With all of the brouhaha over Mobil 1's zinc and phosphorus formulations, I am scrutinizing all of my 993's lubes. One area that I want to address is a 2nd to 3rd gear gearbox crunch that I sometimes get, most notably coming out of T1 at Summit or T1 at VIR. I don't get it all of the time, but when I do hear it, I cannot help but think that I am making expensive noises. My box is stock, has had the third gear synchro already replaced with a stock brass one and uses Redline shockproof lightweight synthetic gear lube.

So, do I go with Mobilube 75W-90 SHC gear lube (http://www.lufteknic.com/Merchant2/m...ode=lubricants)? Another Redline? Amsoil? Swepco 201 GL5 Multi-Purpose 80W-90 Gear Lube (http://www.lnengineering.com/store/c...products_id=40)?

I tried a search, but maybe I'm using the wrong keywords, for there was hardly anything out there. I'm also certain this has been discussed for G50 trannies, but I just can't find the threads here. Any advice, experiences or threads would be most appreciated.

 

I don't know what the answer is but I have almost exactly the same scenario in my G50 once in a while. 2nd to 3rd upshift under heavy acceleration. And I also had the synchros replaced a year ago (with stock brass) and it still does it sometimes. (I'm running SHC fluid.) But it only seems to be at certain places on the track with the car under a heavy load having just come out of a turn onto a straight. So I've started wondering if it has something to do with the mounts. Could it be the trans mounts are flexing just enough under load to cause the linkage not to line up perfectly? Just a thought. My solution so far has been to just pause between 2nd and 3rd for a breath. When I do that, there is no crunch.

 

Mark, if you use a gear lube that is slippery, ie one designed for an LSD specifically, like Mobil 1 75w90 then it becomes too slippery for the syncro to grab the gear and spin it up properly. This is one of the factors of why the Mobil 1 Delvac SHC works better than the standard Mobil 1 75w/90 and is the oil Porsche motorsport was using in the 996 GT3s.

 

Greg - Thanks for the comments.

Geoffrey - Thanks for the info. Where do I source this stuff out and what is the weight? On Charles Navarro's site (also posted above), he sells this stuff: http://www.lnengineering.com/store/c...products_id=39 Is this it?


Mobilube SHC Delvac 1 75W-90 Synthetic Gear Lubricant

Mobilube SHC 75W-90 and 80W-140 are fully synthetic drivetrain lubricants engineered to meet the most demanding extended drain and OEM warranty requirements. These products are designed for use in heavy duty drivetrains that require gear lubricants with excellent load-carrying capability and where extreme pressures and shock loading are expected The state-of-the-art technology in Mobilube SHC 75W-90 and 80W-140 delivers unequalled performance for low and high temperature applications, including outstanding oxidation stability, wear protection, corrosion resistance, improved shear stability, extended service capability, and excellent fuel economy.

Mobilube SHC, also known as Mobil Delvac Synthetic Gear Oil, is the factory fill from Porsche on factory cars and is different from Mobil 1 Synthetic gear lube typically sold at local auto parts stores. We recommend this gear lubricant in G50 and later manual gearboxes (or any gearboxes calling for a GL5 lubricant) for both aircooled and watercooled Porsches with or without limited-slip differentials. Although also compatible with earlier Porsche gearboxes, Swepco 201 is a better choice for these gearboxes in our personal experience (including 901 and 915, as well as VW manual gearboxes).

These products meet API MT-1/GL-5 EP gear oil service classifications and are MIL-PRF-2105E quality level. The outstanding performance of these products is confirmed by their approvals for use in axles covered by Eaton Roadranger (E500TM) and ArvinMeritor Extended Warranties of 750,000 miles, with extended oil drains of 500,000 miles. They are also approved by Mack against GO-J Plus (75W-90) and GO-J (80W-140) extended service classifications.

The performance capabilities of today's heavy duty on- and off-highway equipment have vastly improved in terms of load, torque, speed, and reliability through innovative powertrain designs. These designs have increased demands on axle lubricants, requiring them to deliver higher levels of performance. For heavy duty axles, friction control, wear protection, thermal stability, shear stability, rust and corrosion prevention, and seal protection are features that must be balanced to provide extended gear and seal life, smooth operation, improved fuel economy and high load, high torque capability over a wide range of applications.

 

Yes, that is it.

 

Cool. Thanks, Geoffrey!

 

Being a natural skeptic ...

I can appreciate that the lube will make a difference. But I have a hard time understanding how the lube will make a significant difference when the "crunching" on the shift only happens in certain corners (Mark cites T1 at Summit or VIR, for me and others out here it's T12 at Thunderhill). Wouldn't you expect this to be more related to flex in the system (motor mounts and transmission mounts) than lube choice?

 

Just to clarify, I am running SHC and I still get the 2-3 crunch now and then on certain corners.

 

I'm not implying that the gear oil will cover a mechanical issue.

 

Tom,

I thought I had read about people having synchro issues that were cured or reduced by changing gear oil. Maybe I just imagined it. I don't think so, though.

 

I have the same issue and basically solve it by not using 2nd gear (DE car only). This year, I was planning on installing solid transmissions mounts. Has anyone tried them, and if so, did they this issue?

 

This is what I use......

It is the replacement for SHC LINK

 

Dell,

That's what I linked in the first post. Have you had shifting issues? Did you ever try the Mobilube SHC Delvac 1 75W-90 and not like it?

To Geoffrey: Is this Mobilube SHC Delvac 1 75W-90 lube the 75W-90 that you referred to as being too slippery?

Thanks, guys.

 

I can see a less slippery lube helping a crunch issue when you are shifting too fast for the synchros to keep up, but on corner exit, isn't it more of an alignment issue due to chassis flex? I've tried a few different Mobil1 and Redline oils (although not the one you are asking about) and saw no difference in my 2-3 shift grind while turning.

 

Mark, what you linked was the SHC. Delvac is the NEW formulation and not identical to SHC. I have experienced no problems at all. Just got a fresh fill last week and hitting the track this weekend....I can report back. FYI....I have not used SHC as it was not available when I made the switch last year.

Here are the info sheets on both SHC and Delvac directly from Mobil1......