[tompinney]

Its been a while since I've done a gearbox rebuild and this is a different kind of rebuild to get back into it again so thought I would share it here. This rebuild is actually for Martin Hodge. This is a rebuild for a gearbox destined to go on his old yellow Dunlop Cup racer. I rebuilt the gearbox already on that car several years ago; I can't remember what it actually was but he felt the ratios were too long so he asked me to rebuild a Ti box he'd sourced (it had suffered failed diff bearings) and install a Quaife differential at the same time.

He dropped off the donor C6BSUT Ti gearbox a good many months ago, having removed and sold the Type-B diff in it. Unfortunately in doing this he also sold the crownwheel too, which we would need for the Quaife :facepalm: First problem then was to source a replacement crownwheel. Upon initial stripdown of the box I also discovered that the crownwheel pinion teeth were badly damaged so in fact we would need an entire CWP set.


Ti boxes are few and far between these days, let alone parts for them so after doing some digging I determined that the ZS180 uses the same CWP set, albeit with a different gearset (I think) but that doesn't matter since we'd only need the CWP set. Martin obtained a spare ZS180 box and today we set about trial assembling the Ti box with the Quaife and replacement parts to make sure everything fit and we didn't need any additional donor parts.

Opening up the Ti box.


Stripping down the ZS180 gearbox to remove the countershaft (for the pinion) and diff (for the crownwheel) while Martin cleans the Ti box case in the background.


Crownwheel removed from the ZS180 open diff (on the right) ready to be fitted to the Quaife (on the left)


Crownwheel fitted to to the Quaife. I still need to fit the speedo drive gear and replace the bearings.


Countershaft from the Ti box all stripped down to remove the damaged crownwheel pinion gear which is actually part of the shaft, so the whole shaft needs to be replaced.


Replacement countershaft and pinion gear from the ZS180 (bottom) alongside the chipped Ti shaft. The gears, needle bearings, idler gears and syncros from the Ti box will all be transferred onto the replacement countershaft.


While reassembling the box to check everything fit as expected I noted this damage in the bell housing. The original crownwheel has clearly made contact with the casing when its bearings failed. This won't cause any problems post rebuild but I suspect even if Martin hadn't sold sold the original Type-B diff with the crownwheel it probably wouldn't have been serviceable anyway.


Gearbox reassembled with all the new parts and Quaife to test that everything meshed correctly. We also chose to fit a new gearbox case because there was some additional damage which I wasn't happy with and given we had a better one to hand (from the donor ZS180 box) we chose to use that.


Now that we have a complete undamaged gearbox the next task will be to thoroughly clean the internals of the gearset and with a fresh set of steel cage bearing fitted we can check the input shaft and differential end float measurements and adjust the shims if required.

[JOHNDQ]

Hope you're having better luck getting the correct size shims than I have over last year

[tompinney]

It's been a while since I've been able to make much significant progress on the box, mainly due to the fact that the weather has been either too cold or wet for me to want to consider working outside and I'd been waiting for the RCOC NEC floor tiles to be removed from my garage so I could free up space to work indoors.

First job was to remove the countershaft roller bearing from the bellhousing. Normally you just need to turn the bellhousing upside down and hit the back of the case with boiling water two or three times and the bearing just drops out. We'd tried this previously but it hadn't worked. I hit it five or six time further times with boiling water a few weeks later and still no joy. I tried a bearing puller but the bearing wasn't moving and I was afraid of cracking the case. I then end up flipping the case and using a slide hammer and eventually it started to go, but not without a fight. I've never known one like it and once it was out, I couldn't see any reason why it put up such a fight. Note all the greasy, gritty residue underneath where the bearing had been, caused by the failure of the box.


Next job was to thoroughly clean the inside of the box ready to reassemble. The bellhousing after.


Here is inside the case before, more of the greasy residue and grit from the failure.


Case all sanitary ready for the new bearings


Next onto the input shaft dissaembly.


