elwood

iTrader: (1)

I have one, along with a Panhard rod and Heim Joints at all suspension points. I've read Susko's info. So far, it seems well made and durable, but there are two issues I want to resolve:

1. There's a low groan and vibration in 5th gear. I'm not 100% sure, but I think it's related to the pinion angle (angle between driveshaft and 3rd member). When I shift down to 4th it improves. I've had the tri-link for a few years now and experimented with different angles. It changes, but I haven't managed to eliminate it.

2. The car won't launch very well. I'm running 225/50-15 Dunlop SP Sport 9000s, and I can't get the car to hook up solidly until 3rd gear. It doesn't squat much under accel, and I realize that's mostly a function of suspension geometry, which is somewhat fixed.

I'd like to hear your experiences with tri-links.

jgrewe

iTrader: (1)

Are you sure you're not hearing gear noise? A lot of noise gets transfered very well to the back 'echo chamber' of the chassis/hatch area when you get rid of rubber bushings.

What kind of racing/driving are you doing that it won't hook up? Road racing we are almost never below 3rd gear so the torque mulitplication isn't that high. Drag? I don't know if the suspension system can give the geometry you relly need to plant the rears for a good hard launch.

elwood

iTrader: (1)

I'm not sure what kind of noise I'm hearing. Here are some more details:

a. It's vibration more than noise, wich is a minor difference, but might be significant
b. The vibration is only significant in 5th gear -- if I downshift to 4th at the same speed, it all but disappears
c. There wasn't any additional noise in 5th gear before I installed the tri-link
d. I still have the interior, and the car isn't particularly noisy otherwise -- minimal roadnoise / no suspension clunks

As for the type of racing -- it's mostly track days on road courses, but I like to run my car against my friends on the street from time to time, too. I don't think it will be a major handicap on a road course, since as you said, I probably won't be below 3rd gear. But, I was curious to see what others have experienced. The way it is now, it's tough to pull away from a light quickly without lighting up the tires.

jgrewe

iTrader: (1)

Interesting... at first I would suspect u joints but the fact the noise goes away in a different gear points elsewhere. They still might be the problem but the driveshaft speed is constant with the rearend, not the tranny.

Does the noise come and go with different load on the driveline? If it does I would suspect pinion angle still. Gear noise will have more of a whine to it than vibration.

The rules the tri link was designed to fit originally really limit what you could do with geometry. We put the front mounting point as high as we could to get rid of the squating problem these cars have and to try to get some advantage on planting the tires coming out of a corner. Before this set up, the highest rate people ran on IT cars was about 170lbs/in in the rear. Jim and I coming from auto-xing liked stiffer cars and we started out with 300lb/in in the rear and 450 up front.(Jim and I were business partners renting race cars when he started Gforce, that is where the testing was done on the Gforce parts)

With out a lot of anti squat it will be tough to put down a ton of power for a launch, the instant center is too low.

elwood

iTrader: (1)

To check my math on all this, I worked a few hours today with a fried that's an engineer/mechanic who does work on a variety of exotic cars. I used his magnetic protractor, and we tried to ensure even angles at tranny to driveshaft and driveshaft to rear pinion (those little hash marks are tough to read accurately). When that didn't eliminate the 5th gear vibration, we tried slight angle changes above and below the equal setting recommended by Susko in his guide. The 5th gear vibration varied slightly in intensity at the different settings, but never disappeared.

To address your points above:

Driveshaft Speed: Doesn't seem to matter much. At constant road speed, the vibration is there in 5th gear, but absent in the other gears.

Load: The vibration disappears when there's no load.

At one point in the past, the vibration would disappear in 5th gear if I drove above 85 mph. I didn't want to speed all the time (or drive at high revs in 4th), so I started adjusting the pinion angle so I could drive in 5th gear at legal speeds. The condition is worse now than when I started.

Any insight is deepy appreciated.

Kentetsu

The fact that the issue changes from 4th gear to 5th would suggest (to me, at least) that the cause lies within the transmission. Nothing in the rear end changes between the two gears, right?




.

peejay

The 5th gear 80mph rumble is how I know it's time to change transmissions soon.

Interestingly, I recently bought a trans from a junkyard and threw ATF in it because it was the fastest way for me to fill the trans, and I didn't want to put the $15/quart stuff in there before I knew if the trans was any good or not.

Had the 5th gear rumble as bad as any trans I've had! But it had all six gears and shifted okay and made no horrible noises, so I rolled with it. Drove it a few hundred miles and swapped in the good stuff. Rumble GONE.

So, er, try running heavy gear oil (mine is something like 85W140) before all else.

elwood

iTrader: (1)

I like the idea of changing the gear oil. While I'm at it, I'll probably change the stuff in the axle too. What brand did you use?

I did a little research, and some of the older posts warn against GL-5 because it contains high levels of Extreme Pressure (EP) additives that are sulfur-based and can cause corrosion on our bronze synchros. This may be true, but I'm a bit leery of the info, since it all seems to be based on an Amsoil white paper . . . and guess what? Amsoil rates the best!

