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Anyone changed their gen 1 OB's 5th gear?


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7 replies to this topic

#1 superu

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Posted 11 May 2011 - 11:32 AM

I've got a 95 legacy with 5MT, 3.90 nFD and am swapping for a 99 OB 5MT with 4.11 FD, BUT it looks like reading other posts, folks don't like the 5th gear in OBs.

Looking at the numbers:

my 95 leg, foresters, impreza RSs, etc. Most 5MTs run a 7.80 5th gear ratio, but Outbacks have a .871 5th gear ratio. I've read on another forum someon swapped an RS 5MT with 4.11s into his OB to get the batter 5th/overdrive gear.

I'm turning 27" tires and the 4.11s should do that better than my 3.90s did, but I'd like to keep a lower RPM in 5th. currently I do like 3K RPMs at 70 MPH (although witht he tires I'm actually turning 75MPH), and my wife's 03 OBS with 3.90 FD does 3K RPMs at 70 MPH too. So it would be nice to keep around 3K RPMs (not 3250 or 3500) at 70 MPH with the 4.11s.


SOOOOO, how involved would it be to crack these trannys open to retrieve my legacy's .780 5th gear and put it in this 99 OB 5MT to keep the better overdrive?

#2 renob123

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Posted 11 May 2011 - 01:20 PM

I've got a 95 legacy with 5MT, 3.90 nFD and am swapping for a 99 OB 5MT with 4.11 FD, BUT it looks like reading other posts, folks don't like the 5th gear in OBs.

Looking at the numbers:

my 95 leg, foresters, impreza RSs, etc. Most 5MTs run a 7.80 5th gear ratio, but Outbacks have a .871 5th gear ratio. I've read on another forum someon swapped an RS 5MT with 4.11s into his OB to get the batter 5th/overdrive gear.

I'm turning 27" tires and the 4.11s should do that better than my 3.90s did, but I'd like to keep a lower RPM in 5th. currently I do like 3K RPMs at 70 MPH (although witht he tires I'm actually turning 75MPH), and my wife's 03 OBS with 3.90 FD does 3K RPMs at 70 MPH too. So it would be nice to keep around 3K RPMs (not 3250 or 3500) at 70 MPH with the 4.11s.


SOOOOO, how involved would it be to crack these trannys open to retrieve my legacy's .780 5th gear and put it in this 99 OB 5MT to keep the better overdrive?


It's not the final drives by themselves, it's how the final drives and the gear ratios work together. For example, my 3.90 FD 6-speed hits way higher rpms at 70 than your cars do. My gear ratios are shorter than yours. I'd say that your 3.90 transmission switched to 4.11 final drive would be best for you and your tires, but that's a lot of work.

Jacob

#3 superu

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Posted 11 May 2011 - 04:54 PM

It's not the final drives by themselves, it's how the final drives and the gear ratios work together. For example, my 3.90 FD 6-speed hits way higher rpms at 70 than your cars do. My gear ratios are shorter than yours. I'd say that your 3.90 transmission switched to 4.11 final drive would be best for you and your tires, but that's a lot of work.

Jacob



Right, but all other gears are equal (from the subaru tranny chart which floats around), from my 3.90 FD 1-4 and the 99 OB 4.11 1-4, just the 5th is different... So given those numbers, I'd suspect that with the 5th from my legacy (.780) instead of the 5th in the 99 OB (.871), I'd have a better highway overdrive, with the 4.11s... The chart shows foresters and imprezas (OBS and RSs) have the same 1-5 as my legacy, with OBS having 3.90 and newer RSs with the 4.11s.

So I think all else being equal, the taller 5th from my legacy in the OB tranny would be a good setup, combined with the 4.11s...

Does that make sense or is there a critical factor I'm missing, which is entirely plausable?

#4 renob123

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Posted 11 May 2011 - 05:04 PM

Right, but all other gears are equal (from the subaru tranny chart which floats around), from my 3.90 FD 1-4 and the 99 OB 4.11 1-4, just the 5th is different... So given those numbers, I'd suspect that with the 5th from my legacy (.780) instead of the 5th in the 99 OB (.871), I'd have a better highway overdrive, with the 4.11s... The chart shows foresters and imprezas (OBS and RSs) have the same 1-5 as my legacy, with OBS having 3.90 and newer RSs with the 4.11s.

So I think all else being equal, the taller 5th from my legacy in the OB tranny would be a good setup, combined with the 4.11s...

Does that make sense or is there a critical factor I'm missing, which is entirely plausable?


No, you're on the right track. I just wanted to caution you that FDs are not everything. When the gear ratios are the same, however, FDs are pretty much everything:grin:

I guess now you're down to looking at the % differences and considering whether they're worth the work/downtime/money to swap 1 gear.

Jacob

#5 el_freddo

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Posted 12 May 2011 - 01:49 AM

Posted Image

You don't have to split the half cases to swap 5th gear.

