LT77 gearboxes and longevity of the earlier units

[KKson]

Well the SEAC gearbox is buggered with synchro crashing on 2nd, 3rd and 4th, unless I change gear really slowly, which does hamper performance somewhat....... I have got a spare D model LT77 gearbox that I was going to get rebuilt and then have a quick swap over. The 'box in the car however is a later and stronger F model. I've read that the later boxes had larger layshaft bearings.

Rather than having the car off the road for any period I am keen on the quick swap over, but does anyone know if the D type box can handle the almost 300bhp of the SEAC? Will the box just wear a bit quicker than a rebuilt F type unit. If I get a couple of years out of it, then that would be fine, and then I can swap back the rebuilt F type at that point. Does anyone have much experience regarding the differences and longevity of the various LT77 models?

Thanks.

[900T-R]

For some reason, ´93 Chim 430s all seem to have ´B´ suffix LT77s. All I can tell is that mine has 149.900 miles, according to the service history from before I got it it has been out of the car once before but only to reseal it as far as the paper trail goes, it has been coping with a dyno verified 300 hp since 2013 and is still sweet as a nut - so much so that I decided to retain it even though I literally have left no stone unturned in the restomod process (in its finishing stages now) otherwise...

Oil is clean, input shaft bearing has no play whatsoever that I can find. If in doubt I would replace, upgrade the input shaft bearing as a matter of course though - if it starts wearing away, the swarf will quickly kill the internal oil pump (plastic gears) or so they say

Edited by 900T-R on Thursday 25th March 10:44

[rev-erend]

Its not a quick job to remove the box, when my and a mate did it it was a day to remove and a day to put it back minimum.

So, I could call a gearbox expert like gearbox man and just ask about the different types and longevity. I suspect any old box
is a gamble. Could last 2 miles or 200,000.

Next question would be cost and turnaround time. If they can do it in say 2 weeks then for me its a no brainer.

https://www.gearboxman.co.uk/

[KKson]

rev-erend said:

Its not a quick job to remove the box, when my and a mate did it it was a day to remove and a day to put it back minimum.

So, I could call a gearbox expert like gearbox man and just ask about the different types and longevity. I suspect any old box
is a gamble. Could last 2 miles or 200,000.

Next question would be cost and turnaround time. If they can do it in say 2 weeks then for me its a no brainer.

Thanks for the reply. DG Sportscars can do it over 2 days, 1 day out, 1 day back in, with rebuilt box and new clutch. The issue is I don't want the car hanging around for potentially 2 weeks while the existing box is rebuilt, plus it would be a pain for DG to have the car sat about for that period.

The spare I have appears to be in good condition. I use a company called Geartech for gearbox and diff work. They reckon they can rebuild the spare for £400 plus VAT max assuming it's just synchro and bearings and no shaft wear. Plan was to get the spare rebuilt, then take the SEAC and rebuilt box over to DG to swap out over the 2 days.

[rev-erend]

That sounds like a good plan.

Don't forget to uprate the lever arm while it is out.

[adam quantrill]

It shouldn't take that long!

With no ramps I can do it in a day out and in. Although I would usually pace myself and do it over 2 days, as I'm not as sprightly as I used to be.

The secret is to move the engine forward just enough, split it off (like for doing the clutch) and then remove the bellhousing.

It comes out quite easily with no bellhousing on.

[KKson]

adam quantrill said:

It shouldn't take that long!

With no ramps I can do it in a day out and in. Although I would usually pace myself and do it over 2 days, as I'm not as sprightly as I used to be.

The secret is to move the engine forward just enough, split it off (like for doing the clutch) and then remove the bellhousing.

It comes out quite easily with no bellhousing on.

Thanks Adam. There's only about an inch in front of the water pump nose before it hits the cross member, so much tighter than in the 390 which had a good 4" of free space. I'm wondering if the water pump will need to come off to give enough room. Also in order to drop the box I'm assuming exhaust manifolds both off also.

Part of me thought I'd do it myself, but the more time I lie and work on the cold concrete floor these days, the more gyp I get with both shoulders.

Just a thought, but if the gearbox mounts are removed, gear knob disconnected and propshaft pulled back, anyone know how far the gearbox will pull backwards, to give access to the bellhousing bolts?

Cheers.

Edited by KKson on Monday 29th March 07:30

[adam quantrill]

Put carpet in your garage - luxury!

For the gearbox yes you disconnect the propshaft and gearstick and shove back as far as it will go. It's not enough to get the input shaft out of the clutch hole though I don't think, which you also need to ensure extraction. Also it doesn't go that far back with the bellhousing still on.

Won't the water pump clear the crossmember when the engine is raised a bit? Or else how do they get it in/out?