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MG MGA - Clutch slave cylinder push rod
| I've a 1960 1600 with the Sierra 5-speed kit installed.|
I was just about to install a new slave cylinder, and I have a new clutch slave cylinder push rod here (Moss P/N 180-200) and, comparing it with the old one, it's 3/8 inch longer (about 10 mm).
The hole where the pin goes through on the old one shows no sign of wear, which could infer that little wear had taken place on the old one, yet it's quite a bit shorter than the new.
The initial problem that got me started was that the clutch would occasionally begin to engage even though I'd have the pedal to the floor. A shortened push rod could certainly contribute to that.
The old one's 9 years old, but mileage-wise it probably has less than 3,000 miles on it.
Can or do these push rods actually wear down lengthwise to that extent over time?
|No, they do not wear in length, but they do wear in the hole. This question comes up a lot, but I never seem to have a spare clutch slave push rod in hand when it happens. Anyone have one handy to measure? If we can get it right I will log it in somewhere for future reference.|
|As Barney notes, the only wear point is the hole in the end. The push rod has nothing to do with the problem of the clutch beginning to engage even though the pedal is depressed to the floor. That is a hydraulic issue where the pressure on the push rod is not being sustained. Either a slightly bad master cylinder, a slightly bad slave cylinder, or a leak in a line. Many new parts are not to the exact, original specification. A too long push rod may be easily shorted--if necessary. A short push rod must be built up by welding or soldering on an extension, a more difficult process. I would try the new push rod before making any "adjustments" to it.|
|The new one I've got here measures exactly 78 mm end to end. It's from Moss, made in China.|
(Whereas the old one I referenced in the above post measures
just a hair under 70 mm)
|I had an incident last summer when trying to drive out of a layby I managed to push the piston right out of the slave cylinder I wasn't aware of what had hapenned until I had been relayed home. I found wear at all possible places, i.e. hole in pushrod, pin, hole in pivot arm for pin, and pivot for arm in gearbox body. I replaced all the bits I could and found a better arm. The suprise was that the rod was around 10mm shorter than the replacement one from Moss but it had a nut jammed on its end. I reassembled, together with a new clutch and all has been fine since.Talking to a friend in the trade he said hammering a nut on the end of the shaft used to be a standard 'trick'. It is not only that the nut makes the shaft longer but it also widens it which makes it effectively longer again as it pushes into the conical end of the piston.|
I have always assumed my old one had been off another car hence the wrong length and the Moss one was correct. I would be very very cautious of shortening any rod as you might fail on the road like I did and h
aving to be relayed home by the RAC.
I will check the dimensions of the master cylinder rods too but I didn't notice a difference when I changed them.
|If your clutch begins to engage while you have the pedal held down you have fluid leaking somewhere. It could be going by the rubber seal in the master cylinder, or getting past the seal in the slave cylinder. You should be able to see fluid if it is leaking from the slave, but if it is the master cylinder it may not show externally. The length of the rod would not cause the original issue that you have of the clutch starting to engage while the pedal is not moving.|
|If you have no leaks, suspect the master cylinder. It develops an internal leak as the seals deteriorate, and shows just the symptoms you describe. If the rod worked fine before, it is not the problem, as they only wear in the hole, as everyone has said.|
I suspect that the longer ones are offered because the suppliers are supplying the smaller midget master cylinder for all applications, and use the longer rod to get more leverage at the other end.
| Thanks for all your comments.|
I didn't want to proceed until I got some feedback on the different push rod lengths.
The whole hydraulic system is older than the hills, so wherever the problem is located, it's sure to be addressed since I'm replacing the master, clutch slave, wheel cylinders, clutch and brake pipes and the four hoses, along with switching to silicon fluid.
|Hi people, back again.|
When I use the old (shorter) slave cylinder push rod, it matches up with the end of the clutch lever where it attaches with the pin.
When using the longer push rod, the push rod has to be pushed into the slave cylinder pushing the piston back around 10 mm, give or take, before it can line up with the clutch lever for attachment.
If I went ahead and used the new (longer) push rod, is there anything I need to be concerned about here?
|You should have to push the piston back to line up the pin. When everything is assembled, you should be able to push the piston back still further; this is the "spare" travel the system uses to self adjust the release position. If you can line up the pin without pushing the piston in, then the piston is sticking on crap in the bore.|
|So, nobody will measure one?|
|Barney; see the 4th post from the top.|
|Yes I know you have two different lengths, but you don't know which one is which. I was hoping someone could measure one that is currently in service, or was in service but currently more easily accessible. So I will now R&R the one on my car to measure it. There will be a small delay. 4:12 pm|
4:47 pm -- The answer is, 2-3/4-inches end to end, 2-7/16-inches from tip to center of hole. The hole is originally 0.3125-inch diameter (standard reamer size), as the pin will be 0.002-inch undersize.
