Thump of a shift - first gear

[forest522]

So, ole Belle (as my daughter calls her) and I have driven many miles together with family and friends. We've searched for and cut Christmas trees in two states...gone on many campouts...driven countless errands...and transported kidos to as many activities all around town. She has always shifted hard into the first gear around 25ish mph.

One guy told me that it was normal...another said...change the filter. I have and will be installing a new pan soon that has slightly more capacity, an easy access drain plug and larger magnet in the base.

I've never seen an accumulation of metal shavings, yet, when changing the fluid.

Does anyone else have a hard shift into first as well? Should I be concerned?

Thank you for your input and/or advice!

 

[cucvrus]

Have you ever checked the vacuum pump? And changed the old dry rotted vacuum lines? That is the first place to look. Keep us advised.

 

[donalloy1]

I gather that they all pop pretty hard into second. Mine sure does! It can be adjusted out if you like. Leaving mine alone. That's the way GM shipped and I'm sticking with program!

 

[forest522]

CUCVRUS - yes, good point, and I failed to mention that. The old and cracked vacuum lines were replaced and I even added a new tee. I have not adjusted or replaced the vacuum pump.

The CDR valve and the hose/lines to it have been thoroughly cleaned/replaced. I will inspect them again soon.

donalloy - i figured that too, just seemed that it was harsh sometimes and normal others...

I think I may have been advised awhile ago to replace a solenoid or some kind of sensor located on the passenger side of the tranny. Seemed like it was an easy project and fairly low cost. I may need to explore that as well.

 

[cucvrus]

Sir I won't pretend to know more then what I already said. I have an issue right now with one of my M1009's It shifts from 1-2 fine but 2nd to 3rd forget it. I bought the Kent Moore tool J33643 that hold the throttle open while you adjust the VCM. Massive fail. I replace the VCM. still the same. I replaced the vacuum pump even though it was creating good vacuum. still the same. I switch everything back and started over. I copied every detail from another M1009 that shifts perfect. Still the same. What it does is shift to 3rd at 50-55 and then when you let off the throotle you can feel it like go into 2nd and then when you get back on the fuel it just hangs there until 50-55 again. I am sending it to the transmission shop. I have had enough of it. I changed a hundred injection pumps and never really thought about the exact setting of the VCM. I just put them back on in the same position that the bolts left on the plastic and test drove everyone after the change and very few ever needed any adjustment. Some were not adjusted when they came in but it was an easy fix. I must be getting old and forgetting something here. But I am sending it out to transmission shop on Monday.

 

[Gripy]

Rus, if adjusting the vac regulator does nothing to change the down stream vacuum then I would look into a new vacuum regulator (or on rockauto: egr valve) if it still does nothing then it would be most likely the trans failing.

as for the OP, push the vacuum regulator towards the firewall for earlier and smoother shifting. If it's still bad then check the vac lines and vac pump; if hose are good then its most likely a transmission issue.

The TM's state a vacuum between the regulator and trans is 8 mmHg. I have mine set to 10-12mmHg for smoother and earlier shifting since I do mostly city driving with my m1008.

 

[cucvrus]

This is an M1009 that I am working on. And I can move that VCM anyway and it makes no difference. I even eliminated the VCM and put the vacuum right to the transmission. Better but not the results I wanted. it will go to the transmission shop on Monday. I don't know what else to do. It needs to be fixed. It is the OEM transmission and I put 90,000 miles on it with out a problem. It currently has 120,000 miles on it and at 30 years old if it needs overhauled so be it. I have others to drive. Thank you for your quick responce it is apreciated. Have a good day.

 

[donalloy1]

CUCVRUS - yes, good point, and I failed to mention that. The old and cracked vacuum lines were replaced and I even added a new tee. I have not adjusted or replaced the vacuum pump.

The CDR valve and the hose/lines to it have been thoroughly cleaned/replaced. I will inspect them again soon.

donalloy - i figured that too, just seemed that it was harsh sometimes and normal others...

I think I may have been advised awhile ago to replace a solenoid or some kind of sensor located on the passenger side of the tranny. Seemed like it was an easy project and fairly low cost. I may need to explore that as well.

Mine hits pretty hard to second unless you are in certain throttle up situations ( 2wd hard top ). Afraid to make any changes because she has been so dependable! My worries have always been adverse wear to drivetrain due to this SLAMMING into second. So far so good. Sticking with program, DMLII sends

 

[nyoffroad]

I did away with the TH400 in both of my trucks so I don't have anything to go by but my memory so here goes.
If I remember correctly on the tranny there is a vacuum modulator and if you pull the hose off of it and look in the tiny hole you should see the head of a very small allen screw. Turning that screw can change the spring/vacuum pressure and I believe how or when it shifts.
I haven't done this since sometime around 1980 or so, so it's possible that I'm totally wrong so keep that in mind.

 

[Iceman3005]

Could also be a bad trans vacuum modulator.

 

[forest522]

Iceman - you know, I thought about that too! So, for 14 bucks...might be a safe repair. Havent installed it yet. The hard shifting is very random.

This is what I have done recently....

So, with the 12 volt conversion, the twin voltage things behind the air cleaner are removed. Hence, no reason for the metal plate there either. I found that the air cleaner, the metal plate, a cross-the-engine-bay wiring loom all seemed to crowd the Vacuum pump and the "t" with the line running forward to the IP. So, yesterday, I removed the metal plate, affixed the wiring loom closer to the now spacious firewall and tidied up all the other wires.

Now with all that down, I can stand on the drivers side and see the vacuum pump and its lines free and clear of obstruction, even with the air cleaner on. I'll take her for a spin today and post with results.

Probably just thinking too much into it...but then again...mysteriously whenever I just spend time playing with this truck...seems to work better. Funny, very much like a woman, spend time with them and they are happier!!!

 

[donalloy1]

I did away with the TH400 in both of my trucks so I don't have anything to go by but my memory so here goes.
If I remember correctly on the tranny there is a vacuum modulator and if you pull the hose off of it and look in the tiny hole you should see the head of a very small allen screw. Turning that screw can change the spring/vacuum pressure and I believe how or when it shifts.
I haven't done this since sometime around 1980 or so, so it's possible that I'm totally wrong so keep that in mind.

Has anyone else done this adjustment recently? I have heard it spoken before. More detail could be very useful here. Thanks in advance

 

[cucvrus]

The best thing I could tell you to do is go to Autozone and buy a new modulator and they come with instructions that tell you everything about the adjusting procedure. I do remember that the instuctions said you only have a few turns. I think the first one I ever adjusted I just went in there and turned it and it came apart. I think you can only turn 2-4 turns in either direction. If that is the problem it is less then $20. Let us know how you make out. I have mine at the transmission shop right now because of late 2-3 shift. And I tired of messing with it.

 

[rsh4364]

Throw a vac. gauge on line from pump if 20lbs. all good.Put vac. gauge on line from vac. regulating valve on IP if 6-8lbs. all good.Check vac. at modulator on trans. If not 6-8lbs. its leaking between reg.valve and modulator.Pretty easy to pin point problem.I ended up replacing vac. pump,regulating valve and all soft lines now shifts like a dream..