Tranny / Clutch / Pressure plate expertise needed

[Miloslav Maun]

Please help me evaluate my problem.

Description:
The transmission grinds when shifting, but only if the revs are above 3000. Othervise, with lower revs, the shifting is OK. The higher the revs, the more loud the grinding is. The grinding is there when both shifting up or down, between all four gears.
I was even trying to double clutch but the grinding did not disappear. The only remedy is to wait till the revs drop.

Background:
The transmission was revised recently. It got new synchro rings (brass), new ATF fluid, some bearings were replaced, etc. This problem was there before (that's why I bought the synchros) and presists till now.

Solution recommended by my mechanic:
Now we've got the tranny out again and my mechanic thinks that the problem could be caused by the pressure plate (there is this three finger type). He says one of the fingers is weaker and when engaging the clutch it can cause some misalignment, etc. I do not exactly understand how the internals work. I was told that the synchros only compensate minor differences and that if the rotation differences are too high due to the improper function of this pressure plate, it could result in grinding.

What do you think? The pressure plate is not a cheap part and I am not sure if this can be the culprit.

Thanks for your suggestions.

[JimVillers]

My thoughts are that your shift difficulties may be caused by the  pilot bearing.  The other likely cause would be the pressure plate as you suggest.   Replacing the clutch disk and the release bearing is always good practice as is resurfacing the fly wheel surface.

[jeffc280sl]

Muf,

Not familiar with the three finger type pressure plate but I am familiar with the later 280SL clutch plate and transmission internals.  I would have thought with the extensive renovation of the trans that the mechanic would have replaced the inexpensive pilot bearing.  It is something to check though.  

It sounds to me that the clutch is not fully disengaging.  At higher engine revs a partial engine load is still present at the transmission causing the grinding.  This could be the result of a weak pressure plate not cleanly and evenly removing the clutch disk from the fly wheel.  If it disengages at a slight angle due to a weak pressure plate the engine load may not be fully removed.

[Miloslav Maun]

May I ask which is the pilot bearing? Is it the number 48 on this picture? The one with the notch?



Then it was replaced by a generic bearing (cost about 15 USD). Maybe we sould get the OEM one...

[waqas]

No, the pilot bearing is # 31 shown in the figure below:

[jeffc280sl]

The pilot bearing isn't shown in the parts diagram you provided.  It is located in a recess in the flywheel.  The very small end of part 45 on your diagram is inserted into the center of the bearing.    I think Jim's comments address the issue of a pilot bearing failure where the tip of the transmission shaft is able to wobble about. This would be very bad for the transmission.

MB used "generic" bearings in the transmissions coming from the factory.  When I replaced mine I think I purchased a C3 grade bearing.  Bearings are rated for tolerances.  I don't think a new generic bearing no 48 is causing your problem.

[Miloslav Maun]

Well, I have just talked to the guy who is working on it and he says that the pilot bearing was not replaced (he thought it did not matter anyway because the input shaft is a bit worn and there would be some play even with a new bearing). The input shaft for a 230 SL is NLA. So I guess I'll buy the pilot bearing, the pressure plate and then we will hope that the end of the input shaft is not so bad, because otherwise I do not know where to get a replacement...

[jeffc280sl]

Muf,

A machine shop may be able to "true up" the end of the input shaft to get rid of the uneven wear.  After that you should be able to purchase a bearing with the same outer diameter as stock with a slighly smaller inside diameter to match the reground input shaft.

I think a slight wobble at this location would over time wear the pilot bearing and the transmission bearing.  A failed pilot bearing in the past may be the root cause of this problem.  This would account for the wear on the input shaft and possibly damage to the pressure plate.

[ja17]

Hello,

Just guessing but it sounds like the key #86 slipped out of the notch in ring #92 during re-assembly.  This will cause a lot of problems. These transmissions hardly ever need synchros. Shift problems are usually a result of the slotted output flange nut #128 coming loose.

[jeffc280sl]

When reassembling my transmission I remember being very concerned about the issue Joe is talking about.  I took the transmission apart several times until I was sure the key and notch ring were aligned properly.