|2.75 inches equals a hair under 70mm.|
|Oh! The one you just bought from Moss is 78-mm = 3-inches long? Did Moss make a mistake on this one? I've been buying these from Moss since at least the mid 80's, and they always work. I think they were always 2-3/4-inches long, same as the one I now have in service (and working well). I'm pretty sure I would have noticed if they changed length. Last record of purchase I have is May 2007, something may have changed in the past 5-1/2 years (not necessarily for the better).|
|Yes, to clarify; the new one I just bought from Moss (180-200), but have not installed, is 78 mm from end to end.|
The one that I had (and have) in the car is the same length as yours, ie: just a hair under 70 mm or 2.75 inches.
|If no one else has an answer, I guess you get to try to install it, and see if it works without binding on the release bearing.|
|If it works, fine. If it doesn't, it's easy enough to remove, shorten and round off the end to the correct length.|
|But if the mod has to be done, it is far more efficient for the supplier to modify the whole batch en mass, rather than lots of people finding the bad part and having to modifying one piece at a time in the field. For a pro shop paid by the hour, the cost to modify one piece may exceed the purchase price of the part.|
This ranks right up there with having to cut some length off of the tie rod ends. Moss even puts an information sheet it the box to tell you what has to be done but they still refuse to do it before shipping the inappropriate parts. I'm not buying it. I just ordered a tie rod end from a different source, and it should arrive today. I am about to find out if the right price will buy a correct part.
If this slave pushrod is actually wrong length, then I suppose next month there will be another information sheet in the package telling the customer they have to fix it themself.
|Agree Barney...Moss should be notified that the part has been made incorrectly. To save time and shipping costs though it's an easy enough problem to correct now that Rick knows what the correct length is.|
|Rick and Barney,|
The same happened to me earlier this year. Fortunately I have a mate who is in the trade, he was well aware of this problem from Moss (UK). He showed me a box of Moss pushrods, with several different lengths all on the same part number (13H21).
He just swapped my long one for a short one, his view being "It's easy to make a short one from a long one, but bloody difficult the other way round."
Could be worth calling Moss and asking for someone to physically check the bin.
|L.R. deOlazarra, -- Please do not drop the ball on this issue. When you report it to Moss, let us know the response, and if they intend to do something to correct the problem.|
|It's been done. Awaiting response.|
|Ok, people, the issue has been resolved. For those of you interested, here is the complete exchange between myself and Moss concerning the length discrepancy of the clutch slave cylinder push rods:|
The clutch slave cylinder push rod I received from Moss is longer
than the one I had intended to replace.
The one I purchased is 78 mm long end to end. The one that I've had in
service is just a hair under 70 mm, or 2.75 inches end to end. The shorter
one fits into the slave cylinder and lines up with the clutch release lever
perfectly for fitment with the clevis pin.
The new longer one from Moss needs to be pushed into the slave cylinder
(pushing the piston back) the difference of the 2 lengths in order to line
up for fitment with the clevis pin.
I brought this up on an MGA forum and one of the respondents, a Barney
Gaylord, measured his and came up with the same measurement as my old one,
that is, 2.75 inches or a hair under 70 mm. Also, a fellow from England has
had a problem with different lengths on Moss slave cylinder push rods over
Personally, I'm not eager to install the longer rod and will retain the
shorter one until I get some verification on why there are 2 substantially
different lengths on these items.
Could somebody in the know on your end explain why the different lengths,
and what, if anything, can be done to clear this discrepancy up? What
happens if someone installs the longer one when the system design calls for
the one I and others have been using, ie the shorter one?
Your e-mail surprised me. We had a problem with these in the Summer and
ended up putting over two thousand of them into the recycling bin.
When I printed your invoice I saw you bought yours in June. You probably got
the first one of the defective ones and when you didn't use it, nobody knew
I've written an order for a new one. It's on its way.
Thanks for your response.
Sorry to have you chew your cabbage twice, but to clarify; what you're saying is that the one I received is from a defective batch, examples of which will no longer be sold by Moss, and that you now stock and sell push rods that are the correct length, one of which you've just sent me?
Another point; concerning the following, embedded in your response: "This Email and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom they are addressed." Do I have your permission to copy and paste this email exchange into a post at the BBS on british-cars.co.uk? Turns out there's a keen interest in clarification and resolution of this issue there.
Again, thanks. :)
You understand correctly. When we find we have a problem, we get right to work to fix it.
I understand that there are times when somebody gets a faulty part they get frustrated. That may cause them to react in a way they are not proud of, or to feel Moss deliberately sold faulty parts. That's simply the knee-jerk reaction to their frustration.
If your desire to use my words is to confirm that Moss does care, please feel free.
|I'm sorry, but the response from MOSS is pure BS. I've been in Quality Assurance as an engineer for 40+ years. I've had numerous discussions with their "Quality" people. They don't have specs, they don't have drawings, they don't do "incoming" inspection. They send a part to a supplier and say "can you make this"? Basically, they rely on customers to inform them of problems, then plead ignorance. Look, MOSS is a small specalized business with a low profit margin. Yes, they provide a valuable service, but, they maintain their market by keeping costs low which means using the cheapest suppliers. We have to keep on them, let them know we'd rather pay a little more and get good parts. |
|G T Foster|
This thread was discussed between 07/12/2012 and 22/12/2012
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