MarkM

Looks like I may be loosing the tranny on my G class SC race car. I have had difficulty shifting up into 3rd in anger for a while, but it was manageable.

At Barber this weekend thought, I was using 2nd quite a bit and missed many critical shifts. Of course that explains why I spun so much and why those pesky I cars got around me!

Now I am finding it hard to get into 1st. I'm assuming this is an internal problem, not a clutch problem. If I'm wrong somebody warn me now please.

Assuming it's the tranny, and I need to pull it, what upgrades should I consider?

- Factory Limited slip - what do these really cost, and where can I get one
- Cooler, is this needed for a sprint car?
- Shifting mechanicals:
Gate shift - Wevo? don't know if people like it or if it's legal in stock classes, overkill?
new shifter, wevo
shift joints, ?

Any thoughts would be appreciated.

38D

A limited slip is ~$1500. You can get them at Guard Transmission(http://www.guardtransmission.com/). A cooler is only necessary if you are running hot (lots of power, etc), but it can't really hurt either.

JackOlsen

My opinions: Get a ZF type limited slip, if you're tracking the car. It will assist under braking, which torque sensing ones don't do. Guard Transmission sells them. A cooler is essential if you race when it's hot, and if you drive more than 20 minutes at a stretch. Without my cooler, I've seen 260 degree tranny temps when the motor has only been 220. This was during 30 minute or less sessions. Gear oil breaks down at a lower temperature (around 200 degrees) than engine oil.

Also, the Wevo gate shift is great.

(Dislosure: I ran a Wevo sticker in the OTC, which makes them a sponsor, in some people's eyes. They didn't ask me to run a sticker, or compensate me for it. I think their products are great.)

38D

Are you sure about that? I seem to remember Jerry Woods saying that gear oil breaks down at higher temps (and that he will run gearboxes up to 250 deg. F).

JackOlsen

I'm waiting on an email back from a tech guy at Swepco for an authoritative answer on this.

RedlineMan

Mark;

You do not mention what symptoms are present when you can't get into gears. If it simply will not go, then it may be classic crappy 911 shifting. You might do well to at least renew all the linkages and pay very close attention to the shift adjustments. If you are getting any grinding, then you know it may likely be synchros.

It could also be clutch wear or impending pressure plate collapse. Here's a test. Put the car in first gear, clutch disengaged, and start the car. Does it move forward at all? Can you only get the car in first when it is stopped and/or not running? Symptoms like that can be clutch failure. The clutch is dragging and this friction makes shifting difficult.

In a normal car, shifting difficulty without grinding is a sure sign of a bad clutch. However, with a 901/915 gearbox, they often times shift so poorly that you can't tell!

MarkM

My first thought was that it was the clutch, but now I'm unsure. I had it out about 8 events ago when the engine was pulled, and it was in great shape.

After the enduro, I had a hard time engaging 1st when the car was stopped, but could start off in 2nd, that's how I was moving around the paddock. However, when I got home and moved it around 1st seemed to work. Could heat have been a factor? If so what does that indicate? Also, I may have had it in 1st before it was started, not sure.

John, I'll try your test when I can, but I store the car offsite and it is already packed up.

My plan is to first replace the bushings and install a good shifter, then do a 'neighborhood test' to uncover any clutch problems. I can also drain the fluid and look for shavings. If it works better, I will wait until my next DE in August to stress it a bit. If I still have issues I'll pull it and deal with the clutch or tranny rebuild then.

Does that make sense?

IPC

Pesky I car driver, just wanting to say Hi. The factory Slips work very well, use a cooler when ever possible. Check all of the shifter bushings and couplings and adjustment is very critical. Any shifter is legal. only a factory slip is. Try Joe Cogbill 1-866-356-2996

RedlineMan

Hey Mark;

I'm always for a measured and methodical plan of attack, especially when it is MY money! I usually do not like to tear into things unless I have strong suspicions and/or evidence of what I am "going in" for. Unless it is quite obvious or catastrophe is seemingly immanent, I prefer to wait until the problem reveals itself in evidence before I act.

Your plan sounds good to me. Best of luck with it!