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Vintage Ford Mustang Tech Advice - October 2014
Beyond the Basics
C4 Reverse Issues
I have a '73 Mustang with a 302 V-8 and a C4 automatic transmission. When the transmission fluid is cold I can shift into Reverse easily but once the transmission fluid gets to temperature I lose my Reverse gear. I can still drive in the forward gears, but I lose the Reverse until it cools down again. Have you heard of this?
Via the Internet
It could be a half dozen things going wrong, David, and with that little of detail it's tough to say. If it is a recent rebuild, there may be a chance that the valvebody has been over-torqued and it's not getting fluid to the servo (or the servo isn't opening). If it were happening all the time I would surmise you probably have a broken tab on the band, preventing it from applying, and that would cause it. The only thing I do know is that you probably have a trip to the transmission shop in your future.
There is one thing I want you to try, however. When the fluid is up to temp, and as you're coming off of acceleration, at 20 mph I want you to manually throw it into low. If it is working properly then you should get engine braking and it should push you forward when it shifts down into First. If it doesn't, you may have a problem with the servo or the low/reverse band. This may eliminate the overrun clutch as the problem. The overrun clutch is used to shift the transmission out of First to Second, where shifting manually uses the low/reverse band. Hopefully you will be able to fix this without pulling the transmission.
My son and I have been restoring our '69 hardtop and we recently had it painted and the painter also installed the vinyl top. The painter wrapped the vinyl all the way around the driprail. I am wondering if this is correct because the driprail molding is nearly impossible to get on. Could you tell me where the vinyl should be trimmed back to so the molding can be installed? I have attached a picture of the vinyl wrapped around the driprail.
I have had a couple of Grandés in the past, but your question made me dig deep into the old vault. You will be trimming the vinyl back some, as it shouldn't cover the entire driprail. However, we need to make sure you have the right driprail moldings first. In 1969-'70 Ford ran the roof covering up the inside of the driprail and secured it with the driprail moldings, which meant that the moldings for Mustangs with a roof covering were bigger than the standard moldings. The standard moldings are C9ZZ-51726 and 27-C, and the ones with vinyl top used a “–D” suffix. The vinyl top version is not reproduced, so if you don't have your originals you may have a problem.
If you uncover the driprail area you'll find that there is a lip on the inside of the top of the rail that the stainless molding “snaps” over. The '69 Ford body manual doesn't specifically show the Mustang vinyl installation, so I am going with what I have seen. On the vinyl top cars I have seen the vinyl comes up to this little lip on the backside, and the larger vinyl top moldings snap over the vinyl to keep it in place. Early '65-'66 cars used a small strip that was pop riveted to the rain channel and then sealed over. So first check and see if you have the correct driprail moldings. If you have the right ones, look at how they attach compared to the snap ledge on the driprail, the vinyl should stop here. Make sure of the shape of the moldings before you trim—you might need to go to a salvage yard or somewhere and look at one before you start pulling back your nice new vinyl top.
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Send your '65-'73 Mustang questions to: Beyond the Basics, c/o Dave Stribling, 2110 Indianapolis Rd., Crawfordsville, IN 47933. Send email to email@example.com.