Titan LSD Rebuild
Last time I was on track, I felt I was struggling with traction when accelerating out of corners. Curiously, much of that grip seemed to return when I ignored my instincts and simply floored the throttle.
My son didn't seem nearly as bothered by the lack of grip. I suppose his instincts are different. Or perhaps just less developed, as I prefer to call it.
Back home, I checked the differential preload. It was zero! With the rear wheels off the ground, I could turn one wheel by hand without the other wheel moving at all.
After watching this video with Ollie from Road and Race Transmission, I decided it was long overdue to rebuild my Titan LSD.
Removing the differential
Getting the differential out of a Caterham isn't particularly complicated in theory. In practice, however, it's quite a challenge.
Remove the boot floor honeycomb panel, transmission tunnel top panel, rear wheels, etc.
Remove the rear brake calipers and support them with cable ties. Disconnect the speedometer sensor, undo the lower damper mounts, toe links and upright mounting bolts. The complete driveshaft and hub assemblies can now be carefully pulled away.
Disconnect the propshaft from the differential by removing the four socket-head bolts. Loosen all four before removing any of them. I used a crowbar against the chassis to prevent the shaft from rotating, an Allen key with a pipe extension to break the bolts loose, and then a short section of Allen key with an 8 mm ratchet to finish the job.
Make a note of the spacers and washers used at each mounting point. Support the differential with a rope tied to the roll bar.
Start with the long upper mounting bolt. This is the difficult part! I used a long 3/8" socket extension and a hammer to drive it out. Whatever you do, don't use a threaded rod as a drift. It will get stuck. Guess how I know. The smooth socket extension happened to be almost exactly the right diameter and could easily be pulled back out.
Remove the two lower mounting bolts.
Expect some oil to escape. Place an absorbent mat underneath and have a container ready.
Carefully lower the differential to the floor. It comes out rear-end first and needs to be rolled (like an airplane banking into a turn) approximately 40 degrees clockwise. Clearance is extremely tight. Removing the breather fitting gives you a few precious millimetres. Be particularly careful of the brake line inside the transmission tunnel. Again, guess how I know.
Disassembly
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| Company23 tool. |
This differential overhaul guide is very helpful.
The threaded bearing carriers can theoretically be removed without special tools, but doing so is difficult and risks damaging them.
Company23 sells a dedicated 7"/7.5" IRS Differential Side Bearing and Pinion Flange Tool.
Instead, I designed and 3D-printed my own tool, which worked perfectly. Another option I've seen suggested is modifying a 100 mm hole saw with an angle grinder.
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| 3D-printed tool. |
Disassembling the Titan LSD itself is straightforward. Once the housing is opened, the internal components are essentially loose. If something doesn't come apart easily, it's probably an alignment issue rather than something that needs force.
Rebuilding the LSD
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| Note ramp cup orientation |
This time I opted for the sintered friction plates, hoping for a longer service life.
Plate assembly order
The components are assembled in the following order, from one end of the differential to the other (right to left in my photos):
Small thrust washer
Small oil washer, grooves facing towards you
Belleville spring, smaller-diameter side facing the housing
Preload spacer shim
Steel plate
Friction plate
Steel plate
Friction plate
Left-hand ramp cup (orientation determines the ramp angles; I use 30/90)
Gears
Right-hand ramp cup
Friction plate
Steel plate
Friction plate
Steel plate
Preload spacer shim
Belleville spring, smaller-diameter side facing the cover
Small oil washer, grooves facing towards the centre
Small thrust washer
Lubricate the plates generously with the recommended differential oil during assembly.
Setting the preload
Preload is adjusted using shims of different thicknesses.
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| Checking pre-load with 3D-printed tools. |
The rebuild kit included pairs of shims in the following thicknesses: 0.3, 0.4, 0.5, 0.6, 0.8 and 1.0 mm.
Titan specifies:
"Shim equally at both ends ±0.20"
I aimed for a preload torque of 54 Nm and, somewhat surprisingly, achieved it on the first attempt using a 0.3 mm shim, just as originally fitted.
