Tacho Thrust Bush Replacement Questions

[hands_aus]

Hey Group,

I am replacing the tacho thrust bush.

What an awkward job! No space anywhere (big hands here): PS reservoir in the way: The small bump on the side of the head (engine) just where I need to remove the T Bush.

I had to buy a deep (but short) 22mm 3/8” socket.

After 'finding’ access I removed the cable connector, then the T Bush. It was worn (1-2mm).

I removed the tacho vertical gear.

It seemed to be ok but there were shiny surfaces on the worm gear where it is making contact.

When I replaced the vertical gear I found a small amount of rotational play when I seated it. The amount of play is small and seems to be enough to allow the end of the shaft to mate easily without being sloppy.

Is there supposed to be some rotational play on the vertical gear shaft?

Is the key on the end of the vertical shaft systemetrical?

I have not installed the new T Bush yet. It is in the refrigerator cooling down. Tomorrow maybe.

thanks

Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[ja17]

Hello Bob,

A slight bit of  rotational play is probably normal. Up and down movement of the gear should almost be illiminated by the new thrust bushing. The early BBB gives and endplay dimension of (0.1 mm to 0.25 mm) .004" to .010' !

Joe Alexander
Blacklick, Ohio

[A Dalton]

One may notice that many change the  top thrust piece and still wind up having to use a shim.  The reason for this is not only gear surface wear , but the fact that there is also another thrust under the gear supporting the other end of the tach shaft. . This one also wears , but not to the extreme the top one does due to the helix cut of the gear putting the rotational pressure on the top thrust.
  If this is found to be the condition, I prefer to use the shiming technique in the BB of measuring the total end play and sandwiching a new spacer of proper size inside the top thrust piece, under the bushing . This will get the original specs back by internaly shimming the top thrust , and b/c the shim is inside the piece, there is no concern of shim wear... the shim stock can even be aluminum, as it's purpose is only dimentional, rather than having a bearing surface to lube. You then wind up with the proper bearing/bush surfaces of the original design, minus the total/combined end play wear of the three pieces.........

[hands_aus]

Joe and Arthur,

Thanks for responding.
It is a work in progress.
The weather here has been awful... wet, windy and miserable.
Hopefully I will have a fresh look at it tomorrow.

Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[bpossel]

Hi Bob,

I replaced my tac thrust bushing last Fall and its a straight forward job.  Joe and others have posted some great "how to" info on this site, which really helps! I seem to recall that I also had a bit of play even after I replaced mine.  I didnt do an exact measurement, and only did it by "feel".  I watched Joe check mine and Davids at this summers tech session.

I will email you a document that contains many of the posts and pcs from this site.  Sort of a summary of stuff already posted.

I wish we could attach other file types besides just .jpg (ie. .doc, . htm(l), ect...)

Good Luck!
Bob

bpossel
Memphis, TN.
1971 280SL
1997 E320

[J. Huber]

I'm in for the same surgery I'm afraid. I have noticed some oil gathering around tach connection. I replaced just the inside seal 3 years ago -- no leak until now. At that time play was maybe 1mm. Figured it was ok.

This morning I did the test for play. While its hard for me to get an actual reading, I am thinking 1-2 mm. Definitely moving up and down. I'm hesitant to go much further since I'm fairly mechanically-challenged...

Would you guys say I should remove the 13mm bolt and pull up the bushing and have a look? If I pull it out -- can I assume it will slide back in if I have to? Or is this strictly a job for my mechanic?

And does the play cause the leak?
Thanks

Oh and Bob P -- mind sending me your doc? I have read through the threads on this -- just wondering about level of difficulty...





James
63 230SL

[Naj ✝︎]

Go on James, you can do it...

You've already removed the big cap with the 22mm hex once, so you can get that far.

http://www.sl113.org/forums/uploaded/naj/200531685839_TachoDrv12.JPG

Remove the small (10mm head) locating bolt, screw the cap back a few turns and pry the bush out with a flat screw driver or similar tool.

Good luck

naj

65 230SL
68 280SL

[hands_aus]

OK,

I have a BIG problem.

With the cold Thrust Bush out of the fridge I oiled (engine oil) it and inserted it into the housing.

It jammed with about one quarter of its length inserted.

I wiggled it around and it ‘clicked’ then it went in. (Obviously was out of alignment.)

However it would not go all the way for some reason.

I then removed it.