Here you can see the reason why it is necessary to strip it down fully, all the gritty paste created by the failed bearings gums up the oil feeds to the moving part, as you can see by the hole on the right and so it needs to be thoroughly cleaned before it can be reassembled.


This is just some of the debris I flushed out of the input shaft oil gallery. The box was spotlessly clean before I started flushing the input shaft, so everyhitng you see here came out of that one shaft. Sparkly!

Luckily I won't have such a mess to deal with on the countershaft because we've had to replace that for new due to the chipped CWP.

All clean ready for me to do the first assembly to measure the input shaft endfloat to check if we have the correct shims or need to order extras.

[tompinney]

Despite my best efforts last weekend I wasn't convincned the input shaft oil gallery was clear of all the greasy debris. I got hold of a small bottle brush and soaked it in petrol and scrubbed the gallery and load more came out with successive flushes.

With the oil gallery now properly clear the components of the input shaft were lubed and reassembled. New bearings and seals installed in the bellhousing too.


Case refitted with just the input shaft installed and a few bolts used to hold it all together ready for measuring the end thrust on the input shaft.


Time to break out the precision tools...


In the process of taking measurements.


With the measurements taken, its time to do the maths.


Unfortunately with all the bits we've changed on the box, the end thrust is out by nearly 0.1mm if I were to use the shims I took out of the box, so Martin is sourcing a single replacement shim to ensure we're all within specification before I complete the rebuild next weekend, hopefully!

[tompinney]

Turns out none of the turbo shims are available from either Xpart or Honda any longer, so Martin managed to obtain the required 0.95mm shim from one of the other racer's spares. It turned up on Thursday and was duly fitted into the gearbox case.


I then stripped down the countershaft again to clean the parts kept from the original shaft and to replace the bearings. I'm glad I did this because when Martin and I stripped the ZS180 box for the donor shaft bback in the Autumn I never noticed that the thrust washer that sits above the pinion gear was trashed. Martin dropped the donor box back off with me again today so I could raid it for a replacement thrust washer.


Countershaft all stripped down and cleaned ready for reassembly.


The Quiafe all cleaned up and the crownwheel bolts torqued down to 110Nm.


I then went to fit the speedo drive gear to the diff only to find the Quaife doesn't have the notch in its body to accommodate the key on back of the speedo drive gear. Not sure if this is an anomaly of this Quaife or standard.


To resolve this issue I took the dremel to the speedo drive gear and removed the key from the underside of it and used some RTV sealant to secure it to the diff, hopefully it, along with the pressure from the bearing will hold it in place and prevent it freewheeling. Fortunately since this is a racer it's no major issue if the speedo doesn't work.


A pair of C3 spec 6208 bearings installed and the diff is ready to go into the gearbox.


The speedo driven gear needed to be stripped down and flushed out, since it too was full of greasy sparkly residue.


And the internals at last back together again


The only thing I couldn't complete on it was to install the differential end thrust circlip. The manual requires a 0.1mm +/- 0.05mm end thrust clearance, but the Qauife appears to be about 1mm wider than the standard Torsen LSD so the old circlip is too big to fit in the groove and Xpart doesn't list one thin enough to fit either, so Martin will be sourcing an alternative from somewhere. Thankfully this can be installed through the nearside drive shaft hole with the box fully assembled, so the box has now been collected by Martin and my work is done.

[GTiJohn]

That's some serious work there!

There's a detailed description of this process in the first ever Viking magazine, available online to club members

[tompinney]

Turns out the Quaife isn't actually wider than a normal diff. Seems the previous owner opened it up for some reason and hadn't torqued it back down fully after. When we tightened it up everything was as expected again and the shimming problem resolved itself.
Given we couldn't ascertain why it had been opened in the first place Martin wisely send it back to Quaife for a service and they discovered a number of broken springs within it which were replaced FOC as part of the service. It's now back in the box and all bolted up ready to go on the racer.