CtrMint

Hi, Sometimes I end up learning the hard way! I've just been through an interesting practical lesson, which I thought I'd share just in case any novices like me make a similar simple mistake. During my diff replacement project, I replaced the handbrake cable, and to make life easier I removed the handbrake lever. At the same time, I decided to refit the lever using the front bolt hole closest to the lever handle, to make the lever sit lower in the tunnel. I originally built the car using the other front bolt hole and hence my lever sat higher. No major challenge. When I reseated the lever in the tunnel I noticed the small cable permanently installed on the lever was at risk of being trapped given the lower position. I believe that's the ground. I disconnected the cable and rerouted it. Unfortunately, I accidentally connected the cable to one of the two side terminals on the micro-switch, and not the small and correct terminal underneath. Silly me. I didn't check the hand brake light because there was no brake fluid in the system due the diff process, so the warning light was permanently on. Having put the tunnel cover, and passenger seat back in, tightened the handbrake and dropped the car off the stands, only now did I check the handbrake which of course didn't work. I had to put the car back on stands, slacken the handbrake, remove the passenger seat and then tunnel cover to just get to the handbrake micro-switch. There was a lot of head-scratching as I could only see the two micros-switch terminals on the side. I couldn't see the small terminal hidden underneath. I didn't appreciate it was even there. I went through all the logical diagnostics I could think. It was only by accident that I spotted the hidden terminal underneath when looking at a replacement part on the CC website parts image. From the image it was clear I'd wired the earth incorrectly. Talk about a silly mistake. Lesson learned.

I assumed it didn't, otherwise we'd be able to fill via the turret, though if I'm wrong hopefully some one will correct me.

Having just replaced mine as part of my diff replacement process, I can confirm they've changed to 42mm, they are also slightly deeper than the 41mm too.

I will be writing up the process for my blog,

Thanks all. Working out the fill wasn't too bad. It was the drain mainly. I know what you mean Chris, wouldn't have attempted if I didn't have the fill released.

thanks..... really appreciate the help.

im thinking its the 24mm...

I'm assuming one of these ?

Any chance some one could confirm the drain plug, is its the really large plug face down or the smaller to the side? Thanks

Hey All,, I've been doing plenty of background reading regarding a gearbox oil change on my 420R. There isn't a huge amount of info out there. I have however come across information on old forum posts inc Pistonheads which says the Mazda 5 speed doesn't have a drain plug, and also there's a bolt near the fill plug which must not be removed, and if removed the box needs a rebuild as it holds some internal parts. eek! Given the uncertainty and since the box doesn't really need an oil change, I'm starting to become slightly less enthusiast. I'm simply trying to be super proactive changing every serviceable item while undertaking my diff project. But as they say, 'if it aint broke', and knowing my luck I'll create a new problem for myself! If any of the regular experts could offer advice I'd appreciate it. I thought it would be as simple as drop oil via an obvious drain plug, then refill same amount, via obvious fill plug. The only challenge being the fill plug access, but that's usual Caterham life. thanks in advance Cheers Mark

I suspect the 420R will be going to Mr Dangerfield at Southcoast for a corner weight session once my new Penske 7500 are installed. I'll ask Paul to review the prop while its there, see if there's any issue from a professionals touch.. At the end of the day, my replacement diff process is entire precautionary. It's not like I had a significant deterioration in road manners, I wanted to service it now (5000miles) so that I didn't push the distance between a refresh. With regards the spacer. I'm going to fit this weekend, when I drop the oil from the gearbox. I'm not expecting a miracle. Out of interest does anyone know the size of the fill plug on the gearbox? I'll need to get some tube before hand. thanks

Thanks Chris, appreciate the input, sounds like a thumbs up. I haven't got that far into the reassembly. Diff is in, but the drive shafts and hubs aren't in yet. The hubs and bearings seem fine, no issues with play or smoothness etc. I've not really checked the drive shafts UJs. What did you find with yours? I noted from your blog that high speed driving caused vibration. While mine hasn't been on circuit, living on the IOM gives the opportunity to get north of 100mph (legally), and there's no vibration. I just have the usual slow speed maneuvering noise, and the on and off torque clonk, which I assume is just backlash.

