69 Trans Removal Questions

**jeff chester** · February 22, 2000, 07:20 PM

Re: 69 Trans Removal Questions

I don't think it matters what gear, although I had the body off my 68 427/390. Don't know the gear weight... jc

**Joe L.** · February 22, 2000, 08:04 PM

Re: 69 Trans Removal Questions

Bob-----

It does not matter which gear that the transmission is in when you remove it from the car. Usually, I leave it in neutral, but that's not critical.

When the trans is out is a good time to replace the fluid with 75-90 wt gear oil which meets GL-4 specifications.

The oil on the bottom of your transmission is probably engine oil which has leaked from the engine gaskets or rear main seal and has been carried back by the cars forward motion. This is a common leak pattern. However, with the trans out, I would replace the rear seal and the 2 side cover shaft seals and the extension housing reverse lever shaft seal. All are available from GM. The rear seal is GM #8673526 and the side seals are GM #3831716.

**Duke W.** · February 23, 2000, 01:04 AM

Manual trans and diff lubricants

I would recommend a synthetic manual transmission lubricant, such as Redline MT-90 (SAE 75W-90 GL-4). Most conventional mineral oil or synthetic "gear oils" meet the more severe GL-5 standard for hypoid gear lubrication. The sulfur based additives required to meet the GL-5 spec can be corrosive to brass, and GL-5 is actually "too slippery" for good synchronizer action. MT-90 is blended for manual transmissions that specify SAE 90, 80-90, or 75W-90. A similar product, MTL, is blended specifically for manual transmissions that specify ATF as a lubricant. Redline also markets synthetic based GL-5 "gear oils" designed specifically for hypoid gear differentials. One is blended specifically for clutch or cone type limited slip differentials and can be used as-is without a the supplemental additive required for a conventional GL-5 gear oil. Though expensive, synthetics in the gearbox and diff can improve synchronizer action, reduce friction, and lower operating temperatures. I think the cost is justified based on a 30,000 mile change interval.

Duke

**Gary Schisler** · February 23, 2000, 07:53 AM

Re: 69 Trans Removal Questions

Good advice by the others. As a footnote, if you have your GM Chassis service manual, this will be a good time to reference the section where it talks about adjusting the linkage. When my manual trans. was out, I used the description of the adjusting procedure to make my own adjusting gauge for my 66 shifter linkage. Obviously your 69 may have measurements very slightly different than my 66. I got some aluminum bar stock and, using the measurements in the Chassis SM, I cut, ground, and bent the stock to the right shape to fit in the slot of the shifter. It was VERY easy to do this when the trans is sitting on my workbench. The procedure didn't really make sense the first time I read it. However, once I had the trans out and on my bench it became clear. It is very difficult to do while this while the trans is in the car. That way, when you have the trans back in the car, the linkage in and connected, you will now have a working gauge that you know will fit.

As a side comment, I like the Mobil synthetic transmission oil. Gary 66 327/350

**Joe L.** · February 23, 2000, 04:43 PM

Re: Manual trans and diff lubricants

Duke-----

You know, after a discussion on this topic some time ago appeared on the board, I did a little research on the subject of transmission gear oils. I've used the Red Line synthetic product for quite some time now, although I thought that it is rated for BOTH GL-4 and GL-5 applications, and have been quite satisfied with it. However, some folks in that previous discussion were of the opinion that GL-5 lubricants should not be used in the earlier manual transmissions for exactly the reasons that you described in your post.

As far as I have ever seen, Muncie transmissions did not have a an API "GL"-series lubricant specification since Muncie transmission production ended in 1974. I believe that the GL-series lubricant designation first appeared after that time, although it is possible that it was used a little prior to 1974. If so, perhaps a 1974 owner's or service manual will include a specification. Otherwise, the transmission lubricant specified by GM was defined by a US Army Ordinance Mil-Spec designation which, to my knowledge, is not exactly relatable to the API "GL"-series specifications.

