Well, I started pulling my B15 tranny apart today to install my friction type LSD and thought I'd share with all of you a little bit of what I found. We all know that B15 trannys hold up to high HP way better than B13/B14 trannys and I've frequently seen many folks wondering what exactly is responsible for this. Unfortunately, there really hasn't been any definitive answer. Thanks to a friend of mine who has many torn apart B13 trannys, I was able to compare and spot some big changes in the B15 tranny. Hopefully what I have found will shed some light on the major differences. I am assuming that the P11 tranny is identical but I don't have one to compare with here.

What we already know:
There is some seperation of the input and main shafts under WOT that occurs in B13/B14 trannys. This puts a great deal of stress on the ends of the gear teeth (at its worst in 3rd) leading to shearing in high HP scenarios. The B15 tranny does not seem to have this problem and thus holds up much better to high HP applications.

But why?:
Obviously the B15 case is significantly different than B13/B14 cases. An addition that was made with the introduction of the B15 tranny is pictured below.

http://www.roastedpavement.com/parts/11.jpg

The two seemingly pointless 14mm bolts pictured actually serve a very important purpose and that is reinforcement. Inside the sleeves that they screw into is a small spring that holds pressure on a check ball (2 springs and 2 check balls total). The check balls contact the two shifter rods that 'ride' the main shaft and essentially hold tension on them when in place. The shifter rods are notched where the check balls contact them and you cannot even remove the case without removing those two bolts first. This is quite a nice improvement over the B13/B14 design where the shifter rods are loose at best. In addition to this, the shifter rod that 'rides' the input shaft sports a much beefier fork and sits with much more stability over the B13/B14 counterpart. Support, stability and reinforcement are obviously greatly improved.

As far as the internals go, everything is different, including the diff. IMHO, it seems like the gear stacks are beefier on the B15 tranny (see pic below). Sorry that I have no comparison pics with a B13 or B14 tranny.

http://www.roastedpavement.com/parts/13.jpg

Probably the biggest difference that sets the B15 tranny apart though is the positioning of the reverse idler gear. To get to the gear, you must take off the small cover pictured below, and remove its retainer pin (also pictured below). This gear is actually held into the tranny case itself (by the retainer pin) and meshes with the input shaft. It basically forces the input shaft to stay completely meshed with the main shaft, yet another reason why there is virtually no play in these trannys.

http://www.roastedpavement.com/parts/3.jpg
Reverse idler gear cover

http://www.roastedpavement.com/parts/4.jpg
Removing the snap ring to take out the retainer pin.

http://www.roastedpavement.com/parts/5.jpg
Threading a small bolt from the cover into the retainer pin to lift it out.

http://www.roastedpavement.com/parts/6.jpg
The actual retainer pin removed.

http://www.roastedpavement.com/parts/7.jpg
After the pin is removed, the reverse idler gear pulls right out of the case.

So to highlight how the input and main shafts stay meshed in the B15 tranny, I give you the following synopsis:

Input shaft: Supported on one end by the input shaft bearing and on the other end by the reverse idler gear and a better design rear bearing, thereby preventing play under WOT.

Main shaft: Supported on one end by the diff final drive gear and on the other by the spring-loaded check balls as well as the bearing race, thereby preventing play under WOT.

http://www.roastedpavement.com/parts/13_2.jpg

Hope this sheds some light on some big differences between the two types of trannys......

Wow pretty cool. B15 tranny here i cooooome!

In my initial post, I forgot to mention the biggest difference that sets the B15 tranny apart. I have added it to the original post.

well whos got a clean b15 tranny for sale. im up for one of those.

so does anyone know if the p11 tranny and b15 trannys are the same??? and do you have to do the same modifications to the b15 tranny as you do the p11 tranny thats explained in the techinical library?

edit: shit nevermind i just read that thread again and answered my own question... sorry that..

matt

Thank you coalitions-el, even I could understand your write-up and pics :tongue: . I fixed my B-13 tranny just last year, but next time that biatch starts acting up, it B-15 tranny here I come!

I think we need a b15 LSD group buy :P

wait a few months on that group buy:) how much do b15 trans' go for these days?
matt

Thank you coalitions-el, even I could understand your write-up and pics :tongue: . I fixed my B-13 tranny just last year, but next time that biatch starts acting up, it B-15 tranny here I come!

No problem, even I was wondering why the B15 tranny was so much better than the B13/B14......until yesterday. ;) I figured I'd try to do a good write-up since I've seen so many other people who wondered as well.

Thanks for the writeup, bro. Very informative. :biggthump
If i ever blow up my P10, I'll know what to look for. ;)

I'm So ganking those pics man ;)

As far as the internals go, everything is different except for the diff. IMHO, it seems like the gear stacks are beefier on the B15 tranny (see pic below). Sorry that I have no comparison pics with a B13 or B14 tranny.

http://www.se-r-list.org/fifth.gear.phtml

just thought it would help a little bit.. although not by much..

http://www.se-r-list.org/images/fifth.gear/Assembled1.jpg

I have noticed before on other (simple case comparo's that the b15 tranny looks alot larger.. any way to take some measurements of the FINAL and gear set? also can you measure input to output shaft spacing? I'm simply curios :p

I have noticed before on other (simple case comparo's that the b15 tranny looks alot larger.. any way to take some measurements of the FINAL and gear set? also can you measure input to output shaft spacing? I'm simply curios :p

I won't be able to get back out and work on the tranny until this weekend, but I am definitely going to. I will most likely have it put back together too, but I can try to take some measurements for you while it's still apart. Can you be more specific as to what measurements you want taken? I understand that you want me to measure the final drive gear but what else specifically are you looking for?

with your caliper(or what ever measure ment tool) I want you to measure the Direct distance in MM from the centers of each shaft(input and output)
I'd Kill for the Sizes of the each of the input and output gears.. but it probably would be worthless :tongue:

ive bookmarked this thread For whenever I feel Competent enough to Tear down my Tranny (100,000 miles from now :D Or whenever i blow the 4th gear synchro away from abuse)

are B15 and P11 trannys the same?

b15 transmission Pinion Gear has less teeth ;) easily resolvable. during the swap I would assume.


In other words.. sorta.. b15 transmission is designed to be very SHORT ;)

OH.. and there is an extra tooth on the 5th gear of the G20 ;)

are B15 and P11 trannys the same?

I am pretty sure the b15 and p11 trannys are the same. They look just a like. They do have different gear ratios though.

From looking at this pic:
http://www.roastedpavement.com/parts/13_2.jpg

and this one:
http://www.se-r-list.org/images/fifth.gear/Assembled1.jpg

It looks like the gears are moved around on the shafts. Normally 5th gear is on top of the input shaft, but now it looks like its in the middle. In the B15 transmission, does the fork move between 2 gears, or one?

here are better pics. this is my new tranny since the 5th gear died in my ser at 44K
http://www.sr20forum.com/showthread.php?t=59871