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#1 |
Registered User
Join Date: Apr 2014
Location: Brantford, Ontario
Posts: 87
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I'm going crazy, need help with trans/gear ratio
I'm going crazy and need help. SBC350 and TH350 transmission. 3.42 rear end, 29.6" tires, TCI 328800 rebuild kit/shift kit, TCI Breakway 240900 torque converter. 60MPH @ 3500RPM!!?? When I installed the torque converter to get it to idle in gear (cam dur. heads etc...) it fixed that problem then had these high rpms at cruise. I tore the transmission down cause TCI and Summit said that it sounds like it was slipping. I found some burnt clutches and steelies. Installed the TCI rebuild kit and now I have the extact same problem! I should only be at 2330rpm according to Summit's gear ratio calculator. I'm outta ideas...
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#2 |
Registered User
Join Date: Jul 2009
Location: Space Coast, Fl.
Posts: 1,050
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Re: I'm going crazy, need help with trans/gear ratio
Hafta ask, you're SURE it's in top(3rd.) gear?
__________________
Dad always said, "Son, WISH IN ONE HAND, and ......." -------------------------------------- -------------------------------------- Current toy trucks: '71 GMC 1500 SUPER CUSTOM short/step, orig. dk. blue, 350/700r, ps,pb, A/C '72 Blazer 2wd, ochre & white, 454, tremecTKO 500 5spd. ps, pb, A/C, tilt Last 10yrs of hobby vehicles, had a FEW more in the 50yrs. before these: '66 Plymouth Belvedere City of Miami cop car clone. '70 Nova 406"sb, 13.5-1, solid roller, Brodix, p.glide/t.brake, back halved, 9" Ford, spool 4.88, cage,ladder bar/coilover, 10.5 tire....... SOLD!! '67 C10 short/step side mount spare -- SOLD!! '72 Jimmy 2wd, 350/350, ps, pb, fun driver, lots of bondo & a shiny red paint job..... SOLD!! '69 Nova 350, 4spd, A/C, ps, p.b, ...SOLD!! |
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#3 |
Registered User
Join Date: Apr 2014
Location: Brantford, Ontario
Posts: 87
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Re: I'm going crazy, need help with trans/gear ratio
Your not the first to ask. I dropped it into 2nd just to be sure and the rpm jumped, put back into D and the rpm dropped back to 3500rpm. So it would appear that it is going into 3rd. Also downloaded a app to track my speed to make sure my speedo is accurate - it is.
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#4 |
Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,627
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Re: I'm going crazy, need help with trans/gear ratio
Maybe it’s your tach!
When you’re cruising at 60 and 3500 rpm, take your foot off the loud pedal. If it still shows 3500 then your tach is wacky. If the rpm drops a bunch you know it’s converter slip. |
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#5 |
Registered User
Join Date: Apr 2014
Location: Brantford, Ontario
Posts: 87
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Re: I'm going crazy, need help with trans/gear ratio
When I take my foot off the rpm does fall down to around 2400/2500rpm... But TCI says it's suppose to be a 2200/2400 stall so it should be fully locked up by that rpm...
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#6 | |
Registered User
Join Date: Apr 2014
Location: Brantford, Ontario
Posts: 87
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Re: I'm going crazy, need help with trans/gear ratio
Quote:
Why would a new converter be slipping? what can I do to fix it? |
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#7 |
Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,627
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Re: I'm going crazy, need help with trans/gear ratio
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#8 |
Registered User
Join Date: Apr 2014
Location: Brantford, Ontario
Posts: 87
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Re: I'm going crazy, need help with trans/gear ratio
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#9 |
Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,627
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Re: I'm going crazy, need help with trans/gear ratio
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#10 |
Registered User
Join Date: Apr 2012
Location: Ocala,Fl
Posts: 733
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Re: I'm going crazy, need help with trans/gear ratio
You are in 2nd gear!
1.52 is second gear for TH350 Adjust your linkages! ![]() From this page...https://spicerparts.com/calculators/...rpm-calculator |
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#11 | |
Registered User
Join Date: Apr 2014
Location: Brantford, Ontario
Posts: 87
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Re: I'm going crazy, need help with trans/gear ratio
Quote:
Holy hell I hope your right! I'm pretty sure it is but I'll have to double check everything. Those #'s are just to much bang on. |
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#12 |
Registered User
Join Date: Dec 2011
Location: winnipeg
Posts: 1,107
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Re: I'm going crazy, need help with trans/gear ratio
I calculated your rpm to be 2441 at 60 with your data
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#13 |
Registered User
Join Date: Apr 2014
Location: Brantford, Ontario
Posts: 87
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Re: I'm going crazy, need help with trans/gear ratio
So my shift linkage was off. I went through it and got it fixed, but didn't fix my problem. Ran a steel line for the vacuum advanced to manifold vacuum. Disconnected the kickdown cable to eliminate it. I tried to check the stall speed of the TCI converter, suppose to be 2200-2400. One way I held the brake and mashed the pedal, went to around 3500rpm. Other way was slowly gave gas till the tires started to brake loose and that was around 2400rpm. I drove in reverse and mashed the pedal, left a fantastic burnout until I stopped. Wish it would do it going fwd... when I down shift from D to 2nd it goes from 3500rpm to around 5000rpm.
