Help: Hard 2-1 downshift suddenly

[sbatty]

First off I need to say that I don't know jack about diesels or allison transmissions yet. I just bought a 2001 K2500 crew cab for a work/play truck. The truck has a gob (315,000) of miles on it but runs and drives well. Just yesterday it started downshifting very hard from 2 to 1. I don't know if it does the same thing in other downshifts because I'm afraid to drive it any faster. It felt and sounded like I hit a big pothole when it downshifted. I checked for DTCs and found a P0106 but that's a MAP performance error which I'm still trying to figure out. Could they be related somehow or do I have yet another problem?

Thanks

 

[Fastorange]

what are the mods on your truck? do you know the person you bought it from? if not, you might have a truck that someone beat the crap out of and limped the trans. However, have you changed your filters yet?

 

[IOWA LLY]

2-1 downshift is C4 releasing and C5 coming on. I really doubt that it was abused enough to hurt C5. They rarely get damaged as they are the largest clutch in the ally.

You should probably start with a spin-on change. But it would be an even better idea to drop the fluid and pan, and cut apart the internal filter to see if you have something going on inside.

 

[sbatty]

Thanks guys. When I bought the truck in February the guy told me that he had just had the trans fluid and both filters changed as well as the gear lube in both diffs. I have no reason to disbelieve him but I guess you never know. I guess the best thing would be to go ahead and change the fluid and filters first. Can someone recommend a fluid? From what I've heard/read, many folks use a synthetic fluid? Would this be the best solution for an old Allison? I have no doubt that this tranny will need rebuilt sooner rather than later due to the mileage (315,000) but I would like to put that off as long as possible.

 

[Jasondt2001]

There's alot of talk about transynd and Amsoil Torque Drive... Mike L I THINK uses a mobil1 type of fluid that he's had luck with... hopefully he'll be by to chime in because I want to know if the mobil1 is as good and cheaper than the other stuff :hug:
Time are hard

 

[IOWA LLY]

You might want to try pulling the valve body, and disassemble it and clean it really well. It might just have some gunk build up in the valves.

 

[Mike L.]

Reset the TAPs with a Tech 2. It is highly unlikely that a valve body will cause a clunk on a down shift Harsh upshifts and down shifts are tie ups. I would not tamper with too much as you probably have a lot of weak parts in the Alli. Stator bushing is probably all but gone in the pump. Rubber components are brittle and ready to crumble, and clutches are glazed and will never bite well again. You also may have some lazy trim and shift solenoids. Playing with the valve body may get you a stuck E shift valve so leave it alone.

 

[racinmike77]

Harsh upshifts and down shifts are tie ups. I would not tamper with too much as you probably have a lot of weak parts in the Alli. Stator bushing is probably all but gone in the pump. Rubber components are brittle and ready to crumble, and clutches are glazed and will never bite well again. You also may have some lazy trim and shift solenoids. Playing with the valve body may get you a stuck E shift valve so leave it alone.

I agree, a rebuild would be great, personally Id buy a used one from a salvage yard and give it a shot. You can pick up a low mileage trans (50K or so) for about $1500.

 

[mainer]

I agree, a rebuild would be great, personally Id buy a used one from a salvage yard and give it a shot. You can pick up a low mileage trans (50K or so) for about $1500.

if you pay more than about 800 for a used tranny your nuts..... they are readily available now, at least the 5spds are

 

[sbatty]

Reset the TAPs with a Tech 2. It is highly unlikely that a valve body will cause a clunk on a down shift Harsh upshifts and down shifts are tie ups. I would not tamper with too much as you probably have a lot of weak parts in the Alli. Stator bushing is probably all but gone in the pump. Rubber components are brittle and ready to crumble, and clutches are glazed and will never bite well again. You also may have some lazy trim and shift solenoids. Playing with the valve body may get you a stuck E shift valve so leave it alone.

In case you missed the first part of my original post, I know nothing about Allison transmissions so a little hand-holding might be required. What is a Tech 2 and what are TAPS? I don't mind reading up on the subject if someone can point me to a good reference site.

