took it apart?

Well yeah and no - I had a strange occurrence after an oil and filter change when I got nothing - no drive in any gear. I drained some and then added some and messed about and it sorted itself out

1981 300D Auto problem?

The transmission was always a little clunky for my tastes but on the whole it worked quite well.

Was there clunking on power off/on?

More in-between if you were being too gentle with it. Decisiveness was the key to a smoother drive.

Given the relative low mileage of your car, I wonder what has been going on to cause this & the other issues that you have uncovered.

I'm pretty much convinced the car has been suffering from lack of use. I think it was owned by an elderly person (who probably had a dog!) who certainly spent a lot of money on body work repairs (new doors W123 300D door retainer question - a CSI dating exercise! neatly welded patches in the engine bay W123 Engine bay paint advice req'd and on the rear end W123 sedan under rear bumper panel)

Stretch · #13 06-02-2011, 10:18 AM

Oh I forgot to say - measuring the play in the splines was quite a challenge as the planetary housing wiggled all over the place on the intermediate shaft. It didn't just rotate slightly on the splines but it kind of rocked on the end of it as well. So misalignment within the gearbox is most likely. The condition of the roller bearings however seems "as new"...

Stretch · #14 06-02-2011, 10:35 AM

I hope this isn't going to upset Henkel but what do you all think of this stuff?

Layback40 makes a good point regarding expansion and contraction and also a good point regarding epoxy coming off and getting stuck in other parts of the transmission...

Can anyone else comment?

Has anyone else used epoxy based solutions like this before?

Here's a link to the one I guess I could use

http://www.rotal.com/_Uploads/355Hysol9466TDS.pdf

whunter · #15 06-02-2011, 07:10 PM

Quote:

Originally Posted by Army

I hope this isn't going to upset Henkel but what do you all think of this stuff?

Layback40 makes a good point regarding expansion and contraction and also a good point regarding epoxy coming off and getting stuck in other parts of the transmission...

Can anyone else comment?

Has anyone else used epoxy based solutions like this before?

Here's a link to the one I guess I could use

http://www.rotal.com/_Uploads/355Hysol9466TDS.pdf

If you plan to sell or junk the car this year it is OK.

Never use glue, plastic or epoxy inside an automatic transmission you want durability from..

.