Register now to get rid of these ads!

Projects Rear-end gear swap

Discussion in 'The Hokey Ass Message Board' started by Phillip A Kilmon, May 2, 2020.

?
  1. 2

    1 vote(s)
    100.0%
  2. 2

    1 vote(s)
    100.0%
Multiple votes are allowed.
  1. Hey guys. I have a 1965 Chevrolet C-10. I just recently went through the engine. Replaced all the bearings. It has 327 300 hp heads with a 292 Comp Cam in it. The heads were built to match the cam. It has a new th 350 Transmission in it with a 373 gear. Drove it pretty hard today. I was turning 3300 rpm at 65 mph. My question is because my club sometimes will drive long distances on the weekends. Would a 307 gear fit in the carrier that is in it now? Yalls thoughts would be much appreciated.
     
  2. Mimilan
    Joined: Jun 13, 2019
    Posts: 564

    Mimilan
    Member

    A better bet would be a 700R-4 trans.
    You'll have a lower 1st to pull off the line and a good cruising o/d with lockup converter.

    With the 0.7 O/D your 3300 rpm will drop to 2310. [and down to approx 2150 with the converter locked in 4th]

    Also the TH350 can be sold to offset costs
     
    Last edited: May 2, 2020
  3. Here’s the problem with the 3.07 idea, you have too much cam for that tall gear. It would be a sick pig out of the hole. 3300 rpm really isn’t a lot of rpm for the highway. We are so used to overdrive and 10 speed automatic transmissions that cruise at 1600 rpm, it’s easy to forget how it used to be. Look at it like this, a Chevy C-60 truck with a Small Block would run on the governor at 4000 rpm all day long, day in and day out. If your engine is built properly, I would not worry about 3300 at all.


    Sent from my iPhone using The H.A.M.B. mobile app
     
    loudbang, fastcar1953, OFT and 2 others like this.

  4. If it's a 3 series carrier, then , yes. There are plenty of formulas out there to calculate RPM,SPEED,TIRE DIAMETER. Might want to look into these before replacing un needed things. Once you start playing around, you'll know what MPH/RPM you'll be at with things............ Investigate before you start emptying your wallet.
    And- I have the same truck......... What is the rear gear? Guessing in the 4.0 range now.....?
     
    loudbang likes this.
    Register now to get rid of these ads!

  5. Mimilan
    Joined: Jun 13, 2019
    Posts: 564

    Mimilan
    Member

    The formula is MPH x Overall Ratio x 336 , then ÷ Tyre Diameter = RPM

    You don't need an online calculator , you can use this formula on your phone.
     
    Last edited: May 2, 2020
    loudbang, gimpyshotrods and j-jock like this.
  6. squirrel
    Joined: Sep 23, 2004
    Posts: 46,117

    squirrel
    Member

    you need a 3 series carrier for the 3.07 gear. The 3.73 uses a 4 series.

    I did that same thing to my 66 suburban back when, I got a 70s van rear that had the right gears and carrier, swapped them into the original 66 rear, it was great. And you can drive around with 3.07 gears and a bit of a cam. Hopefully you have a converter that matches the rest of it, perhaps 2500 stall?
     
  7. derbydad276
    Joined: May 29, 2011
    Posts: 1,310

    derbydad276
    Member

  8. Mr48chev
    Joined: Dec 28, 2007
    Posts: 26,922

    Mr48chev
    ALLIANCE MEMBER

  9. sunbeam
    Joined: Oct 22, 2010
    Posts: 4,853

    sunbeam
    Member

    How short are your tires a 3.73 turning 3300 would need a 25" tire at 65. A 29" tire would give 2800 rpm
     
    loudbang likes this.
  10. Mimilan
    Joined: Jun 13, 2019
    Posts: 564

    Mimilan
    Member

    Allow approx 8% slippage of a non lock-up converter and it would be a 27" tyre

    Edit: With a 27" Tyre and a rear end ratio of 3.08 it would be 2700 rpm at 65 mph.
    A 2500 rpm stall converter would be risking overheating the trans at 60 mph cruising speed.
    Ratios, Stall, and Cams need to be matched to the honest intended usage.

