6 replies to this topic

[1984mini25]

Another ongoing problem. The inside of the nylon pinion gear has worn smooth and so no longer turns the shaft it’s meant to be attached to or the speedo cable/speedo.

 

I’ve so far tried a Loctite adhesive, but for whatever reason (probably the wrong type?) It never set properly so failed again straight away.

 

I then tried chepo 2 part clear epoxy, which has/did work, but that too is starting to now fail, as the speedo is fine when cursing at a steady speed, but bounces wildly when accelerating or decelerating.

 

Simply replacing it with a new one would be the easiest solution, but I need a 17 tooth one and don’t really fancy paying stupid prices for a second-hand one off eBay in unknown/well used condition to find it too is knackered in the same way.

 

And yes I’ve tried Guesswork’s, he doesn’t have any.

 

 

 

[Spider]

Just think out aloud here and not a repair I've yet done.

 

I agree that the price of these particular parts is over the top.

Steel isn't too much of a problem to 'glue' but Nylon can be and especially since it's been in hot oil, I tend to think some of that oil will have permeated the surface.

A 2 part Epoxy or Polyurethane Adhesive would likely work best, but that these parts are a tight or neat fit tends to knock these on the head, however, if you were to open up just part of the gear from one side (I think the bottom would be best) so you could form a 1 - 2 mm thickness of adhesive between the parts, it might work. You could drill the gear but be careful the drill bit doesn't bite and go right the way through. I'd suggest leaving about 1/2 the gear in tact to keep the shaft central within it. The Steel would benefit from being roughed up too though the original shafts were splined, so that I think would be enough. Both parts will need to be surgically clean before applying the adhesive.

I have looked at this once before for when the time comes to carry out such a repair and for me I'd likely drill the bottom end of the shaft to fit a pin through it, positioned such that it's just a little more than the diameter of the Pin above where the Gear sits, then Mill a slot, the diameter of the Pin, across the bottom of the Gear. I'd suggest this would be fine if you had access to the machinery to do this, but if you were paying a shop to do it for you, then it would likely be a much for muchness in cost as a new gear,

[Tornado99]

For a more solid fit, you need to use a thickened epoxy, not the clear type and certainly not the five minute setting type, as that gives poor adhesion and poor hardness.
A JB weld slow setting product will do much better for this. Try roughing up the surfaces with emery or wire wheel dremel. Conside making small notches on the shaft to give epoxy some good mechanical keying.

[1984mini25]

The clear epoxy was a temporary repair, as the other option is to just drive round with no working speedo (or mileage) and just go by the rev counter in each gear (which is what I’ve been doing anyway).

 

Spider –You are right, the shafts are splined and while I was searching for answers for the problem I did come across this video of the issue. As when it first failed the speedo worked as normal at the start of the drive, then started to become erratic and then failed/dropped to zero and failed completely.

 

 

And I have seen 16 tooth pinions (green) are available new for around £25, but from what I can gather despite some being pictured with the shaft, it’s just the gear and needs to be epoxied onto the shaft. But none of the listings I’ve found say what epoxy to use, but then being a new gear id assume the hole wouldn’t be oversize (assuming they are of decent quality) and worn smooth. Either way, using a 16 tooth pinion would cause my speedo to over read anyway.

[Ethel]

Could you improve it mechanically?

 

Cross drill & pin - not sure how well a hole would go with a worm gear, even if the pin is deep enough to be out the way.

 

Could you weld/braze/solder a washer to the shaft & screw, or pin through that ???

 

 

..........................................

 

Daft idea - or genius?

 

If you made up a threaded bush could it mostly be self tightening ???

[1984mini25]

Thinking out loud, would fiberglass resin work? (Minus the fiberglass matting)

[A-Cell]

Nylon gear will need cleaning with isopropyl alcohol to remove the oil, and then drying for about 2 hours in an oven at 60 deg C to remove the water from it.
Clean the oil off the shaft. Roughen the two surfaces with some emery.

Nylon to steel cannot be glued, it has to be bonded.
Use 2 different products. One for each material and stick those 2 different materials together.
On the nylon gear use a 2 part urethane adhesive and on the steel use a cyanoacrylate adhesive.
The urethane will bond to the nylon, the cyanoacrylate will bond to the metal and then the 2 adhesives will bond to each other.
Use JB plastiweld for the nylon and Loctite superglue for the steel shaft.

Apply the Plastic Weld to the Nylon gear, wait a few minutes until it becomes tacky.
Apply Super Glue to the steel shaft.
Assemble them together, the cyanoacrylate will bond to the cured Plastiweld.
Hold for 30 seconds to ensure a good bond.
Leave it for a few hours.

Test the bond strength before reassembling into the gearbox.