Synchronizers and gear oils

[geesamand]

I have a few questions about modern synchromesh designs that have been nagging me.

1) How much of a difference does a GL-4 vs. a GL-5 oil affect synchronization and synchro wear?

2) I see some mfrs using more double- and triple-cone synchros and others recommending friction modifiers to add to the gear oil. Is this to make the GL-5 oils synchronize like a GL-4?

Any other comments on this subject are appreciated.

Dave

 

[Fabrico]

Rather than speculate why not try it. You can always go back. Your main concern would very likely shift to operation.

 

[geesamand]

They all 'work' IME. My concern revolves around chemical and mechanical wear in the long term.

So for example, will using an extra-slick GL-5 wear out the synchros in a tranny designed for GL-4? Even if the GL-5 claims to be synchro-friendly?

Dave

 

[Tmoose]

Some late model Corvette transmissions (ZF?) have a reputation for generating significant quantities of bronze particulate mud and require both special synthetic lubricant and frequent changes to achieve old age. At one point a few years ago I think there was just one lube in the world(maybe by Castrol) that was ZF approved.

 

[TVP]

FYI, ZF maintains a list of approved oils for their transmissions, etc. on their website. Use the following link for more information:

http://www.zf.com/MTAusgabe/appportal.asp?lang=1&mID=1222&app=http:_0__0_

http://www01apps.zf.com_0_kst464_0_..._0_default.asp_1_lang_3_de_2_spc_3__2_hdr_3_1

 

[geesamand]

Interesting tidbit about the vette boxes.

The autos in question are imports. Most of these trannys appear to have been designed around GL-4 properties, but in the last 5-10 years the commonly available lubes are now GL-5 rated. The manufacturers have revised their literature to accept both GL-4 and GL-5 (rumored to be because of pressure from dealerships, who didn't want the hassle and cost of sourcing GL-4 anymore).

So the question remains, is this a semantic difference, or is there a significant difference esp. w.r.t. synchronizer wear and performance?

 

[NickE]

Do these transmissions have two hypoid differentials in them?

Nick
I love materials science!

 

[geesamand]

No, these are common FWD layouts with a helical final drive gear. So the contact pressures probably won't benefit like a hypoid set would.