The 5th gear only needs the rear housing removed to swap it out. The pic above is of an EA gearbox, the difference is in the pinion shaft for the EJ, it will be a lot easier to swap the 5th in the EJ box as I'm not sure that it is possible with the EA...

Posted Image

Here is a split EA box, the lower shaft (pinion) on the EJ's doesn't have the big gear on the end as the centre diff fits in that space...

I would drop the box out to do the job, but I have heard that is possible to do it in your subi if you've got a big enough lift. You need to access the top plate to remove the bolt that holds a retaining arm on the shift selector so that the gear selector shaft can be removed from the selector forks and the rear housing removed.

Swap your 5th gear ratio and then reverse the process ;)

Cheers

Bennie

#6 superu

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Posted 12 May 2011 - 11:20 AM

No, you're on the right track. I just wanted to caution you that FDs are not everything. When the gear ratios are the same, however, FDs are pretty much everything:grin:


yup... I've done me a lots of research on gearing, here and elsewhere! :clap:

But yeah, thanks for the info... In fact I'm sure I got some of my learning from you along the way!

I guess now you're down to looking at the % differences and considering whether they're worth the work/downtime/money to swap 1 gear.

Jacob


This is exactly where I'm at... Is it worth all that to get less than a tenth of a percent gearing difference... It might be in the long run, but then this might just dedicate my car as NOT the highway/road trip car :(

#7 superu

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Posted 12 May 2011 - 11:28 AM

Posted Image

You don't have to split the half cases to swap 5th gear.

The 5th gear only needs the rear housing removed to swap it out. The pic above is of an EA gearbox, the difference is in the pinion shaft for the EJ, it will be a lot easier to swap the 5th in the EJ box as I'm not sure that it is possible with the EA...

Posted Image

Here is a split EA box, the lower shaft (pinion) on the EJ's doesn't have the big gear on the end as the centre diff fits in that space...

I would drop the box out to do the job, but I have heard that is possible to do it in your subi if you've got a big enough lift. You need to access the top plate to remove the bolt that holds a retaining arm on the shift selector so that the gear selector shaft can be removed from the selector forks and the rear housing removed.

Swap your 5th gear ratio and then reverse the process ;)

Cheers

Bennie


UUH OOH Bennie, you might've just made my day!!!! I might have to edit my last post above! ;)

BTW, bennie, I've been scoring for an EJ D/R over on AUsubaru, and I really appreciate the info and help you've given me over there!!

So my latest is this... My reverse died and I sourced a good 99 OB 5MT with 4.11s last week. So I figured I'd at least get 4.11s while I continue my D/R EJ searching, AND I'd have experience ad dropping the tranny.

So at this point, my rear diff and tranny are out of the car and I'm swapping the brackets etc. from my 95 clutch-driven tranny over to the 99 hydro clutch-driven 99 OB 5MT. But I came across info about the high 5th in OBs and I have a lower (.780) in my 95 5MT, so I thought, while I have stuff on the grpound, and am going to open the 95 5MT anyway, maybe (if it's not a huge PITA) I'll look into swapping out the 5th to have a better overdrive than the stock 99 OB 5th... I need to pull the rear case off and am going to crack the box open to look at tht ereverse gear, spo if 5th is on the back when you pop off the rear case, then I might be able to do it!!!!

thanks man!!!

(here's a quick thread I put up asking for info on clutches, when marrying a 99 OB 5MT (which was behjind a 2.5) to ann EJ22)
http://www.ultimates...ad.php?t=122844

#8 GeneralDisorder

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Posted 15 May 2011 - 09:17 PM

5th is accessible from the back of the transmission without splitting the case. However I doubt it will be easy to remove the driven gear from the secondary shaft without a press. It's keyed to the shaft but it's still an interferance fit and will not come off easily. Besides that it's very close to the large rear secondary shaft bearing and the clearance there for prying insturments is small - plus large amounts of prying force could damage the bearing...... And you can't do much heating to the gears or your could destroy their delicate temper. I wouldn't attempt it or if I did I would know when to give up and split the case. It's not that hard to do once you are at that level of dissasembly anyway - just split it, pull the shaft out and press the gear off. Then while you are at it replace the primary shaft's rear bearing - they are always the first to fail. Get the 10-ball bearing for a turbo tranny.

The input shaft gear will come off without a fight. Just don't lose any of the syncro bits.

Also be aware that you are in delicate territory as to what will fit what.... the '99 transmission went through a big redesign and I highly doubt that the driven 5th gear will have the same woodruf key size as the '95 tranny. I ran into a difference in the key sizes between a '95 STi tranny (JDM) and a '98 Legacy transmission causing me to have to use the whole driven shaft in order to get the 5th gear. I put all the STi components onto the Legacy shaft.... it's possible that even more things are differerent betweeen the '95 and '99 transmissions you have - they have a completely different center diff section and possibly incompatible internals. Be very careful what you get yourself into. I have had to make custom shaft keys when doing things like you are talking about. If you don't have machine shop abilities and equipment - better to just leave it to the pro's.

GD

Edited by GeneralDisorder, 15 May 2011 - 09:23 PM.





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