Gm400 gearbox
#1
Gm400 gearbox
can anyone tell me what the v12 gearbox is like in general for reliability? One or two threads lately about issues and I wondered if they are problematic? Is it worth having mine overhauled while the engine is out of the car? What sort of cost would be involved? Many thanks as always for your help.
#2
The TH400 is probably one of the most reliable transmissions ever made. As the successor, the 4L80E is also from 1st to 3rd gear also just a 3L80 (aka TH400) it is just as reliable. I mean, even Rolls Royce used them... And they were fitted from 1964 to 1998 by GM, some even til 2003. Mostly innheavy duty application.
They suffer from hard shifts from D to R or R to D. There are shift improver kits available. Depending on age and transmission fluid service status, I'd consider a rebuild. I'm doing one right now. Don't expect it to be cheap. And ypu won't really find a overhauled one, as the bolt pattern of the torque convertor housing is totally different to that of a GM V8.
They suffer from hard shifts from D to R or R to D. There are shift improver kits available. Depending on age and transmission fluid service status, I'd consider a rebuild. I'm doing one right now. Don't expect it to be cheap. And ypu won't really find a overhauled one, as the bolt pattern of the torque convertor housing is totally different to that of a GM V8.
Last edited by Daim; 07-22-2018 at 12:53 AM.
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ronbros (07-25-2018)
#3
can anyone tell me what the v12 gearbox is like in general for reliability? One or two threads lately about issues and I wondered if they are problematic? Is it worth having mine overhauled while the engine is out of the car? What sort of cost would be involved? Many thanks as always for your help.
#4
Thanks for the info lads. Mine has done 86,000 miles so may be ready. I don’t have a spare £1200 at the moment as the rest of the car has drained my wallet. Will change the fluid and filter and see how I get on. Hopefully it will be ok as miles will be low when she finally gets back on the road.
#7
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#8
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The 400 is a tough old bird in terms of being able to cope with heavy loads and lots of torque ....but exceptionally long life is not a sure thing. Not unusual for a 400 to need an overhaul at 80-100k miles...though many go much longer, it's true. For almost all applications they were calibrated for smooth shifting....which increases wear on the clutch plates.
The best time to overhaul any automatic transmission is before it actually needs an overhaul. And certainly before actual failure occurs.
If done preemptively....or at the very first signs of getting weak....you can often get by nicely with a 'soft parts overhaul'. Clutch plates, seals, gaskets, new modulator on GP. Small stuff. If you wait till the box is slipping badly or has failed, you're likely into a "hard parts overhaul" where you need clutch drums, planetary gears, etc. Things start getting expensive.
Cheers
DD
The best time to overhaul any automatic transmission is before it actually needs an overhaul. And certainly before actual failure occurs.
If done preemptively....or at the very first signs of getting weak....you can often get by nicely with a 'soft parts overhaul'. Clutch plates, seals, gaskets, new modulator on GP. Small stuff. If you wait till the box is slipping badly or has failed, you're likely into a "hard parts overhaul" where you need clutch drums, planetary gears, etc. Things start getting expensive.
Cheers
DD
#9
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the old GM 400 box was engineered back in 1962,released for sale in 1963, not bad for American engineering!
used by many GM cars along with Jaguar ,RR and some trucks , modified by some to handle 2500 lbs.ft. torque !
now we have its grand son 4L80/90E,,, ihave a Diesel suburban(ugh) with close to 200K on it, and trans is perfect, cant say that for the engine tho.
ron
used by many GM cars along with Jaguar ,RR and some trucks , modified by some to handle 2500 lbs.ft. torque !
now we have its grand son 4L80/90E,,, ihave a Diesel suburban(ugh) with close to 200K on it, and trans is perfect, cant say that for the engine tho.
ron
Last edited by ronbros; 07-22-2018 at 12:34 PM.
#11
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the old GM 400 box was engineered back in 1962,released for sale in 1963, not bad for American engineering!
used by many GM cars along with Jaguar ,RR and some trucks , modified by some to handle 2500 lbs.ft. torque !
now we have its grand son 4L80/90E,,, ihave a Diesel suburban(ugh) with close to 200K on it, and trans is perfect, cant say that for the engine tho.
ron
used by many GM cars along with Jaguar ,RR and some trucks , modified by some to handle 2500 lbs.ft. torque !
now we have its grand son 4L80/90E,,, ihave a Diesel suburban(ugh) with close to 200K on it, and trans is perfect, cant say that for the engine tho.
ron
And GM never saw fit, after all those years, to fix the notoriously noisy first gear !