I've also got a P0106 DTC (Manifold Absolute Pressure (MAP) Sensor Performance) that came up at about the same time. I was just starting to figure that one out when this started. Is it possible that the two are related? Would that problem have an affect on the signals the tranny is getting?

Mike L. : As the resident Allison guru, can you recommend a good service manual for the 1000 series allisons? Something that contains rebuild/testing information. When I have to rebuild the trans I'm going to do it myself. I've done some TH400s and a TH700R4 so I'm pretty sure I could do it. What do you think about the used/salvage option?

Thanks, you guys rock.

 

[Cougar281]

Where in Illinois are you?

 

[Mike L.]

In case you missed the first part of my original post, I know nothing about Allison transmissions so a little hand-holding might be required. What is a Tech 2 and what are TAPS? I don't mind reading up on the subject if someone can point me to a good reference site.

I've also got a P0106 DTC (Manifold Absolute Pressure (MAP) Sensor Performance) that came up at about the same time. I was just starting to figure that one out when this started. Is it possible that the two are related? Would that problem have an affect on the signals the tranny is getting?

Mike L. : As the resident Allison guru, can you recommend a good service manual for the 1000 series allisons? Something that contains rebuild/testing information. When I have to rebuild the trans I'm going to do it myself. I've done some TH400s and a TH700R4 so I'm pretty sure I could do it. What do you think about the used/salvage option?

Thanks, you guys rock.

Call me and I'll give you plenty of info.

 

[sbatty]

Cougar281 I'm in south central Illinois about 50 miles south of Springfield

Mike L. I'll give you a call tomorrow. I just gotta figure out what time it is in CA. I never can remember to add or subtract..... Thanks again.

 

[racinmike77]

subtract 2

 

[sbatty]

Just wanted to thank Mike L. for all the information he gave me on the phone. I'm going to get the TAPs cleared tomorrow. I'll let you know how it goes.

 

[sbatty]

Update and new problem...

I just wanted to let everyone know what I found since I thought it was interesting and I learned a good lesson from it.

When this all started I had the SES light on and I found a P0106 (MAP Sensor poor performance) code showing. The hard downshift started at roughly the same time. I made the mistake of jumping to conclusions and assumed I had a trans problem and decided that I needed to get that fixed first. Wrong move. Since the code showed up first I should have gone ahead and fixed it first. Turned out that by the time I got around to looking at it I also had P0101 and P0107 codes as well. I took it to a local guy (only one I could find with the right scanner) and we found out that the Baro sensor was out of range. Unplugged it, cleaned the contacts on the connection and that was the fix. Runs fine, no codes, trans downshifts like before.

Happy ending, right? Not really. I drove the truck home and discovered that during the 2 - 1 downshift the transmission sometimes (1 in 4 times) seems to "neutral out." It seems stuck between shifts like none of the clutches are engaged. If you give it just a little throttle and bring the pump pressure up it bangs into low.

I talked to Mike L. and know what I need to rebuild it and based on what he said about not messing with it, my question is, is there anything I can do to get through a few thousand miles until I'm in a position to rebuild it?

BTW: I never did reset the TAPS since the baro fixed the first problem. I didn't want to screw with it since it was working. Think I should still do that?

Thanks everybody. You've all been a lot of help and I've been learning quite a bit.

 

[Mike L.]

I would reset them and see what happens. Remember that the only scanner that works on an '01 is a Tech 2 and it may take a while to relearn. Other scanners are hit and miss on the '01.

 

[sbatty]

The scanner he has is not a tech2 but he seems to think it will work since it runs GM software. We'll try it and see. Thanks again.

 

[Mike L.]

The scanner he has is not a tech2 but he seems to think it will work since it runs GM software. We'll try it and see. Thanks again.

You are pissing in the wind. NOTHING WORKS. Tech 2 MAY work. You may have to reset a few times to do any good with the Tech 2.

 

[MACKIN]

The 01 TCM's are primitive but yet good. I believe you can clear all taps or reset individually. Tech II only as told


I have a 01 and a GM Tech II

If you needed someone else to say so