FJ 55 LS swap @ driveline questions. (1 Viewer)

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Aug 29, 2020
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new jersey
Hello All,

i have a stock ‘73 FJ55 with a worn out Chevy 350 and Chevy 3 speed trans.

im considering LS swap with LS trans.
QUESTION: Do I really need to upgrade axles & Gears?
I will NOT be using this off road, other than the beach. It will be a street cruiser.

Second question:

im also considering saving money and time and just rebuilding the 350 motor that’s already in it maybe adding some HP.
Will I be able to cruise on the highway ok with the 3 speed?

I would like to hear your thoughts
 
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Brea, Calif.
1. No, you do not have to upgrade the axles/gears, your's are already stronger than what came in the LS equipped Chevys.
2. If you rebuild the 350, you'd be happy with a FiTech or Sniper fuel injection swap on it.
3. Many on Mud will tell you to get rid of the 3 speed, primarily because 1st gear is not synchronized. Know that I pulled a fully self contained travel trailer for 3 years with the stock 3 speed. With that said, know that I whole heartedly encourage the newer LS with 4L60E tranny with a lower 1st gear and over-drive high gear.
 
Joined
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1. No, you do not have to upgrade the axles/gears, your's are already stronger than what came in the LS equipped Chevys.
2. If you rebuild the 350, you'd be happy with a FiTech or Sniper fuel injection swap on it.
3. Many on Mud will tell you to get rid of the 3 speed, primarily because 1st gear is not synchronized. Know that I pulled a fully self contained travel trailer for 3 years with the stock 3 speed. With that said, know that I whole heartedly encourage the newer LS with 4L60E tranny with a lower 1st gear and over-drive high gear.

cool, that’s helpful. I didn’t know if changing my axles was overkill or not for my purpose. I’ll keep them.

I seriously have been going back and forth for days about whether I should do LS swap or not. I just bought the fj55. And it’s in great shape.

If I don’t do LS, I like the sniper idea, would still need to rebuild 350 motor, rebuilt the 3 speed.

QUESTION: If I keep my 350 motor, any suggestions on a 4 speed trans that bolts up??

I think if I can find a better trans so that I’m not screaming doing 70moh on the highway, I may go that route
 
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Problem with switching to a 4 speed is (a) high gear is still 1 to 1, so no help with highway rpm, and (b) you'd need the 4 speed bellhousing adapter, another adapter to mate the 4 speed tranny to your 3 speed transfer-case, re-modify drive shafts due to different length tranny, and some drive shaft flange adaption/changes.
I'm thinking I go fuel injection on the rebuilt 350, and stick with the 3 speed tranny and transfer-case, or go LS with 4L60E if you have the means to do so.
 

Ocho77

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Not sure what gears are in that 55, but I drive my 40 with a SBC and stock 3 speed all over the place. Cruises just fine...can easily do 75, but I don't. Other than the non-syncro 1st gear, it's fine, but even that is rarely bothersome.

Big price difference between a rebuilt 350/3spd vs a full LS swap.
 
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new jersey
Thanks guys.

I believe anything before 1978 is 4.11 course spline so I think I have 4.11 and I have 33’s

i’d like to be able to do 75mph ok With the 3 speed.

But i think I have the funds do LS swap if I decide that. 😬😬

I think my last question, is what are most people doing for the T-case if I do LS and 4L60/4L80?
This is where I don’t have much knowledge and never did it.
Do they make adaptors? Need to modify tail shaft? Divorce the t-case?
-‘73 fj55
 
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Messages
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If you go 4L60E then Advance Adapters has the adapter you will need for your 3 speed transfer-case. You will probably need a better radiator, and auto tranny cooler, auto tranny shifter, and obviously will need to modify drive shafts. Make sure you get all the sensors/senders/harness/computor with the LS. The AA you get should have a home for the 40 pulse VSS you'll need. I make a trick 44" long spedo cable if you get an LS with throttle body at front of the engine. Since you have an FJ55 rear drive shaft length won't be a problem.
 
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new jersey
Thanks again
I found a truck for $400 with a good 5.3 LS and 4l60e.
Ordered the adaptors off advance adaptors too 👍🏻👍🏻


back the driveline question again, should I keep my stock axles?
I was thinking of making hybrids but I’m not super knowledgeable on this....

keep my housing and axles shafts but Add 3rd members from an ‘85 fj60

and also use knuckles and hubs from the fj60 to have disc brakes in the front.
I was told that the 3rd members are interchangeable and that I can use my axles shaft.

a stock 1973 fj55 have a course 10 spline diff

is this true?
 

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