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Project Tomcat, Gearbox Time – Part 3

The next step in this adventure was to start putting all the bits I had acquired together and make it look like a gearbox again.

The first part to be assembled was the new Quaife ATB diff. This needed the speedo gear and new bearings to be fitted.

First I needed to remove the speedo gear from the old TorSen diff. For some weird reason, typically, my gearbox didn’t have the normal, easy to remove, plastic speedo gear. No, it had a metal gear that was a shrink-fit on the diff.

First I used a puller to remove the bearing. I had to gently lever it up a little with a pair of big screwdrivers so I could get the puller under the bearing. It came off easily.

And then by gently putting force on the speedo gear with the puller, heating the ring with a heat gun, and tapping a chisel in behind it, the ring finally came free.

The Quaife then spent the night in the freezer and the next day the (thoroughly cleaned) speedo ring went into the oven at 200c for a few minutes.

The ring dropped straight onto the diff, no issues.

I took the opportunity to slip the new steel cage bearings on the diff too

Once it had all warmed up a bit, I fit the ring gear, and doused the whole lot in gear oil

The diff was ready to go, so it was time to work on the gear clusters.

The first was the input shaft. I didn’t take too many photos of this because it was very messy, but the whole shaft was stripped, the shaft and every gear was scrubbed clean in degreaser, and then each part was rinsed, oiled and refitted to the shaft with new bearings.

This is the completed input shaft.

The main shaft was slightly different because I was swapping everything over to a replacement shaft that didn’t have a damaged pinion gear.

And this is the replacement main shaft assembled, with new needle bearings in the gears, and new bearings on the top

Now that the gear clusters were ready to go, the gearbox casing was next on the list. This had been through some extensive cleaning to get rid of the metal shavings hiding in the crevices.

The new input shaft seal went in first.

Followed by the steel cage input shaft bearing

The mainshaft bearing was next. This needs the little plastic oil guide fitted first

And then the bearing driven in

Interestingly, even though this was a genuine MG Rover bearing, it’s slightly different to the old one in design. Appears more robust.

Before dropping the diff in place the new seals need to be fitted. First was the selector shaft seal. This was tapped in place with a hammer and the inside area slathered in rubber grease

The clutch fork seal needs to be fitted too

Now the diff can be lowered into the case and the bearing settled in place.

The selector shaft needed a quick tickle with some fine sandpaper, to remove the corrosion on the outboard end of the shaft. This isn’t important as this is miles away from the boot or seal, but I still wanted to clean it up and make it smooth

Before assembly, I cleaned the little fork on the end of the shaft. This is the glitter that came off that one part alone

The shaft, fork and detent ball/spring were all assembled. The magnet had also been refitted.

Almost looks a bit like a gearbox again

Now, after a clean, I could slip the selector forks over the gear clusters and lower them into the casing

Next, the reverse gear idler was refitted, along with its little selector. This selector holds the idler up out of the way until you select reverse, where it then slams it down into the gear just behind the selector in the photo.

And the main selector mechanism is bolted into place, making sure it locates correctly in the notch in the selector shaft

It’s a box of gears again!

Before progressing further, I put a handle through the selector shaft and checked that I could selector all 6 gears (including reverse). All gears selected fine, although you did kinda have to jump up, surprise and slam reverse in order for it to select. You are fighting a couple of detents to do so, so it makes sense.

The final steel cage bearing was fitted. Where this bearing seats in the top half of the casing there is another plastic oil guide and a series of shims that need to be refitted first.

Then a thin smear of sealant was run around the cleaned casing face, and the two halves joined again

The reverse gear idler bolt and reverse light switches were screwed into the relevant holes and the last thing to fit was the speedo drive. This was a real pig to remove, so it was no surprise that it didn’t go in completely smoothly.

But it went in, lined up, and was all good to go.

Until I spun the input shaft and heard a weird tinkling rattling sound. And then it stopped. Everything was working fine. Did I imagine something? Was it meant to do that?

After putting so much work into it, I had to investigate. I split the box again. It took about 3-4 Minutes from being assembled, to being completely stripped.

Nothing immediately obvious. I kept digging until I had removed everything from the casing except the diff. I started to remove it, and *tink* out dropped a large chunk of alloy. Shite.

I have an early speedo drive. It has squared-off corners. The laters ones had a nice long taper to their design. Do you know why they changed it? I suspect its because it could catch on the lower support for the speedo drive and break it off…

It should look like this example (as fitted with later, tapered, speedo drive)

Well damn.

Nothing for it but to crack on and hope it’s fine. I cant weld it back on, and I don’t have (and can’t get) a replacement casing. The main part of the housing the speedo drive goes through is quite solid, and it’s a tight fit, so hopefully it won’t go wandering.

