Discussion Forum - Northstar Chevelle Club

Bobs_Place · Vice President

It's time for overdrive

SShink · 3K+ Club

That's another way to skin the overdrive cat. You'll love it once you're on the highway again.

Keep us posted on the project!

Bobs_Place · Vice President

I used the empty Muncie case along with the GVO extension housing to help fit the overdrive unit into it's proper location. Had to notch the floor support back of the O.D. unit but no cutting/welding on the tunnel, just reshape for clearance. Was then able to figure driveline angles and shaft length. I'll have to raise the rear of the car about 1.5in. to the increase the driveshaft angle and reduce the working angle between the trans and D shaft. The car has settled over time so that puts the ride height in the rear back up to where I like it, I'll deal with the front later.

The drive shaft will have to be shortened just over 15 in. to about 39 1/2 in. I didn't like the slip yoke from GVO as it seemed short, after adding in the 3/4 in for movement the yoke would not fully engage the support bushing. I decided to shorten my original yoke to a more acceptable length.

I pulled the tail housing and side cover from the trans, flushed in clean solvent, inspected and reassembled with the GVO housing, than adjusted shift linkage.

The clutch will be next.

Bobs_Place · Vice President

I pulled the bell housing and pressure plate, all looked good. I have a new pressure plate and disc that I picked up at a swap meet cheep $10 last year. I want to replace the disk from the car with the new disc, that disc appears to have a much stiffer spring center than the disc from the car. The clutch was a bit jumpy but the real problem I was having with the clutch "I think" was on deceleration the car would jerk back and forth from about 2000 rpm to idle, I would always have to push the clutch in to stop it. I tightened the posy, adjusted drive line angles, replaced rear suspension bushings, nothing stop the jerking. I'm hoping the weak center springs are the cause.

I'll decide later on the flywheel and clutch assembly and after I test out the new disc, I may still have some trans leaks that I want to clear up also, will add that to the list for the winter.

I didn't like the looks of the pilot bushing so I replaced with new. The new bushing went in tight. When I installed the trans, it didn't just slide in, had to wiggle a lot to get the trans tight to the housing, I thought the disc wasn't centered but after adjusting the freeplay, than holding the peddle down I could not turn the trans freely. I should have checked the pilot bushing. Out with the trans and found the bushing to be tight, with some strip of sand paper and an old input shaft I opened up the clearance. Good now, back in with the trans

Lost in the 60s · President

Could the jerking on deceleration be caused by timing, as it is fully vacuum advanced and the cam may be aggressive enough to not want to idle down smooth. The only time I've had that situation with a clutch, is when some of the dampener springs were broken.

I hope you researched that LUK part number. They are not known to service high performance, mostly stock replacement.

Bobs_Place · Vice President

I have heard/read about timing advance causing the jerking, seems to me I've had the vacuum advance disconnected when setting up the distributor, I don't think it had any affect on the jerking. The engine is not slow to return to idle. I have found that the condition is lessened with a higher idle or when the solenoid for the a/c is not adjusted correctly and causing a higher than normal idle.

I wasn't clear on the two clutch discs, the 8 spring is the disc I am removing and installing the 5 spring, with the 5 spring looking like a much stiffer spring center

As for the Luk part number, I did not do any research but just wanted to see if the jerking changes or goes away, I'll just finish out the season with it, and hopefully help me decide on what clutch to install.

Your comment on the broken damper springs is interesting. Could the dampening of the clutch disc with the broken springs be similar to the weaker 8 spring disc?

Lost in the 60s · President

Yes, the 8 springs do look softer than the 5 spring hub. Some of them, also, appear shiny, like they are collapsed and spinning around loose. That will definitely cause the jumpy clutch while engaging.

Bobs_Place · Vice President

The Exhaust took way longer to modify than I expected, the X pipe interfered with the GVO so it had had to go, may put in a cross over in later . The trans slipped right in like it should, with the clutch peddle depressed and trans in gear I was able to turn the output shaft very easily by hand. Got the drive shaft back from the DL shop and installed. After raising the rear of the car and some rear axle adjustment the Ujoint angles came out very good.

Need to do the electrical hookups and put the interior back together.