    A 700R4 lockup converter helps with slippage and the deeper 3.06 first gear [vs 2,52 in the TH350] helps get it off the line.

    In first gear a 700R4 with 3.73 gears has the same overall ratio as a TH350 with 4.56 gears
    But it has an overall top gear ratio equivalent to having 2.7 gears for highway cruising
     
    Last edited: May 2, 2020
  11. sunbeam
    Joined: Oct 22, 2010
    Posts: 4,853

    sunbeam
    Member

    If it is not a race converter you are looking at 3 to 5 % slip at 3300 rpm you would not be close to stall with a stock converter.
     
  12. jimmy six
    Joined: Mar 21, 2006
    Posts: 6,380

    jimmy six
    Member

    700R4, 200R4, or Gear Venders bolt on OD to a 350. Easiest but might be most expensive with added drive shaft revision as I see it. I had a 3.21 rear the highest available for my car, replaced the entire rear with an 8.8 with 2.74 gears and could not be happier. I do not have a cam and the converter is stock. Cruises ez at 70-75.
     
    500caddy likes this.
  13. OLDSMAN
    Joined: Jul 20, 2006
    Posts: 2,424

    OLDSMAN
    BANNED

    I think it will. I had a 10 bolt with a2.56 gear ratio switched to a 3.08 and had to change the carrier, but I think You could use that carrier for a3.73
     
    Last edited: May 3, 2020
  14. squirrel
    Joined: Sep 23, 2004
    Posts: 46,117

    squirrel
    Member

    maybe we could look it up in the old Chevy truck parts book, eh? then we'll know for sure.
     
  15. primed34
    Joined: Feb 3, 2007
    Posts: 1,044

    primed34
    Member

    I wouldn't worry about it. 3300 aint that high for 327. They came from the factory doing that.
     
  16. 427 sleeper
    Joined: Mar 8, 2017
    Posts: 1,022

    427 sleeper
    ALLIANCE MEMBER

    How big of a converter are you running? 3300 rpm @ 65 mph sounds closer to a 4.10 ratio, assuming you're running a 28" tire. That kind of rpm with that gear, at that speed, you'd have to have a pretty short tire or an extremely loose converter.
     
    JeffB2 likes this.
  17. Budget36
    Joined: Nov 29, 2014
    Posts: 3,464

    Budget36
    Member


    Not with the 700R4, allows more first gear grunt than the TH350 he has now. If he's just looking for cruise RPMs, it's really the 700/200 or an OD unit, I think he'd liike the wake up taking off in the 700 vs the 350 though, shoud still get the 2nd just fine.
     
    gimpyshotrods likes this.
  18. Budget36
    Joined: Nov 29, 2014
    Posts: 3,464

    Budget36
    Member

    How can it run without a cam? ;)

    C'mon, someone was gonna...
     
    jimmy six likes this.
  19. Thank you sir. I will definitely give that some thought. My step father has the 700R4 in his 40 model Chevrolet. 373 Gear but with the 700R4 he has overdrive. Thanks again.
     
    loudbang and gimpyshotrods like this.
  20. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 336

    Neb Hillbilly
    Member

    I personally hate the 700 and it's kids. That low first 3.06 gear makes it hard to launch the car without wheel spin then the split between 1-2 is horrible causing a bog when it does shift. Just has horrible pulling a big trailer. There is a gearset to change the ratio but it is still a light duty tranny. I just put 3.55s in my Chevelle to make for a bit lower cruising rpm but keep the 10 to one combined first gear ratio with my super T-10 If you are looking for an overdrive, I would personally look for a 4l80 and manual valve body it (if you want cheap) or a 200-4r. Or you could always swap in a T56. Otherwise a th350 with a converter and 3.08s isn't horrible.

    Sent from my S48c using The H.A.M.B. mobile app
     
  21. JUSTIN PERSINGER
    Joined: Apr 28, 2020
    Posts: 95

    JUSTIN PERSINGER
    Member

    I had a 66 C10 with a mild build sbc, turbo 350 and 3.73's and it cruised about 3k rpm down the highway. I just went a little slower and enjoyed the view. It did do a mean burn out though in 1st!

