700R4 not downshifting

[mr heavy-chevy]

hello

my 700R4 seems to be working great, but it will not downshift to 2nd or 1st when it should.

getting on the freeway, it won't drop into 2nd for the on ramp.

rolling up to a stop sign, it won't drop into 1st

thoughts?....

 

[1987 GMC Jimmy]

hello

my 700R4 seems to be working great, but it will not downshift to 2nd or 1st when it should.

getting on the freeway, it won't drop into 2nd for the on ramp.

rolling up to a stop sign, it won't drop into 1st

thoughts?....

Is this on your '87? I'd say that '87 700R4's were made on the eve of the transmission being regarded as a good all around unit. Most people say '88 and on, but some include '87. Anyways, I digress. The first thing I would check just as a default for any shift discrepancy is your TV cable. It may need adjustment, or it may be frayed. I've had both happen on my '87. The governor can get dirty or the nylon pinion at the end can strip or break and cause these issues, and the servo can stick, too. If you're not slipping, just not shifting, I'd look at the governor before the servo if your TV checks out. It sounds like you have 1st and 2nd gears, just not when you need them sometimes. Therefore, I don't want to assume your bands are burned because that would mean your transmission would have to come out. I'd think also that if it were a valve body problem, your symptoms would be more severe. And you have reverse working well, which is a good sign. How often do you change your filter and fluid?

 

[mr heavy-chevy]

Is this on your '87? I'd say that '87 700R4's were made on the eve of the transmission being regarded as a good all around unit. Most people say '88 and on, but some include '87. Anyways, I digress. The first thing I would check just as a default for any shift discrepancy is your TV cable. It may need adjustment, or it may be frayed. I've had both happen on my '87. The governor can get dirty or the nylon pinion at the end can strip or break and cause these issues, and the servo can stick, too. If you're not slipping, just not shifting, I'd look at the governor before the servo if your TV checks out. It sounds like you have 1st and 2nd gears, just not when you need them sometimes. Therefore, I don't want to assume your bands are burned because that would mean your transmission would have to come out. I'd think also that if it were a valve body problem, your symptoms would be more severe. And you have reverse working well, which is a good sign. How often do you change your filter and fluid?

thanks

yeah the trans is brand new-fresh rebuilt. guy said he even dynoed it.

its runs good in each gear i select. probably TV cable related...

should wide open throttle should be pulling the TV cable FULLY TAUGHT?...

because all the videos i have been watching do not show this as being correct.

i took it to AAMCO and they adjusted the cable with SLACK in it at the closed throttle position....

i just adjusted it to have slight tension at closed throttle.
it seems to shift a little better.

what would be the potential for damage if i adjust it too tight?
i heard that being too loose is the REAL killer....

ive only put about 150/ 200 miles on it so far with the new transmission.

 

[1987 GMC Jimmy]

thanks

yeah the trans is brand new-fresh rebuilt. guy said he even dynoed it.

its runs good in each gear i select. probably TV cable related...

should wide open throttle should be pulling the TV cable FULLY TAUGHT?...

because all the videos i have been watching do not show this as being correct.

i took it to AAMCO and they adjusted the cable with SLACK in it at the closed throttle position....

i just adjusted it to have slight tension at closed throttle.
it seems to shift a little better.

what would be the potential for damage if i adjust it too tight?
i heard that being too loose is the REAL killer....

ive only put about 150/ 200 miles on it so far with the new transmission.

Yeah, being really loose or disconnected is an execution sentence for the transmission. What I was told, and what I've done is to get someone to push the pedal all the way to the floor and adjust it as tight as possible. I think that ensures that it's nice and tight but not too tight. I've read that a too tight TV cable can make it hard or impossible to get the thing into overdrive, but I'm not aware of the level of detriment to the transmission. All you ever hear about is too much slack. It should be firm at closed throttle. If it has slack, it won't actuate the little fishhook in the transmission properly as you open up the throttle, and it won't change the valve body pressure like it should. It sounds to me like the people at the place didn't adjust it that well, you made it better after the fact, and it would do some good to tighten it up some more. If it was a good rebuild, I'd say disregard the possibility of any governor or servo issues until you adjust your TV cable.

 

[74 Shortbed]

Also make sure the geometry is correct, otherwise cable position between open and closed will not be in the right place.

 

[mr heavy-chevy]

ok ill try and tighten it to FULL PULL at wide open throttle...

the bracket is stock on the motor. and the cable is brand new. guy at the shop installed it and said its working fine. i can pull it by hand and feel it ride smooth against the internal spring pressure.

 

[mr heavy-chevy]

well after over adjusting the cable then backing it off little by little i think i almost have it.....
some times i need to "pump" or "feather" the pedal in the floored position but then it does downshift and launch

so ill keep testing it

 

[mr heavy-chevy]

got it adjusted just right.
drives nice

 

[74 Shortbed]

Glad to hear ya got it fixed..