[Benz Dr.]

I've seen worn input shafts and they usually don't cause shifting problems. They can make the trans jump out of high gear which I've seen a few times.
Shifting has more to do with pressure on the in put shaft and end play defection.
Pressure on the input shaft is noted by grinding gears because the shaft is still turning or under load. Check the clutch free play and make sure it's adjusted properly. It should have about 20 mm of free movement and should be fully disengaged about 2/3 of the way down to the floor. It should engage by about 1/2 way up. If you have it right to the floor and it's just starting to let go you have too much free play. If it engages right at the top you have too much free play. Normally you can just move the push pin ( item 37 ) going into the clutch slave. Too little free play and the throw bearing will turn constantly. It will burn out in less than 1,000 miles if it's too tight.

The other and more common problem is too much end play on the input shaft. It's supposed to be zero but it's usually .020 to .030'' and sometimes as much as a full millimeter. There are shims ( items 50 and 51 ) that you can get in different sizes to set the end play. Any thing more than about .010'' is far too much and the gears will move apart as you shift and not allow the syncro rings to bite properly.

The ring with the notch in it ( item 79 ) is also a potenial problem along with a loose out put shaft nut and a loose nut on the other end of the shaft ( item 75 ) at the 4th gear.

[Longtooth]

While on the topic with lot's of expertise commenting, I'll ask my question.  My 250SL (manual) clutch slips at high acceleration levels in 3rd and 4th gears, but not in 1st or 2nd. When I'm cruising at 80 mph, and hit the throttle to accelerate, I have to do so slowly or back off as th the clutch begins to slip (increasing rpm with no increase in speed).  It's not severe slippage .... very slight (so far... it's been occurring for about two years since I first noticed it, and doesn't seem to be getting worse that I've been able to tell).

All I can think of is that there is that the clutch plate provides insufficient pressure in 3rd and 4th gears for some reason, OR that the mechanical disadvantage in 3rd and 4th (relative to 1st and 2nd gear) provides greater flywheel resistance to the clutch (therefore insufficient pressure for that resistance to torque --- rear wheels are the resistance thru the drive train in 3rd & 4th).

Is there some feature in the clutch slave cylinder or an adjustment in it that would prevent pressure plate from fully engaging? or what?.

[al_lieffring]

quote:Originally posted by Longtooth

While on the topic with lot's of expertise commenting, I'll ask my question.  My 250SL (manual) clutch slips at high acceleration levels in 3rd and 4th gears, but not in 1st or 2nd. When I'm cruising at 80 mph, and hit the throttle to accelerate, I have to do so slowly or back off as th the clutch begins to slip (increasing rpm with no increase in speed).  It's not severe slippage .... very slight (so far... it's been occurring for about two years since I first noticed it, and doesn't seem to be getting worse that I've been able to tell).

All I can think of is that there is that the clutch plate provides insufficient pressure in 3rd and 4th gears for some reason, OR that the mechanical disadvantage in 3rd and 4th (relative to 1st and 2nd gear) provides greater flywheel resistance to the clutch (therefore insufficient pressure for that resistance to torque --- rear wheels are the resistance thru the drive train in 3rd & 4th).

Is there some feature in the clutch slave cylinder or an adjustment in it that would prevent pressure plate from fully engaging? or what?.

Yes, if there is no freeplay between the clutch slave and the throw out lever it can prevent the clutch from fully engaging, back off the adjustment stud untill there is about 1/4 inch freeplay before the throw out bearing makes contact. If there is too much freeplay the clutch pedal will not go over center and stick half way up.

The friction of the clutch does not change in the higher gears, but the amount of torque required to move the car at higher speeds is greater;

In low gear the gear reduction alows the car to move from a stop with very little resistance, but at a very low speed, so the transmission is shifted to a higher gear, the car can now be driven faster, but the load placed on the motor (and clutch) is also higher. So with the 1 to 1 ratio of the high gear the load on the clutch will be the highest.

