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MG MGB Technical - Choke Cable Lock - 72B

Okay, here goes what should be a simple inquiry, on directing me to what I'm not seeing when I look...

I recently had to pull the engine to replace clutch on my 72B. This required as we all know removing the carbs, intake manifold and disconnecting the throttle and choke cables from carb.

The car essentially runs fine, and I never knew a clutch could feel so easy and shift so smoothly, but I digress...

My question is about the dash mount choke cable.

Before all these repairs, when I pulled on the choke cable handle, and turned handle 90 degrees if felt like it locked in place. As car warmed up, I could turn handle back 90 degrees and push cable in a bit to lower idle and again turn cable handle and lock in place again.

NOW... I pull the handle and it pops back in. I can turn it 90 degrees but it doesn't lock in place, I have to hold it out from the dash. It does have some residence when turned 90 degress, but not the locking I'm used to.

I've looked everything over, but can't determine what it was that enabled the handle to lock in place before.

Was handle suppose to lock when turned 90 degrees, and now it just doesn't or ????????

Your thoughts, or should I leave well enough alone.

Thanks for your assistance.
R.W Anderson

Yes, the cable is supposed to lock/unlock when twisted 90º.

Offhand, I do not believe the cable lock mechanism is
serviceable. Over the years, dirt may have fouled the
locking mechanism up a bit. Perhaps a shot of solvent
(ie: carb cleaner) may clean things out a bit.
Daniel Wong

Many of the newer replacement cables don't require you to rotate the knob to lock the cable in position. You simply pull the knob out to the desired position and it remains there until you decide to push it in a bit. RAY
rjm RAY

Hi RW,

I had the same problem and solved it by giving the cable a twist, so that it tends to turn in the direction required to lock it, before locking it with the retaining screw, at the carb end. About one turn, and on mine it was against the twist of the cable wires.

Herb
Herb Adler

Check this out. It may explain the inner workings of the choke 'lock'

http://www.mgb-stuff.org.uk/fueltext.htm#choke
DK McNeill

The link to mgb-stuff is good info. In between blizzards I'll open up the car and see if twisting the cable at carbs helps, or the ideas in the web link.

Thanks.
R.W Anderson

The little "wedge" - actually a woodruff key shape - wears in the centre and at the edge, usually reversing the key in its slot brings the sharp, unworn edge into play and the handle will lock again.

It is essential to turn the handle to the lock position before doing up the carb fixing otherwise the cable twist will unlock the handle in operation.
Chris at Octarine Services

I found that you could fit the knob part into the fixed part two ways around, (since the zinc alloy die castings have a lot of play between the shaft and the hole), and only one of them lets the lock work properly. So maybe check it's in the right way round.
D Balkwill

If it worked properly before you pulled the engine and quit working immediately after, it /must/ have something to do with the engine removal (or just be an incredibly unlikely coincidence....)

Have you verified that you have all the return springs hooked up as you did before? Does it feel harder to pull out & more eager to spring back than it did?
Rob Edwards

The whole feel of the choke at the cable handle end feels different, and of course doesn't lock out. And yes the cable handle end does feel like it wants to go back in on its own. It used to lock at every little position from all out to all in.

The rest of the carb feel, springs - linkage feels fine.

This is another example of I should have taken pictures before I took it apart to see just where cables and springs were to begin with. Everything looks right compared to manuals, but I'm not sure how this compares to how it used to look.

Just another thing to look at come spring thaw.
R.W Anderson

The carb springs should always want to pull it back when it is unlocked, it is not a pull/push choke like some other makes but a pull/spring-back.

All the ones I have seen are such that they can only fit together one way (unless you use brute force I suppose), as shown on that site referenced earlier. The significant amount of rotational play between the two is to allow it to move between the locked and unlocked positions.

As it locked before but doesn't now the obvious thing is that the twist in the cable is tending to unlock it, as has already been mentioned. This should be obvious in the knob or handle turning itself to the unlocked extremity when in the unlocked position, when it should be turning towards the locked, or be neutral at the very least.

However if it was only just locking before, and you now have too many springs on the choke i.e. some from the accelerator, then that could be enough.
PaulH Solihull

There's enough play on the high quality new ones from the usual suppliers for the parts to go either way up Paul.
D Balkwill

Hi,

The photo, below, shows the position of the springs.

