Building a TJ from scratch, need a starting point for bump stops

[Gormy]

Hello,

Apologies for another bump stop question, but I am starting form scratch on a frame and I'm trying to determine what I need. I bought a TJ that I knew had a bad frame and suspension and needed to be completely rebuilt. I used this forum to determine what suspension and body lift to go with. The frame I bought has no bump stops installed at all. No cup to hold the factory bump stop, no extended bump stops, no nothing. I know that the correct way to measure bump stop length is to cycle the suspension once it is in, but I think there has to be a good starting point since I have to buy everything from scratch. I don't want to put all the suspension together and then have to take it apart just to install bump stops. I'm certain others have done this exact lift and know the parts I should install from the get-go. This will be a on-road and on the beach Jeep, that's it. If I need to fine tune and add extra bump stops on the axle side via hockey pucks I will. I'm just trying to set it as close as I can before I assemble everything. I have a set of axles showing up in a few days and would like to bolt them in right away, with the new bump stops already in.

My parts list:
BDS coil springs front and rear that make a 3" lift (034302 front and 034308 rear)
Rancho RS55128 front shocks
Rancho RS55240 rear shocks
Daystar 1" body lift
33" tires will be installed
Factory Dana 30/Dana 35 axles

I know there could be some final adjustments that need to be made to get it dialed in perfectly, but do I start from a new cup and factory bump stops? Do I go straight to a certain extended bump stop length? Since there are only so many combinations of lifts you can do, I'm hoping someone knows the starting point so I'm not installing the new axles and springs, just to partially disassemble and wait for new parts, and then reassemble.

Thanks y'all!

 

[jjvw]

Cycle the axle without springs to find out the extension length.

The bump stops are extended so that the steel cup contacts the axle pad when the shock reaches full compression. Though perfection is not critical. Let the shock be the limit to up travel. The purpose of the bump stop is to make the squishy jounce slow down the last bit of shock travel before it reaches full compression.

 

[Gormy]

Cycle the axle without springs to find out the extension length.

The bump stops are extended so that the steel cup contacts the axle pad when the shock reaches full compression. The purpose of the bump stop is to make the squishy jounce slow down the last bit of shock travel before it reaches full compression.

So with the shocks new and in the box, still compressed with straps, bolt them in and see how much room I still have, and then set the bump stop length to be longer than that when compressed? To throw numbers out there, if there is like 3" of space between upper and lower when the spring is at full compression, find what bump stop will be greater than 3" when fully compressed and buy those?

 

[jjvw]

So with the shocks new and in the box, still compressed with straps, bolt them in and see how much room I still have, and then set the bump stop length to be longer than that when compressed? To throw numbers out there, if there is like 3" of space between upper and lower when the spring is at full compression, find what bump stop will be greater than 3" when fully compressed and buy those?

Let the shock be the limit to up travel. The extension length is not a critical measurement. The goal is to make the jounces work as the shock reaches full compression.

 

[ChasUGC]

I bought a TJ that I knew had a bad frame and suspension and needed to be completely rebuilt.

Pictures, or it didn't happen.

 

[hosejockey61]

So with the shocks new and in the box, still compressed with straps, bolt them in and see how much room I still have, and then set the bump stop length to be longer than that when compressed? To throw numbers out there, if there is like 3" of space between upper and lower when the spring is at full compression, find what bump stop will be greater than 3" when fully compressed and buy those?

Just to be clear, the straps when in the box are not set to anything as far as a specific measurement.

Pull the springs out. Install the new shocks. Jack the axle up until the shocks reach full compression. Then measure the distance between the bump stop cup and the pad on the lower spring perch. That's how much extension you'll need.

 

[Gormy]

Pictures, or it didn't happen.

Here you go. Sourced a good frame and axles with 4.10 gears (will eventually re-gear to 4.56), all new control arms, shocks, springs, brake lines, and more. Pulled the fuel tank and steering box over already. Just got the old frame out from under the Jeep this afternoon and next I'll pull the drivetrain and swap that over (after some cleaning and may as well throw a new clutch in while it's out because why not?).

 

[ChasUGC]

Are you planning to undercoat the new frame while it is bare? I would definitely consider a thick rubberized coat to protect it.

 

[Good Hope]

I believe the shocks you have chosen are for a TJ with zero lift. With my 3” lift I ended up with 239 up front and 256 in the rear. You will note that the 239 is for the front and a 2.5” lift and the 256 for the rear and a 3.5” lift. This combination worked best for me with the goal of balancing up and down travel.

 

[Gormy]

Are you planning to undercoat the new frame while it is bare? I would definitely consider a thick rubberized coat to protect it.

I am not. Rubberized undercoating creates a lot of issues with speeding up how fast the metal decays. This new frame has a nice coat of paint on it, and I plan to spray it often with fluid film to keep it protected.

 

[Andy-WhiteTJ]

I am not. Rubberized undercoating creates a lot of issues with speeding up how fast the metal decays. This new frame has a nice coat of paint on it, and I plan to spray it often with fluid film to keep it protected.

This is the best way to go.

 

[Artsifrtsi]

Here you go. Sourced a good frame and axles with 4.10 gears (will eventually re-gear to 4.56), all new control arms, shocks, springs, brake lines, and more. Pulled the fuel tank and steering box over already. Just got the old frame out from under the Jeep this afternoon and next I'll pull the drivetrain and swap that over (after some cleaning and may as well throw a new clutch in while it's out because why not?).

View attachment 506220

View attachment 506221

As a plus, I bet you can sell the old frame to some of the salt belt members... it looks better than what they post they are fixing...

 

[ChasUGC]

I am not. Rubberized undercoating creates a lot of issues with speeding up how fast the metal decays. This new frame has a nice coat of paint on it, and I plan to spray it often with fluid film to keep it protected.

I was asking a question. Thanks for the input. I have researched the problem and gained additional information and knowledge.

 

[Danarch]

I just installed the BDS 3” lift kit. It came with 2” tall bump stops. I am no expert but they seemed to work well. I didn’t try and cycle the suspension without them in place to see if I could get by with less. Maybe that was a mistake, but I took some value in they designed the system and “should” know. I am confident that if you don’t have enough bump stop, you can lower the axle and fit in a hockey puck between the coils and rebolt them in place. I secured the bump stop after I slide the springs in place to make it easier to get the springs in.