Mathway Steering backlash

[Moderator]

I wrote to Parsons Mathway to ask for help – I wanted to share both our problem and Mark’s prompt and helpful response.

I wrote:

Sent via Mathway contact page 2022/8/11

Our 1974 Nicholson 38 sailboat has its original Mathway steering unit, presumably the Series LS based on your website description. We recently tested the amount of play in the steering, and discovered that there is approximately 5 degrees of looseness in the steering gear box. Let me describe the situation.

When we turn the helm in a given direction, we can see movement of the steering rods all the way to the gearbox. There is very little play in the helm to rods connections – that part is good.

However, at the gear box, we observe quite a bit of play. For example, once the helm has turned the rudder in one direction, when we turn the helm in the other direction, the gearbox tiller arm does not move until the helm has rotated 60 degrees in the new direction. Once that looseness is taken up in the gearbox, further helm movement in the same direction results in tiller arm movement translated into rudder rotation. If we turn the helm the opposite direction, the situation renews. This observation is repeatable in both steering directions.

I believe this is called backlash? Note that in our installation, there seems to be a 12:1 gearing ratio given that the helm moves about 720 degrees to turn the full rudder motion of about 60 degrees.

We like our Mathway steering arrangement very much, and prefer to repair it. Can you help us understand how serious is this amount of wear? Can this 1974 version be rebuilt or replaced? Our sailboat is located in Hawaii, USA, so shipping an oil filled box back to your location is problematic.

Thank you in advance, we look forward to hearing from you.
Marilyn Johnson and Van Eden, Rainshadow 1974 Nicholson 38

Mark responded the next business day with the following:

Hi Marilyn,

Mathway steering should have very little backlash – that’s one of its main advantages. The amount of backlash you describe indicates a problem. 5 degrees of backlash in the final gearbox could be due to worn gear teeth or either of the gear shafts having moved along its axis. Movement could be due to problems with a bearing, or possibly even a lock nut working loose. The gearbox is actually very simple and I should think you can get it refurbished in USA. The only real difficulty will be if the gear teeth are badly worn. It wouldn’t be cost-effective to have new ones made, but if you need replacements we may have a set in stock (possibly used). Can I suggest you remove the gearbox from the boat, remove the steering arm and the large cover on the gearbox and inspect the gear teeth? Once you know what is worn/ broken we can advise how to proceed.

Regards,

Mark
Parsons Mathway Marine

So Van and I are going forward with trying to access that gearbox, next time we get to the boat. We’ll keep this post updated with our findings.

[Moderator]

We got our steering gear box out of the boat, similar to how Trevor said in this posting. We used a 3-jaw puller to get the ball joints and stub arms separated, as described in this post.

FYI – we don’t think we have the Mathway steering version, instead have the Foreman type. The only markings we could find was stamped in the box casting that says RB551. It was originally painted red, which has all but corroded away from the gun-metal casting.

The oddest thing is, once we got the reduction gear box home, there is no more backlash!! We are 99.9% certain that we observed on the boat when this was still installed that the backlash was all from the reduction gear box, but now there is none – turning the “input” immediately rotates the “output” – and vis-versa.

We tried to move the spindle in/out of the gear box to disengage the gears, but no movement could be seen. I don’t believe things fix themselves, but when we tried to take it apart to inspect the innards, we found the 6 screws that hold the top cover down are completely corroded in place. We tried drilling the head off one screw, and it wasn’t easy nor fully successful. They are probably 1/4-2o socket head screws, embedded into the head.

Given the concern about whether we are working on the wrong part, we may clean the reduction gear box up and install it back in the boat to see if the backlash still exists, perhaps from another source? Or maybe removing it from the boat dropped the gears back in place – for now. Certainly the steering system can apply a lot more force to the crown wheel spindle than we can on the bench. If either a bearing race is failing, the gears will separate again and the backlash will return.

Note we did find a nice functioning oil fill plug on the top cover – it takes a 7/16″ socket to remove it. We discovered the gear box oil was nearly gone, and what was left had turned to goo. So we flushed the box with a variety of solvents until we got that gunk out. Now the gears turn more smoothly – there were a few rough spots.

