I'm going crazy, need help with trans/gear ratio - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Anthony14 · 08-15-2018, 01:41 PM

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...

RustyBucket · 08-15-2018, 02:44 PM

Hafta ask, you're SURE it's in top(3rd.) gear?

geezer#99 · 08-15-2018, 02:46 PM

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.

Anthony14 · 08-15-2018, 02:48 PM

Quote:

Originally Posted by RustyBucket

Hafta ask, you're SURE it's in top(3rd.) gear?

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.

Anthony14 · 08-15-2018, 02:50 PM

Quote:

Originally Posted by geezer#99

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.

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...

Anthony14 · 08-15-2018, 02:56 PM

Quote:

Originally Posted by geezer#99

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.

TCI website has a converter slip calculator, I plugged in my info, says my converter slip is 50%!?

Why would a new converter be slipping? what can I do to fix it?

Shinysideup · 08-15-2018, 03:04 PM

You are in 2nd gear!
1.52 is second gear for TH350
Adjust your linkages!

From this page...https://spicerparts.com/calculators/...rpm-calculator

geezer#99 · 08-15-2018, 03:10 PM

Quote:

Originally Posted by Anthony14

TCI website has a converter slip calculator, I plugged in my info, says my converter slip is 50%!?

Why would a new converter be slipping? what can I do to fix it?

Turf the pos tic converter and put the old one back in.
Possible the tic was labeled wrong.

Anthony14 · 08-15-2018, 03:17 PM

Quote:

Originally Posted by geezer#99

Turf the pos tic converter and put the old one back in.
Possible the tic was labeled wrong.

I had to pull the old one out, wouldn't even idle in gear with the stock one... So I can't really just shove that one back in.

Anthony14 · 08-15-2018, 03:17 PM

Quote:

Originally Posted by Shinysideup

You are in 2nd gear!
1.52 is second gear for TH350
Adjust your linkages!

From this page...https://spicerparts.com/calculators/...rpm-calculator

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.

geezer#99 · 08-15-2018, 03:25 PM

Quote:

Originally Posted by Anthony14

I had to pull the old one out, wouldn't even idle in gear with the stock one... So I can't really just shove that one back in.

Tweaking your timing curve will let you use the old one.

Anthony14 · 08-15-2018, 03:37 PM

Quote:

Originally Posted by geezer#99

Tweaking your timing curve will let you use the old one.

I tried a bunch before making the purchase and couldn't get it to work.

geezer#99 · 08-15-2018, 03:41 PM

Quote:

Originally Posted by Anthony14

I tried a bunch before making the purchase and couldn't get it to work.

Did you get close to 20 initial, 12 in mechanical, 10 from vacuum all in by 3200 rpm?

Anthony14 · 08-15-2018, 04:15 PM

Quote:

Originally Posted by geezer#99

Did you get close to 20 initial, 12 in mechanical, 10 from vacuum all in by 3200 rpm?

Yeah, almost exactly that.

trac209 · 08-15-2018, 09:21 PM

I calculated your rpm to be 2441 at 60 with your data

Anthony14 · 08-21-2018, 09:58 AM

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

geezer#99 · 08-21-2018, 10:12 AM

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.

**jocko** · 08-21-2018, 12:52 PM

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?

Anthony14 · 08-21-2018, 01:06 PM

Yep. Checked the speed with a gps and its accurate. I installed the 3.42's myself. Gm 10 bolt 8.5" rear end.

67 chevelle · 08-21-2018, 01:14 PM

Are you sure on the rear gears , do you have enough trany fluid in it , these are basics but I have to ask

Anthony14 · 08-21-2018, 01:28 PM

Yes. Put the gears in myself. If anything a little to much fluid.

**jocko** · 08-21-2018, 09:36 PM

Quote:

Originally Posted by Anthony14

Yep. Checked the speed with a gps and its accurate. I installed the 3.42's myself. Gm 10 bolt 8.5" rear end.

