M1008 Transmission shifting late

[jgb680]

I have an 84 M1008 that is shifting out of first gear very late. I have replaced the modulator and adjusted the vacuum regulator. I also replaced all the hoses going between these. Does anyone know what else would cause the truck to wind first gear all the way out before it shifts?

 

[jgb680]

I am also going to change the fluid one day this week to see if that helps, but I was just wondering if anyone knew what else it could be?

 

[kapnklug]

Maybe a bad vacuum pump, or bad VRV? Mine had a bad VRV (the regulator on the side of the IP) that caused the same symptom. Either way, Get a vacuum gauge (cheap) and T into the vac. line in various places to check the vacuum. The needle will jump around alot, but should significant vac. everywhere

 

[DriverSideImpact1008]

What is your definition of "shifts too late?" At what MPH? Or RPM (if you have tach)

Like 35 mph under normal driving?

I'm not sure what the M1008's shift at. I think my old 1008 shifted from 1-2 somewhere around 15 mph. My 1009 shifts at a little over 20mph.

The way the trucks are geared, 3 speed trans, and low revving diesel does make it seem like it's revving high even if it is working and shifting properly.

 

[jgb680]

It is shifting from 1st to 2nd around 30mph. I also did not have any real problem until I decided to change my modulator a few weeks ago, because it was shifting a little hard. After I changed it the truck drove great for about an hour then it started shifting late.

 

[DriverSideImpact1008]

I had seen something a while ago in a thread about shift points I think it was called, "What are normal shift points." About moving the regulator in or out to adjust the shift points sooner or later. And something about a screw you could adjust to make it shift later and make them more firm.

 

[DriverSideImpact1008]

I found it! Here is the quote from that thread. Might wanna look more into that...

there is a few factors here , i adjusted mine to shift 1-2 15mph ans 2-3 at 20-25mph , you can do that by losing the vacum regulator bolts {3/8 wrench] and pull the regulator back towards the rear fire wall the more you move it back the faster it shifts, now the vacuum pump has to deliver between 22-25 inches of vacuum before the regulator and all hook up you can check he vacuum at the trany vacuum module and it needs to have 12-15 inches at idle for it to shift smooth and quick at ligth trottle, if it does not have between 12-15 inches the regulator is getting old that is if you have 25 inches before the regulator at idle, now there is also a adjustment in the trany module {last result} inside where the vacuum hose plugs in you can turn it in or out with a small flat head, turn it clock wise will make the shift delay and fim up a little, counter clock fast and smooth, even if te cacuum sorce is low you can remove the insert all should make the shifts 20 and about 34 mph, usualy when the regulator at he pump is bad you will only get 7 inches at the trany with it adjusted all the wayback, i get 21-25mpg on my driving it like a old lady and i'm runing 256 gears on my and had 273 gears before {308 stock} i drive about 400 -500miles a week 80% HWY , make sure all the hoses are good you best friend is a vacuum gauge....

 

[jgb680]

I have already tried to adjust tha vacuum regulator and the modulator

 

[jets1959]

My problem was the vacuum pump. They seem to dry up from sitting to long. Mine shifts great now. From frist to 2nd at 15mph and from 2nd to 3rd at 25mph. It was shifting from 1st to 2nd at 25mph and 2nd to 3rd at 35mph. I hope this helps. The vacuum gage will tell you if it is the pump.

 

[jgb680]

I'm going to try to change the fluid first, because it's dirty. If that does not fix it, I will buy a vacuum gauge. I just don't understand how every thing worked pretty well, then I changed the modulator and all this started....

 

[jgb680]

I haven't checked the vacuum everywhere, because I adjusted the vacuum regulator and it made a big difference. It shIfts smoother now, but still late.

 

[Volvo740turbo]

I haven't checked the vacuum everywhere, because I adjusted the vacuum regulator and it made a big difference. It shIfts smoother now, but still late.

Are the hoses on the regulator reversed?

 

[nyoffroad]

Are the hoses on the regulator reversed?

I don't know but sure hope he got it fixed by now, it's been 6 years.. Don't feel bad we all do it.