The Mathway manual says to refill with SAE 30 oil, but we are considering using an SAE 85W-140 API Service GL-5 designed for gear boxes. However, I just noticed that Arild said

 I asked Mark at Parsons Mathway Marine what oil to use, and he recommended “SAE 30 or 15W40”

Note that to one complete rotation of the crown wheel spindle results in 5-1/2 rotations of the companion flange. In other words, we can rotate the crown wheel spindle such that we ultimately result in the rudder motion engaging a different set of crown wheel teeth against the pinion. The crown wheel only turns through about 60 degrees either way from “center”.

If anyone has any advice, we’d love to hear it.

And if anyone knows a part number for ball joints that are good replacements on either end of the drag link, that would be very helpful too.  Ours seem to function, but the boot is completely gone. Seems getting the taper right is very important, and I don’t know which Land Rover part is the right one for a Nic 38!

Cheers-

Marilyn

[Moderator]

Update since my last post – we got the steering box reinstalled. Some lessons learned:

– The steering gear is held down to its mount by 4 bolts. The aft port bolt is threaded into the mount, and is shorter than the rest. It does not use a nut like the other 3 bolts, because there is not room for one.

– The steering arm and gearbox are connected by mating flanges with 4 bolt holes. These bolt holes did not line up when we had the rudder centered, and the helm set to its original “rudder centered” position and the drag link installed. This is because 1 crown wheel rotation results in 5 1/2 turns of the pinion gear, and we had rotated the crown wheel lots when it was on the workbench. We decided to set the stub-tiller so the rudder was centered, rotated the steering arm to make its flange bolt pattern match the gear box flange, and left the helm in a rotational different position. We plan to remove the wheel and see if we can get the hole in the spoke that marked “rudder centered” to be at the top again. I’m not sure if everyone’s helm has this hole in the spoke – this may have been added by the PO when he installed the monitor wind vane, which requires a pin in that spoke hole be engaged with the monitor drive wheel.

– I am delighted to say the tie rod ends I described in the other post fit well. Only caveat is that once the taper is fully seated, the cotter pin hole is completely below the tightened crown nut. But the taper fits so perfectly snug that I cannot imagine the crown nut torque is what will hold those joints together while in use.

– Once we got everything back together, we learned there is no backlash in the gearbox – but there is slop in the rudder shaft coupler! This may have been the original source of the movement, and we just did not realize it due to the poor access/visibility. How we resolve that coupler issue will be the topic of another post (once we understand what happened.)

Marilyn and Van – Rainshadow

[Guy H]

I scoured the ‘net re. couplers and these may be of interest to you https://nabcoparts.com/products/1-3-8-x-1-3-8-two-piece-split-clamp-type-rigid-shaft-coupling-kwys-steel?variant=32744956526689
(Also available in stainless)

[Van]

Well, after much trials and tribulations, we finally resolved the backlash issue in our steering.  In doing so, as you can see above, we pulled out the gear box, flushed it with solvent, filled it with good oil, reinstalled it, and found the problem did not go away.  We then realized there was slop in the rudder post – the upper part, above the coupler, could move relative to the lower part (ie the rudder) by quite a lot, I guess 5 degrees based on our earlier measurements.  You had to look hard to see it, but when you did, it was obvious.

We had noticed earlier that the key in the keyway was low.  Almost an inch was sticking out of the bottom.  I foolishly thought that enough would be left in the upper keyway to lock the two parts together.  Also, try as I might, I could not get the key to move back up.  Fortunately, I have a good friend who is a machinist, and he suggested (in hindsight an obvious suggestion) to just get a little hammer, and tap the bugger back up.  It worked perfectly.  I used a brass hammer.

After the key was fully back in the keyway, the slop was gone. Lesson learned.

Just in case that darn key might slip down again, I clamped a stainless hose clamp around the rudder stock just below the key.  It can’t move now.

Van

[Author]

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