An idiot's guide to swapping LSDs in a Sierra final drive.

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DJ.
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An idiot's guide to swapping LSDs in a Sierra final drive.

Postby DJ. » Sun Feb 07, 2021 10:50 am

Soon after I built my Caterham in 2011 I decided to install an LSD. At the time I was advised by an expert that I should go for a Titan plate diff rather than a Quaiffe ATB and I have enjoyed 35,000 miles, a few doughnuts and some hooning at North Weald since.

Last summer, a very long thread started on Lotus Seven Club forum. A member had a Titan diff fail at less than 8,000 miles destroying his crown wheel and pinion, as the thread developed, it turned out quite a few people had problems, but to cut a long story short, we should all check the preload and service the diff if it dropped below 20 ft/lb. It also turns out that Titan recommend rebuilds every 10,000 miles, something I had not been told when fitting mine :?

My preload was only 13 ft/lb, but as it was mid summer, I decided to chance my luck and wait until winter. Rebuild costs are apparently £250 + parts, £300 minimum and an awful lot more if the plates are heavily worn.

Coincidentally, Matt Haines had just swapped his open diff for a Quaiffe ATB, and told me it was only £480 delivered from burton power. With fitting, this was going to be over £700, but Matt told me I could fit it myself with his help as long as the pinion didn’t need to be disturbed. That sounded like fun, and considering it wouldn’t need regular rebuilds seemed a better option than having the Titan serviced.

Of course, by the time I had the diff out and Matt had some spare time, we were into another lockdown :cry:

Matt agreed to give me remote assistance, and a downloaded guide, so I decided to go it alone. In the next part, you will see this decision might not have ended well.

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Re: An idiot's guide to swapping LSDs in a Sierra final drive.

Postby DJ. » Sun Feb 07, 2021 11:05 am

I had the diff casing on my work bench in my tiny 8’ x 4’ shed, and started trying to remove the rear cover bolts. These were very very tight, and rather unhelpfully had torx heads made of cheese :roll:

I managed to loosen three with a breaker bar, but was struggling to hold the diff, so I put the diff pinion down into my large vise. It wasn’t very stable so I had my arm around it as I pulled on the breaker bar. Next thing I knew, the torx bit had shattered, and I’d lost balance, as I tried to figure out what had happened, I saw something move out of the corner of my eye………..it was the diff toppling towards me! :o I leaped backwards, and the diff plunged towards the wooden floor of the shed. Thankfully, I’d got my legs out of the way and the floor broke the fall of the diff. The diff was undamaged (fortunately it hadn’t landed on the pinion), but I now have a broken plank in the foor of my shed. I do at least still have functioning feet :D

At this point, I decided to spend a couple of days making a very heavy metal base (5/8” steel plate) to secure the diff in two positions:

118_quaiffe_installation_01.jpg


118_quaiffe_installation_02.jpg


I was still back at square one but a lot safer!

I finally got all the bolts out using a long stilson and finally welding nuts to the last few.

118_quaiffe_installation_04.jpg


Back plate off finally!

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DJ.
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Re: An idiot's guide to swapping LSDs in a Sierra final drive.

Postby DJ. » Sun Feb 07, 2021 11:36 am

With the crown wheel exposed, it was time to take some measurements:

118_quaiffe_installation_03.jpg


The run out was only 0.032mm so that was within spec, but the backlash was 0.12mm rather than 0.01 so no wonder it was noisy. I also found the oil seals were both 9.4mm in from the edge of the bearing carriers, there is a Ford tool for setting these, so I realised I would have to make something to ensure they were installed in the same place. I also measeured the positions of the bearing carriers as a rough guide to setting it up later.

Removing the oil seals wasn’t too bad:
118_quaiffe_installation_05.jpg


The bearing carriers were very tight, and I was glad I had made a ¼” steel tool to do this:
118_quaiffe_installation_21.jpg


This tool was very useful when setting the diff up too, so time well spent.

Another tool I needed was made from an old bearing shell. I ground 2mm off the diameter so it was a loose fit inside the bearing carrier and engaged on the small lip of the crown wheel bearing outer shell that needed to be pulled out. Thinking ahead, I cut this in half and ground it until it was just over 9.4mm thick so I could use it to seat the oil seals.

118_quaiffe_installation_22.jpg


I am wary of pulling steel bearings out of alloy housings cold, so after removing the O rings, I heated the bearing carriers to 140C in the family oven (complaints about the smell ensued) and used this set up to pull out the bearing:

118_quaiffe_installation_08.jpg


As the alloy was still hot, it was easy to drift in the new shells using the first one removed

118_quaiffe_installation_09.jpg

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Re: An idiot's guide to swapping LSDs in a Sierra final drive.

