Well, I have been busy rebuilding a transmisson and went ahead with flipping 5th and 3rd gears for AXing. It's been interesting to say the least but not too hard. Here is a shot of the assembled gear stacks.
Geoff

I don't really get what you get out of doing this.
Can you put it in Moron terms?

A close ratio tranny. By flipping 5th into 3rd's place you get a shorter gear. So 5th gear is then also a little shorter too but I don't go 120mph anyway.

Right now AXing, the problem is when to shift to 3rd, we are reving 2nd out to 5000 but sometimes the drop seems too great when you hit 3rd gear unless its a long stretch on course. Soo, you kinda hang at there trying to decide should I shift or not...then the rev limiter hits (5800) so you know you are losing time.
I have a chart on the other computer I can't get too to show the change.. I look for it online.
I am rebuilding this orginal to the car tranny because the other one is having problems. (bearings)
Geoff

The chart:

So, instead of just replacing 5th with another 5th, yo are using the flipped third? Is the tranny together yet? How does it drive? When are we doing mine?

I just ordered a set of Panasport wheels and V Racers

On/in my future setup, I will have a 78 stroke. Thus, giving me a bit more low end UMPF...

My thinking, flipping would not benefit me. Or am I another moron?

Enlighten me...

I already know I'm a moron... but humor me, doesn't that take out your top end?

Using the stock gears on the track or at an AX you will never ever see the "top speed" of the car.
For a race car you gear the transmission so you can use all the gears.


The 901 based gear boxes offer a wide range of gear choices. porsche designated them alphabetically A through ZD (I think) some gears are very rare and costly. A easy way to fill the hole ion your gear selection is by inverting a gear take a Z (29:23) and flip it you now have almost an M (22:29)

There is no reason at all to have gears to go 155 mph if you dont have the power to get the car there. My cars are geared to a max of about 145, but I can use all 5 gears.... The RPM drops on each shift decrease in a good way... 2-3rd is about 1000, 3-4th is about 800 ,4-5th is about 600.. This keeps the car in its power band..

The faster the car is going the harder it is to push through the air.... hence wanting less rpm drops.

close ratio gears lets you get the most out of your engine..

do you have a "street" trans, and a "race" trans? or just one total

ok, now I get it, thanks.... as I said, I know I'm a moron esp. when it comes to AutoX...

Tim,

After reading your post, I am thinking that flipping or changing will benefit me (see my first thought above). See, I am building this car for a specific driver. He is an excellent driver. I feel comfortable sacrificing a little high end for a bit more torque and bite in the bottom end ONLY because he (the driver) can handle all the extra "squirliness" in the tight corners. Constant shifting (up/down) will be smooth thanks to Rennshift.

So, am I correct in my thinking now? That, due to the fact that I could shift sooner, the RPM's drop less, and use 3rd and 4th rather than 2nd and 3rd. Then again, with the closer ratio gearing, you'd be finished shifting and have to start the next shift

The idea as TimT said is to stay in the power band with your gearing. I know top hp for me is 5200 so I want to shift just after that and be in the engines power in 3rd without it dropping revs too far drop out of the top power range. Anywho, I am giving it a try. Nothing lost, nothing gained.

Aaron, I do have another street tranny in the car. It needs attention real soon! That is why I pushed doing the AX tranny now as the next race is on June 21st.

Korijo, I don't have any idea what the power band of your motor will look like other than with all that stroke I would think it would be at lower rev's. Depends on the cam too. Jake Raby puts in a mild cam for bus motors so all the torque is down low. For the bugs he runs those 86a combo's which moves the band up higher.

Geoff

Cam is 86. Prolly puts me right in the middle

Bleyseng,
Did you pull the tranny apart and make this change only using stanard tools? Or do I need to get those "special tools" I see in the catalogs?

Paul

I already had the deep dish 30mm socket from changing first gears. Other than that just a small gear puller. It wasn't a hard job at all but time consuming like assembling a engine. Putting things together and then apart, test fitting, cleaning everything.....I used Red Beard's article plus the factory manual.

I will install it in the car in the next few days.

Geoff

Very interesting transmission changes, of course you are declaring these changes when you AutoX. I would think that this would put a 914 into modified class. If not I will re-read this topic and maybe next year make the change.

