'CY' TH400 shift points

[Jon S.]

Does anybody have any documentation on what the shift points should be for the 'CY' version of the TH400 transmission used in solid lifter cars (69 in particular)? The shop manual doesn't list anything for the CY transmission, and I'm thinking the shift points in the PV manual are for the standard CK version of the transmission. Bizzoco's book lists the 'CY' as a "high shift point" transmission, but doesn't specify.

Thanks in advance.
Jon
#10673

[Terry M.]

Re: 'CY' TH400 shift points

Jon,
We used to have a GM TH400 book at school with that detail information. I don't know if it is detailed enough for your question, but it is spring break so I can't get to it -- hoping that it is still there. This post will expire before school opens, and I am changing internet providers. I'll see if I can overcome all that, or maybe someone else has that GM transmission manual.

[Michael H.]

Re: 'CY' TH400 shift points

Terry,

I have a 1973 printing of a GM/Hydra-Matic "trouble shooting" guide for the TH400 but I see no mention of shift points/speeds, either min or max throttle. It lists all of the various TH400 model codes and applications along with clutch plate count and system pressures but no pressure variation is listed for the different governor pressures per model/upshift speed. I suppose minimum throttle upshift speed would be drastically affected by diff ratio. It would be controlled, basically, by engine RPM, not vehicle speed. I'll keep looking for more info.

[Roy B.]

Re: 'CY' TH400 shift points

If you think your having shifting problems first check the vacuum line going to the Modulator is not leaking , then replace the Modulator because it control the shift points , the Governor over rides the Modulator .

[Jon S.]

Re: 'CY' TH400 shift points

No, I actually think my trans is working just fine, but I'm prepping the car for a PV and just want to make sure it's shifting in the right places. The PV manual calls out the higher shift points for the CY trans in the 'full throttle upshift' test, but not in any of the others. My 'light throttle upshift' has higher shift points than what is specified in the PV manual, so I'm trying to figure out if that is an ommission in the manual or if there is a problem with my transmission.

Thanks,
Jon #10673

[Terry M.]

Re: 'CY' TH400 shift points

Michael that sounds like the book I was thinking of. A dark green cover? I do remember the clutch count in there.

[Michael H.]

Re: 'CY' TH400 shift points

Terry,

Yes, probably the same book. Mostly diagnostic and oil press/vacuum test data. Cutaway drawings of a TH400 and 425 on the cover. GM sent me to a three day school at the Hinsdale GM training center in the 60's and this was part of the misc that came with it. Last half of the third day we talked mostly about the TH400 for the ZL1. Was interesting, especially with Harvey Kenesik as the instructor.

Still looking for shift point data for Jon's original question.

[Terry M.]

Re: 'CY' TH400 shift points

I thought that was the book I got the shift points that are in the TIM&JG from, but maybe not. Seems to me there were colored hydraulic diagrams on fold out pages for each gear range in it also. The other possibility is the TH400 book published by HP Books. That one I have in my own library. I'll look at that when I get home from work this evening.

[Michael H.]

Re: 'CY' TH400 shift points

I just went through this manual again, quickly, but see no mention of shift point speeds. I know I have this info somewhere but not sure where. I'll look this evening.

Did see something interesting that I completely forgot about though. Has to do with the oil level and how to properly check it. I thought I remembered that the level was supposed to show roughly one pint low on the dipstick when cold.(70*) However, the instructions state that the level is supposed to be roughly 1/4" BELOW the ADD line @ 70*. I'll scan and post it later. I wonder if that would be part of judging?

[Terry M.]

TH400 shift points and more.

Gee, I would have expected the level to be at the add line when at 70*. Shows you what I know. Now that you mention it, I never even checked ATF or engine oil level on a PV that I can remember. We routinely look for leaks, but not fluid level. Maybe I was a softie. Now that you raise the issue all the judges lurking here will be on to that.

[Michael H.]

Re: TH400 shift points and more.

I'll send it to you if I can find your email info here in all this rubble. Or, I can post it if anyone is interested. (I'm surprised I found the manual)

[Steve Antonucci]

Re: 'CY' TH400 shift points

Jon,

I think I can help you in another way. If you recall, you and I discussed a
recent acquisition for my 1969 L/78 Camaro project, that being a "CX" THM400.

The CX's also had the high shift points and I'd bet they match the "CY" THM400.

In any event, I am having a shop out west rebuild/restore my CX in the near future. I will get you the owners contact info. I spoke with him at length
and he is quite knowledgeable on these things. BTW, this shop came highly
recommended from the COPO crowd and they all used CX's too.

Steve

[Terry M.]

Re: 'CY' TH400 shift points

Jon,
I am unable to find any shift points specifically for the CY transmission, however reading the "1968-1972 Corvette Operations Manual & Performance Verification Test Guide" I find a value given for approximate shift points for the 1-2 and 2-3 shift on "327 and 350, L36. L68, and LS5 engines," and a separate value for "L88, L89 and LS6" engines. While not specifically mentioning the CY version of the TH400 that option list would seem to me to separate the men from the boys.
If you are able to find specific values, I would like to hear about them.

[Terry M.]

Re: TH400 shift points and more.

Michael,
No need to send it on my account -- I was able to get past security to check the automotive library at school. I brought the officers some doughnuts. We chatted about police cars some. The officer on duty has a 1968 Z28 BB.

"Systematic Trouble-Shooting 400-425 Hydra-matic," First edition (1969) has the fluid checking information on page 18. Third edition (1973) has it on page 6. Just goes to show what one can learn from reading the book. Thanks for your thorough research.

[Michael H.]

Re: TH400 shift points and more.

Yep, funny how we have all these books and never use them. I probably had mine for 15 years before I ever read it completely.