Beetle 4th Gears Between

[HeliMike]

After my initial post \"HERE\" Bruce touched on the fact that the AT code IRS should have a shorter 4th than an AH but didn't get into too much detail.
I am rebuilding an \"AT\" code beetle trans which from what I'm told should have the 3.88 R+P in it. I also have an \"AH\" code (4.12 R+P) tranny sitting around for parts. What I'm wondering is does my AH have a taller 4th than the AT and if it does can I swap 'em over with any kind of whorthwhile improvement in top speed for highway driving.

The tranny in my car now is an AH SSC which I'm assuming has a 4.12 R+P. It has more top-end than my swingaxle did but there's still room for improvement I think. Anyone care to elaborate?
Cheers
 

[Mike Scott]

Hey Mike,

Im sure Bruce knows better but from what I m remember. The 4.12RP amd 3.88RP tranny's both have similar final drive gears (3.88RP and 0.93 4th) approx. = (4.12RP and 0.89 4th). So if all the parts are the same (Which I have no idea), If you combo'd the 3.88RP and 0.89th you'd have a higher top speed. He also mentioned some bus tranny's had a 4th of 0.82 [----better yet for top speed

Help? Say where did you get all those tranny's?

[Mike Scott]

Guess I could of clicked the \"HERE\", whoops.

[HeliMike]

Help? Say where did you get all those tranny's?

:lol:
Yeah, Thanks Mike.  
I put a steering wheel under my pillow after it fell off and when I woke up in the morning the tranny fairy left me some presents!
But seriously, I've got the \"howler\" in my car now, Mikey had a dead AH with no diff hangin around in his garage and that dead AT that you donated. I haven't had a chance to open that one up yet so I don't even know what the hell's going on inside it but it should be repairable though.

BTW did you want the \"howler\" back after I take it out of the car? She'll be coming off the road in roughly 3 weeks for the big makeover so I can get it to you then. Let me know!

[Hansk]

Hey Mike, good to meet ya tonight(again)  Anyway , I did a quicky on line calculation .  I assumed a 3.88 r&p and 24\" tires for all cases and....

.93 4th = 59mph @ 3000rpm
               79 mph @ 4000rpm


.89 4th= 62mph @ 3000rpm
              83mph  @ 4000rpm


.82(bus4th) = 67mph @ 3000rpm
                      90mph @ 4000rpm

I'm kind of thinking that if you actually had 24\" tall tires the .82 would be too tall.  You would be doing much of your freeway driving at only 3000rpm or less. Ya sounds nice and cozy but your poor motor still has to make the power required to go that speed but cooling fan speed is lower.  I'd only do it if you had even smaller rear tires. Just my opinion.   Later

OH and.....
stock 4.12 tranny =58mph @ 3000rpm and 78mph @ 4000rpm (24\" tires)
very close to the stock 3.88 . Was that swing axle a 4.37 ?

[HeliMike]

Hans you're the man! :lol:   Thanks a bunch.  
I've got a beer waitin' for ya next time I see ya.
Time to start haulin' apart my tranny's!

[Hansk]

No worries, it's what I do for fun :wacko:

Keep each tranny in a seperate pile!!!!  everything!!!

[Bruce]

The tranny in my car now is an AH SSC which I'm assuming has a 4.12 R+P. It has more top-end than my swingaxle did but there's still room for improvement I think.

The gearing of your AH trans should be exactly the same as the original stock T3 trans.  Could the improvement in top-end be in your imagination, or did you take RPM readings at speed?

If your current trans is indeed a SSC with AH code, its a pretty rare item.  Very few AHs were made as SSCs.  But you are in luck.  The internals of SSCs are all the same as 002 type bus parts.  That means you can swap the 4th gear from the AH into your AT trans and get the rpm changes Hans posted.  Another alternative is to install a Bus .82 into the AH gearbox.  If the AH gearbox is in better shape than the AT, this could be easier.

To others reading this with any DSC AH gearbox, the gears in those will not swap into an AT trans, and vice versa without doing major parts swapping.