Have done, awaiting a response, but in the meantime thought I'd seek feedback here.

no guys, I'm fitting the new titan from CC as planned. I'm then going have my original diff assessed to see how bad if any the damage is. if it's beyond repair, then I'll bin it, if it's serviceable then I'll service it. In the event it is beyond repair then I'll likely get the Tracsport when the new one fails or I repeat the same process. Of course, since I now have a usable 620R, who knows what might happen. I might loose interest in the 420. Anyways I'm getting mixed views on the spacer via Instagram, can anyone offer some input from experience?

It's a special edition don't you know, comes with an extra racing strip.

Afternoon All, I'm finally on the way to rebuilding my 420R rear end having had a nightmare with various diff carriers. I ended up fitting the carrier from my original diff. At the moment I've only got the Dedion and radius arms in along with the diff, so figure now is the time to fit the gearbox spacer. Before I do fit the spacer, I thought I'd seek feedback. How many people have given it a go? Does it really help reduce noise, especially when reversing etc? Anyone fitted it and found it makes no improvement. Please no Tracsport comments. Thanks

Yeah I've seen it. I've tried the technique with the diff out of the cradle but wasn't a fan, it didn't make the spacing easier.

Yeah I've seen it. I've tried the technique with the diff out of the cradle but wasn't a fan, it didn't make the spacing easier.

I've made a pdf template if anyone else wants to do a similar sort of calculation. Diff Diagram blank.pdf

finally worked out how to calculate the spacing based on the center line of the diff and chassis. I appreciate I can't account for an offset in the gearbox, or even chassis, but I think that's a good compromise. Measurements shown are from original carrier.

Thanks all. Comments have been really helpful. I keep swinging from viewing the topic as me being overly fussy/paranoid to thinking it doesn't matter that much. I guess ultimately I want to repeat the install and reduce any undue wear on the Titan, possibly noise, but that's wishful thinking. There's also the satisfaction of doing the job precisely and correct. I'm pretty much happy on how to approach the top bolt. I'm going make up a jig with an adjustable combination square and measure the diff using that to the box section. That just leaves me with the front lower mounts. I appreciate from the comments the prop might not be straight, but I'd like to try and get the diff as straight as possible. I'm going to try and find the center line through the cage and onto the prop, face plate. I'll use the center of the top bolt, taking a 90dgree square down the center etc. I'll then mark the plate at 12 noon and 6pm. I figure if I rotate the marks to 3pm and 9pm and measure to the same spot on either lower arm I'll identify the offset in the cage with respect to the plate. Assuming the mounts in the chassis are central I can then space according to the measurement offset in each arm with reference to the prop face plate. I will of course measure the thickness of the mounting on the lower arm, just in case there's a variance there. I guess some will be thinking, but why... I know, but I just want to get it bang on.

I don't suppose anyone has any guidance on this, thanks

I've end up swapping the carrier over, the spacing on the bottom mounts was just wrong, I'm sure they don't look parallel too. There's about a 3mm difference between the original carrier lower bolt spacing. I'm really starting to second guess the install process and where the reference point is when making sure the carrier is equidistant. Looking at the older build manual it says' So the diff low bolt mounts should be centralized against the ARB mount? I have to say I've not done that previously, I always aligned it within the chassis mount, as per the Ikea manual illustration. But regardless, if there is such a variance in the carriers as shown by the two I have, where is the reference point? Or am I over thinking things here? Surely the only accuracy comes from the diff itself, shouldn't I be measuring from the drive flange, basically the casing?

Yeah, I appreciate that, but wondered if such a gap was normal. My old carrier was certainly closer.

Hi, I've been working on getting the new diff into the 420R this afternoon, but I can't get away from a feeling something isn't right with the carrier. I've placed the diff into the car using a rod through the top mount and then installed the lower bolts with just enough of the bolt through the chassis and into the carrier. Doing this allows me to test fit the positioning of the diff carrier and measure the spacing etc. What's troubling me is the spacing on the lower bolts. If I place the carrier in the middle at the bottom I'm looking at 4mm spacing on both sides. That seems pretty large too me. Certainly not the spacing I had on my original diff carrier. Looking at the structure of the carrier I can't see that the lower arms could be bent in during shipping etc. Nevertheless I'm left wondering why the gap is so large this time around. Also If I measure the width of the carriers at the bottom mount, there's a different of about 3mm. Any thoughts, should I just space it and carry on? Thanks