It certainly could be my fault. I didn't check/set/change the pinion depth when I re-assembled this gearbox 2 seasons ago.

At Mid-Ohio this weekend I couldn't catch 5th... which led to pitiful laptimes.... in the first session. So, I adjusted the linkage thinking that the fork just wasn't pushing the engagement ring far enough.... next session, same thing. I didn't take the start and watched from a corner station.

So, after that I checked the shift linkage, no major issues. I pulled the shift rod holder to look at the shift forks, again no major problems. So, I decided to pull the gearstack and that's when I noticed the pinion pictured here..... still not sure what the problem was with 5th, but it is probably worn synchros.

I rebuilt this gearbox before the start of last season and only refreshed it with parts I had....flipped synchros, better dog teeth, a few gear changes and no bearing changes. I'm only running 150 ponies through this box.

It looks like the pinion isn't meeting the ring at the right angle, but I'm just guessing. Does anybody have input????

.............sorry for the crappy pics, my camera wouldn't focus on the part I wanted ot show.

could the bearing in the int plate be "walking" so the enagemen is changing?

flexing int plate or worn bearing?

waaayy to many shims/gaskets?

AA

It wouldnt go into 5th because a piece of the pinion gear was blocking it!!

Welcome my friend to the most common failure in 914 tranny's that we see racing them

No joke. This is something we see regularly against the race engines. 1-2 a year that is.

You had a bad R+P to start with. I doubt seriously it had anything to do with your pinion depth. Several years back I had multiple conversations with Roger Sheridan about how difficult it was to find good 901/914 R+P's here in CA. He blew up his 901/914 box with the exact same results you have shown us here. He went to the 915 for the very next season and hasnt looked back.

What I would do: collect 3-4 R+P sets and have them X-rayed and cryo'd before having a known good tranny place set the pinion depth for you (I'd send it to WEVO personally) send it with just the input shaft/pinion shaft/diff in place. You can do this by only assembling the spacers/gears on the two shafts into the intermediate plate. He has to be able to torque down the two large nuts.


Bottom line: make it VERY easy for the shaft/shims to be removed from the tranny intermediate plate so they dont have to fumble with all the other crap associated with setting the depth.


B

Check the race in the case also. This is something else I have seen cause this failure (just like the 915's) The race will spin in the case even though it is supposed to be a "press fit"


B

Funny, at the Laguna event I couldn't catch 5th on Sunday, it felt like the trans was pushing back against the shift rod. While driving around my neighborhood I realized I could shift into 5th no problem if I double clutched. That's what I did for the entire weekend at Buttonwillow. I know I have a problem in the box but for now it works double clutching.

It is pushing back against the selector rod for 5th

I'd have to show you how...



B

How hot does the transmission get?

Good input peeps. Thanks.

The bearing race is still press fit.

The trans does get pretty hot... and I have an open differential. This certainly could add to the problem.

I know what I need to do, go with a Hewland. But, my job here at Ford isn't exactly secure these days. So, it will have to wait.

I had to put a tranny cooler on the FP car I support out of NorCal. I also had to stop running Redline synthetic a few years back. We ran 3 different boxes for our 5-6 tracks.

I ran one channel of the data acq to a temp probe in the tranny.. NOT GOOD. It also had a lot to do with the header we ran. The collector and stinger were directly under the tranny.



B

We had the heat issue in our GTU car. Granted it wasn't a Porsche, but heat will kill gearboxes. We ran no pump and had problems then we got a pump and a cooler and stopped having as many issues. Then we changed gearboxes all together.

There is a reason Porsche quit using the 901 box. It is undersized for engines with more power than the stock 2.0 six cylinder engine. You could build a "better" gearbox for less money than the Hewland, but you should still plan on upgrading. With Proper maintainence and good cooling you can probably get it to live. But you should probably take it apart every few races and check it.

Yeah I shot my tranny with pyrometer at Laguna after some fast laps. It was in 260 range. That may have been due to some radiant heat from my headers?

I spoke with WEVO on MANY occasions about doing a Hewland conversion for the 901/914 tranny. The centerline measurements are identical to the MK's and Hewlands so gear options are plentiful. I was looking for a "lift throttle" upshift solution at the time.

Now I'm taking apart Boxster tranny's...LOL


B

i heard mendiola was onto sequential mid engine boxes...

They are, but we dont need a Ford 9inch diff for a T4 race engine..LOL His are designed for V8 conversions in Sand Rails. It would take 20hp to turn the diff


B

Check the Cover pre-load.

Jerry Woods like the Cover Pre-load at 8-10ths, not the 0.006 Porsche spec.

Ken

We need a stronger tranny period. Scratch the Hewland guts in our case, lets find a way to adapt a boxster tranny to our engines.

I was under the impression that Boxster tranny parts were hard to come by.
A guy named Chris that runs a CHP looking Boxster said that he couldn't get any synchros and had to buy a whole tranny for $1500.00.
Have things changed?

For my situation the Hewland offers enough advantages for not very much extra $$$$. Staight cut gears, dog engagement, usable 2nd gear..... I've been told I need to run the Mk5 gears because of the power.... Mk5 gears can take 240 horsepower, so I'll be in fat city.

I just have to wait a few months to make sure my wife and I still have jobs. So, in the mean time I'll through together another junkyard gearbox to get me through some races early next season.