Imagine a long lever, in low gear it would be like placing the fulcrum nearest the load, the lever moves with little effort, but the load moves only a short distance.
Placing (shifting) the fulcrum toward the middle, the load will move farther but it requires more effort to move the lever.
Moving the fulcrum even further from the load, still more movement, but also higher effort. If the effort required becomes more than the strength of your grip the lever will slip out of your hand.

 

[Miloslav Maun]

Does anybody know if the pressure plate from the 280 SL can be used?

[Naj ✝︎]

Does anybody know if the pressure plate from the 280 SL can be used?

Hello, Muf,

I believe, looking at the Sachs manuals that the answer to your question is NO. 

However, Sachs are listing as current a pressure plate for the 230/250: 1882 217 131

The 280 pressure plate is 3082 121 031.

naj

[waqas]

Yes, if there is no freeplay between the clutch slave and the throw out lever it can prevent the clutch from fully engaging, back off the adjustment stud untill there is about 1/4 inch freeplay before the throw out bearing makes contact. If there is too much freeplay the clutch pedal will not go over center and stick half way up.

The friction of the clutch does not change in the higher gears, but the amount of torque required to move the car at higher speeds is greater;

In low gear the gear reduction alows the car to move from a stop with very little resistance, but at a very low speed, so the transmission is shifted to a higher gear, the car can now be driven faster, but the load placed on the motor (and clutch) is also higher. So with the 1 to 1 ratio of the high gear the load on the clutch will be the highest.

Imagine a long lever, in low gear it would be like placing the fulcrum nearest the load, the lever moves with little effort, but the load moves only a short distance.
Placing (shifting) the fulcrum toward the middle, the load will move farther but it requires more effort to move the lever.
Moving the fulcrum even further from the load, still more movement, but also higher effort. If the effort required becomes more than the strength of your grip the lever will slip out of your hand.

Al, nice explanation.

I have a follow-up question: when you talk about adjusting the freeplay between the clutch slave and the throwout lever, how exactly do you overcome the force of the lever?  Even without the return spring, the lever is pushing hard on the slave's pin, and it's impossible to move by hand. So how exactly do you have ANY play between the slave cylinder pin and the lever?

I recently replaced both the rubber boots on the slave cylinder and the lever/bellhousing opening. I removed the return spring, and then had an assistant push the clutch down all the way; then I tied the lever to the nearest subframe to keep it there (through the same hole on the lever where the spring is attached). This allowed me to remove the pin and replace the boot on the slave. (it had disintegrated)

So, how does one adjust the play on the slave pin when the clutch lever is pushing down hard on it? (not counting the force of the return spring)

[Longtooth]

Al Lieffring -- wrt my slightly slipping clutch in 3rd & 4th gears (my Nov 5 post) question about the slave cylinder's possible contributions, and your subsequent post (Nov 6) that related the freeplay (between end of push-rod and throw-out lever)  to possiibly being insufficient and thereby causing reduced pressure of pressure plate against the flywheel ---- I did a couple of things. 

With your information I looked up adjustment of the slave cylinder push-rod in my Service Manual.  The service manual specifies the method of adjusting free-play, and the magnitude (4 mm).  The method is as simple as you described....
1. unhook spring, 2. push yoke lever back toward pressure plate until it stops at initial contact to the pressure plate spings --- virtually no force required to move it, 
3. Measure free-play (distance the pushrod can move from contact at pressure plate springs to yoke contact (leaving the yoke pushed toward pressure plate contact). 
4. Adjust freeplay (if needed) by loosening the hex nut (nut that cinches position of push-rod with respect to the pressure pin (pressure cylinder), and rotating the push pin (threaded pin) in or out (as needed to get the 4 mm free-play between end of push pin and it's contact point with the yoke lever).
5. Tighten the hex nut back against the pressure pin (pressure cylinder).
6. Re-attach the return spring.

