FastMover

I have a bit of a problem. Ever since I changed out converters in January I have had a nasty shudder when I am coasting starting from about 48 mph down to 38-39 when the converter unlocks. I have had mechanics drive the car and they tell me the shudder is from the rpm's being to low for the cam and that it is normal with aftermarket cams that are made to run at a higher rpm. This is fine and all but my question is what would happen if I had the lock-up mph raised so that under part throttle the converter doesn;t lock until 48-50 mph? It seems like I am always right around 40mph driving around and it is annoying with the shudder happening. I know gas mileage will suffer but are there any other downfalls of doing this. I spoke to Ed Wright and he said he could set it to lock at the mph that I want.

Opinions please...

Jim

Ragtop 99

iTrader: (7)

Most people only experience shudder under part throttle acceleration when there is a load but not enough pressure to hold the clutch.
Are you sure it is a shudder and not cam surge? You don't experience the shudder under moderate acceleration in that same speed range? does the same problem happen if you let the converter lock-up in 3rd gear?

Cam surge can be cured through tuning w/o changing lock-up. you might experiment with 3rd gear. you may find lock-up in 3rd works fine at 40 mph but you want 4th gear set to 50 mph.

FWIW, I didn't have that problem with the thunder cam on my car and lock-up would stay engaged on coast down to about 35 mph.

FastMover

This problem started after I changed converters in Jan. I had been running a SY3500 for over a year with no problems. I first switched to a TP4400 and noticed the shuddering problem when I was coasting. I sold that converter and bought a Vig3200 and it did the same thing. I have checked everything possible in the driveline and it is all perfect. I have had an independent mechanic check it as well as a GM tech and they both say that it is the cam. I had run the cam since Nov. with the SY3500 and it worked perfect. They say it is when the cam is at to low of an rpm. It does the same shudder in 3rd gear as well. This is what is confusing me because when I put it in 3rd the rpm's are at 1900-2100. How can the programming change this?

Thanks.

Jim

Ragtop 99

iTrader: (7)

I just have a hard time accepting that it is shuddering at 1900 rpm in 3rd gear because of the cam. Even with a bad cylinder, I had no issues with the TR 224 112 cam above 1600 rpm.

What is your idle speed at? Do you have your IAC count down around 30 when the motor is fully warm at idle? Have you tried opening the TB just a tiny bit more by turning the TB set screw about 1 full rotation?

FastMover

I am not sure what the IAC is set at. I had the throttle body adjusted by Mike Norris @ Norris Motorsports in FL. He drilled my throttle body 1/4" and set my IAC but I don't remember at what number. I will try and reach him tomorrow. Would this really cause the car to shudder? To me it seems to be a mph issue more than a rpm related one. Once the converter is unlocked the car is perfect.

Jim

Ragtop 99

iTrader: (7)

once the converter is unlocked there is no load on the engine. Get/borrow ATAP and measure your actual idle speed & IAC count.

FastMover

I will try and get some readings this weekend. what are the numbers I should be looking for? This problem is weird because it showed up after I switched converters. Just out of curiosity would a different converter cause less shudder? As I said before I never had this problem when I was running the SY3500. I thought maybe a looser converter might not cause as much shudder.

Thanks.

Jim

Ragtop 99

iTrader: (7)

SY3500 is larger and heavier than the other 2 9" converters and that could smooth out the surge a bit. Larger converters are easier to lock-up too.

Look for a hot (go out and put some miles on the car and then measure) IAC count around 20 - 40 in gear at a stop. If you are above 50 I would adjust the TB to open it it a bit (1 turn) and let more air in.

FastMover

Thanks for your help. I will try and get some readings this weekend. I spoke to a few people and they didn't seem to think that the IAC being to high would cause a shudder. They said it would just cause the car to idle rough and maybe want to stall.

Jim

FastMover

I went out an autotapped the car. The IAC count was right around 28-30. Would going with a different converter eliminate some of this problem with the shudder?

Jim

FastMover

I just got a message back from Ed Wright regarding raising the lockup mph on my TA. He says that some of the shops he does work for have him raise the converter lock up mph to about 45 and it usually helps to minimize if not eliminate the shudder that seems to be an effect of cam lag at a low rpm. I will probably be trying this out because I need to send him my pcm to delete the shift firmness so I can install my TransGo.

Later.

Jim

FastMover

TTT <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" />

Ragtop 99

iTrader: (7)

you can give Ed a try, but personally I believe there is another issue. I have no problem on coast down with shudder locking up at 40 mph with both the TR cam and an XE-R cam.

Pro Stock John

iTrader: (34)

I'd just raise it to 45mph.

Mine is about 45mph now...

Too low a few years ago and the car was goofy.

FastMover

That is what my buddy said. He has a cammed mustang and it bucks real bad when the rpms are to low. How come I am experiencing this when there are mutiple others with the same setup that are not? Ragtop said his was smooth above 1200rpm and Patrick G said he had his lockup lowered to 35mph <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" /> and it is perfect.

Later

Jim

WILWAXU

iTrader: (6)

Yeah.. Ed set mine at 30mph. Locks up like a clock. No issues.

FastMover

Patrick G said he he thinks it is the rear end going out. I had it in at the dealer and he said the rear looked like it was fine. The shudder only occurs when the converter is locked so I doubt the rear would have any effect on this shudder problem. Could it be a problem with the cam?

Jim

Pro Stock John

iTrader: (34)

I would get a funny shudder feeling in my car and a buddy's car when the converters would lock up too low... car shakes when you give it light throttle... kind of like having a clutch'd car and trying to have it fulling engaged at 5mph.

FastMover

So what could be causing this problem? Nobody I have spoke to can seem to determine what is causing this shuddering.

Suggestions? Anybody?

Jim <img border="0" title="" alt="[Sad]" src="gr_sad.gif" />

WILWAXU

iTrader: (6)

Sounds like the lock up clutch is "glazed".

Lubeguard make a product for "deglazing" the clutch, but I haven't used it yet.

Here's my very uneducated answer...
Untill you get computer tuning the computer pulls line pressure as the lock up clutch engages.. this cause the lock up clutch to slip.