Hey guys,

I used the day to take my spare TH400 apart. I am glad I did and didn't just fit it as I was told to...

The input shaft has LOADS of slack. I don't mean a few fractions of an inch, I mean about 3/8". FAR too much. The tranny has around 130k miles on the clock and going by what I found inside, it seems like all 130k were driven hard whilst neglecting the car...

This thread will deal with the tear down, inspection, upgrade and rebuild of my TH400.

I'll do a lot of pictures, as you can see. If you have questions about what you see or what I do, give me a shout!

 

At first. Read this article.

https://www.sonnax.com/tech_resources/237-playing-with-transmissions-setting-total-endplay-to-prevent-th400-gear-train-failure

you need to buy sets of adjustments shims.
This gave a soft- light gear shift from P to D and R and from D to R

I did an intermediate clutch upgrade. from three friction to five, from 4l85e.
This gave a soft- light every gear shift.


LOW GEAR PLANETARY
TCI Low Gear Planetary Sets 229700

https://www.summitracing.com/parts/tci-229700
this is if you want a sharp - quick start.

But there is a two bad thing, a very noisy first gear . And price.

 

I was basically only looking for shift point adjustment (modulator) and improvemnt of R to D shifting. Of course a general service and clutch upgrade too. Didn't want to replace any gears.

 

The bushing kits are pretty cheap Daim so l would suggest renewing them while you are in there.

 

Yep. All bushings will be done. Clutches, bushings and a few bits and bobs

 

im fairly certain my trans was replaced... with the trans plaque give me any idea of what it might've come off of? Blue tq converter and pan and shifts at 4500

 

i dont know if this helps , but a few years back ,i had three T400 trans, was moving and no time to try to sell, brought them to scrapyard , got $25. US for each!

also at that time had three V12 engines, YUP , got $25. US for each!

cried when the yard dropped all into a GIANT shredding machine, it banged and shook loud noises.

value is in the eye of the beholder!

 

The torque convertor should be standard silver. Blue is uprated. Shifting at 4500 rpm (on full throttle?) Would indicate a bad setup...

 

 

Jag bellhousing bolt pattern is more or less unique so if it bolts to your jag engine it came from a jag.

 

xjs trans are GM, any GM th400 will fit. Rated @ 450 input ft lbs. of torque.

 

 

The case is not standard. I think it is the same as some AMC models had. One from a GM model with a V8 won't fit... BUT the guts will..

 

i took a look at latest TCI 400 trans cases and parts, nice for the money.

but i still would go for the 4L85E trans, simply because OVERDRIVE 4th.

 

I am sure you would, Ron, but 3 speeds belongs to this car like vinegar on fish and chips!

 

Knowing nothing about the gearbox that comes as standard on the v12 or gearboxes at all for that matter. what is the general perception of the 3 speed box. Good bad or ugly!

 

People here seem to hate the fact, that it is a three speed transmission. Sure, Jaguar went 4 speed later on but effectively and in my opinion, the 3 speed is the better choice. Less likely to go wrong and the tranny can with stand a lot more power than the V12 could make. 1200 hp and something like 800 nm vs. 300 hp and around 450 nm. The 3 has a few little down sides... One being, that it lacks an overdrive (3rd has a 1:1 ratio). A pro side for quarter miles is, that 1st goes to 120 kph (so about 70 mph).
As there is a huge aftermarket supply for parts, ranging from torque convertors with a higher stall speed, to reinforced shafts, gears, shift improvement kits, full manual shift (via selector lever) kits, different valves, different... you can basically tweak it to match your taste. Shifting fast and hard or sluggish and smooth.

 

i get it!

the longjohn guy wants to use a 6L80 GM trans , yup 6 speeds, actually a good idea.

but for the money may as well go all the way, GM now has an 8speed???

but that may be a little bit MUCH! donno.

pic of my old 4 speed 700R4, rebilt with a B&M kit in it, works great, and with my low axle ratio ,i couldnt live without overdrive.

 

So how do the the different diff ratios apply with this gearbox. I only know of two types . Which is prefable and why are there different ones. Is it for different engine sizes? Sorry if this sounds daft but if you don’t know about these things you have got to ask!,

 

The standard 5.3l has a 2.88 diff ratio. The 6 cylinders have the 3.54. The 2.88 balances the lack of overdrive out. Which can cause a sluggish acceleration... But that is a can.