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Hot Rods RPM's too high on 700R4

Discussion in 'The Hokey Ass Message Board' started by Rick Dilts, May 7, 2021.

  1. Rick Dilts
    Joined: Aug 24, 2018
    Posts: 29

    Rick Dilts

    So I'm running a 700R4 behind a SBC400. The rear end is an 8.8" geared at 3.27. I'm trying to get the TV cable set correctly, which I think it's close, but my RPM's are running way to high down the highway. At 65 mph I'm over 4,000 RPM's. It is shifting into OD, which it does between 45-50 MPH so I don't think it's staying in 3rd. I can see and feel it shift up, but the RPM's are crazy.
    Has anyone run into this issue or know what may be causing this?
     
  2. saltflats
    Joined: Aug 14, 2007
    Posts: 10,684

    saltflats
    Member
    from Missouri

    Running that RPM at 65 it is not going in OD.
     
  3. Moriarity
    Joined: Apr 11, 2001
    Posts: 20,998

    Moriarity
    SUPER MODERATOR
    Staff Member

    sounds like it is not even going into 3rd
     
    joel, SlamIam, Kevin Ardinger and 2 others like this.
  4. 1934coupe
    Joined: Feb 22, 2007
    Posts: 4,440

    1934coupe
    Member

    I agree with salt flats. But I can’t help with the problem. I have not run that trans.

    Pat
     
    loudbang likes this.

  5. jimmy six
    Joined: Mar 21, 2006
    Posts: 8,756

    jimmy six
    Member

    Or you don’t have a 3.27 rear gear. Your final ratio would be 2.29 and 4000 rpm would be over 150 mph. Your rpm at 65 should be under 2000 probably closer to 1700.
     
    loudbang, ottoman and egads like this.
  6. cjsavage
    Joined: Oct 28, 2011
    Posts: 58

    cjsavage
    Member
    from eastern nc

    Agree with the above. Also, you have a lockup converter that's good for about 200 RPM reduction if it's working.

    Sent from my moto z3 using The H.A.M.B. mobile app
     
    Elcohaulic likes this.
  7. Moriarity
    Joined: Apr 11, 2001
    Posts: 20,998

    Moriarity
    SUPER MODERATOR
    Staff Member

    I bet you are in second gear, second is 1.625:1 with the rear ratio of 3.27 and a 28 inch rear tire 4000 rpms is 63 mph. have you counted the shifts? seems like second gear to me
     
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  8. silent rick
    Joined: Nov 7, 2002
    Posts: 4,255

    silent rick
    Member

    4 cylinder tach?
     
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  9. Rick Dilts
    Joined: Aug 24, 2018
    Posts: 29

    Rick Dilts

    Yes, it shifts into 2nd at about 17 mph, 3rd at around 30 and then OD in the high 40's. Seems like I have to back off the pedal a bit to get it to go into OD, but the RPM's do drop just slightly when it shifts, but seems like it ramps right back up when I go too much faster.
     
  10. Rick Dilts
    Joined: Aug 24, 2018
    Posts: 29

    Rick Dilts

    Maybe what I should do is take a video of what it's doing and post that so you can see.
     
  11. Belle53
    Joined: Aug 13, 2019
    Posts: 27

    Belle53

    i am not a 700R4 expert , but i have messed with a few.

    with what has been described , the first thing i would check would be the governor. it may be stuck or the gear stripped. easy to do on the drivers side
     
  12. Do some gear math and you’ll get the targeted rpm for each gear at Mph.
    It’s either slipping like hell after 40 and just about ready to quit or it’s downshifting after 40.

    That TV cable has to have everything right, mechanical ratio on the carb arms first, and adjusted right secondly. That’s the eminent failure cause. After that it’s the other external components.
     
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  13. 1971BB427
    Joined: Mar 6, 2010
    Posts: 6,676

    1971BB427
    Member
    from Oregon

    I have 3.73 gears behind a SBC 350 with 700R4 and mine shifts 1-2 at around 20 mph, then 2-3 at around 30 mph, and finally 3-4 at around 45 mph. I cruise at 70 mph at 2000 rpm's.
    I would expect a 700-900 rpm drop when your trans shifts from 3rd to 4th at high 40's mph. Not a slight drop. No idea what's wrong with your transmission, but suspect it might be slipping for whatever reason if rpm's are that high in 4th gear. Even without lockup it wont be that high an rpm.
     