Just to be clear - you're saying you confirmed that your speedometer was accurate with a GPS - or are you saying the speeds you mention in this thread are GPS speeds? If the latter, good to go. If you confirmed the speedometer was displaying accurately - then I'd ask what gear ratio did the 3.42s replace and how did you recalibrate your speedometer (i.e. for it to be accurate with a rear gearing change, the speedometer gearing would also need to be replaced to still be accurate)?

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.

**too much stuff** · 08-21-2018, 09:42 PM

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.

Anthony14 · 08-22-2018, 12:48 AM

Quote:

Originally Posted by jocko

Just to be clear - you're saying you confirmed that your speedometer was accurate with a GPS - or are you saying the speeds you mention in this thread are GPS speeds? If the latter, good to go. If you confirmed the speedometer was displaying accurately - then I'd ask what gear ratio did the 3.42s replace and how did you recalibrate your speedometer (i.e. for it to be accurate with a rear gearing change, the speedometer gearing would also need to be replaced to still be accurate)?

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.

Correct. I used a GPS to confirm and it is accurate. When I rebuilt the trans I counted the teeth on the drive gear for the speedo and used TCI's calculator with my gear ratio and tire size to select the "driven" gear and installed that when I did the rebuild.

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.

Anthony14 · 08-22-2018, 12:49 AM

Quote:

Originally Posted by too much stuff

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.

Haha I did laugh. I hope its something easy and inexpensive.

08-15-2018, 01:41 PM	#1
Anthony14 Registered User Join Date: Apr 2014 Location: Brantford, Ontario Posts: 87	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...

08-15-2018, 02:44 PM	#2
RustyBucket Registered User Join Date: Jul 2009 Location: Space Coast, Fl. Posts: 1,050	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!!

08-15-2018, 02:46 PM	#3
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,508	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.

08-15-2018, 09:21 PM	#15
trac209 Registered User Join Date: Dec 2011 Location: winnipeg Posts: 1,107	Re: I'm going crazy, need help with trans/gear ratio I calculated your rpm to be 2441 at 60 with your data

08-21-2018, 09:58 AM	#16
Anthony14 Registered User Join Date: Apr 2014 Location: Brantford, Ontario Posts: 87	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 Attached Images Last edited by Anthony14; 08-21-2018 at 10:05 AM.

08-21-2018, 10:12 AM	#17
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,508	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.

08-21-2018, 12:52 PM	#18
jocko Senior Member Join Date: Oct 2009 Location: Godley, TX Posts: 17,930	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.

08-21-2018, 01:06 PM	#19
Anthony14 Registered User Join Date: Apr 2014 Location: Brantford, Ontario Posts: 87	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.

08-21-2018, 01:14 PM	#20
67 chevelle Registered User Join Date: May 2013 Location: WEST PALM FLORIDA Posts: 1,174	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

08-21-2018, 01:28 PM	#21
Anthony14 Registered User Join Date: Apr 2014 Location: Brantford, Ontario Posts: 87	Re: I'm going crazy, need help with trans/gear ratio Yes. Put the gears in myself. If anything a little to much fluid.

08-21-2018, 09:42 PM	#23
too much stuff Roadtrip! Join Date: Feb 2003 Location: Grand Rapids MN Posts: 13,691	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. __________________ 67 gmc custom lwb dakota truck. Sold...And bought back 69 swb 4x4 project (in progress) 70 c-10 lwb texas truck 70 4x4/BB/bkts/posi/tach(retired) 70 swb (wifes) 70 jimmy camper 71 K-5 factory 2wd 71 cheyenne 4x4/tach/posi/ plow rig 71 Cheyenne20 BB, buckets, tach, tilt, 4 speed 72 jimmy CST wyoming rig 72 jimmy Colorado rig 72 lifted texas 4x4 3/4 ton burb 65 fury conv. 383/auto 65 chrysler 300 "L" 413 auto

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