polred

New Member

• Sep 27, 2009

• #1

Hi all,first bit of advice i am after on the RRC.I have searched old posts but am still unsure.My question is would the gearbox out of a j reg discovery v8 fit my 94 RRc 3.9?I am in the middle of fitting a Janspeed Single turbo conversion,and was reading the auto boxs are on there limit at 250bhp?I have bought the Disco already,and the drive home was sweet being able to change gears myself and plonk it straight into fifth and potter along at 1200rpm with ease.Also there is alot of whining in the RR,the disco was relatively quiet compared to it.Also what type of box is in the Disco?reverse is beside first if that helps anyone.

Also if the box was do-able would i need RR driveshafts?(manual),sorry for all the questions.hoping to have a busy week ahead and need to suss out what am needing or not.Thanks in advance Paul..

 

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byway-basher

New Member

• Sep 27, 2009

• #2

I think there should be no problem. However what turbo are you putting in thats going to take the output over 250 ponies? Out of the factory the 3.9 only just got over 182 at the flywheel.

I personally wouldnt trust the LT77 gearbox out of a disco that old to last more than a week or two with that kind of power and torque going through it.

Having pondered some whilst I type this...... I am also fairly certain that when overfinch dropped the big chevy engines in the RRC they used the existing ZF auto transmission. Certainly the old 3speed torqueflites from early auto rangies were pretty much indestructable.

 

seight

New Member

• Sep 27, 2009

• #3

You have the LT77 box by the sounds of it. Like byway-basher said these boxes not really up the job. LR had lots of failures. They did revise I think LT77S, not sure about that. However they eventually replace this with the R380. However be aware that there are two versions of this, 2WD and 4WD. The difference being the input shaft. From the outside the R380 looks the same as LT77. Reverse is next to 4th.

 

polred

New Member

• Sep 27, 2009

• #4

its a t25 with an AR in of 60 and exhaust out at 69.Its a Janspeed single turbo kit,apparently they put out around 250 running 5-6psi.I wont bother with the box out of the Disco then if you reckon Overfinch kept the auto boxs.The biting point on the disco in low range is pretty brutal anyhow,i do a bit of towing and the autos been perfect for that so far.Thanks for your advice,Paul.

 

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byway-basher

New Member

• Sep 27, 2009

• #5

Forgot to add..... its not just the box to swap, its flywheel too.

I think the later LT77s were also put into TVRs that were using the rover V8.

In low box I rarely even bother with the throttle in the lower gears, just the clutch alone as tickover is more than enough to get moving along

 

seight

New Member

• Sep 27, 2009

• #6

Yes, overlooked the obvious! Spigot bearing in crank as well probably.

byway-basher said:

Forgot to add..... its not just the box to swap, its flywheel too.

I think the later LT77s were also put into TVRs that were using the rover V8.

In low box I rarely even bother with the throttle in the lower gears, just the clutch alone as tickover is more than enough to get moving along

Click to expand...

 

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byway-basher

New Member

• Sep 28, 2009

• #7

Pondering this overnight, and figured if it were me I would leave the auto in anyway. Not just out of laziness for both driving and actually doing less work. If the box is good for 250, and the engine puts out the same, unless forever driving everywhere with the engine running right at the peak of its powerband there should not be too much trouble. Having a box that is going to change up well below peak most of the time should cope reasonably well, until like all the old ZFs it decides to never get out of first

 

polred

New Member

• Sep 28, 2009

• #8

I was thinking about today and the auto is staying put alright.But it does seem to hold first for a bit sometimes,now that you mention it.When it doesnt change from first when expected,as soon as you lift of to try to get it to change up theres a delay then Bang it changes.That is the most annoying thing,plus the whining.

Got the sump of it tonight,just as well i started the conversion as the pick-up pipe was blocked solid with silicone and crud!Sump into work tmrw to weld in the turbo return pipe,then its mount I/C and fit exhaust.Hopefully done for the week end,looking forward to a drive of it. Paul..