Its legal in the class I run. Wouldn't want to cheat...besides Chris Reale reads everything I post so he would tell!
Geoff

I would'nt tell, I'd just copy you

I just finished putting the rebuilt tranny in. Now all I need is a clutch cable. The old one had 2 strands left so no wonder the petal felt weird.
Drained the oil out of the old tranny and its full of sparkles
The pilot shaft also has lots of play in it which doesn't bode too well.

Geoff

I just drained my tranny oil a few weeks ago and it was full of "sparkles" also. I might have something like 1000 miles on the car since I last changed the gear oil. Is this normal wear? Synchros or what?

In my case I think the bearing in the intermediate plate are bad from drying out. There was "only" 35K on this tranny as the car was driven only rarely before it got T-boned. So its quiet possible that it ran out of oil long ago because its alwasy made noise.
The red arrows point to the location of the bearings that I replaced on the rebuilt tranny. There should be very little movement in the shaft, up/down,side to side. back and forth. The tranny I just pulled, the pilot shaft moved about a half inch up/down causing the pilot shaft seal to fail and leak tons of oil.

Ok Eric, some sparkles are going to be present in the oil just from the gears grinding, etc. Syncho's shouldn't make alot of particles as they are a brake but the oil keeps them lubed. They don't mash against anything, they rub. Dog teeth and sliders can make metal flakes if the synchos are failing and the dog teeth and grinding when you shift.
I would look at the magnetic drain plug for lots of metal. If there is lots of metal attached to the plug that is not good.
Do your gears grind when you shift? I never have driven your car yet to see how it drives.
Geoff

Here's a shot of the 2 intermediate plate bearings.

This is cool info....The only thing that I would add; The drop between 3rd and 4th is now larger....This is the problem that I have on my local track.....3rd is tached out, 4th doesn't pull like I want...I would do the flip 3rd/5th thing and then get another 4th??????cool work!! thanks, herb

Good info Goeff.
So are the ratios of installed gears equiped in 914's for the build yrs all the same? Prolly not...1.7-2.0. Does someone have a chart?
and more importantly can you tell what the OE application was therfore what gears might be found inside w/o taking apart?
I have 4 (I think) 901's out of various yrs and engines. Im wondering what kind of selection I have available to me.

Geoff, you drove it quite some time ago. You mentioned that it shifted real well and in fact I think it still does. I do have to go slow into first so I can mesh the gears or else it'll grind. The magnetic plug had a fair amount of metal on it this time and last.

Hmm, must be gettin old can't remember or was it when it was the awful color before.

All 4 cylinders trannies are geared the same, the only option was the LSD. Hmm, I wonder if that was available in 1969? Is that why the OP Art seats became available because of the LSD?


The thing to do is to pull apart the trannies you have and source out the best sets of gears and sliders. The tailshifter trannies can have better gears and sliders (esp 4-5th) probably because you had to shift slowly and couldn't cram the gears together as easy.
I did re-use the sliders on the rebuilt unit, just too expensive for me at this time.
I had a prefect 1st gear setup that I bought at a swap meet that I used, so all I had to do was install a syncho on a nice 2nd gear, and install the bearings.

I'll have it running in a couple of hours....I hope.

Geoff

Yea it was before it was re-painted.......that same awful color.

I'm pretty sure it was a few weeks after I drove your car and the gearshift knob came off in my hands...... I've learned to be more gentle...

Thats how you know when you are shifting too fast or hard in my car, the damn knob comes off!

Geoff

Geoff,

Did you replace the dog teeth on any of the gears ?? I would like for someone to show the home users how to do this WITHOUT the proper tools. I have spent several hours trying to figure out a removal procedure that doesnt utilize the factory tools.


B

No, I could have but no time for it right now with a "race" this weekend. I used the best sets and they had excellent dogteeth.
Next week I am going to tackle the other tranny so I will take pics as I go.
I get tired of staying up til midnight to finish projects. Took today off so I can finish installing the clutch cable and start it up.
Hell, Blair is already to race. "Is it done yet?" course he slept til noon..

Geoff

Geoff:
I was looking at the results of the last PNWR AX.
Your son has no respect for his elder. This is embarassing for the oldfart brigade. May I suggest
the old broken fingers ploy....one on each hand ought to do it.

ulf is indisposed and won't be making the trip up there . I may come along with Doug Skinner....if I ever hear back from him.

I've replaced the dog teeth on 1st gear without any factory tools. I can't remember if any other gears would be any different than removing them from 1st. IIRC, I think that I just used one or two big screwdrivers to lever it off somehow - been awhile, but I don't remember it being too much of a problem. Come to think of it, I think that I removed the snap ring and removed the synchro, and then re-installed the snap ring to give me something to lever off of.