I was considering the Mobil 1 75W-140 gear oil, which is a GL-5. It does contain the sulfur, but it specifically states that it resists corrosion to copper-based alloys (like bronze). One reason I like Mobil is that an old lubricant specialist I used to work with was always impressed with Mobil 1 because they would supply a lot of test data and it always correlated well with independent studies.

Re-Speed.com

iTrader: (3)

MTL and MT-90 are 2 really popular ones that miata guys use. I personally use MT-90 currently in my car and have liked it over the Amsoil that I had in there previously.

Having talked to a good friend of mine that builds transmission gears (http://www.housemanautosport.com/) about gear oil, he said alot of the new synthetic oils are actually too slippery for the synchros in the transmission.

The one new oil thought that I think I might consider if I ever get a full dog box transmission is Millers Oils with Nano Particles. This seems to gaining quite a bit of respect from racers, manufacturers that deal with oil of that need.

peejay

I just use synthetic Valvoline. I used to use Shockproof Heavy but it needs to be changed every 6000mi or so (the calcium chunks in the fluid have broken down and it loses its "shockproof" properties), so I'm trying something new. Mind you, it's only been in the car for about 1200 miles.

Don't worry about GL-5 or not. Worry about viscosity. MTL should not be used because it's about as thin as ATF. Really, I found there to be no difference between MTL and ATF other than the cost...

elwood

iTrader: (1)

peejay -- how long has the heavy weight gear oil fix lasted?

Kentetsu

I've seen ATF do some amazing things in old trannys.

As far as fluids go, if Lucas makes it then I use it. Period.

elwood

iTrader: (1)

I tried peejay's heavy gear oil fix and so far, the 5th gear rumble is still there. I used Mobil 1 75W-140, and it cost me a total of $35 to try it, so I feel like it was a worthwhile gamble. After reading a few troubleshooting guides for driveline noise, I feel more and more confident that I have bad bearings in the tranny. There are a bunch of places selling bearing kits ($150) and bearing + synchro kits ($300).

1. I've rebuilt quite a few engines, but never a tranny. How difficult is this to do? Are there any special pitfalls?

2. Should I replace the synchros too? Assuming there's no obvious damage, are those things a likely failure point?

3. Is there a recommended source for parts? I asked one eBay seller who the bearings were made by . . . still waiting for a response.

On a positive note, I also swapped my street tires (Dunlop SP Sport 9000s) for my track tires (Kumho DOT-legal road race tires) and my ability to launch improved dramatically. I was able to put down full power in 2nd gear without wheelspin! I don't know if the Kumhos were always that much better or if the Dunlops somehow got hard.

Thanks everybody for the help so far -- I feel like the problem is identified, which is a big step forward.

nofords

iTrader: (9)

I've rebuilt a couple trans and really the only "special" tool is a really long 2 leg puller.

You will need a variety of puller legs, slide hammers etc with a couple of big wrenches.

Depending on what you want, bearings are bearings. I bought bearings off rockauto and used whatever brand they supplied.

Syncro's...well, your already in there and if you are keeping your car around a while, might as well. Make sure you get all new seals and o-rings too.

jgrewe

iTrader: (1)

If you are going into the tranny do the syncros too. They are cheap and easy to do once its apart.

There are two special tools you will need. One is a bearing puller that you can add long threaded rod to so you can reach a bearing on the main shaft. The other is a socket to reach a nut deep on the shaft as well. I made my own by cutting a cheap socket apart and adding a piece of tubing in the middle of it to end up with a deeeeeeeeeep socket.

They are pretty simple once you get a look at them. Remembering the order stuff came apart is the key to putting it back together.

mustanghammer

iTrader: (3)

Our experience with the tri-link (road racing in Improved Touring A/7 and in E Production) is that it doesn't provide great low end traction. With higher HP the situation gets worse. I took my IT7 car to the strip (it has a tri-link) and it spun the tires all the way through 1st and into 2nd even with Kumho V710's installed that had been run through VHT.

On the E Production cars some improvements were noticed when lower control arm geometry was improved by lowering the mounting points on the rear axle (lowered 2.5"). But regardless of the lower control arm fix, using a tri-link on the E Production car meant delaying full throttle application on corner exit.

Basically the tri-link's chassis mount is too low and needs to be about 2-4" higher depending on the car's ride height. This does require some metal surgery on the car's drive shaft tunnel and some extensive fab work. Not really street car friendly.

All that said, the tri-link/pan-hard bar is light years ahead of the stock 4 link/watts setup on a racetrack.

peejay

You mean the *axle* end is too low, right?

I am very very happy with my home brew setup. The axle end is ~4" above the top of the housing and the chassis end is inside the car as low as possible, on top of the driveshaft tunnel. (NOT on the crossmember)

elwood

iTrader: (1)

No, mustanghammer is correct. All three links angle downward from the rear axle to the chassis. During acceleration, this tends to unload the rear axle. To correct this, either the mount points on the rear axle need to be lower, or the mount points on the chassis need to be higher. The two lower links are relatively easy to correct by adding drop attachments on the rear axle -- or by drilling new chassis mount holes above the stock ones.

The upper (tri-link) is more difficult. Since the attachment point on the axle can't be lowered, the attach point on the chassis must be raised. This is what would cause all the extra fab work he outlines. I'm seriously considering it. Montana Kid did something along these lines a while back with his mods.