bump stop length and strut travel

[ray_bandz0]

I'm replacing the worn out dampers and I picked up a set of KYB SB124 rear bump stops. New stock bump stops for the rear are only available as a set with the Motorcraft struts. The problem is that although KYB states this is the correct application for the ST, the bump stop is 1/2" greater in length than stock (stock: 4-3/4" / kyb: 5-1/4"). Considering this reduces strut travel by the same amount, is it better to reuse the old stock bump stops? Wondering if anyone else has run into this issue.

 

[SteveS]

It doesn't reduce travel. The bump stop compresses. It's actually considered part of the suspension.

 

[ray_bandz0]

It doesn't reduce travel. The bump stop compresses. It's actually considered part of the suspension.

I've heard this before as well in other threads, it makes sense with this being a progressive bump stop.

Does this really come into contact with the rear bump stops that often in autocross or track? I've never had stock suspension so I wouldn't know. It had Koni oranges all around and H&R SS when I bought it. When I swapped them out for FA 500s I noticed that the stock rear bump stops were fine, as shown above, and it was the fronts bump stops that were completely destroyed on the bottom half. It was bound to happen with the lower compression of the oranges combined with the big ride height drop, I was just surprised that only the fronts were damaged.

 

[SteveS]

It will depend on how many bumps are encountered on the autocross course or track. If the parking lots and runways are as bad as they were back in the 1980s when I was autocrossing (or for that matter the old Wentzville MAR track I did SCCA drivers school on) then you will hit the bump stops on bumps.

 

[ray_bandz0]

The parking lots in Auto Club Speedway were rough but it's been closed down so the nearest events are held at Angel Stadium in Anaheim. I haven't been but I expect the surface to be smoother there.

KYB technical support responded to my email and reiterated below what you mentioned.
"The jounce bumper compresses during the cycle of the damper the 1/2" difference will not negatively impact the performance of the strut."

I went ahead and installed the KYB bump stops on the rear Bilstein B4 struts. Decided to reuse the stock plastic tube covers and I was able to fit them on the bump stops. The boots that come with the KYB kit don't sit securely. Going to install the set this Friday if I get the chance.

 

[Zeille]

The parking lots in Auto Club Speedway were rough but it's been closed down so the nearest events are held at Angel Stadium in Anaheim. I haven't been but I expect the surface to be smoother there.

KYB technical support responded to my email and reiterated below what you mentioned.
"The jounce bumper compresses during the cycle of the damper the 1/2" difference will not negatively impact the performance of the strut."

I went ahead and installed the KYB bump stops on the rear Bilstein B4 struts. Decided to reuse the stock plastic tube covers and I was able to fit them on the bump stops. The boots that come with the KYB kit don't sit securely. Going to install the set this Friday if I get the chance.

i found that all of the KYB stuff I ordered for my FiST to redo the suspension was all incorrect. even the mounts didn't function properly - i was chasing a peculiar suspension noise for a period of time which was due to the absolutely cooked KYB mounts. it's better to go all OEM. only good part I used from KYB were the bearings. head to the dealer, get all new OEM bump stops, dust boots, mounts, etc.

edit: saw that you can't source just the rear bump stops without ordering motorcraft dampers - just reuse the old bump stops if they're not cracked/broken. 160k miles in california/arizona heat since 2017 & both my front and rear bump stops were in great enough condition to reuse.

 

[ray_bandz0]

i found that all of the KYB stuff I ordered for my FiST to redo the suspension was all incorrect. even the mounts didn't function properly - i was chasing a peculiar suspension noise for a period of time which was due to the absolutely cooked KYB mounts. it's better to go all OEM. only good part I used from KYB were the bearings. head to the dealer, get all new OEM bump stops, dust boots, mounts, etc.

I agree, a lot of their parts have to apply to many applications for cost savings so they don't always have our best interest in mind. If you look at their rear struts for the FiST, the part number 3438002 applies to all trim levels. If the other versions have different spring rates, I don't see how the valving is matched to our application. They're only looking at fitment in this case.

Which mounts ended up being an issue for you? I have Motorcraft in the front shocks and KYB in the rear. I do want use all stock parts, it's just unfortunate that you can't buy any of the rear components separately.

 

[Zeille]

I agree, a lot of their parts have to apply to many applications for cost savings so they don't always have our best interest in mind. If you look at their rear struts for the FiST, the part number 3438002 applies to all trim levels. If the other versions have different spring rates, I don't see how the valving is matched to our application. They're only looking at fitment in this case.

Which mounts ended up being an issue for you? I have Motorcraft in the front shocks and KYB in the rear. I do want use all stock parts, it's just unfortunate that you can't buy any of the rear components separately.

KYB fronts went bad. rears are fine - i still have them on my car.