The GTM Supercar Build Log

Archive for September, 2010

Proper Calibration of the Brandwood Cable-Shift’s Fore/Aft Motion

Saturday, September 25th, 2010

Since I’ve had the GTM on the road (some 330 miles now) I have had a problem with it randomly popping out of reverse or first gear when starting from a stop, usually only when the box was cold. No grinding, just pops out, as if it wasn’t fully engaged. If I firmly put it back in gear it would then start moving fine. I figured either the cable that controls the fore/aft motion (that allows you to enter the various gears) was not calibrated properly, or my trans was injured.

I contacted Brandwood this week and they promptly replied with instructions as to how you should properly calibrate the cable-shift’s fore/aft range of motion. The directions I received with my cable-shift system were very general and really did not discuss this calibration at all, so I simply ran the cable and connected it and tightened up the jam nuts that hold it on place. With proper instructions in hand I could see that my cable was ‘calibrated’ in such a way that it had plenty of range for 2-4 shifts, but it was about a 1/2″ short of pulling the shift rod out of the transmission all the way on the R-1-3-5 shifts. No wonder I was having problems! With the proper calibration performed, I took the GTM out for a while and had zero issues. Nice!

Here is how to properly calibrate your Brandwood Cable-Shift system for proper fore/aft motion to ensure proper gear engagement:
1. Disconnect the fore/aft cable from the shift rod ‘coupler’ at the ‘ball and socket’
2. Push the transaxle shift rod forward, into the transaxle
3. Pull the shifter handle down, as if you were selecting 2nd or 4th gear.
4. Check that the ‘ball and socket’ connector moves past the shift rod ‘ball stud’
5. Pull the transaxle shift rod out, away from the transmission
6. Push the shifter handle forward, as if you were selecting 1st gear.
7. Check that the ‘ball and socket’ connector  again moves past the ‘ball stud’ on the shift rod. You should see  a slightly greater range of motion from the ”ball and socket’ connector in each direction than the ‘ball stud’ on the shift rod. This ensures that the cable is pushing/pulling the shift rod into/out of the transaxle all the way.
8. If the range of motion is lacking in the ‘1st gear’ direction (ie: when you pull the shift rod out), ‘tighten’ the rearward jam nut . If the motion is lacking when going to grab 2nd or 4th, tighten the ‘forward’ jam nut (the one that is closest to the  motor).
9. Once the range of motion is calibrated properly, put the shift rod in neutral, and the shifter handle in neutral. The ‘ball and socket’ connector should be able to slide over the ‘ball stud’ connector.

Here is a pic of how my calibration ended up looking.

Floormats

Saturday, September 25th, 2010

An exciting update! I ordered the GTM floormats from Factory Five last week and received them the other day. I was concerned with their fitment when I ordered as they have malleable/bendable sections that match the shape of the footboxes, and I wasn’t sure if the added padding from the Dynamat I used would mess with that or not. Fortunately, they fit great. You can form the floormats so the bendable sections conform to your interior very well. The logo is not super colorful, which I’m glad for, as that would have been kind of gaudy.

Driving Notes, and Sticky Shifting Issue Update

Sunday, September 19th, 2010

The GTM has been seeing consistent usage whenever it has not been raining here. Odo is now at 311 fun-filled miles. Yesterday the wife and I went for its longest drive to date – 50 miles straight and it ran great. Today I took it out for another spirited 40. I’m starting to get into WOT usage in 1st and 2nd now and getting a feel for the car’s power more. Tons of power, and I’m glad I’m on DOT legal slicks. Street tires would be absolutely useless under a heavy right foot. A WOT 3-4 shift at 3rd-gear red line breaks the tires loose. A WOT romp through 1st and 2nd spins the tires most of the way. Braking is much, much better since messing with the bias balance bar. I have some tire rubbing issues with the rear tires rubbing the inside aluminum over dips in the road at speed (stiffer springs!), and the front left tire rubs the body on some turns at speed, or while going down/up an incline while turning (ie: driveways, ramps). Not sure how to address that one yet, but it is a common issue, apparently. I have been gradually filing away at the body where it rubs to see if that can give enough clearance. Raising the ride height a 1/4″ all around might do the trick as well. The ‘what is that noise’ radiator aluminum support mod I made recently is doing its job.