    Sent from my XP8800 using The H.A.M.B. mobile app
     
    loudbang likes this.
  22. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 1,111

    ekimneirbo
    Member
    from Brooks Ky

    Transmission Dims 001.jpg Congratulations, you are the one millionth hot rodder to discover that that going to a high geared rearend so you can enjoy the power you built in your engine............has turned the vehicle into a highway cruizing nightmare. The conundrum is that if you switch to a lower gear in the rear, you pretty much negate what you did building your engine. With the cam you have, you may really have poor performance overall with no parts complimenting each other.

    Bite the bullet and sell your 3 speed tranny to Hot Rodder 1,000,001 and get an overdrive. 700R4 is good but you might look at a 2004R as they are closer in size and you can probably use the same driveshaft. You will get an even lower first gear ratio (I think), and highway cruzing will be enjoyable. Cruzing instead of cursing;) With either of the overdrives, your 3300@65 should become about 2200.
    View attachment 4670499
    View attachment 4670500
    View attachment 4670502
    View attachment 4670503
    Transmission Pics.JPG
     
    Last edited: May 3, 2020
    loudbang likes this.
  23. I have a C-60 and the gas mileage is horrible at 4-5 mpg in the 3000-4000 rpm range. He needs a 260* cam and shoot for around 2200 rpm at 65 in a C-10. The mileage could be in the 15-18 mpg range. ;)
     
    ekimneirbo and loudbang like this.
  24. squirrel
    Joined: Sep 23, 2004
    Posts: 46,117

    squirrel
    Member

    huh, my wife has a modern little sporty car that cruises at close to 4000 rpm, and it gets 30 mpg. I think being a C60 has a lot more to do with your crappy mileage,than the high rpm does.
     
    RMR&C and Montana1 like this.
  25. Would that be an over cammed V-8 or a turbo 4cyl? :D
     
  26. gimpyshotrods
    Joined: May 20, 2009
    Posts: 17,147

    gimpyshotrods
    ALLIANCE MEMBER

    700R4. Hands down winner.

    Better off the line, better up top, too.

    Set it up to lock the converter in 4th, with no extra crap, but that, and then go enjoy the ride.
     
    loudbang and Montana1 like this.
  27. CNC-Dude
    Joined: Nov 23, 2007
    Posts: 854

    CNC-Dude
    Member

    700r definitely, that truck is too heavy for a 3.08 gear with that cam. Swap trannies and have the best of both worlds!
     
    loudbang and Montana1 like this.
  28. oldiron 440
    Joined: Dec 12, 2018
    Posts: 1,507

    oldiron 440
    Member

    A good friend of mine drove his 64 Chysler 300 k with a 4.57 gear the 90 miles to and from the strip before he had a hauler. He'd set the 413 at 4000 rpm and let it burn fuel.
     
    loudbang likes this.
  29. Mimilan
    Joined: Jun 13, 2019
    Posts: 564

    Mimilan
    Member


    I have never heard of a Non electronic 4l80 , The only manual valve bodies were full manual shifting for racing
    The valve bodies alone were $600+ [not cheap]
    I wouldn't be concerned with the lower 1st in a street vehicle, most trucks usually had a granny 1st gear.

    In a race car that shifts at 7000 rpm it would be a problem. 7000 rpm in 1st would drop to 3704 rpm in 2nd which would be "off the cam"
    On a street car the same ratio drop is more friendly eg 3500 rpm in 1st would drop to 1852 rpm in 2nd.
    Or if you're just cruising around town 2500 rpm in 1st would drop to 1323 rpm in 2nd [which is below stall speed on the converter so the engine will still pull]

    As the engine [and vehicle] speeds increase the ratio drops need to be a lot closer. It is always best to have the widest ratio spread where there is the most torque multiplication [1-2]

    @Phillip A Kilmon The 700R4 was constantly upgraded by GM , the best being the last. It was designated 4L60 [not the 4L60E variant] and the year was around 1991
     

Share This Page

Register now to get rid of these ads!

Archive

Copyright © 1995-2020 The Jalopy Journal: Steal our stuff, we'll kick your teeth in. Terms of Service. Privacy Policy.

Atomic Industry
Forum software by XenForo™ ©2010-2014 XenForo Ltd.