Mostly back together again, with a smear of sealant on the face

Completely back together.

Always remember to trust your gut. If something doesn’t sound or feel right with a job like this, it’s always worth stripping it down and checking. I’d hate to have filled the box with aluminium shavings on the first drive, just because I didn’t want to strip the box again whilst it was on the bench.

Now I could fit the last remaining seals; the diff seals. I went with the early type as at the time I didn’t know what style my shafts/box had. Turns out the box had one of each. The early seals like these will work with both early/late shafts, but the late seals only work with late shafts.

A new boot was fitted to the selector shaft

And finally, the new clutch release bearing was fitted, to a well-greased fork/shaft

That’s the gearbox done. Ready to refit.

I’ll likely be looking to refit that sometime in the near future, but it should really be a two-person job.

Another part of the gearbox rebuild plan was to replace the bushes and U-Joint pins in the shifter. I bought a UJ rebuild kit and poly bush kit from eBay.

The U-Joint on mine was very sloppy, with lots of play internally. I used an angle grinder to cut the head off the pins that go through the joint, and then a punch to push them out.

The factory fitted bushes were a hard plastic, with a metal tube. The pin was a loose fit in the sleeve, the sleeve a loose fit in the bushes and the bushes loose in the housing.

The new solid “Nylatron” bushes pressed in by hand

The bushes in the UJ got the same treatment

The bushes in the UJ were worse. They were soft and very loose.

Everything was reassembled with new bolts.

One other little trick I did was to notch both sides of the area that goes onto the selector shaft in the gearbox. The theory is that when I tighten down the bolt through the shaft that it will clamp the UJ on to the shaft. This will remove slack from that area too.

Speaking of notching that part, always remember to wear proper protection when using a power tool. The cutting disk on the grinder got caught in the cut and came apart. Shame to lose a good disk before its time.

The last part of the shifter refurb was to remove the old rubber bushes and press in the new poly bushes.

The big round bush was so soft I pressed it out by hand just by using the handle of the hammer. Take note of the orientation of the bush before pressing it out, one side is dished.

I needed to use my press to press the new bush into place

And finally the rear bush. This was a pain to get on. In the end, I had to hammer the flare on the end of the tube down a bit so I could get the new bush on.

Don’t forget to transfer over the tubes

That’s the shifter done, ready to refit. Should make a big difference, between the sloppy UJ and the soft rubber bushes.

The final thing I did to round off a day of working on the Tomcat, was to look into why the valve covers were haemorrhaging oil like crazy. It was so bad I wondered if there even were gaskets under the covers…

I whipped the bolts out of the front cover and removed it. The gasket was old, hard, and completely flush with the cover.

It was obvious where the oil had been leaking past the seal; everywhere.

Look how nice and clean it is in there. I’m pleased to see that they obviously cleaned the head and cam boxes when they did the headgasket. A shame they used too much of the wrong sealant on the cam boxes though. It does appear they weren’t lying when they said ARP studs had been fitted, which is a bonus.

As it turns out, in the junk that was in the locked boot, there were some various gaskets. New and unused. One of them was a nice new rubber valve cover gasket. A perfect fit. I cleaned everything up and fit the cover with the new gasket.

The rear cover was worse. It was just pouring oil everywhere.

This one had the older metal style gasket, which was compressed completely flat on the sealing surface. No chance of sealing.

Once again, very obvious where the oil had been bypassing the gasket

And again, there was a new gasket, just sitting there, in the boot, ready to be fitted. Why on earth you would go to the effort of doing a headgasket, only to not use the new valve cover gaskets you have sitting there, I will never know. This is the level of stupidness I’m dealing with on various parts of this car that were touched by the PO.

A very thin smear of sealant went on both sides of the gasket, and the cover was refitted with the new gasket. Time will tell, when I can run the car again, if it stops the leaks, but I strongly suspect it will help.

I also replaced the seal on the oil filler cap, as this too was completely flat. I’m a big fan of changing these. They are easy and cheap to do, and you get to reuse the original cap.

Old seal, completely flat
New seal sits slightly proud of the surface

The final touch for the day was to give the top of the dipstick tube a quick tidy up and a coat of satin black. This was previously peeling and rusty.

Hopefully I will have a new heater pipe sorted shortly, and that will be a huge relief. The car won’t be back on the road for Christmas like I hoped, but should be back in the new year.

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Rob Murray
Rob Murray
2 years ago

Good write up, and good diligence for tracing where the rattle came from.
Let’s hope the speedo drive continues to work.