I also removed the vertical gear shaft.

My trusty torch revealed a male key on the end of the oil pump shaft that would match the slot in the end of the vertical gear shaft.

I aligned that slot with the matching key of the internal oil pump shaft and the shaft now seems to be correctly inserted.
(The protruding length of shaft matches the tacho cable connector length when held against the head.)

I then re-inserted the Thrust Bush. It went in like last time.

It has jammed completely.

It won’t turn or ‘click’ like last time.


What do I do now?


I have a feeling that I should have inserted it dry or used sewing machine oil and wiped it off.

Can I use a piece of pine wood with a hole to accommodate the vertical gear shaft and give it a tap to see if it re-aligns?

I can’t pull it out. It won't budge.

I would hate to have to replace the head just because I was ham fisted in trying to replace the Thrust Bush.


James, take note.


Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[bpossel]

Bob,

I dont recall having exactly the same issue as you, but I do recall while working the bushing in, it got stuck a bit.

What I ended up doing was to put an ice cube into a small plastic baggie and held it on the top of the bushing.  The ice cooled the metal bushing and shrank it just enough to slip it back out...  If the ice melts in the baggie, just replace with another cube until the bushing is cold again...

Give this a try.  Hope it works out for you.
Bob

bpossel
Memphis, TN.
1971 280SL
1997 E320

[erickmarciano]

same think that happened to me > i used a plastic hammer and tapped it on each side till I got it out . took me one hour . good luck you will get it . i was told to sand the piece a little after .

1971 280sl
1962 VW
1954 Allstate vespa
1958 gs150 vespa
1962 gs160 vespa

[hands_aus]

Job Done.

BUT the end play is just as bad as the original Thrust Bush.

Let me say ‘this is not a job for a ‘total amateur’ like me.

While everything wasn’t going smoothly I cursed myself for being a cheap skate and not having it done professionally at $128.00/hour.

However now that I have the bush installed and I know all the correct procedures I wouldn’t hesitate to do the job again.

In fact I intend to fit shims to the old Thrust bush between the bronze bush and the aluminium holder then re-install it and see how it goes.

Many times I used my multigrips on the Thrust Bush to break it out of being jammed in the head. This may not be the best approach but I tried using ice and tapping it into a different alignment. Without success.

A couple of burs formed on the Aluminium housing so I filed them smooth and cleaned it up. Then I tried again and again and again.

Eventually the bush went in and settled right down. I aligned the bolt hole with the bolt already mounted in the side of the head.

I tightened the bolt and checked it was through the hole.

After installing the new o-ring seal I finished by adding the tacho cable.

At this point I have not started the engine.

I have some questions…

Should I have poured some engine oil down the centre of the Thrust Bush before final assembly? Do I really need to worry about this?

If I crank the engine without actually starting it, will that be enough to pump some engine oil into the Thrust Bush?

Thanks for the help

Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[ja17]

Hello Erick,
Even the pros run into difficulties from time to time. A simple job can turn into a days work without warning! Don't get discouraged.

It nice to pre oil the  gears, however they will be oiled soon enough when the engine starts.

You could unscrew the top fitting and drip some oil into the gears if your concerned.

Joe Alexander
Blacklick, Ohio

[A Dalton]

<<In fact I intend to fit shims to the old Thrust bush between the bronze bush and the aluminium holder then re-install it and see how it goes.
>>

 Measure the end play before you remove the tach drive piece and then you will know the exact requirement for the internal bushing spec...
 That is the best way to shim for total assembly wear.
The other reason for proper end pay [ aside from oil pump drive failure fear] is that the drive gear is constantly being worn from the rotaional force wearing across the gear cut facings everytime the gear moves up/down.. this is the last place you want wearing and a part you  do not want to be buying b/c both pieces have to be changed as a set and they are BIG $$$$..[ although the new replacement kit has been modified w/larger bearimg surface for better wear longevity].
  A .25 cent,  accurately measured, internally sandwiched shim ,in the correct place, fixes all..........

[J. Huber]

Glad you got through that Bob. Sounded scary. keep us posted on your shimming.

I went ahead and had a closer look at my situation. Both my bushing and my gears seem to have fairly minimal wear. So I have put them back in. Fortunately, my bushing slid right in. Maybe its because my garage is about 30 degrees (F) right now! It is important that the gear seats correctly for the bushing to go all the way down.

