I have a ’77 Firebird Formula. I am going to be getting some brake stuff for it soon. I need to know whether it has the standard or F41 suspension. I’m thinking maybe having a rear sway bar on it means it has the F41 suspension, but I’m not sure. Thank you.
Carl Garcia - Via Internet
Rocky Rotella responds:
Carl, a rear sway bar was standard equipment on any Second-Gen Formula. During the early ’70s, it and the front sway bar were typically slightly smaller in diameter than those found on a same-year Trans Am. Where a Formula was equipped with 11⁄8-inch (front) and 5⁄8-inch (rear) bars, the Trans Am was fitted with 11⁄4 and 7⁄8-inch units, respectively. Buyers could equip a Formula with 15-inch wheels and tires, and stiffer Trans Am-spec underpinnings by selecting the Y99 option.
Beginning in the mid-’70s, Pontiac made its Radial Tuned Suspension (RTS) package standard equipment on the Formula, and 15-inch wheels and tires were part of it. Pontiac toned down the Trans Am’s suspension slightly for ’77 by teaming the same 11⁄4-inch front sway bar with a 5⁄8-inch rear unit. Formula buyers could acquire the same suspension package as the Trans Am by selecting GR70-15 tires (either black or white lettered). They were an extra cost option over the standard FR78-15 tires.
To determine if your Formula is equipped with Trans Am-level suspension, look for “GR70-15” tires in the list of equipment found on its window sticker, buildsheet, or factory-to-dealer invoice (available from PHS Automotive Services) should you have any on hand. If you do not see the tire option, then your ’77 Formula is equipped with the base suspension package for that particular model year.
Improving upon it is relatively easy. In addition to used units from similar year Trans Ams, there are many aftermarket options available that will bolt in with little to no modification, too.
Rev it Up
Hi, I’ve been a long-time subscriber and finally have a question for you. The factory tach on my ’71 T/A has quit. Will the GM OEM ’73-’76 unit work on my car? It has two clips in the back where my ’71 T/A has just one. What needs to be done to hook it up? Thank you.
Mark Hyken - Via Internet
Rocky Rotella responds:
Mark, thanks for being a subscriber. We’re glad to help out.
A tachometer typically requires three connections for normal operation—one to a 12V source for power, one to the negative terminal on the ignition coil for RPM signal, and one to ground. As you’ve found with your ’71 Trans Am, Pontiac was among the few manufacturers that utilized a two-wire tach lead during that era.
You’re probably saying, “Wait, there’s only a single wire coming from my Firebird’s tach harness!” While you’re absolutely correct from a visual standpoint, where Second-Gen Firebirds are concerned the tachometer was grounded through the cluster. Pontiac didn’t use an additional 12V lead in ’70-’71 models. Instead it used the voltage transmitted through the negative side of the coil to dually power the tach and provide RPM signal. That explains the single brown wire found in your car’s tach harness, which runs through the firewall and to the coil.
Pontiac employed a more-typical three-wire design for the Firebird beginning in ’72. It was again grounded through the cluster, but used an L-shaped plug containing a brown-colored wire for the negative coil terminal and a pink/black-colored wire, which plugged directly into a 12V terminal on the fuse block.
The factory tach on my ’71 T/A has quit. Will the GM OEM ’73-’76 unit work on my car?
I haven’t yet found anything that states or suggests Pontiac’s reasoning behind the change, but it may be related to the fact that Pontiac began offering the Unitized ignition that model year. The Unitized unit (and the HEI unit that followed) requires 12V for normal operation, where the power lead for the points-type system coil is resisted down to about 9V. Pontiac may have decided that the tachometer can function more consistently and/or reliably with its own power source beyond that drawn off an electronic ignition coil.
Auto Instruments in Martinsville, Virginia, rebuilds and/or restores most any gauge found in classic Pontiacs (www.autoinstruments.com), and that includes those in your Firebird. I spoke to the company’s Gentry Zentmeyer to inquire about the services available for your particular tachometer and learned that rebuilding two-wire tachometers isn’t an option, unfortunately. The circuitry required just isn’t available any longer; any rebuild requires converting it to a three-wire connection.
Gentry suggested, just as you noted, that installing a typical three-wire tach would be the most cost-effective solution - that would be any 8,000-rpm unit used in ’72-’76. Simply connect your existing tach lead to the replacement tachometer’s vertical terminal, and fashion a short length of wire that connects its horizontal lead to a nearby 12V source, such as a positive post on an adjacent gauge. That should attain normal functionality. He added that even if Auto Instruments was to rebuild your Trans Am’s original tach, you’d still have to create that same 12V jumper, so it’s a simple modification you’ll need to perform regardless of what method you choose for your Firebird.
I suggest you consider having your existing tachometer rebuilt by a company like Auto Instruments. With pricing that starts at $195, Gentry’s option guarantees that you’ll have your Trans Am’s original unit returned, and it’ll function reliably and accurately for years to come. Depending on how much you would have to spend to purchase another used tachometer, it may not be worthwhile. You may not be able to verify its operational condition and/or accuracy, and you could wind up in a situation where you’ve added another dead tachometer to your collection of parts.
Whatever you do, rest assured that getting your Trans Am’s tachometer back in action should require nothing more than one extra wire.