Getting back to the sticky shifting issue I reported previously in regards to the main shift cable getting too hot. I ordered some Earl’s Flame Guard which came recommended on the forums. I finally received it this week so I unhooked the shift cable, slipped it on, and called it good. No issues arose during the 50 mile drive yesterday (in low 50’s weather). Today was warmer (mid/upper 60’s) and I drove the shit out of the car. After 40 miles the shifter started getting sticky, but not as bad as it  had previously without protection, and it cooled down quite quickly. I never had any problems arise while using the temporary high temp reflective wire loom on the shifter cable so I ordered up a Thermotec heat sleeve that reflects 90% of radiant heat up to 2000 degrees, which I will slide over the Earl’s Flame Guard sleeve for even more protection. This winter I will have the exhaust coated as well to reduce temps, and probably come up with a heat shield to go between the exhaust and transmission/shifter cable surface.

“Is that a Lambo?” tally: 6

Windows Tinted

Thursday, September 16th, 2010

Got the GTM’s windows tinted. In hindsight, I should have had them tinted while I was building the car, but I thought the inspectors would gripe about that. Turns out they would not have cared.

To get the windows tinted ‘properly’ I removed both windows and brought them to the shop. They were able to apply the tint and bevel the corners so it is completely seamless. Turned out great, and completes the ’stealth’ look. I also hit 224 miles on the odo today.

“What the Hell is that Noise?” And the fix.

Tuesday, September 14th, 2010

Saturday I took a friend out for a spin in the GTM since he was bothering me about it so much. Not that I’m going to turn down a chance to take the car out for a nice cruise. After a bit, I started to get on the go-pedal. As I hit 90mph this loud, I mean LOUD, repetitive banging noise erupted from the front of the car. At first I thought it was the engine so I slowed down right away. Noise vanished. Hit the gas again, brought it up to 90 and the noise started right back up. Throttle response was fine, no power loss, and this time I could tell it was definitely in the front of the car somewhere. As I gradually slowed the noise got ’slower’ and then vanished. I assumed the tire was rubbing on something that had broken loose, as it sounded like aluminum banging against something.

I got the car into the garage and looked around and did not find anything out of the ordinary. Odd. Later that night I went back out to the garage and peered through the mesh in the nose/mouth at the front of the car and saw ‘it’. I remembered that earlier in the drive that day I had scraped the pavement with the underside of the car when I hit a dip in the road. I figured it was the skid bars that had scraped, but I was wrong. The bottom portion of the radiator cowl aluminum had to have been flexing from air buffeting into the radiator and when I hit the dip in the road the front edge of the very middle of the aluminum bit into the pavement hard, ripping a couple inch long tear down the middle of itself. In hindsight, I had always wondered about that aluminum as it was always very pliable, and really wasn’t surprised that this had happened. I reached under the car and ’shook’ the aluminum and found it was now extremely weakened and would easily ‘bow’ upwards into the bottom edge of the radiator. Couple that weakness with air pressure at 90mph+ speeds and it created one hell of a racket.

To fix the aluminum I had to figure out a way to support it so it wouldn’t bow and flex under air pressure. I created two aluminum brackets that would mount to the side of the radiator cowl, and to the bottom aluminum piece as the solution. A bend in the aluminum was added for support/rigidity, and to direct air up into the radiator. I jacked up the aluminum panel that needed support to parallel (relative to the ground) and set to attaching the brackets. Once riveted in place, I pulled the jack out and the aluminum held its now supported parallel position very well. The bottom of the radiator cowl is now very sturdy and does not flex and move around. To strengthen the ‘torn’ aluminum in the middle I riveted a flat aluminum piece in place to add rigidity (not pictured).

