Gearbox dead - where from here ?

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I've had my 4.0L engine upgraded to 5.0L using the V8D package which has been running very nicely, but it looks like my gearbox has let go. It's a V8S so has the same LT77 as the early Chimearas and Griffiths ( I think). It makes a horrible grinding noise in all gears, related to road speed. I assume the extra torque has been too much for it.

What are my options from here ? Should a rebuilt standard LT77 be OK or should I be upgrading something in the gearbox or even switching to another gearbox ? Any suggestions who could do this ?

Thanks

Note - I've posted in general rather than S Series as I believe some of the options may come from the Chim/Griff

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Thanks. I was planning to do a lot more track days next year so it will be in for quite a bit of spanking. In fact it was a bit of spankage this year that caused the issues with this gearbox. Is there a weak point in the box that could be improved while it is being refurbished ? Any recommendations for specialists ?

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QBee said:

+1 - the LT77 was fitted to the early 430 Chims, which produce not far short of 500 power/torque, so should be well capable of handling the power of your V8D lump.

Nice, aren't they? The V8D lump, I mean.

It was a real pain getting it running with the megasquirt but very nice now. Checking the dyno plot, it says 314/328 peak bhp/torque so that's well below those 430 Chims you mention although 500bhp sounds a lot from a 4.3L, no ?

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TvrJohn said:

you need to contact Reid Racing ? supplies the TVR Challenge teams

Is that Readman Racing / Grantura Engineering ? Their website refers to BorgWarner T55 gearboxes but not LT77. Is the LT77 used in Challenge cars ?

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From this thread : http://www.pistonheads.com/gassing/topic.asp?t=125...

"The LT 77 was last used in 1994 and has a Suffix H - this is a bullet proof box capable of running 300 Hp and 280 Ft Lbs. It has widened gears, larger diameter layshaft and has a dual syncro on 1st & 2nd. The oil pump was also increased in width. The H was also known as the LT77S.

Go search for the lettering of at least G but preferably H on the box."

My engine exceeds this spec ??

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peteA said:

gifdy said:

It was a real pain getting it running with the megasquirt but very nice now. Checking the dyno plot, it says 314/328 peak bhp/torque so that's well below those 430 Chims you mention although 500bhp sounds a lot from a 4.3L, no ?

I think he meant Griff / Chim 500 ie 5 the litre V8 engine - TVR 'stated' 340 Bhp from memory so yours sound healthy!

Oops Makes sense

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brett84 said:

I'm looking to get mine done next year and have been recommended these guys
http://www.ashcroft-transmissions.co.uk

Thanks - from their website they look like they know what they're talking about. I'll give them a ring

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phillpot said:

gifdy said:

It makes a horrible grinding noise in all gears

I'm guessing 5th is an overdrive gear in the LT77 so "normally" things should be a bit quieter in 4th because the drive goes straight through, lot less load on the bearings/gears?

Have you tried draining the oil to see if it looks "very metallic" or maybe a tooth or two will fall out (some gearbox's have a built in magnet to hold metal particles)?

I'll have a look at the oil but pretty sure it's the box. Ashcroft say the LT77 isn't strong enough for this torque level and recommend the R380 instead. I'll also swap the oil for this difflock stuff to see if it will quiten it while I work out what to do.

Thanks for advice so far.

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phillpot said:

gifdy said:

I'll have a look at the oil but pretty sure it's the box.

Not suggesting an oil change will cure anything, sounds like it's way past that but depending what comes out with the oil, bits of teeth, bearing, synchro ring etc. might give you an idea whats gone wrong?

Yep, will report back. Job for next week, I' m off to the pub to drown my sorrows.

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mk1fan said:

Get it fixed and get on the S-Club Tour next year. Be nice to see a 300+bhp S harassing the 'other' models.

I read the reports with envy ! Sounds a good laugh, I need advice on how to get a pass though. Don't know how you chaps swing it. Track days are definitely on the cards but the driver may be a weaker point than the gearbox.

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Just changed the oil and filtered the old stuff through a cloth. No sign of metal, nor on the drain plug. I was expecting to see half my gearbox in there. Very odd.





I've put the difflock fully synth in so we'll see if there is any change.

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TV8 said:

Hi OP , any news please? I wondered if the Difflock made any difference?

Unfortunately not. Brought it to work today - still sounds awful.

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macdeb said:

Gifdy, YHM

thanks - responded.