Herb

Herb Adler

Thanks for the photo too, and I think that is how I have the springs hooked up.

I'm waiting on outside temps getting back up to freezing or above so I can pull distributor to have it rebuilt this winter, I'll compare photo to what I have and see if a twist here or there with cable changes anything.

Something changed between then and now.

Who knew such a simple task/item could generate a long series of responses.

Thanks again.
R.W Anderson

RW,

I never worked on one (at least not at the dash end) but I always assumed the locking took place right at the handle end. If that is so, then if it is loose in the dash, the entire housing would turn instead of the just rod turning in the housing. So, is it tight in the dash?

Charley
C R Huff

The locking does indeed take place at the handle end (in any position from fully out to fully in), and the outer does have to be secured in the dash for that to happen.
PaulH Solihull

Perhaps these photos may help to visualize what the choke locking mechanism is like and does. If, somehow, the spring locking ring comes loose, falls off, breaks - the cable locking key (as I call it) will either loose sufficient tension or fall out all together and you will lose resistance for locking or locking capability altogether. Hopefully this is helpful.

Robert Muenchausen

The dash end of cable is secure and has not been apart. The only part of the cable system that was touched was to disconnect cable at carb end. During the period of disconnect, the housing or inner cable may have turned, but the handle in the dash is secure and reads upright. So if anything moved it must have been less than visible.

And I may have re-tightened the cable end at the carb assembly to a different spot on cable, but springs are as shown in above photos.

I may, when it gets above freezing, disconnect cable from carb assembly and see how the cable lock works when not attached to carb.
R.W Anderson

However, RW, there is some small possibility that your cable has lost its cable locking key - perhaps it fell out? I know it sounds improbable, but I have seen similar mechanisms where the key (or ball, or other device) or the spring retainer have worn or lost tension.

The original posting seems to indicate that this problem came on suddenly and improbably, and that makes me wonder if the key didn't fall out if the dash mounted pull knob had been pulled out to a point where the locking key fell in against the inner cable, and when the knob was pushed back in, the inner shaft knocked/rolled the key out somehow. Until you move the locking ring/spring back enough to see inside, as in the photos, you may not know for sure. A remote possibility to be sure, but stranger things have happened.
Robert Muenchausen

I had a non-locking new cable... turned out to be the little plastic half-circle locking key (in the photo posted above) had worn after only a couple of attempted locks.

Replaced it with a piece of appropriately filed bolt of the correct diameter and voila - best locking cable I've ever had in an MG!

When I last had my carbs apart, I also put the choke linkage cable between the two carbs the wrong way up. It felt really weird until I remedied it.

The photo of the springs above doesn't show the third spring which goes on where the throttle cable attaches - ahhh - the variations!
Curtis Walker

Oh, great - with my eye sight ability in dark places; I'm suppose to be looking for a small part that may have dropped out while inadvertently pulling the cable too far out of the dash, when it was disconnected!!!!!!

Unfortunately the explanation of a part falling off makes the most sense. I'll crawl in there with a bright light and look around on the floor, etc. for a tiny part. OH, and with strong glasses too.

Thanks.
R.W Anderson

Another view of the carb end of the choke cable system.

Robert Muenchausen

Unless the retaining spring had been moved from its correct position the locking key cannot fall out, and certainly not fall inside - see the later pictures here http://www.mgb-stuff.org.uk/choke.htm

Unless it had the incorrect locking key of course, easily corrected as Curtis describes.
PaulH Solihull

Well, as often happens, it looks like this thread just became relevant to my 68 GT. It has always taken a lot of effort to pull the choke on mine, and I had thought of changing it to a T-handle to get a better grip. Also, yesterday when it was about 20 F it was hard to start and I noticed that I was only getting about 3/4 of the full choke travel.

Now, based on Robert's photo, it seems mine is rigged up side down. My choke cable comes in from the top and the free end of the cable is attached to the choke lever instead of to the bracket arm. Maybe this has something to do with the fact that 3 years lapsed from when I pulled the engine for rebuild and when I replaced it. Or it is possible that I duplicated the way it had been done when I bought it since most everything else was wrong with this engine.

Just to clarify, I have twin SU HS. This pic is for HS and not HIF isn't it?

