TH350 issues

[tycharles]

I've got a 85 c10 with a 305 and a th350c and sometimes it takes a few seconds of the truck running to get the transmission to shift into gear. Start up the truck, quickly shift into gear and sometimes nothing happens. Is this normal or something to be addressed? There is also sometimes a faint high pitched whistling noise when the truck is in R, 1 or 2. Doesn't do it in drive. Wondering if there might be a vacuum leak somewhere that may be causing both of these issues. Any help is much appreciated

 

[NickTransmissions]

I've got a 85 c10 with a 305 and a th350c and sometimes it takes a few seconds of the truck running to get the transmission to shift into gear. Start up the truck, quickly shift into gear and sometimes nothing happens. Is this normal or something to be addressed? There is also sometimes a faint high pitched whistling noise when the truck is in R, 1 or 2. Doesn't do it in drive. Wondering if there might be a vacuum leak somewhere that may be causing both of these issues. Any help is much appreciated

Not normal at all; you're having delayed engagements which can be caused by vacuum leaks. These vac modulated transmissions need/rely on a consistent vacuum signal to function properly. So find and fix any vacuum leaks and see if your delayed engagements resolve.

Also, put a vacuum gauge on the hose going to the modulator - see what the vacuum reading is. Should be at least 12hg at idle...Also make sure the modulator is healthy by testing it with a vac hand pump (or simply replace it if it's real old).

 

[tycharles]

I will do that and report back, thank you!

 

[75gmck25]

Vacuum modulators come with different color stripes. IIRC, green seems to be the most common, and red stripe has an adjustment screw to adjust shift points. Not sure about the black stripe or those with both red and black. Do a little research before your purchase.

 

[tycharles]

Not normal at all; you're having delayed engagements which can be caused by vacuum leaks. These vac modulated transmissions need/rely on a consistent vacuum signal to function properly. So find and fix any vacuum leaks and see if your delayed engagements resolve.

Also, put a vacuum gauge on the hose going to the modulator - see what the vacuum reading is. Should be at least 12hg at idle...Also make sure the modulator is healthy by testing it with a vac hand pump (or simply replace it if it's real old).

I replaced the modulator with a B&M unit. The old one seemed very old. I put new rubber hose on both ends of the hard line, took out the valve, cleaned the passages in it and removed the spring. I followed this guys instructions to a T -

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No delays going into gear but haven't driven much yet. Shifts are definitely more firm.

There was about a half quart of fluid that spilled out when I removed the old modulator so I'm thinking it was overfull. Now the whistling seems to have gotten louder. I'm thinking maybe there is a tiny hole in the hard line. Doesn't happen in Drive only in R,1 or 2. Fluid looked great, not dark at all. Any idea what else this whistling could be?