Cheers
DD
#12
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Tis in the genes!!!
Our first post WWII family car was a 50 Pontiac fast back. Straight eight and three on the tree. Talk about first gear noise....
But, dad and mom kept it til he gave up driving. Passed it on my brother. He drove it for some more. then swapped it in for a pickup. used for used ??
Carl. l
Carl
Our first post WWII family car was a 50 Pontiac fast back. Straight eight and three on the tree. Talk about first gear noise....
But, dad and mom kept it til he gave up driving. Passed it on my brother. He drove it for some more. then swapped it in for a pickup. used for used ??
Carl. l
Carl
#13
It seems typical in Jaguar V12 service that the TH400 doesn't last much longer than 100,000 miles. The steel disks in the clutch pack typically break up at the scallops around the edge. When mine went then first and third gear were engaged at the same time, and that quickly burnt the fluid.
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Greg in France (07-22-2018)
#14
It seems typical in Jaguar V12 service that the TH400 doesn't last much longer than 100,000 miles. The steel disks in the clutch pack typically break up at the scallops around the edge. When mine went then first and third gear were engaged at the same time, and that quickly burnt the fluid.
#15
Time will tell. My xk8 and xkr both had the famous jag sealed for life gearbox and I sat there with the thermal gauge after counting every drop in and out after a fluid change. Hope it’s going to be ok but on the plus side if it does fail me I know everything will be new on the way out!,,,
#16
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my suburban 4L80 has no noise from any gear,, 200K and holding! i actually tow with some times.
almost forgot, my Buick GN with LS2 and 4L80E , perfect all around street car, suspesion mods made it handle lightyears better, also 2002 Camaro brakes!
ron
Last edited by ronbros; 07-22-2018 at 01:37 PM.
#17
Too bad you are not local to me in Texas USA. I have a NEW-IN-BOX THM400 (3L80) that I would sell for the price of a rebuilt unit.
It is still in the wood ship crate with steel bands. I think it was made in the early 1990s for all 5.3 XJ-S from 1989 onward.
Part number EBC3654N. I would guess shipping to Europe would end up costing more than you could get a reman locally.
I have a 1988 C2500 Chevy Pick-Up that has a THM400 and thought about stripping the Jaguar internals and putting them in the Chevy case but the truck is working fine so no point I guess. It would be a waste of a good Jaguar gearbox to fix a common Chevy truck.
bob
It is still in the wood ship crate with steel bands. I think it was made in the early 1990s for all 5.3 XJ-S from 1989 onward.
Part number EBC3654N. I would guess shipping to Europe would end up costing more than you could get a reman locally.
I have a 1988 C2500 Chevy Pick-Up that has a THM400 and thought about stripping the Jaguar internals and putting them in the Chevy case but the truck is working fine so no point I guess. It would be a waste of a good Jaguar gearbox to fix a common Chevy truck.
bob
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ronbros (07-25-2018)
#18
Too bad you are not local to me in Texas USA. I have a NEW-IN-BOX THM400 (3L80) that I would sell for the price of a rebuilt unit.
It is still in the wood ship crate with steel bands. I think it was made in the early 1990s for all 5.3 XJ-S from 1989 onward.
Part number EBC3654N. I would guess shipping to Europe would end up costing more than you could get a reman locally.
I have a 1988 C2500 Chevy Pick-Up that has a THM400 and thought about stripping the Jaguar internals and putting them in the Chevy case but the truck is working fine so no point I guess. It would be a waste of a good Jaguar gearbox to fix a common Chevy truck.
bob
It is still in the wood ship crate with steel bands. I think it was made in the early 1990s for all 5.3 XJ-S from 1989 onward.
Part number EBC3654N. I would guess shipping to Europe would end up costing more than you could get a reman locally.
I have a 1988 C2500 Chevy Pick-Up that has a THM400 and thought about stripping the Jaguar internals and putting them in the Chevy case but the truck is working fine so no point I guess. It would be a waste of a good Jaguar gearbox to fix a common Chevy truck.
bob
is is it worth doing the math?
#19
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