To measure the preload, I designed and 3D-printed another tool, allowing me to use a torque wrench.
Before closing the LSD housing, thoroughly remove any remains of the old threadlocker.
Do not reuse the old bolts.
Apply Loctite 2701 and tighten the new bolts to 32 Nm, according to the Titan instruction leaflet supplied with my differential.
Refitting the LSD into the differential casing
Grease the bearing carrier threads and O-rings before installation. This makes adjusting the backlash considerably easier, as the carriers need to turn smoothly.
Follow the Ford workshop manual for the complete procedure.
Setting the backlash
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| Backlash adjustment |
In short:
Install the differential and adjust the bearing carriers until the backlash is approximately 0.01 mm, with the carriers hand-tight.
Tighten the right-hand bearing carrier by four castellations.
The final backlash should then be approximately 0.12 mm.
I found it useful to lock the driveshaft flange by using its bolts against a spacer block. This prevents unwanted rotation while taking measurements.
This video demonstrates the backlash adjustment procedure.
Once adjusted, lock the bearing carriers and tighten the locking bolts to 20 Nm.
Apply sealant to the differential cover and tighten the cover bolts to 53 Nm.
An unexpected detour: Damaged brake line
At some point during removal or refitting, I managed to damage the rear brake line running through the transmission tunnel.
Rather than simply replacing the damaged section with another rigid pipe, I decided to install a braided stainless-steel brake hose.
This also allowed me to relocate the T-piece to a less vulnerable position, away from the differential and other moving components.
Unfortunately, accessing the brake line required removing the aluminium panel underneath the transmission tunnel.
The panel was secured by approximately 30 pop rivets.
Removing them turned out to be fairly straightforward once I figured out the technique. I drilled off the rivet heads, then used a 3 mm nail (an ordinary woodworking nail!) and a hammer to punch the remaining rivet bodies into the chassis tubes.
The panel was later reattached using 4 mm aluminium blind rivets.
I also designed and 3D-printed a bracket for the brake-line T-piece. The bracket secures both the T-piece and the flexible hose, keeping everything safely away from the rotating components.
Refitting the differential into the car
Refitting is essentially the reverse of removal, although a few lessons learned made the process somewhat easier.
Make the mounting spacers fit properly. Before reinstalling the differential, I used a file and drill to enlarge the spacer bores by a few hundredths of a millimetre. They had previously been an extremely tight fit on the mounting bolt, which I suspect contributed significantly to the difficulty of removing it. There is no obvious reason for these spacers to fit so tightly. Hopefully, the differential will be easier to remove next time. I also applied a little grease to the bolt.
Manoeuvre the differential into position. It goes back in the same way it came out, nose first, rolled approximately 40 degrees clockwise. This is not easy. Be creative! A jack and some rope are very useful here.
Install the two lower bolts first. I found it easiest to fit them without the spacers initially. Having a helper makes a big difference. I positioned the differential from underneath while my helper inserted the bolts.
Install the long upper bolt. Again, a helper is almost essential. I aligned the differential from above through the boot opening while the bolt was inserted.
Fit the spacers and washers. Remove one bolt at a time and insert the appropriate spacers. Use washers to eliminate as much lateral clearance as possible, but don't force them in or compress the rubber bushes sideways. Tighten the mounting bolts to 54 Nm.
Reconnect the propshaft to the pinion flange. Apply threadlocker and tighten the bolts to 58 Nm. No washers. I carefully used a ring spanner between the flange and differential casing to prevent rotation while tightening.
Reinstall the driveshafts and suspension components. Remember to reconnect the speedometer sensor before refitting the brake calipers.
Fill with differential oil. Fill until oil begins to flow from the filler opening. The capacity was approximately 1.5 litres in my case. I filled mine through the breather opening using a funnel and hose. It worked, but took a surprisingly long time.
Check carefully for oil leaks.
Bleed the rear brakes.
Refit the boot floor and remaining panels.
Running in the rebuilt LSD
According to Titan, the rebuilt LSD should be bedded in with normal driving, avoiding situations where the differential locks up.
Which, in a Caterham, is easier said than done!
