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Drive shaft length/Speedo. Difference

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by 86blazerk5, Aug 18, 2000.

  1. 86blazerk5

    86blazerk5 1/2 ton status

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    Hey guys, I just got my truck back today, I had my 4 inch lift installed and my 33s on custom wheels. Soon I will have pictures posted for you guys. I am in love with the truck all over again........ I have two questions though, Does anyone know how much diiference is in the speedometer with 33s. I was once told to allow about 10 mile per hour difference, but I dont think its that much. i was think more like 5 mph. What do you guys think? My other question is that the shop who installed my lift kit said that i might want to have my drive shft lengthened. They said the call rough country and see what they say first. You arent suppose to need to on a 4 inch lift but they said that it has pulled out of the t-case about 4 inches and that I might want to at least look into the posibility. I think it drives fine. Is this normal. Do some of you guys with 4 inch lifts drive shafts pull out about an inch and a half also? All help apprecaited. Thanks!
    Ike

    Jeep, what every boy dreams of... K5 what every man owns!!!
     
  2. jcg

    jcg 1/2 ton status

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    When my 4" kit was installed they just lowered the T-case an inch. There's spacers on the bolts that hold the cross-member to the frame. Just pull the bolts out, lower the cross-member a little and put the spacers between the member and the frame and bolt it back up.
    For your speedo, the difference between stock tires and 33's is about 10 mph. When I got my truck it had 31's on it but the speedo was still geared for 28's (I didn't know this). When I put my 33's on I thought it was only 5 mph off. I'm amazed I didn't get a ticket since it was really off by 10.

    Joe
    Rochester Institute of Technology Team Mini-Baja
    88 Jimmy
     
  3. 86blazerk5

    86blazerk5 1/2 ton status

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    I forgot to mention that my t-case was lowered exatly as you desribed. The bolts were taken out and the spacers were put on the oposte side of the crossmember droping it 1 inch. But the drive shaft still sticks out anbout an inch and a half.
    Ike

    Jeep, what every boy dreams of... K5 what every man owns!!!
     
  4. 84k5

    84k5 1/2 ton status

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    I also recently got a 4" lift and 33s installed. My driveshafts were long enough without the transfer case drop. I had to have one installed though, because the front driveshaft was hitting the crossmember. I also had to get the exhaust pipe under the front driveshaft rerouted. You might want to check this, if you haven't already, because there was less than a 1/4" clearance on mine. $50 at the local muffler shop, and presto, plenty o clearance.

    Brian
    84k5, 4"Skyjacker lift,33x12.5 Goodyear MT/R, 15x10 Bajas
     
  5. Blazer1970

    Blazer1970 1/2 ton status

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    Speedometer error with bigger tires is a percentage, not a constant difference in MPH. Assuming 30 inch stock tires, 33s will make a 10% difference (if the stock gears are still in place). When 60 mph is indicated, you are really going 66:

    0 = 0
    10 = 11
    20 = 22
    30 = 33
    55 = 60.5
    70 = 77
    80 = 88
    90 = 99
    100 = 110

    and so on.

    Tim

    1970 Blazer CST 4X4 350 SM465 NP205
    1987 Suburban 4X4 350
    1988 Chevy Pickup 4X4 350
     
  6. Emmettology 101

    Emmettology 101 3/4 ton status

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    I am running a 6" with NO t-case lowering and the stock driveshaft. The shaft is pulled out of the t-case quite a ways, but I have had no problems over the 2 year si Have had the 6" on and I had a 4" before that ith no problems either.

    I dont believe in lowering the t-case, you just loose ground clearance.

    Mike
    1982 GMC Jimmy - <font color=green>Emmett</font color=green>
    http://emmett.coloradok5.com
     
  7. 86blazerk5

    86blazerk5 1/2 ton status

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    Oh S*@&, I almost got a ticket today. It is a good thing i asked. I thought that you were going slower then your speedo said, Not Faster. Yikes, I passed a cop today with his radar gun out and everything and I guess I was probably going at least 10 over then. Yikes, Thanks Guys. Oh, and I Guess that the drive shaft thing is not a problem.
    Ike

    Jeep, what every boy dreams of... K5 what every man owns!!!
     
  8. 89 Blazzer

    89 Blazzer Registered Member

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    This is amazing, about 5-7 days after I do something to my truck, someone has questions that are related to what I just finished. First it was headers/duals, then the camshaft/intake, now a 4" lift!
    I had to have my rear driveshaft lengthened about 2" after I put an add-a-leaf and 4" blocks that gave my a little over 6" lift in the rear. The guy at Denny's Driveshafts (dennysdriveshaft.com) said to push the transfercase yoke in all the way, then pull it out 1.5" to allow for movement. Measure center to center from the transfer case yok u-joint to the rear end yoke. This would be your total length. I ended up having mine done locally, should get it back in a few days. I needed to lengthen it because the slip yoke was only about 1.5" in the transfer case. That would have pulled out going over some of the railroad tracks around here! Also, my transfer case is lowered with the spacers.
     

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