F series diffs

[whatthe?]

Ok, as some would know I recently did a diff in my supra. After removing said diff and opening her up it was discovered that;
a) it wasn't an LSD even though plate code stated F293
b) I had chewed 6 pinion teeth and a roughly equal number of crown teeth.
Since I have ordered a truetrac from the states I wanted to get out of a "mean time" diff as cheaply as possible. I headed off to pickies to grab me an MX73 F292 diff thinking all would be good. Open centre, same crown and pinion, possibly same case.
Discovered pretty soon that the case, whilst similar wasnt actually the same. Since I was busy at work Stitt was kind enough to take said pair of diffs of to the diff shop to have one good one made up out of the two.
Imagine my surprise when the shop rang me to say that neither crown, pinion nor centre would fit in my old housing! Luckily he was able to salvage my old centre and find a pinion and crown from his collection.
I went down there to pick up the diff and discovered that the cressida pinion was 10mm bigger in diameter at it's narrowest point and the cressi crown was 15mm bigger at it's widest point. couldnt really measure centres (as one was in the rebuilt diff) but the dude said it wasnt compatible so WTF? I thought all F series bits fit in all F series diffs?

[wilbo666]

Ok, as some would know I recently did a diff in my supra. After removing said diff and opening her up it was discovered that;
a) it wasn't an LSD even though plate code stated F293
b) I had chewed 6 pinion teeth and a roughly equal number of crown teeth.
Since I have ordered a truetrac from the states I wanted to get out of a "mean time" diff as cheaply as possible. I headed off to pickies to grab me an MX73 F292 diff thinking all would be good. Open centre, same crown and pinion, possibly same case.
Discovered pretty soon that the case, whilst similar wasnt actually the same. Since I was busy at work Stitt was kind enough to take said pair of diffs of to the diff shop to have one good one made up out of the two.
Imagine my surprise when the shop rang me to say that neither crown, pinion nor centre would fit in my old housing! Luckily he was able to salvage my old centre and find a pinion and crown from his collection.
I went down there to pick up the diff and discovered that the cressida pinion was 10mm bigger in diameter at it's narrowest point and the cressi crown was 15mm bigger at it's widest point. couldnt really measure centres (as one was in the rebuilt diff) but the dude said it wasnt compatible so WTF? I thought all F series bits fit in all F series diffs?

That is VERY strange...! One possiable thing that I could think of is that for some reason you had a SA63 or XX import T series rear end fitted? Have you got you 'new' diff back in? If the tailshaft is too long that would furthur indicate that you had a T series to start with...

Cheers
Wilbo

[JustCallMeOrlando]

I'm inclined to agree with Wilbo. An Australian Supra should've come with an LSD, and the size difference doesn't make sense!

[whatthe?]

Diff is back in again, but it was made up in the same housing using bits the diff guy had. He didnt mention anything about it not being F series, but then he didnt seem to understand why I was so perplexed that the cressi diff bits wouldnt fit in so maybe he's not a toyota enthusiast and didnt know the difference. Are there any other ways to tell physically if it's a T sereis rear end? (Aside from my truetrac not fitting in it of course which is NOT how I'd like to find out)

[ZZT231]

Diff is back in again, but it was made up in the same housing using bits the diff guy had. He didnt mention anything about it not being F series, but then he didnt seem to understand why I was so perplexed that the cressi diff bits wouldnt fit in so maybe he's not a toyota enthusiast and didnt know the difference. Are there any other ways to tell physically if it's a T sereis rear end? (Aside from my truetrac not fitting in it of course which is NOT how I'd like to find out)

Measure the size of the crown wheel, if it's smaller then 7.5 inches, you haven't got an F Series Diff...

Anyone correct me if I'm wrong...

[whatthe?]

Measure the size of the crown wheel, if it's smaller then 7.5 inches, you haven't got an F Series Diff...

Anyone correct me if I'm wrong...

The diameter of the crown from the cressi diff is 7.5" or approx 185mm. The crown out of my supra diff is approx 170mm

How hard is it to fit an F series back in again if thats not what it currently has?

[JustCallMeOrlando]

Depends. That definetly sounds like you have a T-series. In that case, to fit an F-series the easiest option is to swap the rear subframe. There is 4 massive bolts and the whole thing drops out. The subframes are slightly different.

This is what I had to do because my car came with a T-series rear also.

[whatthe?]

I cant comprehend why someone would have changed the whole subframe over at some stage. The transaxle code is definately F293 on the ID plate so it rolled out of the factory with an F series. Even the new tailshaft I had to fit with my manual conversion went straight in without a problem and that came from a manual MA61 with f series. I dont get it

[whatthe?]

Just out of interest would a F292 out of a MX73 normally bolt straight into an MA61, housing and all?

[JustCallMeOrlando]

I'm pretty sure Peewee's swapped MA61 diffs into his Cressida, so yeah, I'm pretty sure they swap.

[whatthe?]

Well, that would seem to confirm it then, seems I'm off to pickies to remove the ass end of an MA61! (The cressi diff housing was to big to fit into my current rear end setup). At least if the cressi diff will fit the normal MA61 rear I dont need another housing or ratio, I'll just whack my truetrac straight into that

[JustCallMeOrlando]

Get someone to give you a hand, it's rather massive. Trust me

[brett_celicacoupe]

Even the new tailshaft I had to fit with my manual conversion went straight in without a problem and that came from a manual MA61 with f series. I dont get it

F and T series have the same tailshaft mouting flange pattern, however the F series mounting flange sits a little further toward the front of the car compared to a T series.

still very strange

[whatthe?]

just to re-iterate and make sure I'm not heading off to waste money for no reason;

- All F series diffs have a 7.5" or 185mm crown
- A T series diff is similar in appearance but not as long or big and carries a 170mm crown
- For diff conversion from T to F for MA61 the rear subframe is required, 4 huge bolts to drop it out (I'll have a look under mine to see what this entails)
- An MX73 F292 should bolt directly into an MA61 with F series rear end

Does all of that sound correct to everyone? If theres a way to get an F in that doesnt involve dropping huge hunks of metal on myself i'd love to hear it....

[mrshin]

I can confirm I have swapped several MX73/MA61 diffs around with no issues at all. Identical to look at. You must have a T...

[JustCallMeOrlando]

Matt, all of the above sounds right. The T-series is similar in appearance, but smaller. The 170mm you measured is the same as 6.7" which is what the T-series is rated at.

[whatthe?]

Cool, thanks fellas +1s all round

[JustCallMeOrlando]

I'll see if I can dig up pictures of the differences.

[JustCallMeOrlando]

Differences in tailshaft length

T on left, F on right

T on left, F on right

T-series subframe

[Norbie]

I cant comprehend why someone would have changed the whole subframe over at some stage.

Someone probably broke the rear end at some point, either by doing skids or some sort of smash, and it was repaired using whatever was available at the time.