My free-play was possibly up to a mm ... likely less... when I checked it.  To loosen the hex nut I needed a thin 13mm open end wrench to hold the pressure pin's hex end since it's got a thin surface..... and I didn't have a thin 13 mm  open end wrench.  I tried needle-nose pliers, but couldn't get enough purchase on the pressure pin hex end.  I finally resorted to buying a "needle-nose" vice-grip plier at the nearest hardware store to get enough of a grip on the pressure pin hex end to loosen the hex nut. 

I adjusted the free play (rotated threaded push rod further into the pressure pin) to 4 mm, and re-tightened the hex nut (up against the pressure pin hex end), and re-attached the return spring.

Test drove... problem gone (i.e. the slightly slipping clutch in 3rd and 4th at high speeds or at high torque range).  No problem dis-engaging  or down - shifting  or upshifting (the other end of the problem spectrum if too much free play exists).   I live on a hill, and it's always been easy to slipclutch if I press it going up the hill in 3rd... but not this time, so problem was definitely insufficient free-play.. so I have to have a little tete' a' tete with my mechanic who should have known better (he installed and adjusted the new slave cylinder a couple of years ago... and "readjusted" it about a year ago... so he apparently doesn't know tha the free-play needs to be ~4 mm.

Thanks for your guidance.

[Benz Dr.]

It really doesn't work that way.
There isn't enough pressure from the slave cylinder to make the pressure plate move without stepping on the pedal. When you don't have enough free play it tends to burn out the throw out bearing because it will spin all the time. It's not designed to do that and they will burn out - expect this in the near future.
The clutch pedal will always have the same free play if it's set up right as the clutch disc wears. The piston inside of the slave cylinder will slowly move out as the disc wears yet  the free play dimension will stay the same. A slipping clutch is more likely a worn clutch plate or dammaged pressure plate. If the free play was zero and the piston was at the bottom of the cylinder somehow forcing the pressure plate to move then maybe it would slip. This isn't a mechanical linkage system where no free play instantly relates to a slipping clutch. If you have any free play at all it shouldn't slip. The fluid has to be under pressure to make the slave piston move so it would have to be set up VERY tightly for it to be a mechanical problem.
My expirience with these cars is if the clutch is slipping in high gear the clutch disc is worn out.  You can wear a full millimeter of material off of the disc which is just about even with the top of the rivets that hold the disc together. Even if it was a free play problem you now have a new one. The clutch disc may be worn from this slipping problem and the flywheel is likely scored.
How old is the clutch disc?

Your problems may not be over.....

[Longtooth]

Dan,

Your analysis may be correct, but it doesn't explain why 1) my clutched slipped in 3rd and 4th before I adjusted free-play from near 0-1 mm  up to the prescribed 4mm at the Push-Rod to Yoke Lever, and 2) it then Stopped slipping after I made the adjustment to 4 mm.  I was also very skeptical that the slight clearance (free-play) would have that much effect, but the Service Manual prescribes a whole 2mm free-play between the throwout bearing and release levers on the pressure plate, so there would possibly be a good reason for it. 

My own best guess is that the free-play at the throwout bearing under temperature operating conditions is reduced by the thermal expansion of the pressure plate and transmission housing.... though I cannot substantiate this at all with an engineering analysis to support it, so it probably doesn't play a primary roll.  But, that having been said, say for example an expansion or other factor for some reason reduces the free-play at the release lever to throwout bearing by 1 mm.  This translates to a 2 mm reduction at the yoke lever to push rod at the slave cylinder end.  Therefore, if there were less than 2 mm freeplay at the push-rod to yoke lever end at non-operating conditions, the throwout bearing would be pressing against the pressure plate release levers when at operating conditions.  If as in my case the free-play at the push-rod to yoke lever was only 1 mm and even less, then there would be a 0.5 mm interference between the throw-out bearing and pressure plate release levers.... which reduces the pressure plate's pressure on the clutch driven plate... hence allowing some slippage under high torque conditions --- which was the symptom on my car --- 3rd and 4th gears only, and only under highest torque conditions.

