Vacuum Tank Sizing

[Gojira94]

I have the 'baseball.' As the vehicle was originally built and sold, it had no A/C, no CAD, no cruise, just vacuum to run the heater controls. I'm only adding cruise. Is the 'baseball' tank adequate for these 2 functions, or should I be looking to replace it with the 'football' if I'm adding cruise?

[89 MJ]

I would guess that it will be sufficient. My truck had AC and 4wd with the little vacuum reservoir. 

[eaglescout526]

Replace with the football from the Renix era if you can. If not, run a second baseball 

[Eagle_SX4]

Just would like to add that there are 2 different football reservoirs. One that has 2 sides and 4 ports with internal check valves, not available new. The other is the same size but only has one chamber, one port and relies on an external check valve to function, this one is available new.

[Gojira94]

Thanks all for the replies. I'll give the one I've got a go, if it doesn't seem adequate, I think the one-chamber football is what I'll look for.

[89 MJ]

3 minutes ago, Gojira94 said:

Thanks all for the replies. I'll give the one I've got a go, if it doesn't seem adequate, I think the one-chamber football is what I'll look for.

If they don’t think it’ll work, you should probably disregard what I said  . That said might be worth a shot if it’s not much more work. 

[Gojira94]

1 minute ago, 89 MJ said:

If they don’t think it’ll work, you should probably disregard what I said  . That said might be worth a shot if it’s not much more work. 

 

Well, it's an easy thing to swap, even with a completely assembled vehicle. I'm all over the map right now, pulling together vacuum lines, EVAP, fuel, etc. so I'm trying to sort things that could easily wait into a list.

[Gojira94]

Interesting find in the boneyard- a 94 XJ showed up. I snagged a football reservoir with a single port. Just the one port for manifold vacuum. It uses a check valve at the HVAC. This XJ didn't have cruise so the tee where it would have connected was capped. I'd imagine in 94 it would have used a check valve there as well if cruise equipped (no, no check valve for cruise). This XJ had obviously been sitting in a tree row for a while, but it hissed when I disconnected the line from the reservoir. I like the simplicity of the setup, so I'm going to try it out as pulled, with no check valve at the cruise servo.

[AZJeff]

On 2/12/2025 at 11:23 AM, Gojira94 said:

I have the 'baseball.' As the vehicle was originally built and sold, it had no A/C, no CAD, no cruise, just vacuum to run the heater controls. I'm only adding cruise. Is the 'baseball' tank adequate for these 2 functions, or should I be looking to replace it with the 'football' if I'm adding cruise?

The football type reservoir was used on all the later XJ’s.  I cannot see how using on an older XJ or MJ would cause any issues in terms of storing residual vacuum.

[eaglescout526]

18 hours ago, Gojira94 said:

Interesting find in the boneyard- a 94 XJ showed up. I snagged a football reservoir with a single port. Just the one port for manifold vacuum. It uses a check valve at the HVAC. This XJ didn't have cruise so the tee where it would have connected was capped. I'd imagine in 94 it would have used a check valve there as well if cruise equipped. This XJ had obviously been sitting in a tree row for a while, but it hissed when I disconnected the line from the reservoir. I like the simplicity of the setup, so I'm going to try it out as pulled, with an identical check valve at the cruise modulator.

If these can be used on Renix easily, then I’ve got two of them I’d like gone from my stash. 

[Gojira94]

On 2/19/2025 at 10:44 AM, eaglescout526 said:

If these can be used on Renix easily, then I’ve got two of them I’d like gone from my stash. 

 

It looks like in 91 they just tried to simplify the setup with a single vacuum line for the tank and accessories fed by it, all the way through 2001 on the XJ. Electrical control of the servo changed from 5 wires to 4 to operate from VSS signal feedback in the ECU, but it was still vacuum modulated. It appears no check valve was fitted for the cruise servo vacuum source, just for the HVAC vacuum controls.

 

 

[eaglescout526]

10 minutes ago, Gojira94 said:

 

It looks like in 91 they just tried to simplify the setup with a single vacuum line for the tank and accessories fed by it, all the way through 2001 on the XJ. Electrical control of the servo changed from 3 wires to 4 to operate from VSS signal feedback in the ECU, but it was still vacuum modulated. It appears no check valve was fitted for the cruise servo vacuum source, just for the HVAC vacuum controls.

 

 

Suppose one could do this to a Renix set up. Don’t see why not but that canister must hold some good vac to operate HVAC and cruise. 

[Gojira94]

Not sure for a Renix vehicle equipped with CAD and cruise. But it might work for all 3 systems with an additional T and feed line to the CAD added in.

[Eagle_SX4]

47 minutes ago, Gojira94 said:

 

 

Which part is the check valve? 15?

[Gojira94]

12 minutes ago, Eagle_SX4 said:

Which part is the check valve? 15?

 

Yes.