I recently purchased a 1990 Corvette with a six speed manual transmission. I took it in for an oil change, and the mechanic was unable to remove the transmission filler plug because the inside of the hex hole in the plug was stripped. I bought a new plug at the dealer, but am not sure how to get the old plug out. Any suggestions? The dealer said they would try to get the old plug out for $90, but if they couldn't I would have to replace the transmission!!!
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Re: Transmission filler plug on 1990 six speed
Mike-----
I've got good news and bad news for you. First, the good news: under most operating conditions, the lubricant fluid in your transmission does not require periodic replacement. So, you probably don't need to change the fluid.
Now the bad news: the filler plug is the only way to check that the transmission has the proper level of lubricant. Of course, if there appears to be no transmission leaks, then it's unlikely that you require fluid. ZF 6 speed transmissions usually are pretty leak-free.
The problem that you have experienced is a fairly common one. The transmission case is aluminum. The transmission plugs are steel or cast iron (steel, in your case). Dissimilar metal (galvanic) corrosion sets up in the threads and makes the plugs almost impossible to remove. Once the internal hex or allen head is rounded off, it's virtually impossible to remove the plug using any normal extraction methods.
Now, more good news and bad news. First, the good news: you definitely WON'T have to replace the transmission (unless it has other problems besides the plug).
Next, the bad news: you will likely have to remove the transmission from the car and disassemble it so that the plug can be removed from the case. Once the case is empty of contents, the plug can be removed by one of several methods. It can be drilled out until paper thin and then removed with a sharp dental pick-like instrument. Or. it can be removed via EDM (electroless discharge machine) which some better equipped machine shops will have. Personally, I don't recommend trying to diassemble a ZF unless you have the proper tools and experience, so you'll likely have to send the transmission out for this work. It will be expensive, but you can get a transmission rebuild at the same time.
One more thing and a lesson to be learned for folks with any aliminum case transmission: ALWAYS, ALWAYS, ALWAYS apply an anti-sieze agent to the threads of plugs installed in aluminum case transmissions before installing the plugs. Clean the threads THOROUGHLY and APPLY ANTI-SIEZE to them EACH AND EVERY TIME that you remove the plug(s) for any reason.In Appreciation of John Hinckley -
Re: Transmission filler plug on 1990 six speed
Joe: can add insight into the cost of a ZF6 repair. First off, the tool/fixture required to dis and re assemble the tranny runs about 1500 bucks and its definitly needed for the job and only a few rebuilders have the fixture. Once the gearset is removed from the case, a 40 ton press and heat sources and chilling sources are needed to remove the gears from their shafts(not splined like t-10 and muncie but rather tight friction fits). Didn't make sense for me to get the tool/fixture and fool with heating gears and chilling shafts , so i sent the wounded ZF6 to Rockland gear in upstate New York. their labor fee is $750 plus parts. ZF6 too heavy for UPS so trucking expenses also need to be figured in. Bottomline- don't speed shift a ZF6 unless ya got an extra 1500 to 2000 bucks laying around. MikeComment
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Re: Transmission filler plug on 1990 six speed
I'd leave it alone. How critical is it to change the gear oil? What is the factory recommendation?
That said, you might try welding a nut or a bolt to the plug. Something that will allow you to get a good bead on between the plug and the thing with a hex head you weld onto it. The heat of the welding will also help free the plug.
Before you drain the transmission of its old oil, make sure that both plugs will turn. You don't want to find out that the fill plug is stuck after you freed up the drain plug and drained the old oil.Comment
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Re: Transmission filler plug on 1990 six speed
follow-up on cost to repair a ZF6( in my case the only obvious problem, without the benefit of opening the dern thing up, was the third gear synchronizer--it always raked going into 3rd gear after i missed a shift 1/2 way down a 1320 run)Got call today from Richmond Gear with fee: 2708 bucks for the synchro, 3rd gear and all bearings and seals(they won't guarantee without new bearings) and labor.Gonna be a little more delicate with the puppy here on out. mikeComment
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