Questions about R380 and rebuilt Tcase

SARTech

Well-known member
If you were following my rebuild project you saw that everything was going great until I drove the rig. It appears the transmission 2nd gear syncros are out and the mainshaft splines are done. So im looking at ordering a transmission and transfer box from Ashcroft. Any other suggestions? When making the order they ask about add ons/upgrades. What is your recomendation? For the transmission the offer a HD rear support, is that worth it? For the transfer box they offer sleeved casing, and upgraded diff; ATB or HD cross pins?
My main goal of this project is to make the rig as reliable as possible, and fix the things my wife didn't like about it. I have another transmission and tcase I could install but they have unknown miles, currently they are good but don't know for how long.
 

AdamSanta85

Well-known member
I went through the same. I ended up with...

R380 Stumpy + taller 5th gear (I didn't see need for the HD shaft unless you might end up running a TD5 or Cummins in future)
T-case with cross pin/sleeved (not sure if I needed those upgrades)

Been very happy with both.
 

Uncle Douglas

Well-known member
I'd suggest the stumpy with hd bearing option, its not a HD shaft, its the bearings in the case. There are pictures of the dramtic difference between the hd and stock.
Biggest thing is to get a tcase with a crossdrilled input gear so that spline wear is a non issue on your new one.
 

SARTech

Well-known member
I'd suggest the stumpy with hd bearing option, its not a HD shaft, its the bearings in the case. There are pictures of the dramtic difference between the hd and stock.
Biggest thing is to get a tcase with a crossdrilled input gear so that spline wear is a non issue on your new one.
Thanks Uncle, I had emailed Ashcroft this morning inquiring if their rebuilt tcase come with the cross drill input gear. Awaiting a reply.
 

DiscoDavis

Well-known member
Is it possible to get a shorter 5th?

Even with a stock r380 and a 1.4 my 5th gear will bog so much more than the same car, similar if not same tune, that has an lt77.
 

Red90

Well-known member
Is it possible to get a shorter 5th?

Even with a stock r380 and a 1.4 my 5th gear will bog so much more than the same car, similar if not same tune, that has an lt77.
There are three different 5th gear ratios in both LT77 and R380. 0.83 (pre-TDI diesel), 0.77 (all TDIs) and 0.73 (all V8s). A TDI with a 1.4 transfer case should easily pull them all. If not, you need some engine tuning.
 

SARTech

Well-known member
Ashcroft replied and said that the rebuilt transfer boxes come with cross drilled input gear assemblies. So that is a plus.
 

DiscoDavis

Well-known member
There are three different 5th gear ratios in both LT77 and R380. 0.83 (pre-TDI diesel), 0.77 (all TDIs) and 0.73 (all V8s). A TDI with a 1.4 transfer case should easily pull them all. If not, you need some engine tuning.
I have a very chunky 110 and likely a very tall 5th gear. The motor is tuned. I guess I am going to ask ashcroft what 5th ratio this gearbox has.
 

Red90

Well-known member
Top gear should be as high as possible while being usable on flat ground with no head wind. This give you the best mileage. You should then shift down for hills. Weight should not really impact 5th gear choice since weight does not add much to flat ground power draw. Aerodynamics are what matter, so things on the roof or a big lift are bigger impacts for highway power requirements.

My 110 is 6800 pounds with a NA Isuzu (less power than a TDI). Top gear is equivalent to 0.71 5th and it has no problem pulling it. Can cruise at 75 mph all day. The weight slows it down on the hills, but that is not what top gear sizing is based on.
 

SARTech

Well-known member
I ordered the transmission and transfer box. I keep telling myself its all to make it reliable as possible. Thanks for the advise and input. I ordered the extras recommended and kept the gearing stock. I never had issues with the gearing and honestly don't need the rig to go fast, I have other vehicles that do that.

Thanks guys.
 

DiscoDavis

Well-known member
Top gear should be as high as possible while being usable on flat ground with no head wind. This give you the best mileage. You should then shift down for hills. Weight should not really impact 5th gear choice since weight does not add much to flat ground power draw. Aerodynamics are what matter, so things on the roof or a big lift are bigger impacts for highway power requirements.

My 110 is 6800 pounds with a NA Isuzu (less power than a TDI). Top gear is equivalent to 0.71 5th and it has no problem pulling it. Can cruise at 75 mph all day. The weight slows it down on the hills, but that is not what top gear sizing is based on.
I promise you I drove an identical variant of my car with about 1 ton extra weight in it and this thing had the original LT77 and 5th gear would pull away easy, my unloaded car (same car, with stumpy R380) will bog and spike EGTs in 5th gear as I watch him pull away.

Both 200tdi, both 1.4 t case, and Naplm has tuned both of them. Some minor differences in exhaust, intercooler etc

Driver of the 'identical' car even said yeah they feel the same right up until you hit 5th. It just won't go as easily. Trust me I wish it was a simple 'tuning' issue but even tweaking the boost, and bumping up the fuel I cannot get it to match his performance. Lets say I get the best possible intercooler and a more free flowing exhaust and bump the fueling up still, it makes me wonder why the difference is in 5th gear.
 

Red90

Well-known member
You have some other issue. The TDIs have nearly flat power curves from 2000 rpm and up. This means the gearing has little impact as long as you are above 2000 rpm. There should be no way you are below 2000 rpm at highway speed.

Both my 90 and 110 have higher top gears than what is possible with a 1.4 and there is no problem with them pulling on the highway. They both run out of rpm before they run out of power. In fact, I would be happy with even higher gearing.
 

Red90

Well-known member
The dyno below of a 300TDI before and after tuning holds pretty well with what my experience shows with a stock turbo. Power is more or less flat from 2100 to 3100 rpm with real peaks below 2500. What this means is that if you have gearing that puts you at 2600 rpm and 70 mph and you change to gearing that goes to 2400 at that speed, the power output is still about the same and what the wheels see is the same. You just want to make sure you do not drop off of the cliff on the left.

Now, if your power curve does not feel flat in that rpm range, there is something that needs to be fixed.

 

Red90

Well-known member
This would be a 1.4 with the old 5th gear (0.83). Basically you will drop off the power cliff at 75. Can probably hold 5th down to 45.
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This is stock 300TDI gearing (0.77 5th). 80 is about it. A little over 50 is when it should start to bog down in 5th.
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This is with the 0.732 5th. You'll run out of power before gearing. Should pull from 55.
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DiscoDavis

Well-known member
I never hold 5th at 45mph with the 200 and 1.4, it will bog unless I am very flat or maybe going downhill. I will shift into 5th after 55mph. On a flat I will barely hit 70-75

I can do it with my V8 D1 w 1.2 but not the diesel.
 
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