Installing a T5 five speed into a '78-'88 g-body

T5 into a g-body

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contributed by J. Matthew Daugherty

I always figured it'd be difficult to do a manual tranny in a car that hadn't been produced as such for around 7 years. Since a lot of people want to do this swap, but the details scare them off (as they did me for a long time), here's more info:


I used an 84-92 F-body hydraulic bellhousing


Can't very well have a manual tranny with out a clutch pedal and a brake pedal that works with it, and the linkage that works with it. Available to me, I had available, a set of pedals from an '82-'92 f-body (camaro / firebird) and a brake pedal assy. from an '85 Monte Carlo SS (g-body). The bolt pattern for the f-body pedals at the firewall is the same width as the g-body pedals setup, but the bottom two bolts are higher up in the f-body pedal carrier. No big deal. cut the back ears off the g-body pedal hanger, weld that onto the back of the f-body hanger and all of a sudden that bolts to the firewall / brake booster.
   f-body        g-body        w/g-body
  ___   ___     ___   ___     ___   ___
  |o|   |o|     |o|   |o|     |o|   |o|
  | |   | |     | |   | |     | |   | |
  |o|   |o|     | |   | |     |o|   |o|
  ---   ---     |o|   |o|     |o|   |o|
                ---   ---     ---   ---

On the f-body pedal assy, there are support rods that are bolted to the end of the bolt that the pedals pivot on. In the f-body, these rods go downward and are held at the bottom by the u-bolt that goes in from the firewall to hold the master cylinder. The right side support rod, I kept in my SS, it fit nicely. The left side rod, I left off for now, as it doesn't clear the fuse box in a g-body.

Next problem: the brake booster

The pushrod going into the booster was a tiny bit long. What worked was to simply tweak the part of the pedal hanger assy. that limits the rearward travel of the brake pedal so that the brake pedal comes back far enough. This did not affect the brake light switch or cruise control vacuum release switch. No need to destroy a brake booster to modify the pushrod in it, right Bill?

Next up: moving stuff around

In the g-body, there were a few uses for the cruise control harness hole in the firewall. This hole is right under the brake booster, and tough to see.
  1. In the manual transmission cars ('78-'79 Monte Carlos, '78-'81 El Camino's etc.) this was the hole through which the pushrod for the mechanical clutch linkage went through. There was a grommet in those cars around that pushrod. In the manual transmission cars of those years with cruise control, I have no idea where the harness came through
  2. In the g-bodies with an automatic and no cruise, this hole did not get drilled open by the factory (source: an unmodified '85 SS with 200-4R and no cruise)
  3. In the g-bodies with an automatic and cruise control, the cruise harness consisted of wiring and a vacuum line that wen through this hole.
On all these cars, there were 2 dimples around the hole. On the '78-'81 manual shift cars, these dimples were used to hold in place a grommet around the mechanical linkage pushrod. These 2 dimples line up almost exactly with the 2 holes in the master cylinder from an '84-'92 f-body. So.... the cruise harness on my car was relocated through the grommet / hole normally reserved for the speedo cable. Snug fit, but an easy mod.

Master Cylinder

As previously mentioned in the "moving" section, the dimples *almost* provide a perfect template for the '84-'92 f-body master cylinder. Make it easy on yourself: pull the brake booster (4 bolts inside, 2 on the brake master cylinder, get the pushrod off the brake pedal) and hold the brake master cylinder out of the way. This will allow easy access to installing the master cylinder for the clutch.

Once the firewall is accessible, place the clutch master cylinder into the cruise harness hole and align it so that it points upward in the cabin. Point the master cylinder towards the attachment pin on the clutch pedal, keeping in mind the plastic line that goes to the slave cylinder must reach the bellhousing. Drill the 2 holes using the master cylinder as a template. Use the U-bolt from the f-body to hold it in place.

At this point, you should place the brake booster back in place, and you then can install the pedals, keeping the right side support rod as mentioned above, putting the nuts on the threaded ends of the U-bolt, the 4 nuts on the brake booster, attaching the pushrod from the clutch master cylinder onto the clutch pedal, and the brake pushrod onto the brake pedal. Hook up the vacuum lines for cruise control, brake light switch and that's about done.

One other change I made was that in the f-body, there is a white plastic clip that holds the clutch pushrod to the clutch pedal. Due to the not-so-ideal angle of that pushrod, I eliminated that clip, and hold the pushrod to the pedal with a clip from an f-body brake pedal. This is simpler than it sounds.


The driveshaft situation is easy. Either get yours cut to fit, or find an application that is the right length. Mine happens to be a driveshaft from a '67-'69 Camaro / Firebird with TH400 transmission. This shaft will also work for a TH700-R4 swap into your '78-'88 g-body as the T5 and TH700-R4 are the same length.

The crossmember was moved forward so the rear 2 holes of the crossmember lined up with the front 2 holes of the cars frame and an extension was bolted to the crossmember which goes to the tranny. The drivers side holes for the crossmember will not be on the pre-'84 g-bodies because GM added an extension to the frame to easily accept the TH200-4R on the '83 Hurst Olds and all '84 and up g-body frames.

Cutting the floor is an unfortunate aspect of the swap. But entirely worth it! The f-body T5 is canted towards the driver so the hole will not be on center.

Once the transmission is in, double check the floor hole for the shifter, bolt up the slave cylinder to the bell housing, and double check that your master cylinder is good for the clutch. Mine leaked and so the transmission couldn't be shifted. Replaced that and it shifted great.

The End

The installation of the transmission should be no sweat for those of you doing all this so I've skipped that information.

The methods I used for *my* installation. I'm convinced there are other master cylinders that might line up better, a braided hose from the master cylinder to the slave cylinder would be better than the solid plastic line, and I probably could have modified the pedals for better angles on the brakes / clutch, used other pedals and adapted those to the car. And so forth. It has worked flawlessly for 4000 miles so far though. 45 minutes in a St. Louis traffic jam with no problems.

A variation on this swap is to use '78-'81 g-body mechanical linkage / pedals and the bellhousing for an '83 T-5 equipped Camaro / Firebird. While the mechanical linkage may be preferred by some, the hydraulic clutch provides for a more livable setup on the street, longer clutch life, easier to find replacement parts, more room for headers, and it was what I had available to me.

If you go with mechnical linkage and bellhousing, you can use the hydraulic clutch fork from the hydraulic T-5 f-body for a very quick clutch release (to bang gears fast) This tech tip has been another word of wisdom from....(drum roll)..Crazy Bill.

Please email me with how you did *your* swap on your Monte Carlo (or A / G-body) so that the information can be shared. The response I received in email requesting this information was large so I know that any info that can be shared would be appreciated.

I want to thank the Monte Carlo List, the Olds G-body list, and my friend Crazy Bill, whose general outlook was "It's only a car" right before he proceeded to cut the hole for the shifter.

These pictures were added 7, March 2002, courtesy of Jim Brady.