Trans shift issue

[Skinny]

Since my M1031 came home and I got it running, the trans has been doing a classic late shift issue. Now that my 6.2 is running good, I've started the diagnosis on it.

First road test, it was shifting at 37mph and 50 mph. I had only 5" of vacuum at the modulator. I fixed some vacuum lines and got a slightly higher number. I then cranked the IP vacuum all the way and got 15" at idle. I figured this was still on the low side but much better than I had before. Roadtested, still the same issue.

Today I ran a straight line from the vacuum pump down to the modulator bypassing all the factory lines and valve. I was getting 23" of vacuum at the modulator. Roadtested, my shift point went down slightly to 32mph and 47mph. This still seems way too high.

Followed the TM and disconnected the down shift plug on the side of the transmission. Roadtested, same as above.

I know the next obvious thing to do is a line pressure test to determine if it's the governor or an internal valvebody issue.

Just for some feedback so far, has anyone had a failed governor? What are you guys experiencing for governor failure (and I don't mean Arnold Schwarzenegger...get to da Choppa)? It seems like most people with this issue have a failed modulator or leaking vacuum line issue. Nothing I read on SS so far has mentioned replacing a governor which leads me to believe they are fairly bulletproof. Other than late shifts, they seem to be consistent, fairly firm, and the fluid looks great. This trans has no lag or delays when putting into gear which makes me think the valvebody and clutches are in great shape...only has 6600 miles on it which I believe. The interior shows no signs of being over 100,000 miles old.

 

[dependable]

Did you determine that the modulator itself was good? Assume you have checked fluid. I would replace the filter. Most 1031s have low mileage, so the problems are more likely from sitting or contamination rather than wear.

 

[Skinny]

My new red stripe modulator didn't fit, the OD was slightly larger than the one that came out...not sure why but couldn't install it. It's an ATP unit I bought from RockAuto. Either way, the original one in the truck has a dry vacuum line. I also pumped it up with a vacuum pump. It holds and actuates the same way as the new one.

Fluid is very clean like it has been recently been changed. I do have a new filter, I can change it when I get it into the shop just to eliminate it as being a problem.

I would assume the TH400 isn't super sensative as far as level or fluid brand name? I'm used to working on late model stuff that you need to confirm the fluid temp before adjusting the level they are so sensative. Not to mention they become problematic if you don't use the OEM factory fluid.

 

[Warthog]

You are only suppost to have 8" of vacuum at half throttle.

This is what the vacuum regulator on the side of the injector pump is for.

All covered in the TMs.

http://www.steelsoldiers.com/cucv/50568-cucv-throttle-vacuum-valve-adjustment.html

 

[Skinny]

I still do not understand why it basically shifts at redline no matter how much vacuum is at the modulator or if the downshift solenoid is used. I don't have a tach but my online gearing calculator is showing shift points at 3400-3600 rpms.

I will go through the correct regulator adjustment again. What boggles me is going from 0" to 23" at the modulator should make a TH400 go from banging gears at WOT to Granny shifts at low throttle inputs. I'm lost...it's like the modulator isn't doin anything.

 

[atvcat33]

my 1009 shifts at 38 and 47 mph too. no other issues, goes into gear fine, no slipping. but the faster i take off the smoother it shifts. but if i baby it around it will give me whiplash when it shifts..... i tried the same things as you. i am going to just take it in and have a professional look at it. i really want to swap with a th350 or 700r4

 

[Skinny]

You may just have really high line pressure which could be the valve in the oil pump or valvebody. If line pressure is too high, all other pressures like governor or modulator will be off.

The TH400 is pretty stout. Not the best transmission as far as gear ratios are concerned but still good which is why I want to keep mine.

I think a worthy investment is an oil pressure gauge. I think if I can't figure mine out, I will have to break out the gauge and do pressure checks for all major pressures.

 

[Roadrunner 161]

.

 

[beltfedonly]

high shift

I had the same probelm on my M1009 and changed the modulator ( was not leaking) and it cured the problem.

 

[Skinny]

I got my M1031 at the shop now. I will be doing a ton of maintenance along with a 4" lift install and 37's. When it's up on the lift, I am going to pull the modulator and governor to see if something bad comes up with either one.

 

[MikeOneZeroZeroNiner]

What ended up being the issue with your transmission? I used to have an identical problem with my m1009. But now it just won't shift out of first, unless I play with the shift lever for 5 minutes straight.