For all I know the asm or other factors and tolerance conditions use up most of the 2 mm required free-play at the throwout bearing to pressure plate release levers... or for all I know there's less than 2 mm free-play in my particular car.  Hence, a 4 mm free-play is required at the slave cylinder push rod to yoke lever in order to have no pressure applied by the throwout bearing on the pressure plate release levers under those thermal expansion and tolerance conditions.  The total full travel of the throwout bearing is 10 mm (nominal) with a new driven plate, or 7 mm with a worn driven plate.  I assume my driven plate is worn... how much I can't say, but it (clutch plate --- i.e. "driven plate") was replaced when the engine was rebuilt 16k or so miles ago.

Having driven the car for nearly 2 years with this very slightly slipping clutch business I know all the cases where I'm going to start getting clutch slippage... speeds and acceleration (attempt) levels,  hills in 3rd and more in 4th, etc.  I know the locations where I normally accelerate onto the freeways from on-ramps and start to slip the clutch as I try to get to the 80 mph far left lane.  I've tried in past to find out my  0-60 speed from standing starts and unfortunately have had to back off the acceleration a bit when I hit 3rd and again at 4th to stop the clutch from slipping.

The change after adjusting the slave cylinder push rod to yoke lever free-play was instantaneous and I put the car thru all the same paces and then pressed it even more so that I could determine whether there was any slippage under any condition I could muster... and which would have created severe and long duration slippage --- but I got none, zero, notta!   I drove the car until the engine/transmission were heated up greatly ... still no slippage.

My schematics of the slave cylinder and yoke/throwout Bearing free-play condition, free-play adjusting conditions, and the slave cylinder parts that are used in the adjustment are attached.  This shows, for example, why a 2 mm required free-play at the throwout bearing to release levers translates to a 4 mm required free-play at the slave cylinder push rod to yoke lever.... among other things, such as how the push rod & lock nut relates to the pressure pin in the slave cylinder for the adjustment of free-play.  

The distance from yoke lever pivot to slave cylinder push rod pin CL is 2x that of the distance from the throwout bearing CL to the yoke lever pivot  --- scaled from Service Manual section drawings in Section 25/0, Figure 25-0/2 "Clutch, General Data, Dimensions, &Tolerances".  The freeplay dimensions prescribed in the Service Manual for throw-out Bearing to Pressure Plate release levers (dim "g" in the drawings) are listed in the table on page 25-0/1c.    Dim "g" is given as 2 mm for all models.  Since the yoke pivot distance to the push rod is 2x that from pivot to throwout bearing, a 2 mm free-play requirement at the throwout bearing translates to a 4 mm free-play requirement at the push rod (2x 2 mm = 4 mm).  This 4 mm push rod to yoke lever freeplay is also the required specified dimension in adjusting the slave cylinder --- (called the "Extraction Cylinder" in the Service Manual) in the section "Adjustment of Hydaulic Clutch Actuating Mechanism" in Job No. 29-6, page 29-6/2.

[Benz Dr.]

Some 280SL units have no adjustment at all and they simply self adjust as the plate wears. The early cars do have adjustment but there really isn't very much pressure on the throw out bearing while driving. The bearing may spin as you drive but it's not under any load. Constant load would make it run hot and it would be damaged over time.
Clearly it was too tight and now this adjustment seems to have fixed it. The only question that comes to mind is why did you drive it like that for so long? Assuming you knew something was wrong with it why didn't you get to it sooner or take it to someone who could fix it? It's hardly rocket science you know..... ( lol )

[Longtooth]

Dan, I need to correct my prior note regards any replacements on the clutch.  The entire clutch asm was replaced (from the original) 2500 miles ago: new disk, pressure plate, pilot bearing, & throw-out bearing, among some other things.  The reason I had the clutch replaced is that it began slipping severely on high accelerations.  After the clutch replacement I noticed slight slippage stilll occurred on high acceleraions in 3rd and 4th. I returned the car and the slave cylinder was replaced with a new one.  Test drive showed no slippage was occurring.  The shop that did the work was the same shop that did the clutch (an MB shop with a guy that's been doing the W113's since he worked for MB in Europe on them (Austria).  After a few drives I noticed slippage was still occurring slightly in 3rd & 4th on high acceleraions.  I returned to have it "adjusted" for no charge.  It still occurred slightly however, so I kept driving it without pushing hard on accelerations at high torque rpm's in 3rd and 4th. 