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  14. silent rick
    Joined: Nov 7, 2002
    Posts: 4,255

    silent rick
    Member

    can you feel the trans slipping? is the motor actually turning that rpm?
     
  15. Rick Dilts
    Joined: Aug 24, 2018
    Posts: 29

    Rick Dilts

    It doesn't feel like it's slipping. The engine is would pretty high so... I'm bringing it into a transmission shop next week. I've reached my peter principle and know when to admit when I'm beat. I just hope that there is an easy (cheap) fix and not something serious going on. I don't have 10 miles on this transmission.
     
    rockable likes this.
  16. 55blacktie
    Joined: Aug 21, 2020
    Posts: 307

    55blacktie

    Based on my experience (not recent), I should think that it would shift into overdrive between 40-45 mph. You should also be able to sense the torque converter lockup, which is kind of like shifting into a higher gear. I would not continue driving it until the problem is fixed. Getting the TV cable right is crucial. I would also drop the pan and look for torque converter clutch material.
     
  17. buzz4041
    Joined: Nov 14, 2008
    Posts: 294

    buzz4041
    Member
    from Texas

    Is your engine really turning the RPM your gauge says. I had my dip switches on tach in the wrong configuration my first time out and showed these exact signs. Once it was verified and dip switches set correct all is good.
     
  18. Mr48chev
    Joined: Dec 28, 2007
    Posts: 28,819

    Mr48chev
    ALLIANCE MEMBER

    The 3.23 gears might be part of the issue. 700R4 usually works best with around a 3.7 gear.
    Looking up the gear ratios of the trans shows The gearing that was used was 3.06 for first gear, 1.63 for second, 1 for third gear, and 0.7 for fourth gear, essentially a 30% overdrive. The reverse gear in this transmission is 2.9.
    Looking at this calculator with the 3.23 gear and if you have a 28 inch tall tire you should be showing 1900 rpm at 70 Calculate RPM for Given Speed(MPH), Rear Gear Ratio, and Trans Gear Ratio (purperformance.com)

    Playing with the numbers shows that at 65 in second gear = 1.63 you would be doing 4106 rpm. Confirming what Moriarity said in post 7

    This is actually an electric vehicle speed rpm tire size calculator but outside of having to figure in the trans overdrive ratio to get either the engine rpm or rear end ratio right it is seriously simple to use.
    Tire Size, RPM, Speed, and Differential Ratio Calculator (advanced-ev.com) Probably the easiest one with a guy with a 1 to 1 output on the trans to put in three factors and get the fourth.
     
  19. winduptoy
    Joined: Feb 19, 2013
    Posts: 2,373

    winduptoy
    ALLIANCE MEMBER

    https://www.cpttransmission.com/tech_tvcable.htm

    "The proper adjustment of the TV cable is based on the TV plunger being fully depressed with the engine at wide-open throttle. When the TV cable is properly adjusted the movement of the TV plunger in the valve body is calibrated to the movement of the fuel delivery system."
     
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  20. silent rick
    Joined: Nov 7, 2002
    Posts: 4,255

    silent rick
    Member

    that's what i'm trying to get at. if the trans isn't slipping and the the motor is actually turning that rpm, then the trans has to be dropping into 2nd or 3rd gear.
    i have a 700R4 behind my desoto hemi and at 70mph i'm only at 1850rpm but i have less rearend gearing(need some 3.50's). the tach seems to be reading double where it should be reading. either it's set up for a 4 cylinder application or the trans is slipping big time or it's dropping into 2nd gear.
    a competent trans shop should be able to hook up a gauge and set the tv cable properly.
     
  21. Rick Dilts
    Joined: Aug 24, 2018
    Posts: 29

    Rick Dilts

    I did drop the pan and it was completely clean, which is good.
     
  22. Rick Dilts
    Joined: Aug 24, 2018
    Posts: 29

    Rick Dilts

    I thought about maybe the tach being off. It idles at about 1,200 which seems normal and maybe if it is off, it's accentuated at higher speed, but it seems like it should be off at idle too. I'm guessing the transmission shop will be able to figure that out, like you said.
     
