Jump to content

New t-box = air-raid siren 'scream'


Turbocharger
 Share

Recommended Posts

I've fitted a new 1.2 ratio t-box after replacing the seals and gaskets. I was worried that the engine wouldn't pull the gearing on 33" tyres, but it seems ok. The box is screaming loud enough to make pedestrians stop and point as I pass - the pitch rises quickly to a high 'C' at 45mph, but quickly hits 'top A' in low box. If I vary my speed just right, it sounds like a 1980s police car siren, and at constant speed the older residents are running to ring the church bells because ze Germans are coming.

When I fitted the box I (conned some friends with tea and biscuits and they) installed it with the cross-drilled gear that came with it, but it wouldn't bolt up to the autobox, it fouled on the output shaft. I swapped it for the non-crossdrilled gear that I had in the old box, and it bolted up sweetly.

I think the screaming sound is one of three things:

1: That nice Mr Ashcroft offers 28 and 26 tooth input gears; it didn't occur to me to count the teeth on the two gears I have - is it possible that I'm 2 teeth short on the non-drilled one I swapped in? (surely a horrific banging noise and a sudden lack of drive, rather than a meshing sound)

2: I've not set the backlash up properly and I need to read the manual to get the input gear endfloat correct

3: The teeth have 'worn in' with the crossdrilled gear, and I need to replace the autobox output shaft so I can use the crossdrilled gear (and set it up correctly)

Any views?

Link to comment
Share on other sites

What did the old input gear come out of? A 1.2 or 1.4? I wouldnt have thought it would work at all with the wrong gear, but guess you may be getting a constant misalignment of the gears causing all that noise.

Dont Ashcrofts also offer an extension to modify the output shaft of auto boxes to fit the LT230 box to fit the cross drilled gear? - may be confused on this one - see link below

http://www.ashcroft-transmissions.co.uk/index.php?act=viewProd&productId=47

Link to comment
Share on other sites

Thanks. The old input gear came out of (I believe) a 1.6 ratio box - it was nippy but a bit "revvy" at speed, and it dropped into t/c lockup just above 35mph on big tyres. The RR manuals quote t/c lockup at 55mph, and 1.2/1.6 * 55mph = 40mph so it seems to compute.

The Ashcroft output shaft (LR offer the same part too, but probably 3x the price!) is the right part, and is my suggestion under 3) - but I'm loathe to spend the money if I just need to correctly shim the gear that I have got, or add oil or something equally obvious and cheap.

Link to comment
Share on other sites

I think the number of teeth on input gear you are using are wrong for the box you are using. My first thing would be to remove the gear and count the teeth on both - you have to nearly remove the gear to shim it properly anyway. Then (or even before taking my advice!) i'd speak to Ashcroft and see of the part in the link is what you need.

Link to comment
Share on other sites

If you mesh a gear with a gear that does match there will be a bang,

as the teeth / pitch etc has to rotate 360 deg and a wrong number of toothed gear won't

My bet would be mismatched parts in terms of wear patterns, coupled with set up being wrong

it is almost never the case that "They wear in with time Sir" more you just can't

cope with the noise :lol:

Nige

Link to comment
Share on other sites

If you mesh a gear with a gear that does match there will be a bang,

as the teeth / pitch etc has to rotate 360 deg and a wrong number of toothed gear won't

Thats what i thought, but wouldnt a 1.6 input gear have a different number of teeth to a 1.2, but just possibly mesh ok with the 1.2 intermediate gear?

Link to comment
Share on other sites

Mo - does it really NEED oil? I wasn't going far...

Update: I've spoken to the nice people at Ashcroft and somehow they snake-charmed my credit card out of my wallet.

For completeness, the old t-box is 12DxxxxxxA, 1.6 ratio and had a non-crossdrilled gear. The new t-box is 28DxxxxxxE, 1.2 ratio and came with a crossdrilled gear. I fitted the non-drilled gear into the 1.2 ratio box and it came with a free banshee.

Ashcroft are now sending me FTC 5090 and I'll put the crossdrilled gear back in its rightful place. She did say that they might whine as the gears bed in, but it shouldn't make people point and stare. I guess the tooth pitch could match if the tooth count is different but the diameter is slightly smaller? Fingers crossed the box isn't full of swarf after 2 miles of testing, eh?

Edit: incidentally, my local LR dealer offered me the part, on 3-day order, but Ashcroft have supplied one ex-stock at half the price.

Link to comment
Share on other sites

... aaaand it's back on the road. Thanks to Ashcrofts for the bit (though it would have been helpful to put my name on the label, it got lost in Stores at work for a while :)) and I've reassembled it.

The gearing's a bit tall (2200rpm at 70mph) but that's just an excuse to squeeze more out of the VGT.

The input gear endfloat is circa 0.5mm - too much, though there's no nasty noises or excessive shunt. Does anyone know what the movement should be? The manual talks about 0.05mm "pre load", which is negative endfloat in my mind??

Link to comment
Share on other sites

Hi just an add on , the early transfer cases , had gears with 14deg pressure angle (very strong) this angle was changed on later boxes (not sure when but I think D onward) to 22deg to reduce noise. Check the gear width early gears are narrower than later gears, the tooth count is the same but they will not run together. Ian Ashcroft

Link to comment
Share on other sites

Hi just an add on , the early transfer cases , had gears with 14deg pressure angle (very strong) this angle was changed on later boxes (not sure when but I think D onward) to 22deg to reduce noise. Check the gear width early gears are narrower than later gears, the tooth count is the same but they will not run together. Ian Ashcroft

Is that whats detailed on your site here?:

http://www.ashcroft-transmissions.co.uk/index.php?act=viewProd&productId=8

Suffix A&B boxes accept the 'old' input gear type and C onwards accepts the new type.

Link to comment
Share on other sites

... aaaand it's back on the road. Thanks to Ashcrofts for the bit (though it would have been helpful to put my name on the label, it got lost in Stores at work for a while :)) and I've reassembled it.

Hey John, that happened to me too. Our storeman dropped some gears in my desk with a sarcastic 'these must be for you'.

I bought the ZF output shaft with longer splines to match the cross-drilled gear. Open wallet surgery indeed!

The input gear endfloat is circa 0.5mm - too much, though there's no nasty noises or excessive shunt. Does anyone know what the movement should be? The manual talks about 0.05mm "pre load", which is negative endfloat in my mind??

That is correct if you are using new bearings. They will bed in and the degree of pre-load will relax in time. This is quite a common engineering practice.

I was lucky enough to have a live demo by one of Ashcroft's men building an LT230 at Billing last year. He explained the preload issues, but most valuable of all - I could actually feel how tight the shaft was when set correctly. It should be checked with the intermediate shaft out so you can rotate it enough to get a good idea of resistance.

The shaft should not spin, rather have a slight tightness about it.

HTH

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...

Important Information

We use cookies to ensure you get the best experience. By using our website you agree to our Cookie Policy