How to change the transmission for freeways?

T

twozzie

Active member
1997 D90 V8 4.0 Automatic.

Everything runs ok but I want to be able to run at freeway speeds using existing engine? It gets to 70 ish and thats it, I dont want it to go much faster but I dont want it screaming its guts out and then dropping to 55 when I go up a hill.

Is there a simple swap out for the transmission or a way to change the gearing?
 
E

ezzzzzzz

Well-known member
Not enough info. What tires are you running? How many miles on the engine? Any transfercase swaps by PO? You should be able to run 70 with room to spare.
 
1of40

1of40

Well-known member
As a comp my stock engine(173k), trans, tcase with 4:11’s and 33” 255/85’s cruised ok at 75mph@2.8rpm, round trip from DC to Vermont in Sept. I’d been happy at 65 but nobody travels under 70-75 on that route.
 
T

twozzie

Active member
ezzzzzzz said:
Not enough info. What tires are you running? How many miles on the engine? Any transfercase swaps by PO? You should be able to run 70 with room to spare.
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160K on the engine, original transmission, engine, std tires and wheels 265/75R16. The car is regularly serviced by my local British specialist who knows his stuff so I dont think there is anything 'wrong' per se. It does get to 70 even 75 but on an incline it slows to 55 unless I drop a gear then it goes into screaming mode.
 
R

Red90

Well-known member
Fix the lack of power. It should have tons of power. You should be able to happily do 90 with a 4.0. Most likely the timing chain is stretched and/or the timing sprockets are worn.

If your knowledgeable mechanic thinks it is fine, get a new mechanic.
 
V

Viton

Well-known member
Napalm00 said:
Romerdrive?
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It would be tricky to use with an automatic (ALL '97's were)
You'd have to shift into N first, engage the RomerDrive, and then shift back into D. Not impossible, but difficult while trying to maintain current speed.
 
rocky

rocky

NAS-ROW Addict
Loud definitely. But screaming.....not really. I'm on old 255/85 MT with 3.54 diffs and 1.2 TC.
 
uc4me

uc4me

Well-known member
twozzie said:
It does get to 70 even 75 but on an incline it slows to 55 unless I drop a gear then it goes into screaming mode.
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My 97 is all stock and I will say on those long steeper inclines it will (and always has) drop from 75mph to 55 pretty quickly. Aside from flooring it for the kickdown gear I just shift to 3rd before it gets to 58mph where it kicks down automatically and whines.
 
T

twozzie

Active member
Found a couple good threads on the 1.2 / 1.4 transfer case (thank you all). How do I tell whats installed, is it stamped somewhere?
 
jymmiejamz

jymmiejamz

Founding Member
Callsign: KN4JHI
I cruise with mine at around 3k RPMs at 70 mph all the time (I have 4:11 gears in the axles). Is it that it won't physically go over 70 or you are afraid to push it?
 
T

twozzie

Active member
jymmiejamz said:
I cruise with mine at around 3k RPMs at 70 mph all the time (I have 4:11 gears in the axles). Is it that it won't physically go over 70 or you are afraid to push it?
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It'll go above 70 but it doesn't sound good, it's ok at 70, just the damn inclines
 
rocky

rocky

NAS-ROW Addict
twozzie said:
Found a couple good threads on the 1.2 / 1.4 transfer case (thank you all). How do I tell whats installed, is it stamped somewhere?
Click to expand...



Here is more information on the LT230 and the answer to your question. It's rare to see a ratio change. Usually done due to off road usage. What speed are you seeing at 2k rpm?

https://www.ashcroft-transmissions.co.uk/transfer-boxes/lt-230.html

Suppose you could swap the TC to a 1.003 unit but it will be slower off the line.
 
jymmiejamz

jymmiejamz

Founding Member
Callsign: KN4JHI
twozzie said:
It'll go above 70 but it doesn't sound good, it's ok at 70, just the damn inclines
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A higher gear ratio, such as a 1.003 LT-230 would just make it worse on inclines. The reality is that the 4.0 V8 is underpowered in general, and yours is probably worn out. Rather than messing with gear ratios (assuming your truck is stock), I would look at rebuilding your motor or replacing it with a 4.6.
 
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