Despite all of the internet doomsday predictions....
AJRS insists on running mobile 1 tranny fluid.
I've been doing it for 12 or so years now with zero problems

I'm making an assumption that this is done for heat reasons more than anything else.

He also does not experience as high of a failure rate as the internet doomsdayers discuss. Granted he will switch from a 901 to a 915 at 250hp...

but his T4 car runs 205hp out of a 2.2L
He has an F 1st gear (904style main) and uses it regularly.
people claim that you CAN'T use first gear with 200ft lbs... yet he has had this tranny on the track for 4-5 seasons now without any problems.

Hmmm...
maybe the internet doomsdayers aren't all they are cracked up to be?

brant
FJOSV

I agree with Brant, Mobile 1 is good stuff. I never liked the way Swepco shifted and the Redline stuff just seemed to create a lot of extra vibration. The tranny just didn't seem as smooth with redline. Mobile feels great.

Straight cut gears and dog ring engagement are the way to go. If you go with a MK5+ box you will have to put a good cooling system on it. You will be very close to its limits.

One thing that many people forget in racing and in the chase for HP, if you don't finish you have no chance to win. In Kevin's case the Honda Prelude and Caterham/Lotus 7 have more than adequate gearboxes to start with. Same with the RX7.

we have actually now switched from the mobil 1 75-90W

over to the Mobil 1, 140W
(available at semi truck supply shops in a 5 gallon drum)

anybody need 4 gallons of left over 75-90W in my garage? ha...

brant

We run nothing but Mobil1 in all the late model tranny's. I run Swepco in STREET cars. I'm up to 4 tranny's now that dont shift when they have 20miles of street driving on them. Common denom: Redline Synth in all of them for a short period of time.


KenH,

I'm betting this was a stock tranny that was never checked. You would be amazed at how few people actually have the proper tools to set pre-load on the diff. I can only think of 10+ shops across the USA that have a decent selection of pinion shims.


B

I certainly didn't check the pinion depth..... but I also didn't change any parts that effect the pinion/ring mating. I only changed out 3rd, 4th and 5th gears for shorter ratios... no bearing changes. I was anticipating going to a Hewland eventually.

Seperate question, that I'm sure everybody already knows but me. Does a 915 bolt up to a 4 cylinder? Can I move the ring over to the correct side? Is it a feasible solution?

You want a 76 912E tranny. It is a direct bolt up 915 tranny with a T4 clutch input splines.

Yes. You can easily flip the diff and run a WEVO shift solution if you choose. You can also go to straight cut gears (dog ring box)

It would be cheaper/easier for you to switch to a MK/Hewland solution.

Unless you measured the gears coming out and the gears going in and KNOW for sure that they are identical.. you should have checked pinion depth. Not all gears are created equal. You see/hear of us talking about switching out gears, but no one ever talks about the consequences.

We ran with 3 boxes as I mentioned above. All 3 had LSD's. One was partially disassembled until we needed it for a race. All the gears where pre measured so we wouldnt mix gears sets against the "pre-set" R+P of the 3rd tranny.

You are doing fine with what you have. Slap another tranny in it like you mentioned and go on your way


B

I hear you Brad. Considering the cost of the "rebuild" 2 seasons ain't too bad. I knew I was cutting corners when I did it. I can't help it, I'm cheap.

Another question on the 915... Ignoring the clutch spines, since I'm fitting a new 7.25" clutch and pressure plate tilton and they're relatively cheap, will other 915 boxes bolt up to the 4 cylinder, or is it just the 912 box?

Ironinally the 915 2nd, 3rd, and 4th line up quite well with the 3, 4 and 5 ratios I've been running. I'm just thinking of building a more solid back-up solution and then wait on the Hewland for a bit longer.

Yes. You can actually bolt a new 996/997 GT3 tranny to your 914 engine. It weighs more than the 914 engine, but you could.

Yes. All the 915's are direct bolt up. The 915 pilot bearing is the same bearing used in the 914 flywheel.

The big difference: 914 uses a push clutch and the 915 uses a pull clutch. This is VERY easy to get around.


B

I have never seen the tool to setup ring and pinion, could it be done with a dial indicator, kinda like checking the backlash on a cam gear or intermediate shaft gear?

how do you set the preload on the diff and how much?

Set pre-load.

Remove the o-ring gasket from the cover. Set the cover on the bearing. Using 4 bolts on opposite sides of the cover tighten them equally until there is a "even" gap all the way around the cover and the case. Note - exert as little pressure on the cover as possible. Measure the gap. Look for .008-.01" gap. To change the gap the wheel bearing has to be removed and shims are placed under the bearing. Shims are available from the dealer.

At several of the vintage races I have seen some of the old Can-Am cars barely make it through a weekend without R&P failure. They all looked just like yours. I have seen several of the HSR/HSR-West R&Ps that failed and they were all the same too. Most of the 2L class 911s and 914s run a cooler and pump system to get cooled oil on the R&P as I started to do a few years ago and so far I have had no failures. Most setups I have seen have a nozzle over the R&P and another over the gear cluster. A handy addition is the temp plug adapter that Jim Patrick sells that replaces the speedo plug and lets you use a VDO gauge to keep an eye on the temps.