6 speed on a 420R

[Andy Mac]

 

 

[Geoff Brown]

IMO unusual for a six speed to be so noisy so early in its life. My six speed is mostly silent after eight years & 21000 miles running on humble Halfords 80/90 GL4 mineral.

Others here will probably say similar (John Vine excepted !) so as with all things Caterham your gear box lost the lottery of reliability.

Before leaping to conclusions it would be best to check that the box is situated correctly in the chassis. Any contact of the casing with the chassis could cause NVH that would be misconstrued as a box problem. 

Also check the viability of the rear box rubber mounting & that the whole assembly is correctly torqued up to the box & chassis. A spanner check of a 'grunt & a half' would suffice.

If it continues to be very noisy then it looks like a Winter project.

[David_Long]

One thing worth checking (as you are getting magnetic plug build up) is that the speedo drive blanking bung is not being ground away. In some boxes the bung contacts the redundant clog that drives the old speedometer drive and the bung needs to be left slightly out from being fully pushed home. I don't know if that would be the source of noise but it wouldn't help. 

[7 wonders of the world]

Since the noise is only in 6th and therefore not driving thro the gearbox its possible the source may be else where, and just more noticable.

Prop joints or LSD are more that capable of transmitting noise thro the chassis - since you are close to all 3 it can be difficult to distinguish if your not familiar with these cars.

Post 3 would be noticeable in all gears as the speedo drive is on the mainshaft, the cap should never be left partially home as these, in both 5 & 6 speed boxes, are not to pop out leading to a catastrophic loss of transmission oil and almost certain box failure very shortly afterwards.

Either lockwire the cap in place or if using a wheel speed sensor for the speedo blank it off correctly, this also alleviates the common oil weep for the speedo drive seal too.

[aerobod - near CYYC]

I would also look at the position of the gearbox on the rear mount, if the rubber has softened a bit or the bolts are loose, the gearbox may be touching the chassis, significantly increasing noise levels.

[ScottR400D]

The overrun in 6th on my 6 speed is and always has been noisier than in other gears and others on here have said the same. 

It's not horrifically so, doesn't scream at you or anything, just typical gear noises. I hardly think about it but dropping to 5th immediately reduces the noise. 

[Wrightpayne]

Mine is noisy in 6th when off throttle and I've put it down to a well worn Sierra CW&P supplied by SCP.

With fairly rigid mounted transmission components there is always a bit more noise than you'd expect, especially if you are used to a modern tintop.

[ScottR400D]

#7 Why would a worn CWP make a noise on overrun only in 6th? Certainly not the case as far as I'm concerned, it's always been like that with two different makes of diff and is only significant in 6th, nothing noticeable in 5th, a little bit in 4th. 

[Alan Reeves]

why would it be at all normal to make a noise in 6th ?

my last car was a 260 bhp 6 speed and it was quiet and did 18k miles when i sold it

surely there must be something wrong....

 

 

[Grant_7]

Same for me as #6.

[ScottR400D]

#9 There are lots of reasons Alan, none of which imply that something must be wrong. 

However, as the OP seems to think his car is undrivable, then there could well be something wrong but unless we get to hear it we won't know. 

In all honesty I find it impossible to believe anyone has a 'silent' 6 speed.  

 

[Andy Mac]

Maybe I am ultra critical and maybe 'they all do that sir' might be the case. I am happy for any local seveners to pop by and take it up the road to confirm or dismiss my concerns.

Before I commit to an expensive overhaul.

I'm in wokingham.

[John Vine]

Re #2:

Others here will probably say similar (John Vine excepted !)...

Well, it's true that my 6-speed did play up recently, to the extent that I had to lift the engine and take the box to Phil Stewart for some TLC, but the box had done almost 50K miles over 13 years.  Up until its hissy fit, it ran beautifully, with a silky change and very little noise.  (That's using CC's own-brand gear oil - aka Comma SX 75w-90 GL4 Semi Synthetic.)

JV

[SM25T]

Have you checked the oil level in gearbox and diff ? .... and then buy some good hearing protection.

[Alan Reeves]

im with JV, mine was not noisy neither was the Diff which is why i never understand why owners live with it? I did have a strange sonic vibration? noise with a replacement diff ( higher geared 3.14 ) but phil replaced it immediately and it was fine...drifting a bit away from the 6 speed issue but..

 

[SLR No.77]

Mine was noisy until I had the MTL drained out and fitted a more sensible, normal oil.

Stu.

[timb2117]

I know its a hornets nest but just rebuilt mine (with stellar help herein) and the gearbox guy swore by straight 30w engine oil...Previously I ran Redline Mtl, she's quiet, slick shifting and all better now, I'll probably change the box oil at least yearly...

[Andy Mac]

Wow, can the oil make that much a difference. I have just replaced the oil with MTL redline! Sounds like that may have been a mistake.

[ScottR400D]

I, like many others, have run MTL for some time with no ill effects.

I wouldn't comment on the use of engine oil, they have additives not found in gearbox oil and vice versa for however significant that all is? Over the years there have been many cars (and motorcycles) that have used engine oil in the box. It's usually best to follow a manufacturer's recommendation, at least as far as grade and type is concerned.

 

 

[SLR No.77]

Redline MTL definitely makes the gearbox noisier, in my mind that can only mean more wear as well. My car is a road car not a race car so normal GL4 gearbox oil is perfectly suitable. MTL does solve a slight drag going into 2nd gear when the engine is cold, but this only applies for the first few minutes after which on standard oil there's little difference. If the gearbox is rebuilt this can be corrected anyway, it's only a clearance issue.

Stu.

[timb2117]

Thanks Scott I would have expected a far bigger roasting :) and Stu that was one of the major reasons I tried MTL then took box out and rebuilt it, second was atrocious. Andy if you've put it in just see how it goes and decide then, as you say a second opinion cant hurt either.

[aerobod - near CYYC]

There are two other grades of MTL available from Redline that may be a better oil for the 6-speed, depending and how and where it is used. I've used MTL (75W80), MT85 (75W85) and MT90 (75W90), MT85 is the one that works best for me.