Transmission help

Discussion in 'Ranchero Tech Help' started by JerryDaWolfman, Oct 23, 2019.

  1. JerryDaWolfman

    JerryDaWolfman In Second Gear

    Messages:
    30
    Hey guys! I need a some help. My 75 Rancheros C6 transmission is acting up. When the car is cold the trans works just fine, but when it warms up it starts screeching and is very hesitant to catch gears. As if it is fighting itself to catch gears. I don’t know if this is a sign to rebuild it or just replace something in it. Any help is appreciated!!
     
  2. handy_andy_cv64

    handy_andy_cv64 In Maximum Overdrive SILVER MEMBER

    Messages:
    9,663
    Location:
    Everett, WA
    First question--what is the color and condition of the fluid? Anything uglier than red is spelling trouble. Your description makes me think that heat is causing a fluid lubrication loss, as well as delaying the upshifts.
     
  3. colnago

    colnago In Maximum Overdrive

    Messages:
    1,101
    Are all of the gears having problems catching? Problems on the down-shifts, or just up-shifts? Problems in reverse as well? How long has it been doing this?

    Like Andy suggested, check the fluid first. It's easy and free. Also, is the fluid at the right level? My C4 has a small drip, and it will be hard to shift if the fluid gets low.

    Joseph
     
  4. Clark

    Clark In Maximum Overdrive

    Messages:
    2,267
    Location:
    Brighton, Colorado
    How many miles on that C6? I used to get about 90,000 miles on a front seal and 120,000 between rebuilds. Age was also a factor for the internals.
     
  5. JerryDaWolfman

    JerryDaWolfman In Second Gear

    Messages:
    30
    I did a service to it about 4 months ago and the color was a tad dark but not that bad.
     
  6. JerryDaWolfman

    JerryDaWolfman In Second Gear

    Messages:
    30
    I serviced it about 4 months ago and it was a tad dark but not that bad. It did sit for about 7-8 years before I got it. The new fluid is still a good color but it’s got a slight metallic color.
     
  7. JerryDaWolfman

    JerryDaWolfman In Second Gear

    Messages:
    30
    I have no idea. I got it from somebody who got from a trade who let it sit about 7-8 years.
     
  8. colnago

    colnago In Maximum Overdrive

    Messages:
    1,101
    Hopefully somebody smarter than me will jump in, but I think you just answered your own question.

    Joseph
     
    JerryDaWolfman likes this.
  9. Burnout

    Burnout In First Gear

    Messages:
    20
    More info needed. What do you mean by "catching gears"? Slipping on breakaway?, or not going into gear right away?, or not shifting?, or slipping shifts?

    Working okay when cold and showing symptoms when warm usually indicates worn or burnt clutches. Knowing which clutch pack would depend on when it's acting up. But if it has any bad clutches it would be just as well for you to overhaul the entire transmission. If you're going into the trans... change them all.

    Your noise could be the torque converter, but usually a noisy converter (on a non-lockup trans) will always be noisy. Same as with the clutches... if you're going in , change the converter. Stock converters aren't that expensive and putting your old converter on an overhauled trans will be putting any contamination from your old problem into your fresh trans. Be sure to flush the trans cooler also.

    BTW, color of fluid is no indicator of condition. The red color of ATF is a dye used for ID'ing fluids in the factory. Some mfgr's use dyes that last longer than others. A good indicator of fluid condition is odor. If it smells burnt, like an ash tray, you've got a problem. But I've had transmissions that the fluid smelled okay and upon teardown found a burnt clutch pack.

    Sitting for years isn't good for an automatic. They are full of rubber lip seals, internal and external, that harden over time especially when they're not being exercised. The C6 in particular has a weak seal in the forward drum. They harden faster than the other seals and once hardened cause problems in all forward gears. A complete teardown is required to change the seal, so overhaul it and change them all.

    I would check the trans pressure before you pull the trans. That will tell you things you can't check once it's out of the car.

    Hope this helps.
     
    JerryDaWolfman and colnago like this.
  10. JerryDaWolfman

    JerryDaWolfman In Second Gear

    Messages:
    30
    Thank you very much for the information!! When I say “catching gears” I mean it’s very hesitant to shift, as if it tries to shift but can’t. The only way it shifts is when I left off the gas (lower the RPMs) and then it has a better chance of shifting.

    But from all that you said my best bet would to just rebuild it, and that’s what I was leaning more to anyways. I really appreciate it tho man!
     
  11. Huevos

    Huevos In Maximum Overdrive

    Messages:
    3,202
    Location:
    Nor Cal
    Vacuum modulator?
     
    pmrphil likes this.
  12. Burnout

    Burnout In First Gear

    Messages:
    20
    If I'm reading you correctly, it sounds like late shifts. If that's the case then you could have low engine vacuum to the trans. Check the vacuum line for any leaks. Stick a vacuum gauge on the vacuum line at the modulator on the rear of the trans and look for engine vacuum (15"hg or more at idle) or just put your finger over the end and see if it has strong suction. If you have good vacuum you could have a bad modulator. Modulators are cheap and easy to install so you could try that (be sure to get an adjustable modulator). If it has an adjustable modulator (most are) you can give it "one turn out" (CCW) to lower shift points. The adjuster is in the vacuum port where the hose slips on. use a little pocket screwdriver. Be careful about lowering shift points with the modulator, you're lowering line pressure and if you go too far you can cause slipping/damage. Vacuum will only address your shift points, it won't do anything about the noise coming from your trans. Even if you're gonna overhaul the trans, check your vacuum first so you don't put in a new fresh trans and still have problems.
     
  13. colnago

    colnago In Maximum Overdrive

    Messages:
    1,101
    Also, modulators have different-colored stripes for different applications. And some screw in, while others slide in and are held in place by a bracket. Try to find out what the C6 was used in, or just remove the modulator and take it with you to the parts store (or post pics here).

    Joseph
     
  14. Burnout

    Burnout In First Gear

    Messages:
    20
    Screw in modulator is thru 72. Push in modulator is 73-up. It's easy to tell from the outside... no bracket holding it in = screw in, with bracket = push in. Green stripe is standard passenger car modulator.
     
  15. colnago

    colnago In Maximum Overdrive

    Messages:
    1,101
    I didn't remember the year swap, or the stripe applications. It sounds like the C6 didn't come with his Ranchero, though, so it could be from anything. I currently have a C6 from a '71 in my '67 F250. Before that, I had a car C6 in the truck.

    Joseph
     
    JerryDaWolfman likes this.
  16. JerryDaWolfman

    JerryDaWolfman In Second Gear

    Messages:
    30
    Mine has the push in
     
    colnago likes this.
  17. handy_andy_cv64

    handy_andy_cv64 In Maximum Overdrive SILVER MEMBER

    Messages:
    9,663
    Location:
    Everett, WA
    Looking at the fluid color doesn't tell you if the dye changed; it tells you if the fluid broke down under high heat, which will make the color brown, indicating a transmission problem.
     
    pmrphil likes this.
  18. Clark

    Clark In Maximum Overdrive

    Messages:
    2,267
    Location:
    Brighton, Colorado
    Just looked back at the records for my '75 GT. The first C6 rebuild was at 135,000 miles in 1985. The second was at 183,000 miles in 1993. My rebuild man told me that age was the factor for the second rebuild. As Burnout was writing, the internal rubber parts had all hardened and failed. Rebuild man told me these parts had been upgraded with that second rebuild.
     

Share This Page