FJ55 rear third member compatibility (1 Viewer)

ST8ROCKS

Kevin
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I want to get rid of the welded diff in my 55 for daily driving. I have a 92 fj80 parts truck. From what I have read it sounds like they are compatible. One on thread someone posted that something on the fj80 third has a different bolt pattern.

Does anyone know what I would need to do to get this to work? I'm trying to determine if I can save money this way or should just look for a third out of a 40.
 
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The rear third out of the 80 will bolt right in. The flange will have a different bolt pattern. You can get a flange that has a dual pattern. If the 80 has a round flange you can clock the drive shaft 45 degrees and redrill the holes using your drive shaft as a guide.
 

tucker74

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double check that. Not exactly sure when the switch from coarse spline to fine happened, but my 78 is fine spline 4.10. In 79 the 40's went to a 3.70 ratio
FJ/FZJ80s were all 4:10s, the '91 will have the SF rear axle which is what you want ;)

Tucker
 

Josie'sLandCruiser

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Hi All:

Sorry, you have incorrect information.

The US-market pre-1978 40/55 Series came with coarse-spline diff pinions.

The US-market 1978 FJ40/55 came with fine-spline 4.1 diffs. The 1979-87 US-Market FJ40/60 have fine-spline 3.7 ratio diffs.

The 1988-89 FJ62 has 4.1 ratio fine-spline diffs. The 80 Series has had fine-spline 4.1 ratio diffs through the whole series (1990-98.) IIRC, the 1990-92 used the (big) 8.75 inch diffs both front and rear, while the 1993-98 have a high-pinion 8 inch diff up front and a low-pinion 8.75 diff in the rearend.

Regards,

Alan


From what I have read on the forum all FJ40/55s and FJ80s were a "coarse spline" 4.10
 
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The 1988-89 FJ62 has 4.1 ratio fine-spline diffs. The 80 Series has had fine-spline 4.1 ratio diffs through the whole series (1990-98.) IIRC, the 1990-92 used the (big) 8.75 inch diffs both front and rear, while the 1993-98 have a high-pinion 8 inch diff up front and a low-pinion 8.75 diff in the rearend.

You mean 9.5", not 8.75".

The diffs are the same for full-float and semi-float.

The early gears, at least up to '78 were 4:11, which is a 37t ring and 9t pinion.

The later years, at least 93+ were 4:10, which is a 41t ring and a 10t pinion.

FYI: 4:10s and 4:11s are different ratios by 0.27% You would not be able to notice this difference even on dry pavement at highway speed. Your tires are likely off by more than this if they're not brand new.

Josie is perfectly correct referring to all of them as 4.1.
 

cruiseroutfit

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Also fwiw, all 80 Series (90-97) used the high pinion 8" in the front axle and whats commonly called the 9.5" in the rear.
 

ST8ROCKS

Kevin
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So... can I use the third member out of my 92? Sorry getting a little confused here by posts.
 

cruiseroutfit

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The rear 80 Series diff ONLY will physically bolt into the front or rear housing of any FJ40/55/60. Depending on the drive shafts you plan to use, you will likely need to swap the pinion flanges on the 80 Series diff to match. I didn't catch what year your FJ55 is... if it has a course spline pinion you can't just swap the flanges, you will need to purchase a different flange. All of which we could help you source if it comes down to it. Hope that helps.
 

ST8ROCKS

Kevin
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My 55 is a 1972. I have a 92 parts truck so I plan on swapping the third member and using the flange. I think I should have all the parts I need.
 

cruiseroutfit

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My 55 is a 1972. I have a 92 parts truck so I plan on swapping the third member and using the flange. I think I should have all the parts I need.

So long as the driveline you plan to use matches the 92' flange your in business. Worst case you can re-drill the flange or order a flange. LMK if we can help out with anything else, we have all the diff gaskets and axles seals you might consider changing while in there too.
 
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So long as the driveline you plan to use matches the 92' flange your in business. Worst case you can re-drill the flange or order a flange. LMK if we can help out with anything else, we have all the diff gaskets and axles seals you might consider changing while in there too.

possible to get more info on this?
Im about to put fj60 third members in my fj55

So I can’t take my 55 flange and put it on the 60 third member??

where can I buy a flange that fits?
 
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possible to get more info on this?
Im about to put fj60 third members in my fj55

So I can’t take my 55 flange and put it on the 60 third member??

where can I buy a flange that fits?

This depends on the year of your FJ55 and the FJ60. 1/74-8/84 used the same flange pattern.
 

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