Postby DJ. » Sun Feb 07, 2021 12:00 pm

By the way, if anyone reading this wants to do the same, I am happy to lend these tools out to members as long as they are returned

Removing the crown wheel from the Titan wasn’t as bad as I had feared after my experience with the rear casing bolts. The guide suggested removing several bolts and loosening the others 5 turns before hitting the bolt heads and this worked well in the vise, I had plenty of newspaper to stop the crown wheel teeth being damaged if it dropped.

It was back to the oven to heat the crown wheel to 100C before bolting it to the Quaiffe unit:

118_quaiffe_installation_10.jpg


I must have done a better job cleaning the oil off, as I didn’t get complaints this time. The guide recommends pulling it on with old bolts and then using new bolts. Here it is still hot with old bolts:

118_quaiffe_installation_11.jpg


Not everyone fits new bolts but for £20, it seemed a safer option, so I did buy 10 new bolts from Burton and installed them with some locktite when it was cold. 83Nm is pretty tight, but the Quaiffe unit has some handy flats to hold it with a large adjustable spanner.

118_quaiffe_installation_13.jpg


Knocking new bearings onto the unit was straight forward, but care has to be taken that the bearings are not mixed.

118_quaiffe_installation_14.jpg


And here the unit is back in the casing with the bearing carriers installed:

118_quaiffe_installation_16.jpg

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Re: An idiot's guide to swapping LSDs in a Sierra final drive.

Postby DJ. » Sun Feb 07, 2021 12:15 pm

If anyone is still reading……..

I always knew the hardest part would be setting the backlash, and I wasn’t wrong. As Matt had said, the crucial thing is the pinion set up hadn’t changed. To set the pinion it is necessary to have some special tools, and I wouldn’t want to try and set the whole diff up from scratch. I only had to worry about moving the crown wheel left and right.

I soon got the knack of adjusting the backlash, but when I preloaded the bearings, it threw it out and the crown wheel was very hard to turn. I knew I must be doing something wrong, so called on my guru Matt. It turns out I had misread the guide and I was adding preload to both sides, not just the bearing on the right. Next day, I had another go and after an hour or so, I was happy that the backlash was reasonably consistent. Ideally it should be 0.01mm all around, but the best I could achieve was between 0.01mm and 0.02mm with slight variations in different places. It says differences in backlash should not exceed 0.03mm, and I fet it safer to make sure it didn’t get tighter than 0.01mm in any place.

Finally replacing the bearing carrier locking tabs was a relief. I replaced the back plate complete with new hex head bolts that I had bought in case I have to open it again:

118_quaiffe_installation_19.jpg


You will notice, I have been too lazy to clean the outside at all :oops: . Finally, I used my special tool as a drift to fit the oil seals:

118_quaiffe_installation_20.jpg


Fingers crossed I have done everything correctly and it works!

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Jasonmpk
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Re: An idiot's guide to swapping LSDs in a Sierra final drive.

Postby Jasonmpk » Sun Feb 07, 2021 12:35 pm

Great write up. Diffs are always special black magic boxes that very few people dare to explore. As you have said, experience and the right tools are key to setting them up, I used a specialist as I am no diff expert and i didn't have the tools for my English std one.

Great read though and well done.

Jason

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locost220
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Re: An idiot's guide to swapping LSDs in a Sierra final drive.

Postby locost220 » Sun Feb 07, 2021 1:50 pm

Great read Duncan, well done.
Locost book chassis, Undergoing testing post rebuild :D :?
Robin Hood 2B, keeping me sane
Sylva Leader, stuck to the trailer

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DJ.
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Re: An idiot's guide to swapping LSDs in a Sierra final drive.

Postby DJ. » Sun Feb 07, 2021 1:53 pm

locost220 wrote:Great read Duncan, well done.


Thanks Richard, I thought it about time I contributed to the forum, you and Jason have been doing all the hard work :)

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Re: An idiot's guide to swapping LSDs in a Sierra final drive.

Postby nelmo » Sun Feb 07, 2021 6:44 pm

Great write-up Duncan... although I must be a special type of idiot because I still didn't understand it all :D :oops:

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Re: An idiot's guide to swapping LSDs in a Sierra final drive.

Postby DJ. » Sun Feb 07, 2021 6:49 pm

nelmo wrote:Great write-up Duncan... although I must be a special type of idiot because I still didn't understand it all :D :oops:


Well, I will reserve judgement on whether I do until I drive the car :lol:


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