Author Topic: 700R4 Transmission Question - 1st Gear only...  (Read 162 times)

Offline 6wt

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700R4 Transmission Question - 1st Gear only...
« on: November 06, 2018, 10:11:14 AM »
1984 Chevy C10 350 700R4  computer gone, running external electronic lockup for overdrive

Last night after coming to a stop upon starting I only have 1st gear; it would not shift into 2 / 3 / or 4 OD.  Limped to a parking lot.  Checked the trans fluid and trans temp; both normal.  Trans fluid like new, not burnt, smelled and felt like new.  Shut engine off, crawled under and visual inspection all looked normal; no leaks, linkage intact, all wires looked okay.  About a 15 minute inspection.  Started up engine to limp along in 1st gear.

Truck started off okay and now shifted okay…  I have started it again and went on short 1 ~ 20 miles drives.  No apparent problem.  Seems to be shifting okay.  Now I am scared to death of getting stranded on the highway or towing my 2000lb boat/trailer.

My guess is this situation is not an isolated incident.  Any ideas or suggested next steps?

Thanks in advance.
Craig
« Last Edit: November 06, 2018, 10:22:21 AM by 6wt »

Offline bd

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Re: 700R4 Transmission Question - 1st Gear only...
« Reply #1 on: November 06, 2018, 12:00:23 PM »
How long has the transmission been in service?  If the transmission is still under warranty contact the seller/rebuilder before you do anything. 

Chances are great that some fine debris caused the governor to stick temporarily.  You can remove and inspect the governor if you wish or continue to drive the vehicle to determine whether there are repetitive symptoms.  The governor spool valve should move freely with the motion of the weights with zero binding.  Wash the valve thoroughly with a good aerosol solvent like Berrymans B12 or engine starter fluid.  Make sure the driven gear roll pin is secure and that the drive gear and driven gear teeth aren't worn or apple cored to the point of skipping.

Another possibility was a momentarily stuck 1-2 shift valve for the similar cause of fine debris binding the spool valve.  If you decide to drop the trans pan, check for fine debris accumulation in the bottom of the pan and whether the debris is magnetic, dark paper flakes, plastic, or non-magnetic metallic particles.
Rich
It's difficult to know just how much you don't know, until you know it....
In other words... if people learn by making mistakes, by now I should know just about everything!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline 6wt

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Re: 700R4 Transmission Question - 1st Gear only...
« Reply #2 on: November 12, 2018, 08:01:55 PM »
Thank you very much for your reply.  It is greatly appreciated!

Here is an update from driving the truck daily for the past five days.  No problems or symptoms have reoccurred.  The truck is shifting firmly and crisply at the expected rpm/load points over a variety of speeds.

I have not dropped the pan yet.  But after re-reading your reply I believe it is a good idea to inspect and remove any possible fine debris that may be there.

Thank you again for making the distinction for the different types of debris that may occur as a clue to point me in the right next step inspection point.

Offline bd

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Re: 700R4 Transmission Question - 1st Gear only...
« Reply #3 on: November 12, 2018, 09:57:45 PM »
Just be aware before you tear everything apart that it may have been a one-time event never to recur.
Rich
It's difficult to know just how much you don't know, until you know it....
In other words... if people learn by making mistakes, by now I should know just about everything!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)