Charley
C R Huff

If your choke is stiff at the dash, just check that things aren't too stiff at the carbs themselves, by working the choke linkage bar at the carbs - also making sure it's properly moving the jets and pressing on the adjustable throttle screws appropriately.

Assuming that feels and looks good, yes, try turning the linkage bar up the other way (again checking for good range of motion). Now try the choke knob again - better?

The correct bolt size to fashion a new metal locking key is 5/16th" - see here: http://www.mgexperience.net/phorum/read.php?1,1413354,1413354#msg-1413354

It's certainly something I'll do whenever I'm replacing choke cables in the future - much more robust than the small plastic bit, with a decent ability to lock.
Curtis Walker

I have never seen a locking bit made of plastic! All OE ones and most aftermarket ones have a steel part.
Chris at Octarine Services

I second Chris!
Charley - You can greatly reduce the effort to operate the choke by rerouting the cable. I drill a 1/4 hole through the fresh air intake box directly in front of the choke cable on the dash, then run the cable straight forward through these holes from the dash, and approach the carbs from the top. The holes will be about straight down from the LH-most bar of the fresh air grille; it will go through both front and rear side of airbox - you can see the installed cable by looking down the grille. Drill from underhood but first look under dash to see what you don't want to hit. It works on all carbs, but you need to juggle end fixings to suit your setup. Shorten the cable as appropriate. This eliminates about 2/3 of the cable and most of the bends, which is where all the resistance comes from (also lets you use up cables that are too short!). You will not believe how nicely the choke works!

FRM
FR Millmore

FRM.

Thanks for the tip. I get what you mean, but want to double check one thing. When you say "...and approach the carbs from the top" do you mean the opposite of Richard's picture about 6 posts back?

Unfortunately I have a Catch 22 going on here. It's going to be about 10 F here tonight, so I'm not going to feel like working on it, but if I don't, it probably won't start. Oh well, I guess that's what the diesel Benz is for.

Charley
C R Huff

Charley-
Yes. Bring the cable in from the top, anchor the housing to the bracket with the swivel fitting that usually goes on the throttle lever as shown. then use the little end trunnion to fasten the inner to the lever. Usually the ends can be swapped like this, though some are a little short for the thicker lever. There are long and short end trunnions. It leaves you with only a single gentle 90deg bend in the cable. I always come near to breaking my hand if I'm used to the normal hard pull, it comes out so easily this way. The normal installation has about 360deg or more of bend and depending on routing, some of them are pretty sharp.
Also helps a bunch to have a 3/4" (I think) open end cut off to about 2 1/2" long to deal with the cable nut behind the dash.
I got the '10F here too, but I've also got 4ft of white crap that I've been shoveling for 4 days so I can get my car to the shop to put the winter tires on!

FRM
FR Millmore

Thanks FRM,

Mine is routed in from the top and the housing is anchored to the bracket. So maybe routing it with fewer bends will solve the hard pull.

Good luck getting through that 4ft of snow. We're supposed to get some this weekend, but only up to 4in. I guess I'd better put my winter tires on the Benz today or tomorrow.

Charley

C R Huff

The choke cable on a 68 should come up from the bottom. What confuses is that the inner then has to attach to the fixed bracket, and the outer to the moving lever, which to many seems completely wrong. It works fine when everything else is OK. The run of the cable has to be free of obstructions so that it can move up and down freely with the lever, as well as everything being free and lubricated. However the main thing to look out for, and it applies whether the cable comes up from below or goes down from above, is that when the choke is half-pulled the lever makes a right-angle or close to it with either the inner or outer that is moving it. If the lever starts off in this position then as the choke is pulled it doesn't have to move very far before it has pulled the lever almost *in line* with the inner or outer, and it won't pull any more or turn the shaft any more, even though it may only be half or three-quarters pulled at the carbs. Conversely if the lever is too far the other way it can make it very stiff to start moving.
PaulH Solihull

Thanks Paul,

When I get out there to check it, and get it disconnected, I can check to see which part is causing the problem. Since I can't get full choke, I suspect that the 90 degree at the half way point is not correct on mine. When I couldn't get full choke the other day, nothing was stuck or jammed, so that is probably an adjustment issue.

Charley
C R Huff

And another photo of another approach - different from Original - which also moves the choke mechanism.

Robert Muenchausen

This thread was discussed between 29/11/2010 and 10/12/2010

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