This topic covers several different areas, so I hope this is the correct forum to ask this question in, so here goes:

Last August, I had a Midwest 3000 stall torque convertor put in my car. I drove the car from August til December, when it went into winter hibernation without any problems.

This past May, I completed a heads/cam swap on my car. I put in a custom ground 228/224 .571/.568 112LSA +2 Comp cam in my car along with a set of Stage 2 heads with 2.02/1.57 REV valves. In addition to the heads/cam, I also installed an ASP underdrive pulley (stock alt pulley), LS6 intake, Rollmaster double roller timing chain, and a new oil pump (in case it matters). The car was taken to Speed Inc and tuned by Jim.

So, to get to the problem... I didnt notice til after the heads/cam swap. When I just had the convertor, I was okay. When I am driving around between 1400-1800 RPM at cruising speed, if I am feathering the gas, just to keep the car going the same speed, the whole car shakes. Sometimes its barely noticable, but other times, it can get quite violent. Some people have described this as cam surge (which is why I am posting this in Internal Engine).

I've never been in a cammed car before, let alone one with a 112LSA and a high stall convertor. My friend told me that its probably my convertor.

So anyway, after only 900 miles on the car, the transmission blew up. The trans was just rebuilt 5000 miles ago, and the trans shop said that theyve never seen a 4L60E go bad so fast. Well, they told me it was because I was running too much power through it. I am putting down 405.5 RWHP, which yeah, I know is quite a step up from stock, but I thought for sure that these transes could take quite a bit of power. Mind you, my car has NEVER been to the track, and other than on the dyno and a couple times on the highway, my car is never even taken to WOT. As much as some people find this hard to beleive, I do not beat on my car.

I realize this post is getting long, so I'll try to end it soon, but basically, I got the trans rebuilt, and the car is still doing the surging while cruising. The best way I can describe it, is, it is a forward and back motion. Almost like if you were in a manual transmission car, and you were accelerating in too low of a gear.

So, what should I do? Is this normal for a cammed car?
Am I destined to keep blowing transmissions every 900 miles?
Do I need a race trans built to take my power?
Is there something wrong with my convertor?
Should I get it retuned?

Help! This is driving me nuts, and I am afraid that my car will keep breaking down on me.

Thanks for reading my long book/post...

 

Welcome to the club of big cams and tuning issues, what is causing this is your fuel maps changing over because of detected fuel trims This is due to the variables the world provides and unless you undertune it's very hard to get it just perfect. I have been back to my tuner a couple of times for same issue and though it has gotten better it hasn't totally gone away. I've heard though after a few trips your tuner should be able to hammer it out.

The surging is your converter unlocking and locking cause of computer tune.

Hope this helps.

Oh and BTW I blew my Race-built 4l60e after 1200 miles. Blew the 5-gear planetary on the second time I ever got on it from a stop. After talking to builder of tranny and manufacturer of the planetary we came to the conlcusion the one I had was defective and they then shipped us out a new and improved one they had not yet released at the time 6k miles now and no problems so far

Look me up under same name on Ls1.com since I know you are there too that's where I mainly reside.

 

The surge is one thing but I'm not so sure that is entirely the culprit. Did your tuner delete torque management? Doing so and pushing a great deal of power through it will/could cause premature failures of a tranny. If your car hits a hard upshift at WOT, I'd look into that area, too.

 

Maybe you should try changing the speed at which the TC locks. Jim set mine to lock at 45 in OD (1800 rpm w/my 3.42s), its much better now.

 

Thanks for all the great info guys. I think I will have to give Speed Inc a call on Monday and see what they think.

To answer Jabroni's question, yes, torque management was deleted, but we're not talking about any full throttle upshifts here. Just lazy driving around town with my foot barely on the gas pedal.

Heres another question. Why should I have had torque management deleted? If it could extend the life of the tranny, why not just have it turned back on?

Thanks everyone for the info!

 

TM will pull all timing from your motor in the event of an "abusive" manuver. basically every launch or every time you've hammered it on the highway at 65-70mph and it downshifts to second when it hits third kiss the timing goodbye and the car falls on it's face

I used to have this problem before my H/C and computer tune.

 

I have a big converter in my car with a cam that is much larger than the one you have. I am know exactly what problem you are talking about. The foreward and backward motion you talk about really does feel like a manual trans car that you were trying to run at 200 rpm in too high of a gear.

The jerking motion is not caused by the torque converter locking and unlocking. It is caused by the engine surging which then quickly loads and unloads the drivetrain back and fourth and causes the jerking motion. It only happens during lazy driving conditions, when you are just barely on the gas, or maybe when you just let the gas off. It will usually occur between the speeds of 30-45 mph.

My car does this all the time. My old 6 speed cam car did it all the time, too. The fix was simple in the 6 speed car, just downshift to the next lower gear while cruising in town. I would just usually drive in 3rd when I used to drive in fourth in low speed limit areas.

Try this once and see what happens. When the car is doing the jerking think, maintain the same throttle position so the car continues to jerk back and fourth. Then, with your left foot press the brake pedal slightly, just enough so the brake lights will come but not enough to start to cause the car to slow down. Pressing the brake pedal causes the torque converter to automatically unlock, and the jerking motion should stop immediately. This test will tell you if you and I are talking about the same problem. If this is the case, the fix for you will probably just increase your torque converter lockup speeds so that the engine is running a higher RPM whenever the converter is locked and it won't surge.

In my case I drive around in with the trans in 3rd unless im on the freeway. With the stock torque converter lockup speeds, the converter will lock up in 3rd at 29 mph or so. I like the converter to lockup as soon as possible because it helps my car accelerate up to the speed limit without the engine running 4000 rpm because the converter is so big. So, in the end I just deal with a little surgeing.

Hope this info helps

Jordan

 

Wow, Jorday, thank you so much for such a great reply. It sounds like you nailed it on the head. I talked to the place that I ordered my Midwest convertor from and he said that with the kind of power I am making, I shouldn't be seeing any problems with the convertor. I talked to Speed Inc, and Larry told me that he hadn't heard of this problem before, but would be willing to bump up the speed at which the convertor locks.

I will try driving around in 3 around town (at the expense of fuel economy no less!), but when I get a chance, I'll take it up to Speed Inc and have them change the speed for me.

Once again, thanks a million. This thread should be remembered by all, since it appears that its not all that uncommon of a problem with a setup like I am running.

 

Yah, just about every cam car I've rode in has had this problem to some degree. Obviously, the bigger the cam, the worse it is.

My 6 speed B1 cammed car did it, as did my camaro when I had the B1 in it. Now I have a comp XE-R 228/236 on a 112. Problem got slightly worse with the bigger cam.

Later,
Jordan

 

Well, for an update, I took my car back up to Speed Inc today, and Jim adjusted my torque convertor lockup speed. I think he set it to 45 mph, and on the way home I did notice a difference. The convertor doesn't lock up as easily, but I also don't get the low RPM surging.

Thanks everyone for all the great info. If anyone else has this problem, the general consensus is get your lockup speed increased, but apart from that, its pretty normal.

 

How about some steeper gears? Get your RPM up faster....