Lift before regearing? - JeepForum.com
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post #1 of 9 Old 05-21-2021, 04:43 PM Thread Starter
DeeDubz
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Lift before regearing?

I have a 87 YJ that I wanna put a 2.5 or 4 inch lift on. It needs to be regeared. My top speed on the freeway is 55mph at 3600rmp. My question is which one should I do first or does it even matter?

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post #2 of 9 Old 05-21-2021, 05:29 PM
jbolty
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does not really matter except lift means change in tires which affects gearing. If you have the axles pulled to regear do the lift at the same time and save effort. so I guess the answer is both at once.

what motor, trans, what gears do you have. what tires are you wanting?

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post #3 of 9 Old 05-21-2021, 07:41 PM
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Quote:
Originally Posted by DeeDubz View Post
I have a 87 YJ that I wanna put a 2.5 or 4 inch lift on. It needs to be regeared. My top speed on the freeway is 55mph at 3600rmp. My question is which one should I do first or does it even matter?
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Originally Posted by jbolty View Post
does not really matter except lift means change in tires which affects gearing. If you have the axles pulled to regear do the lift at the same time and save effort. so I guess the answer is both at once.

what motor, trans, what gears do you have. what tires are you wanting?
Pretty much what @jbolty said.

55 MPH at 3600 rpm seems like you are over-geared. Higher RPM at speed as a result of too tall of a gear.

Are you running a 5 speed or a 3-speed auto?

at 2.5" of lift you could run 32 or 33 inch tires (depending upon the lift) what size tires do you have now?

What size tire are you considering after the lift?

Here is a calculator tool you can use to determine your RPM at Speed based upon your info: http://www.grimmjeeper.com/gears.html

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post #4 of 9 Old 05-22-2021, 05:16 AM
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I am curious if you are running the factory tach converted to your SBC and if it is accurate. 3600 at 55 is a lot of RPM's and suggests that the tach either is not accurate or you already have a steep gear in it. My 87 3 speed auto turns 3200 RPM at 70 MPH. I have 30's and 3.55 gears.

If you cannot fix it with a hammer then it has to be an electrical problem.
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post #5 of 9 Old 05-22-2021, 07:53 AM
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Definitely sounds like the tach is wrong to me.


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post #6 of 9 Old 05-25-2021, 02:23 PM Thread Starter
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Quote:
Originally Posted by Luuca View Post
Pretty much what @jbolty said.

55 MPH at 3600 rpm seems like you are over-geared. Higher RPM at speed as a result of too tall of a gear.

Are you running a 5 speed or a 3-speed auto?

at 2.5" of lift you could run 32 or 33 inch tires (depending upon the lift) what size tires do you have now?

What size tire are you considering after the lift?

Here is a calculator tool you can use to determine your RPM at Speed based upon your info: http://www.grimmjeeper.com/gears.html
ITs a 3 speed auto. Once the tires need to be replaced im going to go with 33s. Thanks for the calculator

Quote:
Originally Posted by Boojo35 View Post
I am curious if you are running the factory tach converted to your SBC and if it is accurate. 3600 at 55 is a lot of RPM's and suggests that the tach either is not accurate or you already have a steep gear in it. My 87 3 speed auto turns 3200 RPM at 70 MPH. I have 30's and 3.55 gears.
The tach is correct I can tell the engine is running high rpm from the noise. Im not sure what kind of gears I have. I hate to ask but how would one find out?
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post #7 of 9 Old 05-25-2021, 02:37 PM
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Quote:
Originally Posted by DeeDubz View Post
ITs a 3 speed auto. Once the tires need to be replaced im going to go with 33s. Thanks for the calculator



The tach is correct I can tell the engine is running high rpm from the noise. Im not sure what kind of gears I have. I hate to ask but how would one find out?
foolproff way is to take off the diff cover and count the teeth on the ring and pinion. The number is probably etched in as well but just count them.
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post #8 of 9 Old 05-25-2021, 06:33 PM
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This question is only from reading others information here, so bear with me. This was the first thought that came to me when reading the rpm vs speed the OP posted.

Doesn't the auto come with much lower gear ratio than manual? Is it possible that someone stuck 4.10 manual gears in or did a swap from another YJ not knowing there is a difference? If I remember correctly, the Dana 35 is on the rear and is a pretty weak differential. Maybe the PO had one blow up on him and swapped.
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post #9 of 9 Old 05-26-2021, 05:09 AM
Boojo35
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Quote:
Originally Posted by 93YJ4FUN View Post
This question is only from reading others information here, so bear with me. This was the first thought that came to me when reading the rpm vs speed the OP posted.

Doesn't the auto come with much lower gear ratio than manual? Is it possible that someone stuck 4.10 manual gears in or did a swap from another YJ not knowing there is a difference? If I remember correctly, the Dana 35 is on the rear and is a pretty weak differential. Maybe the PO had one blow up on him and swapped.
Yes. The thought is that if the tach is accurate then the gears have been swapped thus why it is suggested to count the teeth on the ring and pinion.

If you cannot fix it with a hammer then it has to be an electrical problem.
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