Since the clutch was new with new parts where they count with respect to slippage, and the shop mechanic said that there had been no oil or other crap on the clutch or flywheel when he originally replaced everything, I assumed either there was something amiss in the re-assembly (read $$$ to find out), or that there was an adjustement in some aspect of the slave cylinder that needed to be improved.  Recall that the slippage was slight, only at highest torque rpms, and only in 3rd and 4th... suggesting insufficient pressure ... pressure plate springs?... oil now having gotton in and reduced friction on the plates?..... something worn before it's time?

In the meantime, another W113 owner (psmith) had participated in Starfest's gymkana or whatever it's called and told me he'ed had a blast doing it (it was his first time... and btw, he got best time in class to boot).  Anyway, that got me back to thinking about my high speed slight slippage problem and I resolved that I would get this taken care of once and for all, no matter what ... and no matter how much work I had to do to make sure it was done right, whatever the problem was.
 
That's why I asked, as a last resort, whether there was something related to slight slippage that might involve the slave cylinder.  As I said before I wasn't counting on this being the problem, but my philosophy is get the easiest possibilities out of the way first.  So, I was somewhat elated to find my free-play between push rod and fork contact was <1mm.... thinking / hoping that by adjusting it to spec it might just do the trick.... hopeful, but leary.  After adjusting to spec (4 mm freeplay at the push-rod to yoke (fork) contact, from <1mm as it was), and finding the problem immediately went away, I mentioned in my note that I'd have to have a "tete a' tete" with the mechanic.  It's my supposition that the "adjustments" he did were not to spec, but I can't understand why if that were the case.  He's an experienced W113 mechanic.  My suppososition may be wrong though, so I'll have a talk with him to find out why the free-play was incorrectly adjusted in the 1st place.  FYI, the lock nut was cinched down reallly tight (far more than necessary), so there had been no relative displacement of the push rod to the pressure pin since his last adjustment... in other words, there had been no possible way for the slave cylinder adjustment to go out of whack.

BTW, I took a drive today to Monterey, top down balmy clear weather we're having.... 78-82 F.... for lunch on the warf with my wife as passenger for a change ('nuther story on why she's normallly disinclined).  This added more mass to the car (I'm not saying how much), so if the clutch was still going to slip, this 55 mile each way day trip ought to find it out.  I drove like there was no tomorrow as far as highest acceleration levels at highest torque range at highest speeds in 3rd and 4th.... up hill, over dale, etc.  I pressed it on every opportunity to get some slippage.... Nary a hint of slippage occurred on the entire drive in either direction.  Half the drive was at 80-85 mph, up to 100 mph in a couple of "passing" instances, under hard full acceleration (no slippage)... the other half at ~60 - 75 in Sunday afternoon lollygaggers traffic. 

So my conclusion must be (logically) that, given new clutch components 2500 miles ago, a new slave cylinder 2250 miles ago, that the slave cylinder free-play was and had been mal-adjusted relative to MB specs and that therefore the throw-out bearing was indeed pressing slightly and sufficiently against the pressure plate spring retraction levers to prevent full pressure plate spring pressure from being applied to the clutch disk... thence flywheel. 

I'll watch (listen, feel) for a return of any slippage under high torque high speeds in 3rd and 4th never-the-less.  If it returns I'll be damned if I'll be able to deduce what the problem would be though.       

[Benz Dr.]

That explains it very well. You do need a ceratain amount of free play that's for sure.

 It's one of the reasons I like to do a lot of test driving on all the work I do. Most cars stay for a week or two after I'm done and sometimes I find more things wrong. Since most of these cars come from more than an hour away ( that would be close ) it's important that I get them right.