LLY Allison with a coasting to stop lunge

[hans1159]

I have had on ongoing issue with my truck when I am coasting to stop and when I get under ~5mph, it may lunge. The brakes easily control it, but I have to be very vigilant in stop and go traffic. When this started happening around 100k, I dropped the tranny pan, changed the internal/external filters, and started swapping over to Mobil Delvac Syn ATF. I have done 2 subsequent pan drains and external filter switches. This helped the frequency of the lunging occurrence, but not solved. I put 1100 miles on the truck this weekend in northern CA and had it happen ~20 times. If I stop normally breaking the whole way to stop, it doesn't seem to happen. It only happens when I am in relaxed stopping mode with those extended coasts waiting for the light to change, etc.

I don't see an RPM rev causing this. Tach doesn't show that and I don't hear an increase in sound (lots of window down, radio off trying to figure this out).

The truck is a 2005 LLY with 110k miles. It has been used mainly for recreational boat towing (5k lb dual axle rig) or hunting. Mainly hiway miles and very few short trips. About 15% of the miles were towing. Stock engine except for Chevy dealer performed air filter upgrade to the large round filters. Stock driveline except for the transfer case pump upgrade kit from Merchant Automotive. All services performed by me with stock Delco/Allison parts/fluids since new with very conservative service periods.

Any help would be appreciated. I love my truck and have been trying to solve this for almost a year now.

Thanks,
Craig

 

[hans1159]

One detail neglected - no codes from a garbage ODB scan tool.

 

[tbk5]

it is possibly the wheel hub. I had the same problem. It almost felt like the ABS kicking in at 5mph. As it was explained to me, when the hub begins to go, it affects sync with the tone wheel on the hub.

 

[hans1159]

tbk5 - I think this is separate from the phantom ABS activation a lot of us deal with. I have been living with that and the ABS light for 50k miles. I was going to do the hubs at 100k because I run larger aggressive tires, but have been waiting on that to figure out this more important issue first.

 

[1953drtelco]

Subscribing

 

[redrob]

hans1159 ,did you check your hubs for play?

 

[hans1159]

redrob, I haven't. Are you just referring to the standard jack up the front end and try to wiggle the tire vertically and horizontally test?

If I find play, would this just relate to my ABS issue? I don't see how the front end would relate to the lunging issue when in 2wd mode.

Thanks for any insight.

- Craig

 

[darkone98]

Does it feel like it wants to push through the brakes? Could possibly be a torque converter issue.

 

[hans1159]

darkone98, Yes, it almost has an acceleration feel to the lunge. That is why I was trying to figure out if the engine was surging (like a fuel delivery type issue).

How would a guy test the torque converter? I have seen some unscientific posts about basically doing a brake lock acceleration test, but am not going to do anything until I understand what to do, what I am looking for, and what damage could be done doing the test.

Thanks for your assistance.

Craig

 

[darkone98]

I am not sure how to test one, but It certainly sounds like a bad converter. Mike L is the guy you would want to talk to.

 

[Mike L.]

Have a Tech 2 hooked up and watch the turbine speed sensor to see how fast it goes to 0 when coming to a stop.

 

[hans1159]

I am now living in San Jose CA. What would be a reputable shop that I want to do business with? I don't necessarily need my truck so I could drive somewhere on a weekend, leave it and take a loaner, and come back the following weekend. I don't drive during the week right now so the only miles on the loaner would be to/from San Jose.

In the next year, my wish list of truck improvements is:
1) Fix this tranny? lunging issue
2) Fuel Delivery and Filtration improvement
3) Front end (Hubs, replace weak factory tie rods/steering components, Leveling Kit and possibly a control arm/shock type setup or ball joints/shocks at a minimum)
4) Real front bumper

Thanks for any assistance.
-Craig

 

[rmallen30]

possible fpr that spikes mine does this in my lly not sure if that helps

 

[hans1159]

Fixed!!

The likely culprit was the torque converter based on formum feedback and phone discussions all over the country. I chose Inglewood Transmission Service to solve this for me. Mike is great to work with, knowledgable, and still has that passion for his work. I felt comfortable leaving my truck with him. I was kept informed over the week they had it down in LA.

Mike found that the torque converter sprag had failed and allowed both rotations and that I did have some clutch damage. This gave me an excuse to go forward with a blueprinted transmission job and a Dave Goerend torque converter.

Not only did Mike work on the tranny, he also looked into and diagnosed my ongoing ABS activation issue, noted a rusted caliper making for a spongy brake pedal feel, and had my U-Joints replaced and driveshaft balanced at a nearby shop.

Prior to the fix:
- Lunging conditions when coasting to stop.
- Gas pedal applied while braking - vehicle WOULD push through brakes right away.
- Felt sluggish off the line, but I could always get up to speed and my mpg hadn't fallen off. I didn't realize how this had changed over 8 years of driving the vehicle until it was fixed.
- I drove over 10k miles with these conditions and I wasn't willing to throw money at it until someone KNEW what was wrong (or it stranded me).

After the fix:
- No lunging so far.
- Brakes will hold truck with slight rpm applied.
- More initial power to get going.
- Still in learn mode for the 400 miles I put on it this weekend driving home so some of the shifts felt punchy, others felt long.


If every place I went to treated me and my vehicle this way, I would sell most of my garage equipment back home in MN.


- Craig Hanson

 

[NJ_LLY]

Mine did the same thing a while ago. The cause was a converter that took a shit and clogged the valve body causeing the valve to stick. It also ate all rhe clutches. It's easy to tell if that's the case just drop the pan and look for material. Mine never through codes till it finally limped at a traffic light.