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MG MGA - MGAMaster Cylinder Push Rods
|I am looking for a pair of M/C push rods from someone's spares collection (aka junk box). They don't have to be pretty, just useable. The Moss number is 180-040. mgcarnut at sbcglobal dot net|
These are easy to make up from stock 5/16" steel rod. They are 4.25" long with a threaded portion of 1.75". The ends that go into the m/c are rounded to match the concave plunger. See attached pic. I made mine from stainless only because I had some lying around.
I still have one of the originals you could have but the threads are not perfect............Mike
|Sorry, I forgot to say the threads are 5/16" UNF|
|Think they used a half nut to lock them in place once adjusted rather than a full width nut.|
|Mike and JB, many thanks for your responses. With all the info supplied, a pair of home-made rods will do the job.|
|Close, but no cigar. The push rod is 5/16 diameter with a slight taper at the blunt end, so the rounded tip is smaller where it fits into the master cylinder piston, and with 5/16-24-UNF thread.|
According to the SPL, the 1500 model is a plain rod with two hex nuts, implying that one of the nuts has to be jammed against end of thread to be one with the rod, providing wrench flats to turn and hold the rod during adjustment, while the other nut is used as jam nut against the clevis. I just took a picture (see attached image) of these parts in my 1500 car, and indeed there are two (thin) hex nuts on each rod. For the record, I don't recall ever buying thin nuts in my life, so these must have been on the car when I bought it in 1977.
According to the SPL, the 1600 model has a cold headed hex in the middle of the rod, and one hex nut to be used as jam nut against the clevis, as shown in the lower picture (but even this is not exactly right). I would appreciate it if someone could take a look at and ORIGINAL 1600 car to verify the smaller (probably 7/16) cold headed hex on the push rod.
According to the SPL's, both models have the same part number (BCA4046) for the master cylinder push rod. This means the early part is superseded by the later part, and all replacement parts will be the later style. So if you want the early style part for concours show, you either find a good original part or make your own.
Furthermore, according to the SPL's, all of the hex nuts are part number LNZ205, which is a zinc plated Nylock nut. I have no idea why a Nylock nut was specified, but that's what the book says. Since I have thin hex nuts on my 1500, I might be persuaded to believe this is an error in the SPL. Part number for a zinc plated jam nut is FNZ205.
those rods are available from any Girling supply, for Germany see here:
|Ever felt that when you look at something and for some reason it doesn't look right, but you're not sure why?|
Happened to me with that push rod picture, until I realised the picture must be flipped so it has a left hand thread!
|Jim,I think its called 'Sod's Law' in the UK, but following a recent house move I'm having a general clear out and sold a pair recently on fleabay. link attached with a picture which may be of interest although no differnt to Barneys picture|
|Yes, the eBay ones look like the later style with the cold headed hex in the middle.|
Sorry about the left handed thread. Is this better? See attached image.
|Barney, you are the man!|
|There was no taper on either of my push rods and they were both 5/16". Even though I have a 1600 there's a good chance then that my original m/c was replaced by a 1500 model. This also explains why I originally had a flat cf raised m/c cover. |
Makes me wonder why they changed the design. There must have been a good reason because the tapered design would have been more expensive to make. I wonder if the diameter of the new one was greater beyond the taper to make them stronger. Perhaps there had been some reported cases of bent/broken push rods when braking hard with disastrous consequences?..................Mike
|I'll take a wild guess (from a bit of engineering background). When the system operates the pedal swings on an arc, and the push rod is misaligned, moving slightly up and down at the input. If the push rod is large diameter, friction in the socket between push rod and piston will tend to cock the piston slightly, which could cause friction and wear between piston and bore. Making the output end of the rod smaller diameter would reduce the piston cocking tendency slightly.|
When these parts are in large enough volume of production it is probably cheaper to forge the tapered end rather than machining it. This is likely done in the same forging setup as cold heading the small hex in middle of the rod and cutting it to length (from a long rod of feed material). The tapered end then also reduces amount of steel used to make the part. The thread would be cut (or more likely rolled) after forging.
|Thanks to all for their comments on my now abandon project. I have been convinced that my idea to install an MGA dual M/C on an MG TD is not advisable. I did not realize that the pedal pressure to stop the car would have doubled. Initially I thought it would take the same pressure if all the pistons were the same size. Special thanks to my very knowledgeable advisor who took the time to get it through my thick skull.|
|Hi Barney, I think my 1600 has the original push rods on the master cylinder - photo attached - see what you think
|Cam, What's the diameter of your rods on the left hand side near the m/c? To me it looks greater than for the threaded portion which should be 5/16" assuming the 1500 and 1600 forks are the same.|
I've dug out one of my old push rods and noticed it is slightly bent and it worries me that the earlier push rods may have been borderline on strength...............Mike
|The push rod on the brake side appears to be bent in both photos. Also it looks to be slightly off center. Then maybe it is my old eyes looking crosseyed at it.|
|Yes, but not bent, i think out of line - look at how the fork fits onto the pedal lever, it's not parallel.|
Cam, You may want to think about spacing the pedal over a wee bit next time you have the kit apart (Perhaps reduce the spacer bush length and pack the other side of the pedal)
This thread was discussed between 18/03/2012 and 21/03/2012
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