  23. vtx1800
    Joined: Oct 4, 2009
    Posts: 1,263

    vtx1800
    ALLIANCE MEMBER

    I've got a 700 R 4 with SBC in ths Stude, 26.9 inch tall tires, 3.54 rear axle and it just loafs down the hiway under 2000 RPM at 55-60. Hope you find the problem!
     
  24. Jmountainjr
    Joined: Dec 29, 2006
    Posts: 1,337

    Jmountainjr
    ALLIANCE MEMBER

    You said that you only have 10 miles on the trans? Was that after a rebuild, or just a used trans new to you? Did you replace the carb, or any linkage recently? The carb linkage geometry for a 700R4 and TV cable adjustment are critical.
     
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  25. Budget36
    Joined: Nov 29, 2014
    Posts: 6,088

    Budget36
    Member

    Take off manually in low. Then around 20mph, manually put it in 2nd, etc. up to OD.
    If you’re feeling 3 up shifts, it has to be in OD, you’d certainly feel if it went into 2nd. and not OD


    For whomever may know, isn’t there a 2-4 relationship in a 700R4?
     
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  26. 1971BB427
    Joined: Mar 6, 2010
    Posts: 6,676

    1971BB427
    Member
    from Oregon

    I have a switch on my dash that provides power to my lockup that I leave in the on position all the time, as my hydraulic pressure switch locks and unlocks the converter. I have turned the switch on or off while cruising at 55 mph, and I don't feel any change at all, so doubt if it was locking/unlocking on it's own you'd feel the change.
    Art Carr transmissions suggests to adjust the 700R4 cable by relaxing adjustment all the way. Then open the throttle wide open, and pull the cable all the way back until it stops; then lock it there. That should set everything as it should be, and no other adjustment needed. Set mine that way and it works fine.
     
  27. Rick Dilts
    Joined: Aug 24, 2018
    Posts: 29

    Rick Dilts

    I had the trans rebuilt and have less than 10 miles on it. Have just taken it down the road a few times to get the TV cable set correctly. It's connected to a 1406 Edelbrock carb. The transmission guy I'm going to take it to said that the geometry on the 700R4 bracket isn't perfect on the Edelbrock carb, but he can get it pretty close so at least it will work.
     
  28. Rick Dilts
    Joined: Aug 24, 2018
    Posts: 29

    Rick Dilts

    Yeah, that's how I tried setting mine too. I thought that should do the trick like all the videos show, but it still didn't feel like it was shifting right, so I finally took the pan off and looked to see if the plunger was being depressed all the way. From what I've read, the little arm that depresses the vacuum plunger should just be touching the end of the plunger when your vehicle is in idle and when it's at WOT, it should be completely depressed in the housing. With mine, it didn't seem like I was getting enough travel in the plunger when I depressed my gas pedal all the way. It would make the plunger disappear when I just used the throttle bracket on the carb, but not when depressing the pedal. So I wasn't getting the full motion of the plunger between idle and WOT. Hope this makes sense. This probably substantiates what the transmission shop guy told me about the geometry not being right with the Edelbrock brackets.
     
    31Vicky with a hemi likes this.
  29. jaw22w
    Joined: Mar 2, 2013
    Posts: 1,189

    jaw22w
    Member
    from Indiana

    What carb? If it's a Holley or QFT, it must have a geometry corrector at the throttle linkage on the carb. I did not see anyone mention that. Not sure if an Edelbrock needs one or not. I have a 700r4 behind a 355 with a 3.80 rear gear and 28" tires. It runs 1800 rpm at 55 mph in OD lockup. Shifts into lockup at the same time it shifts into 4th at about 40 mph.
    The way I always set mine is to wire the carb open at WOT, pull the tv cable all the way out and attach it to the corrector at that point. Works for me.
     
  30. 3quarter32
    Joined: Dec 10, 2010
    Posts: 374

    3quarter32
    Member

    Yes, the Edelbrock does need the correct geometry change with the 700r4. At 70mph/350 rearend/29" tires about 2050rpm. I don't run any electrics so no lockup.
     

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