Took the GTM out today and hit triple digits a handful of times and, thankfully, heard no more of that god-awful noise.

100 miles!

Sunday, September 5th, 2010

Just posting a pic of the odometer ticking off the GTM’s first 100 miles.  130ish now.

To add to previous driving experience notes: bump steer seems better than I originally thought, the back end waddles around a lot at speed, and it doesn’t seem to be from bump steer like I originally noted/suspected. Most likely an alignment issue. Stiffer springs and urethane suspension arm bushings would help, too.

“Is that a Lambo?” tally: 5

Sticky Shifting Dilemma and CAI Reinstalled

Sunday, September 5th, 2010

After each of my several longer drives in the GTM (20 min+) I noticed something that should not be happening – after 20 or so minutes of driving it became really difficult to shift the transmission into gear. I can only describe the feeling as ’sticky’ or ’sludgy’, as it would still shift fine, but it took considerable effort to move the shifter up and down into gears.

My first thought was it was because I did not have the trans oil cooler running. My second thought was that the clutch stopper was potentially stopping the pedal too soon and the clutch was never fully deactivating when shifting and when it heated up it was creating friction, and thus the sticky shifting. I activated the cooler pump, moved the clutch stopper back some more, and hit the road. Same problem after extended driving.

After numerous replies on the GTM forum I turned my attention to the thicker of the two shifter cables that run from the Brandwood shifter box to the trans shift rod. This cable controls the fore and aft motion of the shifting (ie: going into gear), and it also runs very close to the exhaust. The responses I received pointed to a potential overheating issue with the cable, causing the shifting issue. I ordered an Earl’s Flame Guard insulation sleeve for the cable, but in the mean time I used some extra 3/4″ corrugated high-temp resistant wire loom to wrap the shifter cable. I took the car out for the longest drive to date and when I pulled back in the garage the shifting was as smooth as it was when I first started the car. Problem solved :)

With the shifting issue taken care of, I set to reinstalling the cold-air intake. To create a buffer between the exhaust and the intake sleeves I actually just loosened the exhaust collars and rotated them so the bolts that run through the collars would support the intake. I then stuck some Thermotec heat barrier to the bottom of the sleeves where they rest on the collar bolts. I took an extended drive with this configuration and it worked great. Intake air temps dropped from 140+ degrees at speed when previous drives were logged, to 75 degrees. HUGE difference. Leaving the car at idle for several minutes after the 30+ minute drive had the IAT’s sitting at around 100 degrees. Previously the IAT’s would see 150+ degrees while idling. The CAI is pure win.

A Quick Lesson in Brake Bias

Sunday, September 5th, 2010

I haven’t remarked about the braking much until now because I wasn’t that thrilled with it. I wanted to make sure there wasn’t something I had overlooked in the braking system that was causing its sub-par performance before I started whining about it.

That being said, last night I was browsing through the Wilwood pedal documentation and realized the brake pedal has a balance bias bar that I had left at its default setting which puts even pressure on the front and rear cylinders at the same time. In this car, like many sports cars, the front brakes are larger, so naturally we would want a bias up front. We want those fronts to actually work harder.

The balance bar is located at the the top of the brake pedal and connects the two clevises that screw onto the cylinder push-rods. If you turn it clockwise (like tightening a bolt) it will move the pressure bias to the left, or the front braking cylinder if you have the brake lines ran that way. ‘Loosening’ the bar will move the bias to the rear. Wilwood claims in their documentation that maxing out the bias bar to the left (front) will put twice as much braking pressure on the front cylinder in comparison to the rear.

Once I realized this I cranked the balance bar so it was maxed out to give the front brakes as much bias as possible. Test driving so far shows  much, much improved braking performance. If at any point I determine the GTM will need MORE front braking bias then I will have to change master cylinders to get more pressure.