In any event, for at least model year 1979, GM recommended that GL-5 spec lubricants be used in all manual transmissions. In 1979, at least some Corvettes used the Borg Warner "Super T-10" transmission. Although this transmission was an upgraded version of the 57-63 T-10, it's construction and design is not all that different from the earlier trans. As far as I know, the transmission uses brass synchronizer rings and, at least the first gear synchronizer assembly is interchangeable between the two transmissions. Also, Muncie transmissions and T-10-series transmissions were also very similar in design and components, although no components are interchangeable.

So, I guess the bottom line here is if the Super T-10 transmission was designated by GM to use GL-5 spec lubricants, why would GL-5 spec lubricants not also be suitable for an early T-10 or Muncie?

**Duke W.** · February 23, 2000, 06:16 PM

Re: Manual trans and diff lubricants

Well, Joe, my basic rule of thumb is to always follow the manufacturer's recommendations, but when they are over 20 years old, there may be better modern products out there. Most of my opinion on this comes from the Redline technical pamphlets, and I believe their information is based on good science and engineering, not just marketing hype. The hypoid gearset in the diff sees higher loading that the helical gears in the trans, and this is why GL-5s are specified for hypoid diffs. To achieve the EP (extreme pressure) lubrication qualilities required by the GL-5 spec, the sulfer based additives must typically be present, and these additives, according to Redline, may be corrosive to brass, particularly at elevated temperatures, plus the superior boundary lubrication characteristics of the GS-5s actually inhibit optimum sychronizer operation, which require friction to operate properly.

Most modern sidewinder stick shift drive trains usually specify GL-4 oil. Of course, the final reduction in these transaxles is a large helical gear, not a hypoid, so they don't need GL-5 protection. An interesting case study is the ZF transaxle in Panteras and GT 40s. In this case you have both sychronizers and a hypoid gear set in the same housing, sharing the same lubricant, eventhough their lubrication requirements are fundementally different. My friend with the Safir GT 40 uses a special lubricant from Porshce/Audi as they have the same transaxle characteristics as the ZF. I'll make a note to ask him to see a bottle of it to read the specifications. The drivetrain of the C5 is also an interesting example. Though it is typically referred to as a "transaxle" it technically is not because the trans and diff are in separate housings, and each has its own separate lubricant supply.

Manual transmission design has not fundementally changed for nearly fifty years including materials, so I think the GL-4 is adequate, but you raise some good points about the old specs. Maybe one of use should call Redline and discuss these issues. You're closer than I am, what do you say? I think Redline recommends the MTL or MT90 for all converntional manual tranmissions, and I assume it's what all the racers are currently using. I think the four-speeds in all the current NASCAR classes are basically of the same design and materials as our old T-10s and Muncies, but one of us should look into it in more detail.

Duke

**Bob Lanham** · February 24, 2000, 08:06 AM

Redline Products

Where and how do you get them? I don't recall ever seeing them in my area.

**Joe L.** · February 24, 2000, 12:17 PM

Re: Redline Products

Bob-----

Red Line Products are not as widely distributed as the "national brands". Usually, you find them in specialty performance shops, and the like. They are located in Martinez, CA. I don't have their number handy, but I'm sure that you can get it from the information or off the net. Then, you could call them for the location of the nearest distributor. Also, I believe that they sell direct.

**Duke W.** · February 24, 2000, 02:25 PM

Redline will respond

Redline has moved to Benecia. Their web site is redlineoil.com, and there is a lot of good info. I talked to Dave at Redline this morning and invited him to post a response. It turns out that they DO recommend a GL-5 for our four-sppeds, but I'll defer the details to Dave who will, hopefully, have a post for us late today.

Duke

**Dave Granquist** · February 25, 2000, 12:04 PM

Red Line Oil Co.

If you are interested in manual transmission fluid, GM calls for an 80W GL-5.

I would recommend either the LightWeight NS or 75W90NS in the transmission. The LightWeight NS is closer to the original viscosity and would probably offer a little better cold shiftability, the 75W90NS is more widely available and slightly higher viscosity. It should still offer good all around shiftability.

If you have any additional questions feel free to email or call me at (800)624-7958.

Regards, Dave Red Line Oil

Red Line Oil

69 Trans Removal Questions

69 Trans Removal Questions

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