Bobs_Place · Vice President

The wiring is fairly easy, just plugin harnesses to the GVO control unit, the control shuts off the over drive at low speed so as not to burn up the OD clutch. It uses oil pressure from an internal pump to provide the pressure to apply the clutch, the pump turn only when the drive shaft turns. The harnesses are than wired to the power and ground, speed sender, manual control and solenoid. They also provide a shift knob with an on/off switch that can be used to control the overdrive, for normal driving they recommend using the clutch for a smoother shift.

So, I thought why not signal the GVO to go to over drive from the clutch switch but only in 4th gear. So after some time with paper and pencil I was able to com up with a wiring diagram that I thought would work. I used a signal from a 4th gear switch (that switch was used to control timing on these cars back on the 70s) the clutch switch and a hand full of relays to control the over drive instead of the gear shift knob switch.

I finished the trans install, adjusted the clutch, fill the trans and GVO with oil. Than made all wiring connections and tested, assembled the interior.

Only had time for a short drive two nights ago, no highway and needed to make some shift linkage adjustments, so only got into OD at low speed 45-55mph. Shifted very nice from what I could tell.

Today I readjusted the linkage and headed for the highway, pounded out all 4 gears, than just stuffed the clutch one more time I had over drive. To down shift from OD to 4th push the clutch, move the stick into neutral and back to 4th gear, cycle the clutch again and back in OD. Works Great.

SShink · 3K+ Club

Nice job Bob! Glad it worked the way you designed it.

We've got some pretty smart folks in this club.

67ss · 1K+ Club

Very cool.

Lost in the 60s · President

Wow, Bob, that's 5 more relay's than I want to have to figure out...

Bobs_Place · Vice President

I was hoping to do it with less relays, but rather than install a separate clutch switch which would not require a relay I thought it would be easier and more reliable to use the existing clutch switch and a relay to isolate the starter circuit from the clutch signal for the GVO. The 4th gear switch just operates opposite from what I needed, the contacts were closed when they needed to be opened and opened when I needed the closed, so another relay reversed the signal. The relays are very reliable especially when used in a clean, dry environment and with very low amperage, so I don't use them sparing-lee.

I may at some time add one more relay for a full throttle kick down to down shift the GVO , the Gear Vendor people say it works extremely well, and I will like it. Once again I'll use the throttle switch that triggers the air door under the hood.

Bobs_Place · Vice President

As part of installing the overdrive I need to change the gear ratio. The 3.31 was great on the highway in OD but first gear is just to tall, have to slip the clutch to much from a stop and the clutch gets jumpy after driving for a bit. I decided to install the 4.11 from my other housing, OD will be about 2-3 mph faster than the 3.31 in 4th. Eventually I will go to a gear somewhere between the 3.31 and the 4.11 but wanted to try the 4.11 to help me decide.

I checked the backlash and pattern before removing the 4.11 gear, the BL was high and the pattern was not very acceptable. Than pulled the diff assembly from the housing. Rather than pounding on the pinion to remove it, I decided to build a fixture to push the pinion and save the bearings from getting a beating. The fixture worked great.

Had to order shim kits to properly setup the diff gears. Will also have to replace an axle seal again on the right side, I'll try to locate the seal inward if I can to hopefully get away from the worn surface on the axle.

Bobs_Place · Vice President

I found some shims (from a another project) that were good enough to use temporarily to set pinion depth. The gears showed a better pattern by adding more shim until I was up to about .010. I that point the pattern started showing that pinion was to deep, so I pulled .004 back out. I'll measure and replace this shim pack with the correct shim when they get here.

I then shimmed the clutch packs for the posy, cleaned up the right side brakes and diff housing to get ready for final assembly.

I also check the ends on both housings with the alignment bare, only one end showed very good. I don't see any spline ware on the axles so I don't think the misalignment is a problem. Future plans are to install Impala housing ends for 11in brakes and eliminate the "C" clips.

After the shims arrived I installed a .032 shim pack and bearing on to the pinion, assembled into the housing, than installed the diff case, set the back lash (.004-.005) and bearing preload. Painted the gears, pattern cam out good.