See videos...(if they worked) View My Video View My Video View My Video Last edited by Anthony14; 08-21-2018 at 10:05 AM. |
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#14 |
Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,627
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Re: I'm going crazy, need help with trans/gear ratio
Usually when it flash stalls you only get another 400 rpm. It shoulda been 2800 and not 3500.
You got the wrong converter or a bad one from them. |
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#15 |
Senior Member
![]() Join Date: Oct 2009
Location: Godley, TX
Posts: 17,964
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Re: I'm going crazy, need help with trans/gear ratio
Make sure you are referencing actual speed with a gps, your speedo is meaningless if your truck didn’t originally come with that rear gearing, which it didn’t. (Unless you’ve corrected the speedo gearing).
Also - are you absolutely certain you have 3.42s? Last edited by jocko; 08-21-2018 at 01:02 PM. |
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#16 |
Registered User
Join Date: Apr 2014
Location: Brantford, Ontario
Posts: 87
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Re: I'm going crazy, need help with trans/gear ratio
Yep. Checked the speed with a gps and its accurate. I installed the 3.42's myself. Gm 10 bolt 8.5" rear end.
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#17 |
Registered User
![]() Join Date: May 2013
Location: WEST PALM FLORIDA
Posts: 1,174
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Re: I'm going crazy, need help with trans/gear ratio
Are you sure on the rear gears , do you have enough trany fluid in it , these are basics but I have to ask
__________________
68 Long Fleet , ly6 , turbo 350 , 3-5 drop , original paint , front discs 67 Small window , 7 foot bed , tweaked 6.0 LSX 2004R Medium Olive 58 Apache fleet , 235 , offy intake , dual exhaust , 4 on the floor , red/white 69 Long Fleet , Custom , 6.0, 4l60 , AC , Medium Olive |
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#18 |
Registered User
Join Date: Apr 2014
Location: Brantford, Ontario
Posts: 87
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Re: I'm going crazy, need help with trans/gear ratio
Yes. Put the gears in myself. If anything a little to much fluid.
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#19 | |
Senior Member
![]() Join Date: Oct 2009
Location: Godley, TX
Posts: 17,964
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Re: I'm going crazy, need help with trans/gear ratio
Quote:
Also, can you elaborate on your shift linkage being "off"? As in, disconnected, connected incorrectly, etc. Lastly - are you certain you have an 8 cyl tach? ( I watched one of your videos, didn't realize it was an aftermarket tach). Some are adjustable between 4,6,8 cyl - you could have it set for a 6. Just one more thing to check. Last edited by jocko; 08-21-2018 at 09:42 PM. |
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#20 |
Roadtrip!
![]() Join Date: Feb 2003
Location: Grand Rapids MN
Posts: 13,737
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Re: I'm going crazy, need help with trans/gear ratio
Being in Canada, are your RPMs metric?
Sorry, just trying to lighten the mood and maybe make you smile... Hope you get it figured out.
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#21 |
Registered User
Join Date: Apr 2014
Location: Brantford, Ontario
Posts: 87
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Re: I'm going crazy, need help with trans/gear ratio
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#22 | |
Registered User
Join Date: Apr 2014
Location: Brantford, Ontario
Posts: 87
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Re: I'm going crazy, need help with trans/gear ratio
Quote:
When I checked the install of the B&M megashifter i couldn't get the clevis to slide in and out nicely at the trans lever at all the gear positions. So i went through and adjusted the cable and now the clevis will slide in and out of the trans lever without issue at every position as per B&M's instructions. I do have a setable tach; 4-6-8. Its set to 8, but that doesn't mean it's working correctly. |
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#23 |
Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,627
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Re: I'm going crazy, need help with trans/gear ratio
Have you tried your tach settings in the other positions?
What’s your idle rpm? |
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#24 |
Registered User
Join Date: Apr 2014
Location: Brantford, Ontario
Posts: 87
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Re: I'm going crazy, need help with trans/gear ratio
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#25 |
laying low
![]() Join Date: Mar 2001
Location: Searcy, Ark. USA
Posts: 13,271
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Re: I'm going crazy, need help with trans/gear ratio
With that much indicated converter slippage it looks like the fluid would cook and if it's run through the radiator cooler it might make the engine run hotter too. Seems like.
__________________
Boog 69 Chevy stepside, 358/T350, 4.11 posi, 4.5/4 drop, rallys, poboy driver primer is finer 91 Chevy sportside, Tahoe, Yukon & GMC Crewcab All GM..'nuff said. I stand for the flag and kneel at the cross |
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