So in my case it was more exploratory than a repair -- but at least I now know more about this. I still have some play -- and may do the shim before long.

Related: is it common for the tach cable "swivel nut" to get chewed up? Mine doesn't seem to thread on very well. It strikes me as very soft metal.

James
63 230SL

[hands_aus]

quote:Originally posted by J. Huber

Glad you got through that Bob. Sounded scary. keep us posted on your shimming.

I went ahead and had a closer look at my situation. Both my bushing and my gears seem to have fairly minimal wear. So I have put them back in. Fortunately, my bushing slid right in. Maybe its because my garage is about 30 degrees (F) right now! It is important that the gear seats correctly for the bushing to go all the way down.

So in my case it was more exploratory than a repair -- but at least I now know more about this. I still have some play -- and may do the shim before long.

Related: is it common for the tach cable "swivel nut" to get chewed up? Mine doesn't seem to thread on very well. It strikes me as very soft metal.

James
63 230SL

Hey Arthur, Joe, James

Thanks for your replies.

Arthur, I intend adding shims on the inside of the new bush and not the old bush that way the amount I measure will be real and I will not need to compensate for the clean up of the surface of the old bronze bush.

Joe, The car started up with no hesitation at all. I decided not to add oil.

James, You are lucky the bush went back easily.
The thread of the tacho cable connector may be a bit out of shape.
I cleaned the threads on my connector because of that. Then I screwed and unscrewed the collar onto it before re-mounting on the top of the Thrust bush.

I have a friend who has a lathe. I thought of using it to push the bronze bush out of the aluminium housing and then inserting the shims and using the reverse process to push the bush back.

Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[A Dalton]

<<Arthur, I intend adding shims on the inside of the new bush and not the old bush that way the amount I measure will be real and I will not need to compensate for the clean up of the surface of the old bronze bush.
>>

 Yes, that is what to do...you might as well [ seeing your friend has a lathe] , have him face-off the old one and shim it to the total of the other while you are at it...then you have a spare already set/spec for that particular engine to replace the wear of the new one down the road. [ long term thinking..]
That may take some miles , but the original drive set are a high wear item, so might as well.....no cost involved and good insurance...........sure beats the high $$$$ cost of converting over to the new gear set.

[hands_aus]

quote:Originally posted by A Dalton

<<Arthur, I intend adding shims on the inside of the new bush and not the old bush that way the amount I measure will be real and I will not need to compensate for the clean up of the surface of the old bronze bush.
>>

 Yes, that is what to do...you might as well [ seeing your friend has a lathe] , have him face-off the old one and shim it to the total of the other while you are at it...then you have a spare already set/spec for that particular engine to replace the wear of the new one down the road. [ long term thinking..]
That may take some miles , but the original drive set are a high wear item, so might as well.....no cost involved and good insurance...........sure beats the high $$$$ cost of converting over to the new gear set.

Great thinking Arthur.

Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[hands_aus]

As a follow up

After installing a new Thrust Bush I re-checked the end play of the gear shaft. and measured it at about 0.025"
This is not as bad as the original amount of play.

The aluminium injector washer I bought to use as a shim is about 0.048" thick... much too thick.

I decided that the amount of endplay of the shaft at 0.025" is acceptable to me.

So I now intend driving the car for a while before re-assessing the situation.

Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[rwmastel]

quote:Originally posted by hands_aus

The aluminium injector washer I bought to use as a shim is about 0.048" thick... much too thick.

Would that washer have worked with the old Thrust Bushing, or was the wear on that part even greater than the thickness of that washer?

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[hands_aus]

quote:Originally posted by rwmastel

quote:Originally posted by hands_aus

The aluminium injector washer I bought to use as a shim is about 0.048" thick... much too thick.

Would that washer have worked with the old Thrust Bushing, or was the wear on that part even greater than the thickness of that washer?

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

Hey Rodd,

I think the washer would work on the old Thrust Bush but I was reluctant to use it because it is aluminium and might be too soft.

I don't relish doing the job on a 2 yearly schedule.

In time if I need to shim the thrust bush I will use the internal bush method.

Those shim washers are extremely hard to find in my city.

Joe A posted this site http://www.mcmaster.com/ as a possible source.

I spoke to them and they will send to Australia if needed.


Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[A Dalton]

Fairly easy to cut an aluminum shim down to spec by hand with a flat piece of glass with fine emory paper glued to it..
 A mic. comes in handy for trueness......