Demick

JP, I did ok since that is the first time I ever drove the car on dry payment on the Kuhmo's. I kept hitting cones since it turns soo much quicker! I do ok, plus he does have real good driving instincts. He's fast with a car that is undergoing improvements as time and money allows.

On the tranny- folks it was a huge success! God damn thing shifts like new without any, I mean ANY GRINDING in any gears. Very quiet too. Third gear is shorter but nice and in the power band when you shift from second. I might go back to 60 series tires for the street with this set up and use the 50 series for racing only.

This was about a 6 on a scale of 1 to 10 on home car projects. Changing out the dogteeth isn't easy but worthwhile to build a good tranny.

On the old one I pulled. Drained the oil and parts of the bearing cage came pouring out too! yikes . I knew it was dying but I hope the gears are good.

Geoff

What color are the sparkles? Silver or gold?

Sorry, was replaying to the previous page. What color was the cage?

The small caged double bearing set in the intermediate plate is usually the one that is dead. But I have seen every different bearing bad in these trannies.

My guess is lack of oil - Change that tranny oil boys, change that tranny oil.

James

silver and pieces of gold cage..
I think that it has run out of oil by the PO since I have been checking it the whole time I have had it. Plus, it been making a whine ever since I bought it.

I used your article to do the work Red Beard, nice work. Although it would be nice to have the torque numbers on it too.

Geoff

Is it true that 2nd gear is part of the mainshaft, so in order to use any other gears, one must first obtain a rather pricey "904" mainshaft?

Yes, but why do you want to change 2nd gear which is good for a four or a six. Only a V8 or a track car need a different ratio.
AND if you are in that league then step up and buy one and rebuild the whole damn tranny cuz if its old (100k) it will die with high hp or heavy track use.
Most of these tranny were neglected by not changing the oil or poor clutch adjustments so atleast 1st gear sliders are shot, 2nd gear synchros are toast and the intermediate plate bearings are gone.

Geoff

Because if I move 2nd, 3rd, and 4th up into 3rd, 4th, and 5th position with the 3rd and 5th flip-flopped, I will have a big gap between 1st and 3rd.

I have installed a flipped 5th gear into 3rd gear. I have a drop of 500 rpms from 2nd to 3rd which is nice for AX and around town. From 3rd to stock 4th there is a drop of 900rpms, and I have reinstalled a stock 5th gear so highway driving is normal.

Ottos sells the 904 mainshafts if you want one.

Geoff

True. You have a choice of F, 4 cyl. main shaft, or GA, 6 cyl. main shaft, or a 904 main shaft that lets you choose 2nd. I believe Otto's is a good outlet for the 904 mainshaft.

Thanks for the Otto's tip. I'm thinking of 14:37. Am I nuts?

For that 3-4 drop, an "S" 4th gear should put you right in the middle.

One thing to keep in mind -- if you get the 904-type mainshaft (removeable 2nd) then you also need a gearset to put on it. So you get to either locate a real factory 904 gear, or source a repro from somebody like Paul Guard (GT). Not an inexpensive approach...

Yeah, yeah... it's all expensive.



M

What about mainshafts for the 901s for the 911, did they have different mainshafts that you can get?
Its always in life, if you want more choices then you have to pay more money.
Geoff

Since I have to fix the trashed 1st gear synchros, I was going to open up the gearbox out of the car. It is true that I can move 2, 3, and 4 up into 3, 4, and 5 and get a 904 mainshaft and 14:37 gearset for 2nd, but that is a whole lot more expensive than simply doing the 3rd, and 5th flip-flop.
BTW, will it hurt my gearbox to start in 2nd until I can fix 1st gear?

No, this is not true (with the original gears).

2nd drive gear is part of the shaft (hence the need for the 904 mainshaft in order to install different ratio gears).

3rd can't be installed in the 4th position without flipping (changing the ratio). This is because of the different syncro location (one is on the drive gear and the other is on the driven gear.

You can move 4th to 5th (without flipping) to put the original 4th ratio in the 5th position, but all the other gears will require changing to do what you are saying.

You can fix the 1st gear problem without pulling the tranny, just remove the nose cone for access. Besides the synchro check the condition of the dogteeth and slider also. Just changing the synchro won't help much if those parts are muched. Years of grinding 1st gear destroys em.

Geoff

Will 915 gears fit a 901 gearbox, or are they too wide?